From fa3696878bdabbced2ffe383b81c360e850784f1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kamil=20=C5=9Aliwak?= <kamil.sliwak@codepoets.it>
Date: Fri, 25 Jun 2021 20:48:34 +0200
Subject: [PATCH] Fix crash when passing empty strings to bytes.concat()

---
 Changelog.md                                  |  1 +
 libsolidity/codegen/ExpressionCompiler.cpp    |  2 +-
 libsolidity/codegen/YulUtilFunctions.cpp      |  2 +-
 ...l => bytes_concat_empty_argument_list.sol} |  0
 .../concat/bytes_concat_empty_strings.sol     | 27 +++++++++++++++++++
 ...concat_wrong_type_empty_string_literal.sol |  6 +++++
 6 files changed, 36 insertions(+), 2 deletions(-)
 rename test/libsolidity/semanticTests/array/concat/{bytes_concat_empty.sol => bytes_concat_empty_argument_list.sol} (100%)
 create mode 100644 test/libsolidity/semanticTests/array/concat/bytes_concat_empty_strings.sol
 create mode 100644 test/libsolidity/syntaxTests/array/concat/bytes_concat_wrong_type_empty_string_literal.sol

diff --git a/Changelog.md b/Changelog.md
index d59e1f777..f5de44491 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -10,6 +10,7 @@ Compiler Features:
 
 
 Bugfixes:
+ * Code Generator: Fix crash when passing an empty string literal to ``bytes.concat()``.
  * Code Generator: Fix internal compiler error when calling functions bound to calldata structs and arrays.
  * Code Generator: Fix internal compiler error when passing zero to ``bytes.concat()``.
  * Type Checker: Fix internal error and prevent static calls to unimplemented modifiers.
diff --git a/libsolidity/codegen/ExpressionCompiler.cpp b/libsolidity/codegen/ExpressionCompiler.cpp
index cdd608c29..89f9090a4 100644
--- a/libsolidity/codegen/ExpressionCompiler.cpp
+++ b/libsolidity/codegen/ExpressionCompiler.cpp
@@ -1083,7 +1083,7 @@ bool ExpressionCompiler::visit(FunctionCall const& _functionCall)
 					targetTypes.emplace_back(argument->annotation().type);
 				else if (
 					auto const* literalType = dynamic_cast<StringLiteralType const*>(argument->annotation().type);
-					literalType && literalType->value().size() <= 32
+					literalType && !literalType->value().empty() && literalType->value().size() <= 32
 				)
 					targetTypes.emplace_back(TypeProvider::fixedBytes(static_cast<unsigned>(literalType->value().size())));
 				else if (auto const* literalType = dynamic_cast<RationalNumberType const*>(argument->annotation().type))
diff --git a/libsolidity/codegen/YulUtilFunctions.cpp b/libsolidity/codegen/YulUtilFunctions.cpp
index a887c33da..edc1c4ad2 100644
--- a/libsolidity/codegen/YulUtilFunctions.cpp
+++ b/libsolidity/codegen/YulUtilFunctions.cpp
@@ -2473,7 +2473,7 @@ string YulUtilFunctions::bytesConcatFunction(vector<Type const*> const& _argumen
 			targetTypes.emplace_back(argumentType);
 		else if (
 			auto const* literalType = dynamic_cast<StringLiteralType const*>(argumentType);
-			literalType && literalType->value().size() <= 32
+			literalType && !literalType->value().empty() && literalType->value().size() <= 32
 		)
 			targetTypes.emplace_back(TypeProvider::fixedBytes(static_cast<unsigned>(literalType->value().size())));
 		else if (auto const* literalType = dynamic_cast<RationalNumberType const*>(argumentType))
diff --git a/test/libsolidity/semanticTests/array/concat/bytes_concat_empty.sol b/test/libsolidity/semanticTests/array/concat/bytes_concat_empty_argument_list.sol
similarity index 100%
rename from test/libsolidity/semanticTests/array/concat/bytes_concat_empty.sol
rename to test/libsolidity/semanticTests/array/concat/bytes_concat_empty_argument_list.sol
diff --git a/test/libsolidity/semanticTests/array/concat/bytes_concat_empty_strings.sol b/test/libsolidity/semanticTests/array/concat/bytes_concat_empty_strings.sol
new file mode 100644
index 000000000..0dc856262
--- /dev/null
+++ b/test/libsolidity/semanticTests/array/concat/bytes_concat_empty_strings.sol
@@ -0,0 +1,27 @@
+contract C {
+    function f() public returns (bytes memory) {
+        bytes memory b = "";
+        return bytes.concat(
+            bytes.concat(b),
+            bytes.concat(b, b),
+            bytes.concat("", b),
+            bytes.concat(b, "")
+        );
+    }
+
+    function g() public returns (bytes memory) {
+        return bytes.concat("", "abc", hex"", "abc", unicode"");
+    }
+
+    function h() public returns (bytes memory) {
+        bytes memory b = "";
+        return bytes.concat(b, "abc", b, "abc", b);
+    }
+}
+// ====
+// compileToEwasm: also
+// compileViaYul: also
+// ----
+// f() -> 0x20, 0
+// g() -> 0x20, 6, "abcabc"
+// h() -> 0x20, 6, "abcabc"
diff --git a/test/libsolidity/syntaxTests/array/concat/bytes_concat_wrong_type_empty_string_literal.sol b/test/libsolidity/syntaxTests/array/concat/bytes_concat_wrong_type_empty_string_literal.sol
new file mode 100644
index 000000000..afba249f8
--- /dev/null
+++ b/test/libsolidity/syntaxTests/array/concat/bytes_concat_wrong_type_empty_string_literal.sol
@@ -0,0 +1,6 @@
+contract C {
+    function f() public pure {
+        bytes.concat(hex"", unicode"", "");
+    }
+}
+// ----