Always generate code for .selector member access.

Changelog.md

@@ -1,6 +1,7 @@
 ### 0.8.21 (unreleased)
 
 Important Bugfixes:
+ * Code Generator: Always generate code for the expression in ``expression.selector``.
  * Yul Optimizer: Fix ``FullInliner`` step (``i``) not preserving the evaluation order of arguments passed into inlined functions in code that is not in expression-split form (i.e. when using a custom optimizer sequence in which the step not preceded by ``ExpressionSplitter`` (``x``)).
 
 
@@ -8,6 +9,7 @@ Language Features:
  * Allow qualified access to events from other contracts.
  * Relax restrictions on initialization of immutable variables. Reads and writes may now happen at any point at construction time outside of functions and modifiers. Explicit initialization is no longer mandatory.
 
+
 Compiler Features:
  * Commandline Interface: Add ``--ast-compact-json`` output in assembler mode.
  * Commandline Interface: Add ``--ir-ast-json`` and ``--ir-optimized-ast-json`` outputs for Solidity input, providing AST in compact JSON format for IR and optimized IR.
@@ -36,6 +38,7 @@ Bugfixes:
  * Yul Optimizer: Fix ``FullInliner`` step not ignoring code that is not in expression-split form.
  * Yul Optimizer: Fix optimized IR being unnecessarily passed through the Yul optimizer again before bytecode generation.
 
+
 AST Changes:
  * AST: Add the ``experimentalSolidity`` field to the ``SourceUnit`` nodes, which indicate whether the experimental parsing mode has been enabled via ``pragma experimental solidity``.
 

libsolidity/codegen/ExpressionCompiler.cpp

@@ -1659,6 +1659,10 @@ bool ExpressionCompiler::visit(MemberAccess const& _memberAccess)
 	{
 		if (functionType->hasDeclaration())
 		{
+			// Still visit the expression in case it has side effects.
+			_memberAccess.expression().accept(*this);
+			utils().popStackElement(*functionType);
+
 			if (functionType->kind() == FunctionType::Kind::Event)
 				m_context << u256(h256::Arith(util::keccak256(functionType->externalSignature())));
 			else

test/libsolidity/semanticTests/functionTypes/selector_expression_side_effect.sol

@@ -0,0 +1,13 @@
+contract C {
+	uint x;
+	function f() public returns (uint256) {
+		h().f.selector;
+		return x;
+	}
+	function h() public returns (C) {
+		x = 42;
+		return this;
+	}
+}
+// ----
+// f() -> 42