[Language Server]: Add basic document hover support.

Changelog.md

@@ -7,6 +7,7 @@ Compiler Features:
 * Commandline Interface: Add `--no-cbor-metadata` that skips CBOR metadata from getting appended at the end of the bytecode.
 * Standard JSON: Add a boolean field `settings.metadata.appendCBOR` that skips CBOR metadata from getting appended at the end of the bytecode.
 * Yul Optimizer: Allow replacing the previously hard-coded cleanup sequence by specifying custom steps after a colon delimiter (``:``) in the sequence string.
+* Language Server: Add basic document hover support.
 
 
 Bugfixes:

libsolidity/CMakeLists.txt

@@ -155,6 +155,8 @@ set(sources
 	interface/StorageLayout.h
 	interface/Version.cpp
 	interface/Version.h
+	lsp/DocumentHoverHandler.cpp
+	lsp/DocumentHoverHandler.h
 	lsp/FileRepository.cpp
 	lsp/FileRepository.h
 	lsp/GotoDefinition.cpp

libsolidity/lsp/DocumentHoverHandler.cpp

@@ -0,0 +1,126 @@
+/*
+	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/DocumentHoverHandler.h>
+#include <libsolidity/lsp/Utils.h>
+
+#include <fmt/format.h>
+
+namespace solidity::lsp
+{
+
+using namespace std;
+
+using namespace solidity::lsp;
+using namespace solidity::langutil;
+using namespace solidity::frontend;
+
+namespace
+{
+
+struct MarkdownBuilder
+{
+	stringstream result;
+
+	MarkdownBuilder& solidityCode(string const& _code)
+	{
+		auto constexpr SolidityLanguageId = "solidity";
+		result << "```" << SolidityLanguageId << '\n' << _code << "\n```\n\n";
+		return *this;
+	}
+
+	MarkdownBuilder& paragraph(string const& _text)
+	{
+		if (!_text.empty())
+		{
+			result << _text << '\n';
+			if (_text.back() != '\n') // We want double-LF to ensure constructing a paragraph.
+				result << '\n';
+		}
+		return *this;
+	}
+};
+
+}
+
+void DocumentHoverHandler::operator()(MessageID _id, Json::Value const& _args)
+{
+	auto const [sourceUnitName, lineColumn] = HandlerBase(*this).extractSourceUnitNameAndLineColumn(_args);
+	auto const [sourceNode, sourceOffset] = m_server.astNodeAndOffsetAtSourceLocation(sourceUnitName, lineColumn);
+
+	MarkdownBuilder markdown{};
+	auto rangeToHighlight = toRange(sourceNode->location());
+
+	// Try getting the type definition of the underlying AST node, if available.
+	if (auto const* expression = dynamic_cast<Expression const*>(sourceNode))
+	{
+		if (auto const* declaration = ASTNode::referencedDeclaration(*expression))
+			if (declaration->type())
+				markdown.solidityCode(declaration->type()->toString(false));
+	}
+	else if (auto const* declaration = dynamic_cast<Declaration const*>(sourceNode))
+	{
+		if (declaration->type())
+			markdown.solidityCode(declaration->type()->toString(false));
+	}
+	else if (auto const* identifierPath = dynamic_cast<IdentifierPath const*>(sourceNode))
+	{
+		for (size_t i = 0; i < identifierPath->path().size(); ++i)
+		{
+			if (identifierPath->pathLocations()[i].containsOffset(sourceOffset))
+			{
+				rangeToHighlight = toRange(identifierPath->pathLocations()[i]);
+
+				if (i < identifierPath->annotation().pathDeclarations.size())
+				{
+					Declaration const* declaration = identifierPath->annotation().pathDeclarations[i];
+					if (declaration && declaration->type())
+						markdown.solidityCode(declaration->type()->toString(false));
+					if (auto const* structurallyDocumented = dynamic_cast<StructurallyDocumented const*>(declaration))
+						if (structurallyDocumented->documentation()->text())
+							markdown.paragraph(*structurallyDocumented->documentation()->text());
+				}
+				break;
+			}
+		}
+	}
+
+	// If this AST node contains documentation itself, append it.
+	if (auto const* documented = dynamic_cast<StructurallyDocumented const*>(sourceNode))
+	{
+		if (documented->documentation())
+			markdown.paragraph(*documented->documentation()->text());
+	}
+
+	auto tooltipText = markdown.result.str();
+
+	if (tooltipText.empty())
+	{
+		client().reply(_id, Json::nullValue);
+		return;
+	}
+
+	Json::Value reply = Json::objectValue;
+	reply["range"] = rangeToHighlight;
+	reply["contents"]["kind"] = "markdown";
+	reply["contents"]["value"] = std::move(tooltipText);
+
+	client().reply(_id, reply);
+}
+
+}

