Fix crash when passing empty strings to bytes.concat()

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.

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))

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))

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"

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"", "");
+    }
+}
+// ----