Initial implementation of Language Server

.circleci/config.yml

@@ -198,6 +198,19 @@ defaults:
         - store_artifacts: *artifacts_test_results
         - gitter_notify_failure_unless_pr
 
+  - steps_test_lsp: &steps_test_lsp
+      steps:
+        - checkout
+        - attach_workspace:
+            at: build
+        - run:
+            name: Install dependencies
+            command: pip install --user deepdiff colorama
+        - run:
+            name: Executing solc LSP test suite
+            command: ./test/lsp.py ./build/solc/solc
+        - gitter_notify_failure_unless_pr
+
   - steps_soltest_all: &steps_soltest_all
       steps:
         - checkout
@@ -519,7 +532,7 @@ jobs:
           command: apt -q update && apt install -y python3-pip
       - run:
           name: Install pylint
-          command: python3 -m pip install pylint z3-solver pygments-lexer-solidity parsec tabulate
+          command: python3 -m pip install pylint z3-solver pygments-lexer-solidity parsec tabulate deepdiff colorama
           # also z3-solver, parsec and tabulate to make sure pylint knows about this module, pygments-lexer-solidity for docs
       - run:
           name: Linting Python Scripts
@@ -887,6 +900,10 @@ jobs:
     parallelism: 15 # 7 EVM versions, each with/without optimization + 1 ABIv1/@nooptions run
     <<: *steps_soltest_all
 
+  t_ubu_lsp: &t_ubu_lsp
+    <<: *base_ubuntu2004_small
+    <<: *steps_test_lsp
+
   t_archlinux_soltest: &t_archlinux_soltest
     <<: *base_archlinux
     environment:
@@ -1288,6 +1305,7 @@ workflows:
       - t_ubu_soltest_enforce_yul: *workflow_ubuntu2004
       - b_ubu_clang: *workflow_trigger_on_tags
       - t_ubu_clang_soltest: *workflow_ubuntu2004_clang
+      - t_ubu_lsp: *workflow_ubuntu2004
 
       # Ubuntu fake release build and tests
       - b_ubu_release: *workflow_trigger_on_tags

Changelog.md

@@ -4,6 +4,7 @@ Language Features:
 
 
 Compiler Features:
+ * Commandline Interface: Add ``--lsp`` option to get ``solc`` to act as a Language Server (LSP) communicating over stdio.
 
 
 Bugfixes:

libsolidity/CMakeLists.txt

@@ -155,6 +155,12 @@ set(sources
 	interface/StorageLayout.h
 	interface/Version.cpp
 	interface/Version.h
+	lsp/LanguageServer.cpp
+	lsp/LanguageServer.h
+	lsp/FileRepository.cpp
+	lsp/FileRepository.h
+	lsp/Transport.cpp
+	lsp/Transport.h
 	parsing/DocStringParser.cpp
 	parsing/DocStringParser.h
 	parsing/Parser.cpp

libsolidity/lsp/FileRepository.cpp

@@ -0,0 +1,64 @@
+/*
+	This file is part of solidity.
+
+	solidity is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	solidity is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+// SPDX-License-Identifier: GPL-3.0
+
+#include <libsolidity/lsp/FileRepository.h>
+
+using namespace std;
+using namespace solidity;
+using namespace solidity::lsp;
+
+namespace
+{
+
+string stripFilePrefix(string const& _path)
+{
+	if (_path.find("file://") == 0)
+		return _path.substr(7);
+	else
+		return _path;
+}
+
+}
+
+string FileRepository::sourceUnitNameToClientPath(string const& _sourceUnitName) const
+{
+	if (m_sourceUnitNamesToClientPaths.count(_sourceUnitName))
+		return m_sourceUnitNamesToClientPaths.at(_sourceUnitName);
+	else if (_sourceUnitName.find("file://") == 0)
+		return _sourceUnitName;
+	else
+		return "file://" + (m_fileReader.basePath() / _sourceUnitName).generic_string();
+}
+
+string FileRepository::clientPathToSourceUnitName(string const& _path) const
+{
+	return m_fileReader.cliPathToSourceUnitName(stripFilePrefix(_path));
+}
+
+map<string, string> const& FileRepository::sourceUnits() const
+{
+	return m_fileReader.sourceUnits();
+}
+
+void FileRepository::setSourceByClientPath(string const& _uri, string _text)
+{
+	// This is needed for uris outside the base path. It can lead to collisions,
+	// but we need to mostly rewrite this in a future version anyway.
+	m_sourceUnitNamesToClientPaths.emplace(clientPathToSourceUnitName(_uri), _uri);
+	m_fileReader.addOrUpdateFile(stripFilePrefix(_uri), move(_text));
+}

libsolidity/lsp/FileRepository.h

@@ -0,0 +1,53 @@
+/*
+	This file is part of solidity.
+
+	solidity is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	solidity is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+// SPDX-License-Identifier: GPL-3.0
+#pragma once
+
+#include <libsolidity/interface/FileReader.h>
+
+#include <string>
+#include <map>
+
+namespace solidity::lsp
+{
+
+class FileRepository
+{
+public:
+	explicit FileRepository(boost::filesystem::path const& _basePath):
+		m_fileReader(_basePath) {}
+
+	boost::filesystem::path const& basePath() const { return m_fileReader.basePath(); }
+
+	/// Translates a compiler-internal source unit name to an LSP client path.
+	std::string sourceUnitNameToClientPath(std::string const& _sourceUnitName) const;
+	/// Translates an LSP client path into a compiler-internal source unit name.
+	std::string clientPathToSourceUnitName(std::string const& _uri) const;
+
+	/// @returns all sources by their compiler-internal source unit name.
+	std::map<std::string, std::string> const& sourceUnits() const;
+	/// Changes the source identified by the LSP client path _uri to _text.
+	void setSourceByClientPath(std::string const& _uri, std::string _text);
+
+	frontend::ReadCallback::Callback reader() { return m_fileReader.reader(); }
+
+private:
+	std::map<std::string, std::string> m_sourceUnitNamesToClientPaths;
+	frontend::FileReader m_fileReader;
+};
+
+}

