Fix string.concat and bytes.concat assignment to a constant variable.

Changelog.md

@@ -5,6 +5,7 @@ Language Features:
 Compiler Features:
 
 Bugfixes:
+* TypeChecker: Allow assignment of `string.concat` or `bytes.concat` to constant variables.
 
 
 ### 0.8.31 (2025-12-03)

libsolidity/analysis/TypeChecker.cpp

@@ -3271,11 +3271,21 @@ bool TypeChecker::visit(MemberAccess const& _memberAccess)
 	// TODO some members might be pure, but for example `address(0x123).balance` is not pure
 	// although every subexpression is, so leaving this limited for now.
 	if (auto tt = dynamic_cast<TypeType const*>(exprType))
+	{
 		if (
 			tt->actualType()->category() == Type::Category::Enum ||
 			tt->actualType()->category() == Type::Category::UserDefinedValueType
 		)
 			annotation.isPure = true;
+
+		// `concat` purity depends also on its arguments, but this is checked later, in visit(FunctionCall...)
+		if (
+			// This covers `bytes.concat` and `string.concat`.
+			tt->actualType()->category() == Type::Category::Array &&
+			memberName == "concat"
+		)
+			annotation.isPure = true;
+	}
 	if (
 		auto const* functionType = dynamic_cast<FunctionType const*>(exprType);
 		functionType &&

libsolidity/ast/Types.cpp

@@ -3713,7 +3713,9 @@ bool FunctionType::isPure() const
 		m_kind == Kind::ABIDecode ||
 		m_kind == Kind::MetaType ||
 		m_kind == Kind::Wrap ||
-		m_kind == Kind::Unwrap;
+		m_kind == Kind::Unwrap ||
+		m_kind == Kind::BytesConcat ||
+		m_kind == Kind::StringConcat;
 }
 
 TypePointers FunctionType::parseElementaryTypeVector(strings const& _types)

test/libsolidity/semanticTests/constants/type_information_pure_assignment.sol

@@ -0,0 +1,13 @@
+contract A {
+}
+
+contract B {
+    bytes constant creationCode = type(A).creationCode;
+    bytes constant runtimeCode = type(A).runtimeCode;
+
+    function isEmptyCode() public pure returns (bool) {
+        return creationCode.length > 0 && runtimeCode.length > 0;
+    }
+}
+// ----
+// isEmptyCode() -> true

test/libsolidity/syntaxTests/array/concat/bytes_concat_valid_type_literal.sol

@@ -1,6 +1,6 @@
 contract C {
-    function f() public pure {
-        bytes.concat(
+    function f() public pure returns (bytes memory) {
+        return bytes.concat(
             hex"00",
             hex"aabbcc",
             unicode"abc",

test/libsolidity/syntaxTests/array/concat/bytes_concat_wrong_type_empty_string_literal.sol

@@ -1,6 +1,6 @@
 contract C {
-    function f() public pure {
-        bytes.concat(hex"", unicode"", "");
+    function f() public pure returns (bytes memory) {
+        return bytes.concat(hex"", unicode"", "");
     }
 }
 // ----

test/libsolidity/syntaxTests/constants/abi_decode_pure_assignment.sol

@@ -0,0 +1,7 @@
+bytes constant aEncoded = abi.encode(
+    hex"aaaa"
+);
+
+contract A {
+    bytes constant a = abi.decode(aEncoded, (bytes));
+}

test/libsolidity/syntaxTests/constants/abi_decode_pure_assignment_error.sol

@@ -0,0 +1,9 @@
+contract A {
+    function encoded() private view returns (bytes memory) {
+        return abi.encode(hex"aaaa");
+    }
+
+    bytes constant a = abi.decode(encoded(), (bytes));
+}
+// ----
+// TypeError 8349: (142-172): Initial value for constant variable has to be compile-time constant.

test/libsolidity/syntaxTests/constants/abi_encode_call_pure_assignment.sol

@@ -0,0 +1,4 @@
+contract A {
+    function f() external {}
+    bytes constant fCallA = abi.encodeCall(A.f, ());
+}

test/libsolidity/syntaxTests/constants/abi_encode_call_pure_assignment_error.sol

@@ -0,0 +1,11 @@
+contract A {
+    function f(uint a) external {}
+
+    function getA() private view returns(uint) {
+        return 1;
+    }
+
+    bytes constant fCallA = abi.encodeCall(A.f, (getA()));
+}
+// ----
+// TypeError 8349: (151-180): Initial value for constant variable has to be compile-time constant.

