From 5c7214cbe343a57540754accb8a4bbc4db3027bd Mon Sep 17 00:00:00 2001
From: Daniel Kirchner <daniel@ekpyron.org>
Date: Mon, 26 Jun 2023 17:14:08 +0200
Subject: [PATCH] Always generate code for .selector member access.

---
 Changelog.md                                        |  3 +++
 libsolidity/codegen/ExpressionCompiler.cpp          |  4 ++++
 .../selector_expression_side_effect.sol             | 13 +++++++++++++
 3 files changed, 20 insertions(+)
 create mode 100644 test/libsolidity/semanticTests/functionTypes/selector_expression_side_effect.sol

diff --git a/Changelog.md b/Changelog.md
index 06a761e6e..c47d26ba2 100644
--- a/Changelog.md
+++ b/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``.
 
diff --git a/libsolidity/codegen/ExpressionCompiler.cpp b/libsolidity/codegen/ExpressionCompiler.cpp
index 25bd15d5a..fa94d2f58 100644
--- a/libsolidity/codegen/ExpressionCompiler.cpp
+++ b/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
diff --git a/test/libsolidity/semanticTests/functionTypes/selector_expression_side_effect.sol b/test/libsolidity/semanticTests/functionTypes/selector_expression_side_effect.sol
new file mode 100644
index 000000000..cdb7b98df
--- /dev/null
+++ b/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