yul identifiers with leading or trailing dot are restricted

Changelog.md

@@ -8,6 +8,7 @@ Compiler Features:
 
 
 Bugfixes:
+* Yul: NameSimplifier and VarNameCleaner steps could lead to forbidden identifiers with a leading and/or trailing dot, e.g., `let x._ := f()` would get simplified to `x.`.
 
 
 ### 0.8.26 (2024-05-21)

libyul/optimiser/OptimizerUtilities.cpp

@@ -36,6 +36,17 @@ using namespace solidity::langutil;
 using namespace solidity::util;
 using namespace solidity::yul;
 
+namespace
+{
+
+bool hasLeadingOrTrailingDot(std::string_view const _s)
+{
+	yulAssert(!_s.empty());
+	return _s.front() == '.' || _s.back() == '.';
+}
+
+}
+
 void yul::removeEmptyBlocks(Block& _block)
 {
 	auto isEmptyBlock = [](Statement const& _st) -> bool {
@@ -46,7 +57,7 @@ void yul::removeEmptyBlocks(Block& _block)
 
 bool yul::isRestrictedIdentifier(Dialect const& _dialect, YulString const& _identifier)
 {
-	return _identifier.empty() || TokenTraits::isYulKeyword(_identifier.str()) || _dialect.reservedIdentifier(_identifier);
+	return _identifier.empty() || hasLeadingOrTrailingDot(_identifier.str()) || TokenTraits::isYulKeyword(_identifier.str()) || _dialect.reservedIdentifier(_identifier);
 }
 
 std::optional<evmasm::Instruction> yul::toEVMInstruction(Dialect const& _dialect, YulString const& _name)

test/libyul/objectCompiler/leading_and_trailing_dots.yul

@@ -0,0 +1,20 @@
+{
+  function e(_._) {
+    e(0)
+  }
+  e(2)
+}
+// ----
+// Assembly:
+//     /* "source":39:40   */
+//   0x02
+//     /* "source":4:34   */
+// tag_1:
+//     /* "source":28:29   */
+//   0x00
+//     /* "source":26:30   */
+//   tag_1
+//   jump	// in
+// Bytecode: 60025b5f600256
+// Opcodes: PUSH1 0x2 JUMPDEST PUSH0 PUSH1 0x2 JUMP
+// SourceMappings: 39:1:0:-:0;4:30;28:1;26:4;:::i