libsolidity/lsp/LanguageServer.cpp

@@ -0,0 +1,402 @@
+/*
+	This file is part of solidity.
+
+	solidity is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	solidity is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+// SPDX-License-Identifier: GPL-3.0
+#include <libsolidity/ast/AST.h>
+#include <libsolidity/ast/ASTUtils.h>
+#include <libsolidity/ast/ASTVisitor.h>
+#include <libsolidity/interface/ReadFile.h>
+#include <libsolidity/interface/StandardCompiler.h>
+#include <libsolidity/lsp/LanguageServer.h>
+
+#include <liblangutil/SourceReferenceExtractor.h>
+#include <liblangutil/CharStream.h>
+
+#include <libsolutil/Visitor.h>
+#include <libsolutil/JSON.h>
+
+#include <boost/exception/diagnostic_information.hpp>
+#include <boost/filesystem.hpp>
+#include <boost/algorithm/string/predicate.hpp>
+
+#include <fmt/format.h>
+
+#include <ostream>
+#include <string>
+
+using namespace std;
+using namespace std::placeholders;
+
+using namespace solidity::lsp;
+using namespace solidity::langutil;
+using namespace solidity::frontend;
+
+namespace
+{
+
+Json::Value toJson(LineColumn _pos)
+{
+	Json::Value json = Json::objectValue;
+	json["line"] = max(_pos.line, 0);
+	json["character"] = max(_pos.column, 0);
+
+	return json;
+}
+
+Json::Value toJsonRange(LineColumn const& _start, LineColumn const& _end)
+{
+	Json::Value json;
+	json["start"] = toJson(_start);
+	json["end"] = toJson(_end);
+	return json;
+}
+
+optional<LineColumn> parseLineColumn(Json::Value const& _lineColumn)
+{
+	if (_lineColumn.isObject() && _lineColumn["line"].isInt() && _lineColumn["character"].isInt())
+		return LineColumn{_lineColumn["line"].asInt(), _lineColumn["character"].asInt()};
+	else
+		return nullopt;
+}
+
+constexpr int toDiagnosticSeverity(Error::Type _errorType)
+{
+	// 1=Error, 2=Warning, 3=Info, 4=Hint
+	switch (Error::errorSeverity(_errorType))
+	{
+	case Error::Severity::Error: return 1;
+	case Error::Severity::Warning: return 2;
+	case Error::Severity::Info: return 3;
+	}
+	solAssert(false);
+	return -1;
+}
+
+}
+
+LanguageServer::LanguageServer(Transport& _transport):
+	m_client{_transport},
+	m_handlers{
+		{"$/cancelRequest", [](auto, auto) {/*nothing for now as we are synchronous */}},
+		{"cancelRequest", [](auto, auto) {/*nothing for now as we are synchronous */}},
+		{"exit", [this](auto, auto) { m_state = (m_state == State::ShutdownRequested ? State::ExitRequested : State::ExitWithoutShutdown); }},
+		{"initialize", bind(&LanguageServer::handleInitialize, this, _1, _2)},
+		{"initialized", [](auto, auto) {}},
+		{"shutdown", [this](auto, auto) { m_state = State::ShutdownRequested; }},
+		{"textDocument/didOpen", bind(&LanguageServer::handleTextDocumentDidOpen, this, _1, _2)},
+		{"textDocument/didChange", bind(&LanguageServer::handleTextDocumentDidChange, this, _1, _2)},
+		{"textDocument/didClose", bind(&LanguageServer::handleTextDocumentDidClose, this, _1, _2)},
+		{"workspace/didChangeConfiguration", bind(&LanguageServer::handleWorkspaceDidChangeConfiguration, this, _1, _2)},
+	},
+	m_fileRepository("/" /* basePath */),
+	m_compilerStack{m_fileRepository.reader()}
+{
+}
+
+optional<SourceLocation> LanguageServer::parsePosition(
+	string const& _sourceUnitName,
+	Json::Value const& _position
+) const
+{
+	if (!m_fileRepository.sourceUnits().count(_sourceUnitName))
+		return nullopt;
+
+	if (optional<LineColumn> lineColumn = parseLineColumn(_position))
+		if (optional<int> const offset = CharStream::translateLineColumnToPosition(
+			m_fileRepository.sourceUnits().at(_sourceUnitName),
+			*lineColumn
+		))
+			return SourceLocation{*offset, *offset, make_shared<string>(_sourceUnitName)};
+	return nullopt;
+}
+
+optional<SourceLocation> LanguageServer::parseRange(string const& _sourceUnitName, Json::Value const& _range) const
+{
+	if (!_range.isObject())
+		return nullopt;
+	optional<SourceLocation> start = parsePosition(_sourceUnitName, _range["start"]);
+	optional<SourceLocation> end = parsePosition(_sourceUnitName, _range["end"]);
+	if (!start || !end)
+		return nullopt;
+	solAssert(*start->sourceName == *end->sourceName);
+	start->end = end->end;
+	return start;
+}
+
+Json::Value LanguageServer::toRange(SourceLocation const& _location) const
+{
+	if (!_location.hasText())
+		return toJsonRange({}, {});
+
+	solAssert(_location.sourceName, "");
+	CharStream const& stream = m_compilerStack.charStream(*_location.sourceName);
+	LineColumn start = stream.translatePositionToLineColumn(_location.start);
+	LineColumn end = stream.translatePositionToLineColumn(_location.end);
+	return toJsonRange(start, end);
+}
+
+Json::Value LanguageServer::toJson(SourceLocation const& _location) const
+{
+	solAssert(_location.sourceName);
+	Json::Value item = Json::objectValue;
+	item["uri"] = m_fileRepository.sourceUnitNameToClientPath(*_location.sourceName);
+	item["range"] = toRange(_location);
+	return item;
+}
+
+void LanguageServer::changeConfiguration(Json::Value const& _settings)
+{
+	m_settingsObject = _settings;
+}
+
+void LanguageServer::compile()
+{
+	// For files that are not open, we have to take changes on disk into account,
+	// so we just remove all non-open files.
+
+	FileRepository oldRepository(m_fileRepository.basePath());
+	swap(oldRepository, m_fileRepository);
+
+	for (string const& fileName: m_openFiles)
+		m_fileRepository.setSourceByClientPath(
+			fileName,
+			oldRepository.sourceUnits().at(oldRepository.clientPathToSourceUnitName(fileName))
+		);
+
+	// TODO: optimize! do not recompile if nothing has changed (file(s) not flagged dirty).
+
+	m_compilerStack.reset(false);
+	m_compilerStack.setSources(m_fileRepository.sourceUnits());
+	m_compilerStack.compile(CompilerStack::State::AnalysisPerformed);
+}
+
+void LanguageServer::compileAndUpdateDiagnostics()
+{
+	compile();
+
+	// These are the source units we will sent diagnostics to the client for sure,
+	// even if it is just to clear previous diagnostics.
+	map<string, Json::Value> diagnosticsBySourceUnit;
+	for (string const& sourceUnitName: m_fileRepository.sourceUnits() | ranges::views::keys)
+		diagnosticsBySourceUnit[sourceUnitName] = Json::arrayValue;
+	for (string const& sourceUnitName: m_nonemptyDiagnostics)
+		diagnosticsBySourceUnit[sourceUnitName] = Json::arrayValue;
+
+	for (shared_ptr<Error const> const& error: m_compilerStack.errors())
+	{
+		SourceLocation const* location = error->sourceLocation();
+		if (!location || !location->sourceName)
+			// LSP only has diagnostics applied to individual files.
+			continue;
+
+		Json::Value jsonDiag;
+		jsonDiag["source"] = "solc";
+		jsonDiag["severity"] = toDiagnosticSeverity(error->type());
+		jsonDiag["code"] = Json::UInt64{error->errorId().error};
+		string message = error->typeName() + ":";
+		if (string const* comment = error->comment())
+			message += " " + *comment;
+		jsonDiag["message"] = move(message);
+		jsonDiag["range"] = toRange(*location);
+
+		if (auto const* secondary = error->secondarySourceLocation())
+			for (auto&& [secondaryMessage, secondaryLocation]: secondary->infos)
+			{
+				Json::Value jsonRelated;
+				jsonRelated["message"] = secondaryMessage;
+				jsonRelated["location"] = toJson(secondaryLocation);
+				jsonDiag["relatedInformation"].append(jsonRelated);
+			}
+
+		diagnosticsBySourceUnit[*location->sourceName].append(jsonDiag);
+	}
+
+	m_nonemptyDiagnostics.clear();
+	for (auto&& [sourceUnitName, diagnostics]: diagnosticsBySourceUnit)
+	{
+		Json::Value params;
+		params["uri"] = m_fileRepository.sourceUnitNameToClientPath(sourceUnitName);
+		if (!diagnostics.empty())
+			m_nonemptyDiagnostics.insert(sourceUnitName);
+		params["diagnostics"] = move(diagnostics);
+		m_client.notify("textDocument/publishDiagnostics", move(params));
+	}
+}
+
+bool LanguageServer::run()
+{
+	while (m_state != State::ExitRequested && m_state != State::ExitWithoutShutdown && !m_client.closed())
+	{
+		MessageID id;
+		try
+		{
+			optional<Json::Value> const jsonMessage = m_client.receive();
+			if (!jsonMessage)
+				continue;
+
+			if ((*jsonMessage)["method"].isString())
+			{
+				string const methodName = (*jsonMessage)["method"].asString();
+				id = (*jsonMessage)["id"];
+
+				if (auto handler = valueOrDefault(m_handlers, methodName))
+					handler(id, (*jsonMessage)["params"]);
+				else
+					m_client.error(id, ErrorCode::MethodNotFound, "Unknown method " + methodName);
+			}
+			else
+				m_client.error({}, ErrorCode::ParseError, "\"method\" has to be a string.");
+		}
+		catch (...)
+		{
+			m_client.error(id, ErrorCode::InternalError, "Unhandled exception: "s + boost::current_exception_diagnostic_information());
+		}
+	}
+	return m_state == State::ExitRequested;
+}
+
+bool LanguageServer::checkServerInitialized(MessageID _id)
+{
+	if (m_state != State::Initialized)
+	{
+		m_client.error(_id, ErrorCode::ServerNotInitialized, "Server is not properly initialized.");
+		return false;
+	}
+	else
+		return true;
+}
+
+void LanguageServer::handleInitialize(MessageID _id, Json::Value const& _args)
+{
+	if (m_state != State::Started)
+	{
+		m_client.error(_id, ErrorCode::RequestFailed, "Initialize called at the wrong time.");
+		return;
+	}
+	m_state = State::Initialized;
+
+	// The default of FileReader is to use `.`, but the path from where the LSP was started
+	// should not matter.
+	string rootPath("/");
+	if (Json::Value uri = _args["rootUri"])
+	{
+		rootPath = uri.asString();
+		if (!boost::starts_with(rootPath, "file://"))
+		{
+			m_client.error(_id, ErrorCode::InvalidParams, "rootUri only supports file URI scheme.");
+			return;
+		}
+		rootPath = rootPath.substr(7);
+	}
+	else if (Json::Value rootPath = _args["rootPath"])
+		rootPath = rootPath.asString();
+
+	m_fileRepository = FileRepository(boost::filesystem::path(rootPath));
+	if (_args["initializationOptions"].isObject())
+		changeConfiguration(_args["initializationOptions"]);
+
+	Json::Value replyArgs;
+	replyArgs["serverInfo"]["name"] = "solc";
+	replyArgs["serverInfo"]["version"] = string(VersionNumber);
+	replyArgs["capabilities"]["textDocumentSync"]["openClose"] = true;
+	replyArgs["capabilities"]["textDocumentSync"]["change"] = 2; // 0=none, 1=full, 2=incremental
+
+	m_client.reply(_id, move(replyArgs));
+}
+
+
+void LanguageServer::handleWorkspaceDidChangeConfiguration(MessageID _id, Json::Value const& _args)
+{
+	if (!checkServerInitialized(_id))
+		return;
+
+	if (_args["settings"].isObject())
+		changeConfiguration(_args["settings"]);
+}
+
+void LanguageServer::handleTextDocumentDidOpen(MessageID _id, Json::Value const& _args)
+{
+	if (!checkServerInitialized(_id))
+		return;
+
+	if (!_args["textDocument"])
+		m_client.error(_id, ErrorCode::RequestFailed, "Text document parameter missing.");
+
+	string text = _args["textDocument"]["text"].asString();
+	string uri = _args["textDocument"]["uri"].asString();
+	m_openFiles.insert(uri);
+	m_fileRepository.setSourceByClientPath(uri, move(text));
+	compileAndUpdateDiagnostics();
+}
+
+void LanguageServer::handleTextDocumentDidChange(MessageID _id, Json::Value const& _args)
+{
+	if (!checkServerInitialized(_id))
+		return;
+
+	string const uri = _args["textDocument"]["uri"].asString();
+
+	for (Json::Value jsonContentChange: _args["contentChanges"])
+	{
+		if (!jsonContentChange.isObject())
+		{
+			m_client.error(_id, ErrorCode::RequestFailed, "Invalid content reference.");
+			return;
+		}
+
+		string const sourceUnitName = m_fileRepository.clientPathToSourceUnitName(uri);
+		if (!m_fileRepository.sourceUnits().count(sourceUnitName))
+		{
+			m_client.error(_id, ErrorCode::RequestFailed, "Unknown file: " + uri);
+			return;
+		}
+
+		string text = jsonContentChange["text"].asString();
+		if (jsonContentChange["range"].isObject()) // otherwise full content update
+		{
+			optional<SourceLocation> change = parseRange(sourceUnitName, jsonContentChange["range"]);
+			if (!change || !change->hasText())
+			{
+				m_client.error(
+					_id,
+					ErrorCode::RequestFailed,
+					"Invalid source range: " + jsonCompactPrint(jsonContentChange["range"])
+				);
+				return;
+			}
+			string buffer = m_fileRepository.sourceUnits().at(sourceUnitName);
+			buffer.replace(static_cast<size_t>(change->start), static_cast<size_t>(change->end - change->start), move(text));
+			text = move(buffer);
+		}
+		m_fileRepository.setSourceByClientPath(uri, move(text));
+	}
+
+	compileAndUpdateDiagnostics();
+}
+
+void LanguageServer::handleTextDocumentDidClose(MessageID _id, Json::Value const& _args)
+{
+	if (!checkServerInitialized(_id))
+		return;
+
+	if (!_args["textDocument"])
+		m_client.error(_id, ErrorCode::RequestFailed, "Text document parameter missing.");
+
+	string uri = _args["textDocument"]["uri"].asString();
+	m_openFiles.erase(uri);
+
+	compileAndUpdateDiagnostics();
+}