libsolidity/lsp/DocumentHoverHandler.h

@@ -0,0 +1,32 @@
+/*
+	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/HandlerBase.h>
+
+namespace solidity::lsp
+{
+
+class DocumentHoverHandler: public HandlerBase
+{
+public:
+	using HandlerBase::HandlerBase;
+
+	void operator()(MessageID, Json::Value const&);
+};
+
+}

libsolidity/lsp/LanguageServer.cpp

@@ -25,6 +25,7 @@
 #include <libsolidity/lsp/Utils.h>
 
 // LSP feature implementations
+#include <libsolidity/lsp/DocumentHoverHandler.h>
 #include <libsolidity/lsp/GotoDefinition.h>
 #include <libsolidity/lsp/RenameSymbol.h>
 #include <libsolidity/lsp/SemanticTokensBuilder.h>
@@ -144,6 +145,7 @@ LanguageServer::LanguageServer(Transport& _transport):
 		{"textDocument/didOpen", bind(&LanguageServer::handleTextDocumentDidOpen, this, _2)},
 		{"textDocument/didChange", bind(&LanguageServer::handleTextDocumentDidChange, this, _2)},
 		{"textDocument/didClose", bind(&LanguageServer::handleTextDocumentDidClose, this, _2)},
+		{"textDocument/hover", DocumentHoverHandler(*this) },
 		{"textDocument/rename", RenameSymbol(*this) },
 		{"textDocument/implementation", GotoDefinition(*this) },
 		{"textDocument/semanticTokens/full", bind(&LanguageServer::semanticTokensFull, this, _1, _2)},
@@ -417,6 +419,7 @@ void LanguageServer::handleInitialize(MessageID _id, Json::Value const& _args)
 	replyArgs["capabilities"]["semanticTokensProvider"]["range"] = false;
 	replyArgs["capabilities"]["semanticTokensProvider"]["full"] = true; // XOR requests.full.delta = true
 	replyArgs["capabilities"]["renameProvider"] = true;
+	replyArgs["capabilities"]["hoverProvider"] = true;
 
 	m_client.reply(_id, std::move(replyArgs));
 }
@@ -541,19 +544,21 @@ void LanguageServer::handleTextDocumentDidClose(Json::Value const& _args)
 	compileAndUpdateDiagnostics();
 }
 
-
 ASTNode const* LanguageServer::astNodeAtSourceLocation(std::string const& _sourceUnitName, LineColumn const& _filePos)
 {
-	if (m_compilerStack.state() < CompilerStack::AnalysisPerformed)
-		return nullptr;
-
-	if (!m_fileRepository.sourceUnits().count(_sourceUnitName))
-		return nullptr;
-
-	if (optional<int> sourcePos =
-		m_compilerStack.charStream(_sourceUnitName).translateLineColumnToPosition(_filePos))
-		return locateInnermostASTNode(*sourcePos, m_compilerStack.ast(_sourceUnitName));
-	else
-		return nullptr;
+	return get<ASTNode const*>(astNodeAndOffsetAtSourceLocation(_sourceUnitName, _filePos));
 }
 