test/libsolidity/syntaxTests/constants/abi_encoding_constant_error.sol

@@ -0,0 +1,13 @@
+contract C {
+    uint k = 1;
+
+    bytes32 constant a = keccak256(abi.encode(1, k));
+    bytes32 constant b = keccak256(abi.encodePacked(uint(1), k));
+    bytes32 constant c = keccak256(abi.encodeWithSelector(0x12345678, k, 2));
+    bytes32 constant d = keccak256(abi.encodeWithSignature("f()", 1, k));
+}
+// ----
+// TypeError 8349: (55-82): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (109-148): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (175-226): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (253-300): Initial value for constant variable has to be compile-time constant.

test/libsolidity/syntaxTests/constants/block_and_tx_properties_pure_assignment_error.sol

@@ -0,0 +1,80 @@
+bytes32 constant blockhGlobal = blockhash(1);
+bytes32 constant blobhGlobal = blobhash(1);
+uint constant bfGlobal = block.basefee;
+uint constant blobbfGlobal = block.blobbasefee;
+uint constant chainIdGlobal = block.chainid;
+address constant coinbaseGlobal = block.coinbase;
+uint constant diffGlobal = block.difficulty;
+uint constant gaslimitGlobal = block.gaslimit;
+uint constant numberGlobal = block.number;
+uint constant prevrandaoGlobal = block.prevrandao;
+uint constant timestampGlobal = block.timestamp;
+uint constant gGlobal = gasleft();
+bytes constant dataGlobal = msg.data;
+address constant senderGlobal = msg.sender;
+bytes4 constant sigGlobal = msg.sig;
+uint constant valueGlobal = msg.value;
+uint constant gaspriceGlobal = tx.gasprice;
+address constant originGlobal = tx.origin;
+
+contract A {
+    bytes32 constant blockh = blockhash(1);
+    bytes32 constant blobh = blobhash(1);
+    uint constant bf = block.basefee;
+    uint constant blobbf = block.blobbasefee;
+    uint constant chainId = block.chainid;
+    address constant coinbase = block.coinbase;
+    uint constant diff = block.difficulty;
+    uint constant gaslimit = block.gaslimit;
+    uint constant number = block.number;
+    uint constant prevrandao = block.prevrandao;
+    uint constant timestamp = block.timestamp;
+    uint constant g = gasleft();
+    bytes constant data = msg.data;
+    address constant sender = msg.sender;
+    bytes4 constant sig = msg.sig;
+    uint constant value = msg.value;
+    uint constant gasprice = tx.gasprice;
+    address constant origin = tx.origin;
+}
+// ====
+// EVMVersion: >=cancun
+// ----
+// TypeError 8349: (32-44): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (77-88): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (115-128): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (159-176): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (208-221): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (257-271): Initial value for constant variable has to be compile-time constant.
+// Warning 8417: (300-316): Since the VM version paris, "difficulty" was replaced by "prevrandao", which now returns a random number based on the beacon chain.
+// TypeError 8349: (300-316): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (349-363): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (394-406): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (441-457): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (491-506): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (532-541): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (571-579): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (613-623): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (653-660): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (690-699): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (732-743): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (777-786): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (832-844): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (875-886): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (911-924): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (953-970): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (1000-1013): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (1047-1061): Initial value for constant variable has to be compile-time constant.
+// Warning 8417: (1088-1104): Since the VM version paris, "difficulty" was replaced by "prevrandao", which now returns a random number based on the beacon chain.
+// TypeError 8349: (1088-1104): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (1135-1149): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (1178-1190): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (1223-1239): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (1271-1286): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (1310-1319): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (1347-1355): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (1387-1397): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (1425-1432): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (1460-1469): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (1500-1511): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (1543-1552): Initial value for constant variable has to be compile-time constant.

test/libsolidity/syntaxTests/constants/bytes_concat_pure_assignment.sol

@@ -0,0 +1,17 @@
+bytes constant abcGlobal = bytes.concat(
+    hex"aaaa",
+    hex"bbbb",
+    hex"cccc"
+);
+
+contract A {
+    bytes public constant abc = bytes.concat(
+        hex"aaaa",
+        hex"bbbb",
+        hex"cccc"
+    );
+
+    bytes public constant abcCopy = abc;
+    bytes public constant abcGlobalCopy = abcGlobal;
+    bytes public constant abcabc = bytes.concat(abc, abcGlobal);
+}

test/libsolidity/syntaxTests/constants/bytes_concat_pure_assignment_error.sol

@@ -0,0 +1,20 @@
+contract A {
+    function getData() public view returns (bytes memory) {
+        return msg.data;
+    }
+
+    bytes constant abData = bytes.concat(
+        hex"aaaa",
+        hex"bbbb",
+        msg.data
+    );
+
+    bytes constant abgetData = bytes.concat(
+        hex"aaaa",
+        hex"bbbb",
+        getData()
+    );
+}
+// ----
+// TypeError 8349: (133-207): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (241-316): Initial value for constant variable has to be compile-time constant.