libsolidity/lsp/LanguageServer.h

@@ -0,0 +1,110 @@
+/*
+	This file is part of solidity.
+
+	solidity is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	solidity is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+// SPDX-License-Identifier: GPL-3.0
+#pragma once
+
+#include <libsolidity/lsp/Transport.h>
+#include <libsolidity/lsp/FileRepository.h>
+#include <libsolidity/interface/CompilerStack.h>
+#include <libsolidity/interface/FileReader.h>
+
+#include <json/value.h>
+
+#include <functional>
+#include <map>
+#include <optional>
+#include <string>
+#include <vector>
+
+namespace solidity::lsp
+{
+
+enum class ErrorCode;
+
+/**
+ * Solidity Language Server, managing one LSP client.
+ * This implements a subset of LSP version 3.16 that can be found at:
+ * https://microsoft.github.io/language-server-protocol/specifications/specification-3-16/
+ */
+class LanguageServer
+{
+public:
+	/// @param _transport Customizable transport layer.
+	explicit LanguageServer(Transport& _transport);
+
+	/// Re-compiles the project and updates the diagnostics pushed to the client.
+	void compileAndUpdateDiagnostics();
+
+	/// Loops over incoming messages via the transport layer until shutdown condition is met.
+	///
+	/// The standard shutdown condition is when the maximum number of consecutive failures
+	/// has been exceeded.
+	///
+	/// @return boolean indicating normal or abnormal termination.
+	bool run();
+
+private:
+	/// Checks if the server is initialized (to be used by messages that need it to be initialized).
+	/// Reports an error and returns false if not.
+	bool checkServerInitialized(MessageID _id);
+	void handleInitialize(MessageID _id, Json::Value const& _args);
+	void handleWorkspaceDidChangeConfiguration(MessageID _id, Json::Value const& _args);
+	void handleTextDocumentDidOpen(MessageID _id, Json::Value const& _args);
+	void handleTextDocumentDidChange(MessageID _id, Json::Value const& _args);
+	void handleTextDocumentDidClose(MessageID _id, Json::Value const& _args);
+
+	/// Invoked when the server user-supplied configuration changes (initiated by the client).
+	void changeConfiguration(Json::Value const&);
+
+	/// Compile everything until after analysis phase.
+	void compile();
+
+	std::optional<langutil::SourceLocation> parsePosition(
+		std::string const& _sourceUnitName,
+		Json::Value const& _position
+	) const;
+	/// @returns the source location given a source unit name and an LSP Range object,
+	/// or nullopt on failure.
+	std::optional<langutil::SourceLocation> parseRange(
+		std::string const& _sourceUnitName,
+		Json::Value const& _range
+	) const;
+	Json::Value toRange(langutil::SourceLocation const& _location) const;
+	Json::Value toJson(langutil::SourceLocation const& _location) const;
+
+	// LSP related member fields
+	using MessageHandler = std::function<void(MessageID, Json::Value const&)>;
+
+	enum class State { Started, Initialized, ShutdownRequested, ExitRequested, ExitWithoutShutdown };
+	State m_state = State::Started;
+
+	Transport& m_client;
+	std::map<std::string, MessageHandler> m_handlers;
+
+	/// Set of files known to be open by the client.
+	std::set<std::string> m_openFiles;
+	/// Set of source unit names for which we sent diagnostics to the client in the last iteration.
+	std::set<std::string> m_nonemptyDiagnostics;
+	FileRepository m_fileRepository;
+
+	frontend::CompilerStack m_compilerStack;
+
+	/// User-supplied custom configuration settings (such as EVM version).
+	Json::Value m_settingsObject;
+};
+
+}

libsolidity/lsp/Transport.cpp

@@ -0,0 +1,141 @@
+/*
+	This file is part of solidity.
+
+	solidity is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	solidity is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+// SPDX-License-Identifier: GPL-3.0
+#include <libsolidity/lsp/Transport.h>
+
+#include <libsolutil/JSON.h>
+#include <libsolutil/Visitor.h>
+#include <libsolutil/CommonIO.h>
+#include <liblangutil/Exceptions.h>
+
+#include <boost/algorithm/string.hpp>
+
+#include <iostream>
+#include <sstream>
+
+using namespace std;
+using namespace solidity::lsp;
+
+IOStreamTransport::IOStreamTransport(istream& _in, ostream& _out):
+	m_input{_in},
+	m_output{_out}
+{
+}
+
+IOStreamTransport::IOStreamTransport():
+	IOStreamTransport(cin, cout)
+{
+}
+
+bool IOStreamTransport::closed() const noexcept
+{
+	return m_input.eof();
+}
+
+optional<Json::Value> IOStreamTransport::receive()
+{
+	auto const headers = parseHeaders();
+	if (!headers)
+	{
+		error({}, ErrorCode::ParseError, "Could not parse RPC headers.");
+		return nullopt;
+	}
+
+	if (!headers->count("content-length"))
+	{
+		error({}, ErrorCode::ParseError, "No content-length header found.");
+		return nullopt;
+	}
+
+	string const data = util::readBytes(m_input, stoul(headers->at("content-length")));
+
+	Json::Value jsonMessage;
+	string jsonParsingErrors;
+	solidity::util::jsonParseStrict(data, jsonMessage, &jsonParsingErrors);
+	if (!jsonParsingErrors.empty() || !jsonMessage || !jsonMessage.isObject())
+	{
+		error({}, ErrorCode::ParseError, "Could not parse RPC JSON payload. " + jsonParsingErrors);
+		return nullopt;
+	}
+
+	return {move(jsonMessage)};
+}
+
+void IOStreamTransport::notify(string _method, Json::Value _message)
+{
+	Json::Value json;
+	json["method"] = move(_method);
+	json["params"] = move(_message);
+	send(move(json));
+}
+
+void IOStreamTransport::reply(MessageID _id, Json::Value _message)
+{
+	Json::Value json;
+	json["result"] = move(_message);
+	send(move(json), _id);
+}
+
+void IOStreamTransport::error(MessageID _id, ErrorCode _code, string _message)
+{
+	Json::Value json;
+	json["error"]["code"] = static_cast<int>(_code);
+	json["error"]["message"] = move(_message);
+	send(move(json), _id);
+}
+
+void IOStreamTransport::send(Json::Value _json, MessageID _id)
+{
+	solAssert(_json.isObject());
+	_json["jsonrpc"] = "2.0";
+	if (_id != Json::nullValue)
+		_json["id"] = _id;
+
+	string const jsonString = solidity::util::jsonCompactPrint(_json);
+
+	m_output << "Content-Length: " << jsonString.size() << "\r\n";
+	m_output << "\r\n";
+	m_output << jsonString;
+
+	m_output.flush();
+}
+
+optional<map<string, string>> IOStreamTransport::parseHeaders()
+{
+	map<string, string> headers;
+
+	while (true)
+	{
+		string line;
+		getline(m_input, line);
+		if (boost::trim_copy(line).empty())
+			break;
+
+		auto const delimiterPos = line.find(':');
+		if (delimiterPos == string::npos)
+			return nullopt;
+
+		string name = boost::to_lower_copy(line.substr(0, delimiterPos));
+		string value = line.substr(delimiterPos + 1);
+		if (!headers.emplace(
+			boost::trim_copy(name),
+			boost::trim_copy(value)
+		).second)
+			return nullopt;
+	}
+	return {move(headers)};
+}

