Allow basefee as Yul identifier for EVMVersion < london

This was done to prevent basefee from being a breaking change. This change will be removed in 0.9.0.

TODO revert this commit in breaking.

Author: hrkrshnn

libyul/backends/evm/EVMDialect.cpp

@@ -112,14 +112,22 @@ pair<YulString, BuiltinFunctionForEVM> createFunction(
 	return {name, f};
 }
 
-set<YulString> createReservedIdentifiers()
+set<YulString> createReservedIdentifiers(langutil::EVMVersion _evmVersion)
 {
+	// TODO remove this in 0.9.0. We allow creating functions or identifiers in Yul with the name
+	// basefee for VMs before london.
+	auto baseFeeException = [&](evmasm::Instruction _instr) -> bool
+	{
+		return _instr == evmasm::Instruction::BASEFEE && _evmVersion < langutil::EVMVersion::london();
+	};
+
 	set<YulString> reserved;
 	for (auto const& instr: evmasm::c_instructions)
 	{
 		string name = instr.first;
 		transform(name.begin(), name.end(), name.begin(), [](unsigned char _c) { return tolower(_c); });
-		reserved.emplace(name);
+		if (!baseFeeException(instr.second))
+			reserved.emplace(name);
 	}
 	reserved += vector<YulString>{
 		"linkersymbol"_yulstring,
@@ -300,7 +308,7 @@ EVMDialect::EVMDialect(langutil::EVMVersion _evmVersion, bool _objectAccess):
 	m_objectAccess(_objectAccess),
 	m_evmVersion(_evmVersion),
 	m_functions(createBuiltins(_evmVersion, _objectAccess)),
-	m_reserved(createReservedIdentifiers())
+	m_reserved(createReservedIdentifiers(_evmVersion))
 {
 }
 

scripts/error_codes.py

@@ -198,7 +198,8 @@ def examine_id_coverage(top_dir, source_id_to_file_names, new_ids_only=False):
                 # The warning may or may not exist in a compiler build.
         "4591", # "There are more than 256 warnings. Ignoring the rest."
                 # Due to 3805, the warning lists look different for different compiler builds.
-        "1834"  # Unimplemented feature error, as we do not test it anymore via cmdLineTests
+        "1834", # Unimplemented feature error, as we do not test it anymore via cmdLineTests
+        "5430"  # basefee being used in inline assembly for EVMVersion < london
     }
     assert len(test_ids & white_ids) == 0, "The sets are not supposed to intersect"
     test_ids |= white_ids

test/libsolidity/syntaxTests/types/magic_block_basefee_error.sol

@@ -2,14 +2,8 @@ contract C {
     function f() public view returns (uint) {
         return block.basefee;
     }
-    function g() public view returns (uint ret) {
-        assembly {
-            ret := basefee()
-        }
-    }
 }
 // ====
-// EVMVersion: =berlin
+// EVMVersion: <=berlin
 // ----
 // TypeError 5921: (74-87): "basefee" is not supported by the VM version.
-// TypeError 5430: (183-190): The "basefee" instruction is only available for London-compatible VMs (you are currently compiling for "berlin").