[clang-tools-extra] [clang-tidy] performance-unnecessary-copy-initialization: Consider static functions (PR #119974)

[Barnabás Pőcze via cfe-commits]

https://github.com/pobrn created https://github.com/llvm/llvm-project/pull/119974

Static member functions can be considered the same way as free functions are, so do that.

---

1. Not sure how many more tests I should add, since this uses the same code paths as free functions.
2. This is the 5th instance of the `isStatic` matcher in `clang-tidy`.


>From 6a160c92bd1210e1ec340d2d14650cc0c9d91459 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Barnab=C3=A1s=20P=C5=91cze?= <pobrn at protonmail.com>
Date: Sat, 14 Dec 2024 16:57:57 +0100
Subject: [PATCH] [clang-tidy] performance-unnecessary-copy-initialization:
 Consider static functions

Static member functions can be considered the same way
as free functions are, so do that.
---
 .../UnnecessaryCopyInitialization.cpp         |  6 ++++-
 .../unnecessary-copy-initialization.cpp       | 24 +++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp b/clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp
index 034894c11bf2c0..778d1d00250315 100644
--- a/clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp
+++ b/clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp
@@ -104,6 +104,10 @@ AST_MATCHER_FUNCTION_P(StatementMatcher,
                                 hasArgument(0, hasType(ReceiverType)))));
 }
 
+namespace {
+AST_MATCHER(CXXMethodDecl, isStatic) { return Node.isStatic(); }
+} // namespace
+
 AST_MATCHER_FUNCTION(StatementMatcher, isConstRefReturningFunctionCall) {
   // Only allow initialization of a const reference from a free function if it
   // has no arguments. Otherwise it could return an alias to one of its
@@ -111,7 +115,7 @@ AST_MATCHER_FUNCTION(StatementMatcher, isConstRefReturningFunctionCall) {
   return callExpr(callee(functionDecl(returns(hasCanonicalType(
                                           matchers::isReferenceToConst())))
                              .bind(FunctionDeclId)),
-                  argumentCountIs(0), unless(callee(cxxMethodDecl())))
+                  argumentCountIs(0), unless(callee(cxxMethodDecl(unless(isStatic())))))
       .bind(InitFunctionCallId);
 }
 
diff --git a/clang-tools-extra/test/clang-tidy/checkers/performance/unnecessary-copy-initialization.cpp b/clang-tools-extra/test/clang-tidy/checkers/performance/unnecessary-copy-initialization.cpp
index d02bb98cf583cb..b5325776f54c61 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/performance/unnecessary-copy-initialization.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/performance/unnecessary-copy-initialization.cpp
@@ -28,6 +28,8 @@ struct ExpensiveToCopyType {
   template <typename A>
   const A &templatedAccessor() const;
   operator int() const; // Implicit conversion to int.
+
+  static const ExpensiveToCopyType &instance();
 };
 
 template <typename T>
@@ -100,6 +102,28 @@ void PositiveFunctionCall() {
   VarCopyConstructed.constMethod();
 }
 
+void PositiveStaticMethodCall() {
+  const auto AutoAssigned = ExpensiveToCopyType::instance();
+  // CHECK-MESSAGES: [[@LINE-1]]:14: warning: the const qualified variable 'AutoAssigned' is copy-constructed from a const reference; consider making it a const reference [performance-unnecessary-copy-initialization]
+  // CHECK-FIXES: const auto& AutoAssigned = ExpensiveToCopyType::instance();
+  AutoAssigned.constMethod();
+
+  const auto AutoCopyConstructed(ExpensiveToCopyType::instance());
+  // CHECK-MESSAGES: [[@LINE-1]]:14: warning: the const qualified variable 'AutoCopyConstructed'
+  // CHECK-FIXES: const auto& AutoCopyConstructed(ExpensiveToCopyType::instance());
+  AutoCopyConstructed.constMethod();
+
+  const ExpensiveToCopyType VarAssigned = ExpensiveToCopyType::instance();
+  // CHECK-MESSAGES: [[@LINE-1]]:29: warning: the const qualified variable 'VarAssigned'
+  // CHECK-FIXES:   const ExpensiveToCopyType& VarAssigned = ExpensiveToCopyType::instance();
+  VarAssigned.constMethod();
+
+  const ExpensiveToCopyType VarCopyConstructed(ExpensiveToCopyType::instance());
+  // CHECK-MESSAGES: [[@LINE-1]]:29: warning: the const qualified variable 'VarCopyConstructed'
+  // CHECK-FIXES: const ExpensiveToCopyType& VarCopyConstructed(ExpensiveToCopyType::instance());
+  VarCopyConstructed.constMethod();
+}
+
 void PositiveMethodCallConstReferenceParam(const ExpensiveToCopyType &Obj) {
   const auto AutoAssigned = Obj.reference();
   // CHECK-MESSAGES: [[@LINE-1]]:14: warning: the const qualified variable 'AutoAssigned'