libsolidity/lsp/Transport.h

@@ -0,0 +1,101 @@
+/*
+	This file is part of solidity.
+
+	solidity is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	solidity is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+// SPDX-License-Identifier: GPL-3.0
+#pragma once
+
+#include <json/value.h>
+
+#include <functional>
+#include <iosfwd>
+#include <map>
+#include <optional>
+#include <string>
+#include <string_view>
+#include <variant>
+
+namespace solidity::lsp
+{
+
+using MessageID = Json::Value;
+
+enum class ErrorCode
+{
+	// Defined by JSON RPC
+	ParseError = -32700,
+	MethodNotFound = -32601,
+	InvalidParams = -32602,
+	InternalError = -32603,
+
+	// Defined by the protocol.
+	ServerNotInitialized = -32002,
+	RequestFailed = -32803
+};
+
+/**
+ * Transport layer API
+ *
+ * The transport layer API is abstracted to make LSP more testable as well as
+ * this way it could be possible to support other transports (HTTP for example) easily.
+ */
+class Transport
+{
+public:
+	virtual ~Transport() = default;
+
+	virtual bool closed() const noexcept = 0;
+	virtual std::optional<Json::Value> receive() = 0;
+	virtual void notify(std::string _method, Json::Value _params) = 0;
+	virtual void reply(MessageID _id, Json::Value _result) = 0;
+	virtual void error(MessageID _id, ErrorCode _code, std::string _message) = 0;
+};
+
+/**
+ * LSP Transport using JSON-RPC over iostreams.
+ */
+class IOStreamTransport: public Transport
+{
+public:
+	/// Constructs a standard stream transport layer.
+	///
+	/// @param _in for example std::cin (stdin)
+	/// @param _out for example std::cout (stdout)
+	IOStreamTransport(std::istream& _in, std::ostream& _out);
+
+	// Constructs a JSON transport using standard I/O streams.
+	IOStreamTransport();
+
+	bool closed() const noexcept override;
+	std::optional<Json::Value> receive() override;
+	void notify(std::string _method, Json::Value _params) override;
+	void reply(MessageID _id, Json::Value _result) override;
+	void error(MessageID _id, ErrorCode _code, std::string _message) override;
+
+protected:
+	/// Sends an arbitrary raw message to the client.
+	///
+	/// Used by the notify/reply/error function family.
+	virtual void send(Json::Value _message, MessageID _id = Json::nullValue);
+
+	/// Parses header section from the client including message-delimiting empty line.
+	std::optional<std::map<std::string, std::string>> parseHeaders();
+
+private:
+	std::istream& m_input;
+	std::ostream& m_output;
+};
+
+}

scripts/tests.sh

@@ -83,6 +83,9 @@ done
 printTask "Testing Python scripts..."
 "$REPO_ROOT/test/pyscriptTests.py"
 
+printTask "Testing LSP..."
+"$REPO_ROOT/scripts/test_solidity_lsp.py" "${SOLIDITY_BUILD_DIR}/solc/solc"
+
 printTask "Running commandline tests..."
 # Only run in parallel if this is run on CI infrastructure
 if [[ -n "$CI" ]]

solc/CommandLineInterface.cpp

@@ -38,6 +38,8 @@
 #include <libsolidity/interface/DebugSettings.h>
 #include <libsolidity/interface/ImportRemapper.h>
 #include <libsolidity/interface/StorageLayout.h>
+#include <libsolidity/lsp/LanguageServer.h>
+#include <libsolidity/lsp/Transport.h>
 
 #include <libyul/AssemblyStack.h>
 
@@ -56,6 +58,7 @@
 #include <libsolutil/JSON.h>
 
 #include <algorithm>
+#include <fstream>
 #include <memory>
 
 #include <range/v3/view/map.hpp>
@@ -499,7 +502,11 @@ void CommandLineInterface::readInputFiles()
 			m_fileReader.setStdin(readUntilEnd(m_sin));
 	}
 
-	if (m_fileReader.sourceUnits().empty() && !m_standardJsonInput.has_value())
+	if (
+		m_options.input.mode != InputMode::LanguageServer &&
+		m_fileReader.sourceUnits().empty() &&
+		!m_standardJsonInput.has_value()
+	)
 		solThrow(CommandLineValidationError, "All specified input files either do not exist or are not regular files.");
 }
 
@@ -624,6 +631,9 @@ void CommandLineInterface::processInput()
 		m_standardJsonInput.reset();
 		break;
 	}
+	case InputMode::LanguageServer:
+		serveLSP();
+		break;
 	case InputMode::Assembler:
 		assemble(m_options.assembly.inputLanguage, m_options.assembly.targetMachine);
 		break;
@@ -884,6 +894,13 @@ void CommandLineInterface::handleAst()
 	}
 }
 
+void CommandLineInterface::serveLSP()
+{
+	lsp::IOStreamTransport transport;
+	if (!lsp::LanguageServer{transport}.run())
+		solThrow(CommandLineExecutionError, "LSP terminated abnormally.");
+}
+
 void CommandLineInterface::link()
 {
 	solAssert(m_options.input.mode == InputMode::Linker, "");

solc/CommandLineInterface.h

@@ -82,6 +82,7 @@ private:
 	void printVersion();
 	void printLicense();
 	void compile();
+	void serveLSP();
 	void link();
 	void writeLinkedFiles();
 	/// @returns the ``// <identifier> -> name`` hint for library placeholders.

solc/CommandLineParser.cpp

@@ -59,6 +59,7 @@ static string const g_strIPFS = "ipfs";
 static string const g_strLicense = "license";
 static string const g_strLibraries = "libraries";
 static string const g_strLink = "link";
+static string const g_strLSP = "lsp";
 static string const g_strMachine = "machine";
 static string const g_strMetadataHash = "metadata-hash";
 static string const g_strMetadataLiteral = "metadata-literal";
@@ -135,6 +136,7 @@ static map<InputMode, string> const g_inputModeName = {
 	{InputMode::Assembler, "assembler"},
 	{InputMode::StandardJson, "standard JSON"},
 	{InputMode::Linker, "linker"},
+	{InputMode::LanguageServer, "language server (LSP)"},
 };
 
 void CommandLineParser::checkMutuallyExclusive(vector<string> const& _optionNames)
@@ -455,6 +457,7 @@ void CommandLineParser::parseOutputSelection()
 		case InputMode::Help:
 		case InputMode::License:
 		case InputMode::Version:
+		case InputMode::LanguageServer:
 			solAssert(false);
 		case InputMode::Compiler:
 		case InputMode::CompilerWithASTImport:
@@ -633,6 +636,11 @@ General Information)").c_str(),
 			"Supported Inputs is the output of the --" + g_strStandardJSON + " or the one produced by "
 			"--" + g_strCombinedJson + " " + CombinedJsonRequests::componentName(&CombinedJsonRequests::ast)).c_str()
 		)
+		(
+			g_strLSP.c_str(),
+			"Switch to language server mode (\"LSP\"). Allows the compiler to be used as an analysis backend "
+			"for your favourite IDE."
+		)
 	;
 	desc.add(alternativeInputModes);
 
@@ -865,6 +873,7 @@ void CommandLineParser::processArgs()
 		g_strStrictAssembly,
 		g_strYul,
 		g_strImportAst,
+		g_strLSP
 	});
 
 	if (m_args.count(g_strHelp) > 0)
@@ -875,6 +884,8 @@ void CommandLineParser::processArgs()
 		m_options.input.mode = InputMode::Version;
 	else if (m_args.count(g_strStandardJSON) > 0)
 		m_options.input.mode = InputMode::StandardJson;
+	else if (m_args.count(g_strLSP))
+		m_options.input.mode = InputMode::LanguageServer;
 	else if (m_args.count(g_strAssemble) > 0 || m_args.count(g_strStrictAssembly) > 0 || m_args.count(g_strYul) > 0)
 		m_options.input.mode = InputMode::Assembler;
 	else if (m_args.count(g_strLink) > 0)
@@ -910,6 +921,9 @@ void CommandLineParser::processArgs()
 			joinOptionNames(invalidOptionsForCurrentInputMode)
 		);
 
+	if (m_options.input.mode == InputMode::LanguageServer)
+		return;
+
 	checkMutuallyExclusive({g_strColor, g_strNoColor});
 
 	array<string, 9> const conflictingWithStopAfter{

solc/CommandLineParser.h

@@ -56,6 +56,7 @@ enum class InputMode
 	StandardJson,
 	Linker,
 	Assembler,
+	LanguageServer
 };
 
 struct CompilerOutputs

test/libsolidity/lsp/didChange_template.sol

@@ -0,0 +1,6 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity >=0.8.0;
+
+contract C
+{
+}

test/libsolidity/lsp/didOpen_with_import.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity >=0.8.0;
+
+import './lib.sol';
+
+contract C
+{
+    function f(uint a, uint b) public pure returns (uint)
+    {
+        return Lib.add(2 * a, b);
+    }
+}

test/libsolidity/lsp/lib.sol

@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity >=0.8.0;
+
+library Lib
+{
+    function add(uint a, uint b) public pure returns (uint result)
+    {
+        result = a + b;
+    }
+
+    function warningWithUnused() public pure
+    {
+        uint unused;
+    }
+}

test/libsolidity/lsp/publish_diagnostics_1.sol

@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity >=0.8.0;
+
+contract MyContract
+{
+    constructor()
+    {
+        uint unused; // [Warning 2072] Unused local variable.
+    }
+}
+
+contract D
+{
+    function main() public payable returns (uint)
+    {
+        MyContract c = new MyContract();
+    }
+}