test/libsolidity/syntaxTests/constants/math_functions_opcodes_pure_assignment_error.sol

@@ -0,0 +1,12 @@
+contract A {
+    uint256 k = 7;
+    uint256 constant amod = addmod(1, 8, k);
+    uint256 constant mmod = mulmod(1, 8, k);
+
+    bytes data = hex"ffff";
+    bytes32 constant keccak = keccak256(data);
+}
+// ----
+// TypeError 8349: (60-75): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (105-120): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (181-196): Initial value for constant variable has to be compile-time constant.

test/libsolidity/syntaxTests/constants/math_functions_precompiles_pure_assignment_error.sol

@@ -0,0 +1,10 @@
+contract A {
+    bytes data = hex"ffff";
+    bytes32 constant sha = sha256(data);
+    bytes20 constant ripemd = ripemd160(data);
+    address constant addr = ecrecover("1234", 1, "0", abi.decode(data, (bytes2)));
+}
+// ----
+// TypeError 8349: (68-80): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (112-127): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (157-210): Initial value for constant variable has to be compile-time constant.

test/libsolidity/syntaxTests/constants/math_functions_pure_assignment.sol

@@ -0,0 +1,7 @@
+bytes32 constant sGlobal = sha256(hex"ffff");
+address constant addrGlobal = ecrecover("1234", 1, "0", abi.decode("", (bytes2)));
+
+contract A {
+    bytes32 constant s = sha256(hex"ffff");
+    address constant addr = ecrecover("1234", 1, "0", abi.decode("", (bytes2)));
+}

test/libsolidity/syntaxTests/constants/string_concat_pure_assignment.sol

@@ -0,0 +1,17 @@
+string constant abcGlobal = string.concat(
+    "aaaa",
+    "bbbb",
+    "cccc"
+);
+
+contract A {
+    string public constant abc = string.concat(
+        "aaaa",
+        "bbbb",
+        "cccc"
+    );
+
+    string public constant abcCopy = abc;
+    string public constant abcGlobalCopy = abcGlobal;
+    string public constant abcabc = string.concat(abc, abcGlobal);
+}

test/libsolidity/syntaxTests/constants/string_concat_pure_assignment_error.sol

@@ -0,0 +1,22 @@
+contract A {
+    string name = "name";
+
+    function getName() public view returns (string memory) {
+        return name;
+    }
+
+    string public constant abName = string.concat(
+        "aaaa",
+        "bbbb",
+        name
+    );
+
+    string public constant abgetName = string.concat(
+        "aaaa",
+        "bbbb",
+        getName()
+    );
+}
+// ----
+// TypeError 8349: (165-230): Initial value for constant variable has to be compile-time constant.
+// TypeError 8349: (272-342): Initial value for constant variable has to be compile-time constant.

test/libsolidity/syntaxTests/constants/type_information_pure_assignment.sol

@@ -0,0 +1,21 @@
+string constant aNameGlobal = type(A).name;
+bytes4 constant iNameGlobal = type(I).interfaceId;
+uint256 constant minGlobal = type(uint256).min;
+uint256 constant maxGlobal = type(uint256).max;
+
+contract B {
+}
+
+interface I {
+    function hello() external pure;
+    function world(int) external pure;
+}
+
+contract A {
+    string constant aName = type(A).name;
+    bytes4 constant iName = type(I).interfaceId;
+    uint256 constant min = type(uint256).min;
+    uint256 constant max = type(uint256).max;
+    bytes creationCodeB = type(B).creationCode;
+    bytes runtimeCodeB = type(B).runtimeCode;
+}

test/libsolidity/syntaxTests/storageLayoutSpecifier/layout_specified_by_bytes_concat.sol

@@ -1,3 +1,3 @@
 contract C layout at uint64(bytes8(bytes.concat("ABCD", "EFGH"))) {}
 // ----
-// TypeError 1139: (21-65): The base slot of the storage layout must be a compile-time constant expression.
+// TypeError 1505: (21-65): The base slot expression contains elements that are not yet supported by the internal constant evaluator and therefore cannot be evaluated at compilation time.

test/libsolidity/syntaxTests/storageLayoutSpecifier/layout_specified_by_kecak256.sol

@@ -1,3 +1,3 @@
 contract C layout at uint(keccak256(bytes.concat("ABCD"))) {}
 // ----
-// TypeError 1139: (21-58): The base slot of the storage layout must be a compile-time constant expression.
+// TypeError 1505: (21-58): The base slot expression contains elements that are not yet supported by the internal constant evaluator and therefore cannot be evaluated at compilation time.