+tuple<ASTNode const*, int> LanguageServer::astNodeAndOffsetAtSourceLocation(std::string const& _sourceUnitName, LineColumn const& _filePos)
+{
+	if (m_compilerStack.state() < CompilerStack::AnalysisPerformed)
+		return {nullptr, -1};
+	if (!m_fileRepository.sourceUnits().count(_sourceUnitName))
+		return {nullptr, -1};
+
+	optional<int> sourcePos = m_compilerStack.charStream(_sourceUnitName).translateLineColumnToPosition(_filePos);
+	if (!sourcePos)
+		return {nullptr, -1};
+
+	return {locateInnermostASTNode(*sourcePos, m_compilerStack.ast(_sourceUnitName)), *sourcePos};
+}

libsolidity/lsp/LanguageServer.h

@@ -77,6 +77,7 @@ public:
 
 	FileRepository& fileRepository() noexcept { return m_fileRepository; }
 	Transport& client() noexcept { return m_client; }
+	std::tuple<frontend::ASTNode const*, int> astNodeAndOffsetAtSourceLocation(std::string const& _sourceUnitName, langutil::LineColumn const& _filePos);
 	frontend::ASTNode const* astNodeAtSourceLocation(std::string const& _sourceUnitName, langutil::LineColumn const& _filePos);
 	frontend::CompilerStack const& compilerStack() const noexcept { return m_compilerStack; }
 

test/libsolidity/lsp/hover/hover.sol

@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity >=0.8.0;
+
+/// Documenting another contract here.
+contract AnotherContract {}
+
+/// User being documented.
+contract User
+{
+    /// Some enum value.
+    enum SomeEnum
+    {
+        Red,
+        Blue
+    }
+
+    /// publicVariable being documented.
+    SomeEnum public publicVariable;
+//  ^ @Cursor1
+//  ^^^^^^^^ @Cursor1Range
+
+    // not documented
+    mapping(int => User.SomeEnum) someRemapping;
+//                      ^ @Cursor2
+//                      ^^^^^^^^ @Cursor2Range
+
+    /// Documenting the setContract().
+    function setValue(User.SomeEnum _value) public
+//                    ^ @Cursor3
+//                    ^^^^ @Cursor3Range
+    {
+        publicVariable = _value;
+//      ^ @Cursor4
+//      ^^^^^^^^^^^^^^ @Cursor4Range
+    }
+
+    function createAnotherContract() public returns (AnotherContract)
+    {
+        return new AnotherContract();
+//                 ^ @Cursor5
+//                 ^^^^^^^^^^^^^^^ @Cursor5Range
+    }
+}
+// ----
+// -> textDocument/hover {
+//     "position": @Cursor1
+// }
+// <- {
+//     "contents": {
+//         "kind": "markdown",
+//         "value": "```solidity\ntype(enum User.SomeEnum)\n```\n\n"
+//     },
+//     "range": @Cursor1Range
+// }
+// -> textDocument/hover {
+//     "position": @Cursor2
+// }
+// <- {
+//     "contents": {
+//         "kind": "markdown",
+//         "value": "```solidity\ntype(enum User.SomeEnum)\n```\n\n"
+//     },
+//     "range": @Cursor2Range
+// }
+// -> textDocument/hover {
+//     "position": @Cursor3
+// }
+// <- {
+//     "contents": {
+//         "kind": "markdown",
+//         "value": "```solidity\ntype(contract User)\n```\n\nUser being documented.\n\n"
+//     },
+//     "range": @Cursor3Range
+// }
+// -> textDocument/hover {
+//     "position": @Cursor4
+// }
+// <- {
+//     "contents": {
+//         "kind": "markdown",
+//         "value": "```solidity\nenum User.SomeEnum\n```\n\n"
+//     },
+//     "range": @Cursor4Range
+// }
+// -> textDocument/hover {
+//     "position": @Cursor5
+// }
+// <- {
+//     "contents": {
+//         "kind": "markdown",
+//         "value": "```solidity\ntype(contract AnotherContract)\n```\n\nDocumenting another contract here.\n\n"
+//     },
+//     "range": @Cursor5Range
+// }