test/libsolidity/lsp/publish_diagnostics_2.sol

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity >=0.8.0;
+
+contract C
+{
+    function makeSomeError() public pure returns (uint res)
+    {
+        uint x = "hi";
+        return;
+        res = 2;
+    }
+}
+
+contract D
+{
+    function main() public payable returns (uint)
+    {
+        C c = new C();
+        return c.makeSomeError(2, 3);
+    }
+}

test/libsolidity/lsp/publish_diagnostics_3.sol

@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity >=0.8.0;
+
+abstract contract A {
+    function a() public virtual;
+}
+
+contract B is A
+{
+}

test/lsp.py

@@ -0,0 +1,874 @@
+#!/usr/bin/env python3
+
+import argparse
+import fnmatch
+import json
+import os
+import subprocess
+import traceback
+
+from typing import Any, List, Optional, Tuple, Union
+
+import colorama # Enables the use of SGR & CUP terminal VT sequences on Windows.
+from deepdiff import DeepDiff
+
+# {{{ JsonRpcProcess
+class BadHeader(Exception):
+    def __init__(self, msg: str):
+        super().__init__("Bad header: " + msg)
+
+class JsonRpcProcess:
+    exe_path: str
+    exe_args: List[str]
+    process: subprocess.Popen
+    trace_io: bool
+
+    def __init__(self, exe_path: str, exe_args: List[str], trace_io: bool = True):
+        self.exe_path = exe_path
+        self.exe_args = exe_args
+        self.trace_io = trace_io
+
+    def __enter__(self):
+        self.process = subprocess.Popen(
+            [self.exe_path, *self.exe_args],
+            stdin=subprocess.PIPE,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE
+        )
+        return self
+
+    def __exit__(self, exception_type, exception_value, traceback) -> None:
+        self.process.kill()
+        self.process.wait(timeout=2.0)
+
+    def trace(self, topic: str, message: str) -> None:
+        if self.trace_io:
+            print(f"{SGR_TRACE}{topic}:{SGR_RESET} {message}")
+
+    def receive_message(self) -> Union[None, dict]:
+        # Note, we should make use of timeout to avoid infinite blocking if nothing is received.
+        CONTENT_LENGTH_HEADER = "Content-Length: "
+        CONTENT_TYPE_HEADER = "Content-Type: "
+        if self.process.stdout == None:
+            return None
+        message_size = None
+        while True:
+            # read header
+            line = self.process.stdout.readline()
+            if line == '':
+                # server quit
+                return None
+            line = line.decode("utf-8")
+            if not line.endswith("\r\n"):
+                raise BadHeader("missing newline")
+            # remove the "\r\n"
+            line = line[:-2]
+            if line == '':
+                break # done with the headers
+            if line.startswith(CONTENT_LENGTH_HEADER):
+                line = line[len(CONTENT_LENGTH_HEADER):]
+                if not line.isdigit():
+                    raise BadHeader("size is not int")
+                message_size = int(line)
+            elif line.startswith(CONTENT_TYPE_HEADER):
+                # nothing todo with type for now.
+                pass
+            else:
+                raise BadHeader("unknown header")
+        if message_size is None:
+            raise BadHeader("missing size")
+        rpc_message = self.process.stdout.read(message_size).decode("utf-8")
+        json_object = json.loads(rpc_message)
+        self.trace('receive_message', json.dumps(json_object, indent=4, sort_keys=True))
+        return json_object
+
+    def send_message(self, method_name: str, params: Optional[dict]) -> None:
+        if self.process.stdin == None:
+            return
+        message = {
+            'jsonrpc': '2.0',
+            'method': method_name,
+            'params': params
+        }
+        json_string = json.dumps(obj=message)
+        rpc_message = f"Content-Length: {len(json_string)}\r\n\r\n{json_string}"
+        self.trace(f'send_message ({method_name})', json.dumps(message, indent=4, sort_keys=True))
+        self.process.stdin.write(rpc_message.encode("utf-8"))
+        self.process.stdin.flush()
+
+    def call_method(self, method_name: str, params: Optional[dict]) -> Any:
+        self.send_message(method_name, params)
+        return self.receive_message()
+
+    def send_notification(self, name: str, params: Optional[dict] = None) -> None:
+        self.send_message(name, params)
+
+# }}}
+
+SGR_RESET = '\033[m'
+SGR_TRACE = '\033[1;36m'
+SGR_NOTICE = '\033[1;35m'
+SGR_TEST_BEGIN = '\033[1;33m'
+SGR_ASSERT_BEGIN = '\033[1;34m'
+SGR_STATUS_OKAY = '\033[1;32m'
+SGR_STATUS_FAIL = '\033[1;31m'
+
+class ExpectationFailed(Exception):
+    def __init__(self, actual, expected):
+        self.actual = actual
+        self.expected = expected
+        diff = DeepDiff(actual, expected)
+        super().__init__(
+            f"Expectation failed.\n\tExpected {expected}\n\tbut got {actual}.\n\t{diff}"
+        )
+
+def create_cli_parser() -> argparse.ArgumentParser:
+    parser = argparse.ArgumentParser(description="Solidity LSP Test suite")
+    parser.set_defaults(trace_io=False)
+    parser.add_argument(
+        "-T, --trace-io",
+        dest="trace_io",
+        action="store_true",
+        help="Be more verbose by also printing assertions."
+    )
+    parser.set_defaults(print_assertions=False)
+    parser.add_argument(
+        "-v, --print-assertions",
+        dest="print_assertions",
+        action="store_true",
+        help="Be more verbose by also printing assertions."
+    )
+    parser.add_argument(
+        "-t, --test-pattern",
+        dest="test_pattern",
+        type=str,
+        default="*",
+        help="Filters all available tests by matching against this test pattern (using globbing)",
+        nargs="?"
+    )
+    parser.add_argument(
+        "solc_path",
+        type=str,
+        default="solc",
+        help="Path to solc binary to test against",
+        nargs="?"
+    )
+    parser.add_argument(
+        "project_root_dir",
+        type=str,
+        default=f"{os.path.dirname(os.path.realpath(__file__))}/..",
+        help="Path to Solidity project's root directory (must be fully qualified).",
+        nargs="?"
+    )
+    return parser
+
+class Counter:
+    total: int = 0
+    passed: int = 0
+    failed: int = 0
+
+class SolidityLSPTestSuite: # {{{
+    test_counter = Counter()
+    assertion_counter = Counter()
+    print_assertions: bool = False
+    trace_io: bool = False
+    test_pattern: str
+
+    def __init__(self):
+        colorama.init()
+        args = create_cli_parser().parse_args()
+        self.solc_path = args.solc_path
+        self.project_root_dir = os.path.realpath(args.project_root_dir) + "/test/libsolidity/lsp"
+        self.project_root_uri = "file://" + self.project_root_dir
+        self.print_assertions = args.print_assertions
+        self.trace_io = args.trace_io
+        self.test_pattern = args.test_pattern
+
+        print(f"{SGR_NOTICE}test pattern: {self.test_pattern}{SGR_RESET}")
+
+    def main(self) -> int:
+        """
+        Runs all test cases.
+        Returns 0 on success and the number of failing assertions (capped to 127) otherwise.
+        """
+        all_tests = sorted([
+            str(name)[5:]
+            for name in dir(SolidityLSPTestSuite)
+            if callable(getattr(SolidityLSPTestSuite, name)) and name.startswith("test_")
+        ])
+        filtered_tests = fnmatch.filter(all_tests, self.test_pattern)
+        for method_name in filtered_tests:
+            test_fn = getattr(self, 'test_' + method_name)
+            title: str = test_fn.__name__[5:]
+            print(f"{SGR_TEST_BEGIN}Testing {title} ...{SGR_RESET}")
+            try:
+                with JsonRpcProcess(self.solc_path, ["--lsp"], trace_io=self.trace_io) as solc:
+                    test_fn(solc)
+                    self.test_counter.passed += 1
+            except ExpectationFailed as e:
+                self.test_counter.failed += 1
+                print(e)
+                print(traceback.format_exc())
+            except Exception as e: # pragma pylint: disable=broad-except
+                self.test_counter.failed += 1
+                print(f"Unhandled exception {e.__class__.__name__} caught: {e}")
+                print(traceback.format_exc())
+
+        print(
+            f"\n{SGR_NOTICE}Summary:{SGR_RESET}\n\n"
+            f"  Test cases: {self.test_counter.passed} passed, {self.test_counter.failed} failed\n"
+            f"  Assertions: {self.assertion_counter.passed} passed, {self.assertion_counter.failed} failed\n"
+        )
+
+        return min(max(self.test_counter.failed, self.assertion_counter.failed), 127)
+
+    def setup_lsp(self, lsp: JsonRpcProcess, expose_project_root=True):
+        """
+        Prepares the solc LSP server by calling `initialize`,
+        and `initialized` methods.
+        """
+        params = {
+            'processId': None,
+            'rootUri': self.project_root_uri,
+            'trace': 'off',
+            'initializationOptions': {},
+            'capabilities': {
+                'textDocument': {
+                    'publishDiagnostics': {'relatedInformation': True}
+                },
+                'workspace': {
+                    'applyEdit': True,
+                    'configuration': True,
+                    'didChangeConfiguration': {'dynamicRegistration': True},
+                    'workspaceEdit': {'documentChanges': True},
+                    'workspaceFolders': True
+                }
+            }
+        }
+        if expose_project_root == False:
+            params['rootUri'] = None
+        lsp.call_method('initialize', params)
+        lsp.send_notification('initialized')
+
+    # {{{ helpers
+    def get_test_file_path(self, test_case_name):
+        return f"{self.project_root_dir}/{test_case_name}.sol"
+
+    def get_test_file_uri(self, test_case_name):
+        return "file://" + self.get_test_file_path(test_case_name)
+
+    def get_test_file_contents(self, test_case_name):
+        """
+        Reads the file contents from disc for a given test case.
+        The `test_case_name` will be the basename of the file
+        in the test path (test/libsolidity/lsp).
+        """
+        with open(self.get_test_file_path(test_case_name), mode="r", encoding="utf-8", newline='') as f:
+            return f.read()
+
+    def require_params_for_method(self, method_name: str, message: dict) -> Any:
+        """
+        Ensures the given RPC message does contain the
+        field 'method' with the given method name,
+        and then returns its passed params.
+        An exception is raised on expectation failures.
+        """
+        assert message is not None
+        if 'error' in message.keys():
+            code = message['error']["code"]
+            text = message['error']['message']
+            raise RuntimeError(f"Error {code} received. {text}")
+        if 'method' not in message.keys():
+            raise RuntimeError("No method received but something else.")
+        self.expect_equal(message['method'], method_name, "Ensure expected method name")
+        return message['params']
+
+    def wait_for_diagnostics(self, solc: JsonRpcProcess, count: int) -> List[dict]:
+        """
+        Return `count` number of published diagnostic reports sorted by file URI.
+        """
+        reports = []
+        for _ in range(0, count):
+            message = solc.receive_message()
+            assert message is not None # This can happen if the server aborts early.
+            reports.append(
+                self.require_params_for_method(
+                    'textDocument/publishDiagnostics',
+                    message,
+                )
+            )
+        return sorted(reports, key=lambda x: x['uri'])
+
+    def open_file_and_wait_for_diagnostics(
+        self,
+        solc_process: JsonRpcProcess,
+        test_case_name: str,
+        max_diagnostic_reports: int = 1
+    ) -> List[Any]:
+        """
+        Opens file for given test case and waits for diagnostics to be published.
+        """
+        assert max_diagnostic_reports > 0
+        solc_process.send_message(
+            'textDocument/didOpen',
+            {
+                'textDocument':
+                {
+                    'uri': self.get_test_file_uri(test_case_name),
+                    'languageId': 'Solidity',
+                    'version': 1,
+                    'text': self.get_test_file_contents(test_case_name)
+                }
+            }
+        )
+        return self.wait_for_diagnostics(solc_process, max_diagnostic_reports)
+
+    def expect_equal(self, actual, expected, description="Equality") -> None:
+        self.assertion_counter.total += 1
+        prefix = f"[{self.assertion_counter.total}] {SGR_ASSERT_BEGIN}{description}: "
+        diff = DeepDiff(actual, expected)
+        if len(diff) == 0:
+            self.assertion_counter.passed += 1
+            if self.print_assertions:
+                print(prefix + SGR_STATUS_OKAY + 'OK' + SGR_RESET)
+            return
+
+        # Failed assertions are always printed.
+        self.assertion_counter.failed += 1
+        print(prefix + SGR_STATUS_FAIL + 'FAILED' + SGR_RESET)
+        raise ExpectationFailed(actual, expected)
+
+    def expect_empty_diagnostics(self, published_diagnostics: List[dict]) -> None:
+        self.expect_equal(len(published_diagnostics), 1, "one publish diagnostics notification")
+        self.expect_equal(len(published_diagnostics[0]['diagnostics']), 0, "should not contain diagnostics")
+
+    def expect_diagnostic(
+        self,
+        diagnostic,
+        code: int,
+        lineNo: int,
+        startEndColumns: Tuple[int, int]
+    ):
+        assert len(startEndColumns) == 2
+        [startColumn, endColumn] = startEndColumns
+        self.expect_equal(diagnostic['code'], code, f'diagnostic: {code}')
+        self.expect_equal(
+            diagnostic['range'],
+            {
+                'start': {'character': startColumn, 'line': lineNo},
+                'end': {'character': endColumn, 'line': lineNo}
+            },
+            "diagnostic: check range"
+        )
+    # }}}
+
+    # {{{ actual tests
+    def test_publish_diagnostics_warnings(self, solc: JsonRpcProcess) -> None:
+        self.setup_lsp(solc)
+        TEST_NAME = 'publish_diagnostics_1'
+        published_diagnostics = self.open_file_and_wait_for_diagnostics(solc, TEST_NAME)
+
+        self.expect_equal(len(published_diagnostics), 1, "One published_diagnostics message")
+        report = published_diagnostics[0]
+
+        self.expect_equal(report['uri'], self.get_test_file_uri(TEST_NAME), "Correct file URI")
+        diagnostics = report['diagnostics']
+
+        self.expect_equal(len(diagnostics), 3, "3 diagnostic messages")
+        self.expect_diagnostic(diagnostics[0], code=6321, lineNo=13, startEndColumns=(44, 48))
+        self.expect_diagnostic(diagnostics[1], code=2072, lineNo= 7, startEndColumns=( 8, 19))
+        self.expect_diagnostic(diagnostics[2], code=2072, lineNo=15, startEndColumns=( 8, 20))
+
+    def test_publish_diagnostics_errors(self, solc: JsonRpcProcess) -> None:
+        self.setup_lsp(solc)
+        TEST_NAME = 'publish_diagnostics_2'
+        published_diagnostics = self.open_file_and_wait_for_diagnostics(solc, TEST_NAME)
+
+        self.expect_equal(len(published_diagnostics), 1, "One published_diagnostics message")
+        report = published_diagnostics[0]
+
+        self.expect_equal(report['uri'], self.get_test_file_uri(TEST_NAME), "Correct file URI")
+        diagnostics = report['diagnostics']
+
+        self.expect_equal(len(diagnostics), 3, "3 diagnostic messages")
+        self.expect_diagnostic(diagnostics[0], code=9574, lineNo= 7, startEndColumns=( 8, 21))
+        self.expect_diagnostic(diagnostics[1], code=6777, lineNo= 8, startEndColumns=( 8, 15))
+        self.expect_diagnostic(diagnostics[2], code=6160, lineNo=18, startEndColumns=(15, 36))
+
+    def test_publish_diagnostics_errors_multiline(self, solc: JsonRpcProcess) -> None:
+        self.setup_lsp(solc)
+        TEST_NAME = 'publish_diagnostics_3'
+        published_diagnostics = self.open_file_and_wait_for_diagnostics(solc, TEST_NAME)
+
+        self.expect_equal(len(published_diagnostics), 1, "One published_diagnostics message")
+        report = published_diagnostics[0]
+
+        self.expect_equal(report['uri'], self.get_test_file_uri(TEST_NAME), "Correct file URI")
+        diagnostics = report['diagnostics']
+
+        self.expect_equal(len(diagnostics), 1, "3 diagnostic messages")
+        self.expect_equal(diagnostics[0]['code'], 3656, "diagnostic: check code")
+        self.expect_equal(
+            diagnostics[0]['range'],
+            {
+                'end': {'character': 1, 'line': 9},
+                'start': {'character': 0, 'line': 7}
+            },
+            "diagnostic: check range"
+        )
+
+    def test_textDocument_didOpen_with_relative_import(self, solc: JsonRpcProcess) -> None:
+        self.setup_lsp(solc)
+        TEST_NAME = 'didOpen_with_import'
+        published_diagnostics = self.open_file_and_wait_for_diagnostics(solc, TEST_NAME, 2)
+
+        self.expect_equal(len(published_diagnostics), 2, "Diagnostic reports for 2 files")
+
+        # primary file:
+        report = published_diagnostics[0]
+        self.expect_equal(report['uri'], self.get_test_file_uri(TEST_NAME), "Correct file URI")
+        self.expect_equal(len(report['diagnostics']), 0, "no diagnostics")
+
+        # imported file (./lib.sol):
+        report = published_diagnostics[1]
+        self.expect_equal(report['uri'], self.get_test_file_uri('lib'), "Correct file URI")
+        self.expect_equal(len(report['diagnostics']), 1, "one diagnostic")
+        self.expect_diagnostic(report['diagnostics'][0], code=2072, lineNo=12, startEndColumns=(8, 19))
+
+    def test_didChange_in_A_causing_error_in_B(self, solc: JsonRpcProcess) -> None:
+        # Reusing another test but now change some file that generates an error in the other.
+        self.test_textDocument_didOpen_with_relative_import(solc)
+        self.open_file_and_wait_for_diagnostics(solc, 'lib', 2)
+        solc.send_message(
+            'textDocument/didChange',
+            {
+                'textDocument':
+                {
+                    'uri': self.get_test_file_uri('lib')
+                },
+                'contentChanges':
+                [
+                    {
+                        'range': {
+                            'start': { 'line':  5, 'character': 0 },
+                            'end':   { 'line': 10, 'character': 0 }
+                        },
+                        'text': "" # deleting function `add`
+                    }
+                ]
+            }
+        )
+        published_diagnostics = self.wait_for_diagnostics(solc, 2)
+        self.expect_equal(len(published_diagnostics), 2, "Diagnostic reports for 2 files")
+
+        # Main file now contains a new diagnostic
+        report = published_diagnostics[0]
+        self.expect_equal(report['uri'], self.get_test_file_uri('didOpen_with_import'))
+        diagnostics = report['diagnostics']
+        self.expect_equal(len(diagnostics), 1, "now, no diagnostics")
+        self.expect_diagnostic(diagnostics[0], code=9582, lineNo=9, startEndColumns=(15, 22))
+
+        # The modified file retains the same diagnostics.
+        report = published_diagnostics[1]
+        self.expect_equal(report['uri'], self.get_test_file_uri('lib'))
+        self.expect_equal(len(report['diagnostics']), 0)
+        # The warning went away because the compiler aborts further processing after the error.
+
+    def test_textDocument_didOpen_with_relative_import_without_project_url(self, solc: JsonRpcProcess) -> None:
+        self.setup_lsp(solc, expose_project_root=False)
+        TEST_NAME = 'didOpen_with_import'
+        published_diagnostics = self.open_file_and_wait_for_diagnostics(solc, TEST_NAME, 2)
+        self.verify_didOpen_with_import_diagnostics(published_diagnostics)
+
+    def verify_didOpen_with_import_diagnostics(
+        self,
+        published_diagnostics: List[Any],
+        main_file_name='didOpen_with_import'
+    ):
+        self.expect_equal(len(published_diagnostics), 2, "Diagnostic reports for 2 files")
+
+        # primary file:
+        report = published_diagnostics[0]
+        self.expect_equal(report['uri'], self.get_test_file_uri(main_file_name), "Correct file URI")
+        self.expect_equal(len(report['diagnostics']), 0, "one diagnostic")
+
+        # imported file (./lib.sol):
+        report = published_diagnostics[1]
+        self.expect_equal(report['uri'], self.get_test_file_uri('lib'), "Correct file URI")
+        self.expect_equal(len(report['diagnostics']), 1, "one diagnostic")
+        self.expect_diagnostic(report['diagnostics'][0], code=2072, lineNo=12, startEndColumns=(8, 19))
+
+    def test_textDocument_didChange_updates_diagnostics(self, solc: JsonRpcProcess) -> None:
+        self.setup_lsp(solc)
+        TEST_NAME = 'publish_diagnostics_1'
+        published_diagnostics = self.open_file_and_wait_for_diagnostics(solc, TEST_NAME)
+        self.expect_equal(len(published_diagnostics), 1, "One published_diagnostics message")
+        report = published_diagnostics[0]
+        self.expect_equal(report['uri'], self.get_test_file_uri(TEST_NAME), "Correct file URI")
+        diagnostics = report['diagnostics']
+        self.expect_equal(len(diagnostics), 3, "3 diagnostic messages")
+        self.expect_diagnostic(diagnostics[0], code=6321, lineNo=13, startEndColumns=(44, 48))
+        self.expect_diagnostic(diagnostics[1], code=2072, lineNo= 7, startEndColumns=( 8, 19))
+        self.expect_diagnostic(diagnostics[2], code=2072, lineNo=15, startEndColumns=( 8, 20))
+
+        solc.send_message(
+            'textDocument/didChange',
+            {
+                'textDocument': {
+                    'uri': self.get_test_file_uri(TEST_NAME)
+                },
+                'contentChanges': [
+                    {
+                        'range': {
+                            'start': { 'line': 7, 'character': 1 },
+                            'end': {   'line': 8, 'character': 1 }
+                        },
+                        'text': ""
+                    }
+                ]
+            }
+        )
+        published_diagnostics = self.wait_for_diagnostics(solc, 1)
+        self.expect_equal(len(published_diagnostics), 1)
+        report = published_diagnostics[0]
+        self.expect_equal(report['uri'], self.get_test_file_uri(TEST_NAME), "Correct file URI")
+        diagnostics = report['diagnostics']
+        self.expect_equal(len(diagnostics), 2)
+        self.expect_diagnostic(diagnostics[0], code=6321, lineNo=12, startEndColumns=(44, 48))
+        self.expect_diagnostic(diagnostics[1], code=2072, lineNo=14, startEndColumns=( 8, 20))
+
+    def test_textDocument_didChange_delete_line_and_close(self, solc: JsonRpcProcess) -> None:
+        # Reuse this test to prepare and ensure it is as expected
+        self.test_textDocument_didOpen_with_relative_import(solc)
+        self.open_file_and_wait_for_diagnostics(solc, 'lib', 2)
+        # lib.sol: Fix the unused variable message by removing it.
+        solc.send_message(
+            'textDocument/didChange',
+            {
+                'textDocument':
+                {
+                    'uri': self.get_test_file_uri('lib')
+                },
+                'contentChanges': # delete the in-body statement: `uint unused;`
+                [
+                    {
+                        'range':
+                        {
+                            'start': { 'line': 12, 'character': 1 },
+                            'end':   { 'line': 13, 'character': 1 }
+                        },
+                        'text': ""
+                    }
+                ]
+            }
+        )
+        published_diagnostics = self.wait_for_diagnostics(solc, 2)
+        self.expect_equal(len(published_diagnostics), 2, "published diagnostics count")
+        report1 = published_diagnostics[0]
+        self.expect_equal(report1['uri'], self.get_test_file_uri('didOpen_with_import'), "Correct file URI")
+        self.expect_equal(len(report1['diagnostics']), 0, "no diagnostics in didOpen_with_import.sol")
+        report2 = published_diagnostics[1]
+        self.expect_equal(report2['uri'], self.get_test_file_uri('lib'), "Correct file URI")
+        self.expect_equal(len(report2['diagnostics']), 0, "no diagnostics in lib.sol")
+
+        # Now close the file and expect the warning to re-appear
+        solc.send_message(
+            'textDocument/didClose',
+            { 'textDocument': { 'uri': self.get_test_file_uri('lib') }}
+        )
+
+        published_diagnostics = self.wait_for_diagnostics(solc, 2)
+        self.verify_didOpen_with_import_diagnostics(published_diagnostics)
+
+    def test_textDocument_opening_two_new_files_edit_and_close(self, solc: JsonRpcProcess) -> None:
+        """
+        Open two new files A and B, let A import B, expect no error,
+        then close B and now expect the error of file B not being found.
+        """
+
+        self.setup_lsp(solc)
+        FILE_A_URI = 'file:///a.sol'
+        solc.send_message('textDocument/didOpen', {
+            'textDocument': {
+                'uri': FILE_A_URI,
+                'languageId': 'Solidity',
+                'version': 1,
+                'text': ''.join([
+                    '// SPDX-License-Identifier: UNLICENSED\n',
+                    'pragma solidity >=0.8.0;\n',
+                ])
+            }
+        })
+        reports = self.wait_for_diagnostics(solc, 1)
+        self.expect_equal(len(reports), 1, "one publish diagnostics notification")
+        self.expect_equal(len(reports[0]['diagnostics']), 0, "should not contain diagnostics")
+
+        FILE_B_URI = 'file:///b.sol'
+        solc.send_message('textDocument/didOpen', {
+            'textDocument': {
+                'uri': FILE_B_URI,
+                'languageId': 'Solidity',
+                'version': 1,
+                'text': ''.join([
+                    '// SPDX-License-Identifier: UNLICENSED\n',
+                    'pragma solidity >=0.8.0;\n',
+                ])
+            }
+        })
+        reports = self.wait_for_diagnostics(solc, 2)
+        self.expect_equal(len(reports), 2, "one publish diagnostics notification")
+        self.expect_equal(len(reports[0]['diagnostics']), 0, "should not contain diagnostics")
+        self.expect_equal(len(reports[1]['diagnostics']), 0, "should not contain diagnostics")
+
+        solc.send_message('textDocument/didChange', {
+            'textDocument': {
+                'uri': FILE_A_URI
+            },
+            'contentChanges': [
+                {
+                    'range': {
+                        'start': { 'line': 2, 'character': 0 },
+                        'end': { 'line': 2, 'character': 0 }
+                    },
+                    'text': 'import "./b.sol";\n'
+                }
+            ]
+        })
+        reports = self.wait_for_diagnostics(solc, 2)
+        self.expect_equal(len(reports), 2, "one publish diagnostics notification")
+        self.expect_equal(len(reports[0]['diagnostics']), 0, "should not contain diagnostics")
+        self.expect_equal(len(reports[1]['diagnostics']), 0, "should not contain diagnostics")
+
+        solc.send_message(
+            'textDocument/didClose',
+            { 'textDocument': { 'uri': FILE_B_URI }}
+        )
+        # We only get one diagnostics message since the diagnostics for b.sol was empty.
+        reports = self.wait_for_diagnostics(solc, 1)
+        self.expect_equal(len(reports), 1, "one publish diagnostics notification")
+        self.expect_diagnostic(reports[0]['diagnostics'][0], 6275, 2, (0, 17)) # a.sol: File B not found
+        self.expect_equal(reports[0]['uri'], FILE_A_URI, "Correct uri")
+
+    def test_textDocument_closing_virtual_file_removes_imported_real_file(self, solc: JsonRpcProcess) -> None:
+        """
+        We open a virtual file that imports a real file with a warning.
+        Once we close the virtual file, the warning is removed from the diagnostics,
+        since the real file is not considered part of the project anymore.
+        """
+
+        self.setup_lsp(solc)
+        FILE_A_URI = f'file://{self.project_root_dir}/a.sol'
+        solc.send_message('textDocument/didOpen', {
+            'textDocument': {
+                'uri': FILE_A_URI,
+                'languageId': 'Solidity',
+                'version': 1,
+                'text':
+                    '// SPDX-License-Identifier: UNLICENSED\n'
+                    'pragma solidity >=0.8.0;\n'
+                    'import "./lib.sol";\n'
+            }
+        })
+        reports = self.wait_for_diagnostics(solc, 2)
+        self.expect_equal(len(reports), 2, '')
+        self.expect_equal(len(reports[0]['diagnostics']), 0, "should not contain diagnostics")
+        self.expect_diagnostic(reports[1]['diagnostics'][0], 2072, 12, (8, 19)) # unused variable in lib.sol
+
+        # Now close the file and expect the warning for lib.sol to be removed
+        solc.send_message(
+            'textDocument/didClose',
+            { 'textDocument': { 'uri': FILE_A_URI }}
+        )
+        reports = self.wait_for_diagnostics(solc, 1)
+        self.expect_equal(len(reports), 1, '')
+        self.expect_equal(reports[0]['uri'], f'file://{self.project_root_dir}/lib.sol', "")
+        self.expect_equal(len(reports[0]['diagnostics']), 0, "should not contain diagnostics")
+
+
+    def test_textDocument_didChange_at_eol(self, solc: JsonRpcProcess) -> None:
+        """
+        Append at one line and insert a new one below.
+        """
+        self.setup_lsp(solc)
+        FILE_NAME = 'didChange_template'
+        FILE_URI = self.get_test_file_uri(FILE_NAME)
+        solc.send_message('textDocument/didOpen', {
+            'textDocument': {
+                'uri': FILE_URI,
+                'languageId': 'Solidity',
+                'version': 1,
+                'text': self.get_test_file_contents(FILE_NAME)
+            }
+        })
+        published_diagnostics = self.wait_for_diagnostics(solc, 1)
+        self.expect_equal(len(published_diagnostics), 1, "one publish diagnostics notification")
+        self.expect_equal(len(published_diagnostics[0]['diagnostics']), 0, "no diagnostics")
+        solc.send_message('textDocument/didChange', {
+            'textDocument': {
+                'uri': FILE_URI
+            },
+            'contentChanges': [
+                {
+                    'range': {
+                        'start': { 'line': 6, 'character': 0 },
+                        'end': { 'line': 6, 'character': 0 }
+                    },
+                    'text': " f"
+                }
+            ]
+        })
+        published_diagnostics = self.wait_for_diagnostics(solc, 1)
+        self.expect_equal(len(published_diagnostics), 1, "one publish diagnostics notification")
+        report2 = published_diagnostics[0]
+        self.expect_equal(report2['uri'], FILE_URI, "Correct file URI")
+        self.expect_equal(len(report2['diagnostics']), 1, "one diagnostic")
+        self.expect_diagnostic(report2['diagnostics'][0], 7858, 6, (1, 2))
+
+        solc.send_message('textDocument/didChange', {
+            'textDocument': { 'uri': FILE_URI },
+            'contentChanges': [
+                {
+                    'range': {
+                        'start': { 'line': 6, 'character': 2 },
+                        'end': { 'line': 6, 'character': 2 }
+                    },
+                    'text': 'unction f() public {}'
+                }
+            ]
+        })
+        published_diagnostics = self.wait_for_diagnostics(solc, 1)
+        self.expect_equal(len(published_diagnostics), 1, "one publish diagnostics notification")
+        report3 = published_diagnostics[0]
+        self.expect_equal(report3['uri'], FILE_URI, "Correct file URI")
+        self.expect_equal(len(report3['diagnostics']), 1, "one diagnostic")
+        self.expect_diagnostic(report3['diagnostics'][0], 4126, 6, (1, 23))
+
+    def test_textDocument_didChange_empty_file(self, solc: JsonRpcProcess) -> None:
+        """
+        Starts with an empty file and changes it to look like
+        the didOpen_with_import test case. Then we can use
+        the same verification calls to ensure it worked as expected.
+        """
+        # This FILE_NAME must be alphabetically before lib.sol to not over-complify
+        # the test logic in verify_didOpen_with_import_diagnostics.
+        FILE_NAME = 'a_new_file'
+        FILE_URI = self.get_test_file_uri(FILE_NAME)
+        self.setup_lsp(solc)
+        solc.send_message('textDocument/didOpen', {
+            'textDocument': {
+                'uri': FILE_URI,
+                'languageId': 'Solidity',
+                'version': 1,
+                'text': ''
+            }
+        })
+        reports = self.wait_for_diagnostics(solc, 1)
+        self.expect_equal(len(reports), 1)
+        report = reports[0]
+        published_diagnostics = report['diagnostics']
+        self.expect_equal(len(published_diagnostics), 2)
+        self.expect_diagnostic(published_diagnostics[0], code=1878, lineNo=0, startEndColumns=(0, 0))
+        self.expect_diagnostic(published_diagnostics[1], code=3420, lineNo=0, startEndColumns=(0, 0))
+        solc.send_message('textDocument/didChange', {
+            'textDocument': {
+                'uri': self.get_test_file_uri('a_new_file')
+            },
+            'contentChanges': [
+                {
+                    'range': {
+                        'start': { 'line': 0, 'character': 0 },
+                        'end': { 'line': 0, 'character': 0 }
+                    },
+                    'text': self.get_test_file_contents('didOpen_with_import')
+                }
+            ]
+        })
+        published_diagnostics = self.wait_for_diagnostics(solc, 2)
+        self.verify_didOpen_with_import_diagnostics(published_diagnostics, 'a_new_file')
+
+    def test_textDocument_didChange_multi_line(self, solc: JsonRpcProcess) -> None:
+        """
+        Starts with an empty file and changes it to multiple times, changing
+        content across lines.
+        """
+        self.setup_lsp(solc)
+        FILE_NAME = 'didChange_template'
+        FILE_URI = self.get_test_file_uri(FILE_NAME)
+        solc.send_message('textDocument/didOpen', {
+            'textDocument': {
+                'uri': FILE_URI,
+                'languageId': 'Solidity',
+                'version': 1,
+                'text': self.get_test_file_contents(FILE_NAME)
+            }
+        })
+        published_diagnostics = self.wait_for_diagnostics(solc, 1)
+        self.expect_equal(len(published_diagnostics), 1, "one publish diagnostics notification")
+        self.expect_equal(len(published_diagnostics[0]['diagnostics']), 0, "no diagnostics")
+        solc.send_message('textDocument/didChange', {
+            'textDocument': { 'uri': FILE_URI },
+            'contentChanges': [
+                {
+                    'range': {
+                        'start': { 'line': 3, 'character': 3 },
+                        'end': { 'line': 4, 'character': 1 }
+                    },
+                    'text': "tract D {\n\n  uint x\n = -1; \n "
+                }
+            ]
+        })
+        published_diagnostics = self.wait_for_diagnostics(solc, 1)
+        self.expect_equal(len(published_diagnostics), 1, "one publish diagnostics notification")
+        report2 = published_diagnostics[0]
+        self.expect_equal(report2['uri'], FILE_URI, "Correct file URI")
+        self.expect_equal(len(report2['diagnostics']), 1, "one diagnostic")
+        self.expect_diagnostic(report2['diagnostics'][0], 7407, 6, (3, 5))
+
+        # Now we are changing the part "x\n = -" of "uint x\n = -1;"
+        solc.send_message('textDocument/didChange', {
+            'textDocument': { 'uri': FILE_URI },
+            'contentChanges': [
+                {
+                    'range': {
+                        'start': { 'line': 5, 'character': 7 },
+                        'end': { 'line': 6, 'character': 4 }
+                    },
+                    'text': "y\n = [\nuint(1),\n3,4]+"
+                }
+            ]
+        })
+        published_diagnostics = self.wait_for_diagnostics(solc, 1)
+        self.expect_equal(len(published_diagnostics), 1, "one publish diagnostics notification")
+        report3 = published_diagnostics[0]
+        self.expect_equal(report3['uri'], FILE_URI, "Correct file URI")
+        self.expect_equal(len(report3['diagnostics']), 2, "two diagnostics")
+        diagnostic = report3['diagnostics'][0]
+        self.expect_equal(diagnostic['code'], 2271, 'diagnostic: 2271')
+        # check multi-line error code
+        self.expect_equal(
+            diagnostic['range'],
+            {
+                'end': {'character': 6, 'line': 8},
+                'start': {'character': 3, 'line': 6}
+            },
+            "diagnostic: check range"
+        )
+        diagnostic = report3['diagnostics'][1]
+        self.expect_equal(diagnostic['code'], 7407, 'diagnostic: 7407')
+        # check multi-line error code
+        self.expect_equal(
+            diagnostic['range'],
+            {
+                'end': {'character': 6, 'line': 8},
+                'start': {'character': 3, 'line': 6}
+            },
+            "diagnostic: check range"
+        )
+
+    # }}}
+    # }}}
+
+if __name__ == "__main__":
+    suite = SolidityLSPTestSuite()
+    exit_code = suite.main()
+    exit(exit_code)

test/solc/CommandLineInterface.cpp

@@ -158,7 +158,7 @@ BOOST_AUTO_TEST_CASE(multiple_input_modes)
 	};
 	string expectedMessage =
 		"The following options are mutually exclusive: "
-		"--help, --license, --version, --standard-json, --link, --assemble, --strict-assembly, --yul, --import-ast. "
+		"--help, --license, --version, --standard-json, --link, --assemble, --strict-assembly, --yul, --import-ast, --lsp. "
 		"Select at most one.";
 
 	for (string const& mode1: inputModeOptions)