[clang-tools-extra] [clang-tidy] Fix invalid fix-it for macro expansions (PR #227984)

[Peiqi Li via cfe-commits]

https://github.com/voyager-jhk updated https://github.com/llvm/llvm-project/pull/227984

>From 2c83c3b872d4df82693e1422a06f7bcabd932529 Mon Sep 17 00:00:00 2001
From: voyager-jhk <voyager.lpq at gmail.com>
Date: Thu, 1 Oct 2026 15:20:28 +0800
Subject: [PATCH 1/2] [clang-tidy] Fix invalid fix-it for macro expansions

Do not offer a fix-it for one-character strings from macro expansions.

Fixes #222970
---
 .../performance/PreferSingleCharOverloadsCheck.cpp  | 13 ++++++++-----
 clang-tools-extra/docs/ReleaseNotes.md              |  5 +++++
 .../performance/prefer-single-char-overloads.cpp    | 10 ++++++++++
 3 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/clang-tools-extra/clang-tidy/performance/PreferSingleCharOverloadsCheck.cpp b/clang-tools-extra/clang-tidy/performance/PreferSingleCharOverloadsCheck.cpp
index d5d1784c0a0b7..a62ef1254e806 100644
--- a/clang-tools-extra/clang-tidy/performance/PreferSingleCharOverloadsCheck.cpp
+++ b/clang-tools-extra/clang-tidy/performance/PreferSingleCharOverloadsCheck.cpp
@@ -101,11 +101,14 @@ void PreferSingleCharOverloadsCheck::check(
   if (!Replacement)
     return;
 
-  diag(Literal->getBeginLoc(), "%0 called with a string literal consisting of "
-                               "a single character; consider using the more "
-                               "efficient overload accepting a character")
-      << FindFunc
-      << FixItHint::CreateReplacement(Literal->getSourceRange(), *Replacement);
+  const auto Diag = diag(Literal->getBeginLoc(),
+                         "%0 called with a string literal consisting of "
+                         "a single character; consider using the more "
+                         "efficient overload accepting a character")
+                    << FindFunc;
+  if (!Literal->getBeginLoc().isMacroID() && !Literal->getEndLoc().isMacroID())
+    Diag << FixItHint::CreateReplacement(Literal->getSourceRange(),
+                                         *Replacement);
 }
 
 } // namespace clang::tidy::performance
diff --git a/clang-tools-extra/docs/ReleaseNotes.md b/clang-tools-extra/docs/ReleaseNotes.md
index 94e0f279d1c6c..8b32c22542aeb 100644
--- a/clang-tools-extra/docs/ReleaseNotes.md
+++ b/clang-tools-extra/docs/ReleaseNotes.md
@@ -295,6 +295,11 @@ infrastructure are described first, followed by tool-specific sections.
   {option}`ForRangeLoopClasses` to configure container classes that can be used
   as sources in range-based `for` loops.
 
+- Improved {doc}`performance-prefer-single-char-overloads
+  <clang-tidy/checks/performance/prefer-single-char-overloads>` check to
+  avoid offering fix-its for string literals originating from macro
+  expansions.
+
 - Improved {doc}`readability-convert-member-functions-to-static
   <clang-tidy/checks/readability/convert-member-functions-to-static>` check by
   fixing a crash when checking a const-qualified method declared with the
diff --git a/clang-tools-extra/test/clang-tidy/checkers/performance/prefer-single-char-overloads.cpp b/clang-tools-extra/test/clang-tidy/checkers/performance/prefer-single-char-overloads.cpp
index 46bbf3c20f8fd..14af39aded0b6 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/performance/prefer-single-char-overloads.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/performance/prefer-single-char-overloads.cpp
@@ -146,6 +146,16 @@ int Macros() {
   // CHECK-MESSAGES: [[@LINE-2]]:37: warning: 'find' called with a string literal
 }
 
+#define TOKEN_SEPARATING_CHARACTER "_"
+// CHECK-FIXES: #define TOKEN_SEPARATING_CHARACTER "_"
+
+void foo() {
+  std::string a;
+  a += TOKEN_SEPARATING_CHARACTER;
+  // CHECK-MESSAGES: [[@LINE-1]]:8: warning: 'operator+=' called with a
+  // CHECK-FIXES: a += TOKEN_SEPARATING_CHARACTER;
+}
+
 void SubstitutedTemplateType() {
   Wrapper<std::string>().value.find("a");
   // CHECK-MESSAGES: [[@LINE-1]]:37: warning: 'find' called with a string literal

>From 0a60ba84777b0b0ab9131df8c9c8c549abc78964 Mon Sep 17 00:00:00 2001
From: voyager-jhk <voyager.lpq at gmail.com>
Date: Mon, 5 Oct 2026 15:11:53 +0800
Subject: [PATCH 2/2] Check all concatenated string tokens for macro expansions

---
 .../performance/PreferSingleCharOverloadsCheck.cpp     |  4 +++-
 .../performance/prefer-single-char-overloads.cpp       | 10 ++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/clang-tools-extra/clang-tidy/performance/PreferSingleCharOverloadsCheck.cpp b/clang-tools-extra/clang-tidy/performance/PreferSingleCharOverloadsCheck.cpp
index a62ef1254e806..4f62bd2be7d83 100644
--- a/clang-tools-extra/clang-tidy/performance/PreferSingleCharOverloadsCheck.cpp
+++ b/clang-tools-extra/clang-tidy/performance/PreferSingleCharOverloadsCheck.cpp
@@ -11,6 +11,7 @@
 #include "../utils/OptionsUtils.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
 #include "llvm/Support/raw_ostream.h"
+#include <algorithm>
 #include <optional>
 
 using namespace clang::ast_matchers;
@@ -106,7 +107,8 @@ void PreferSingleCharOverloadsCheck::check(
                          "a single character; consider using the more "
                          "efficient overload accepting a character")
                     << FindFunc;
-  if (!Literal->getBeginLoc().isMacroID() && !Literal->getEndLoc().isMacroID())
+  if (std::none_of(Literal->tokloc_begin(), Literal->tokloc_end(),
+                   [](SourceLocation Loc) { return Loc.isMacroID(); }))
     Diag << FixItHint::CreateReplacement(Literal->getSourceRange(),
                                          *Replacement);
 }
diff --git a/clang-tools-extra/test/clang-tidy/checkers/performance/prefer-single-char-overloads.cpp b/clang-tools-extra/test/clang-tidy/checkers/performance/prefer-single-char-overloads.cpp
index 14af39aded0b6..58f28f8ff9ecf 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/performance/prefer-single-char-overloads.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/performance/prefer-single-char-overloads.cpp
@@ -156,6 +156,16 @@ void foo() {
   // CHECK-FIXES: a += TOKEN_SEPARATING_CHARACTER;
 }
 
+#define SEP "_"
+// CHECK-FIXES: #define SEP "_"
+
+void ConcatenatedMacro() {
+  std::string s;
+  s += "" SEP "";
+  // CHECK-MESSAGES: [[@LINE-1]]:8: warning: 'operator+=' called with a
+  // CHECK-FIXES: s += "" SEP "";
+}
+
 void SubstitutedTemplateType() {
   Wrapper<std::string>().value.find("a");
   // CHECK-MESSAGES: [[@LINE-1]]:37: warning: 'find' called with a string literal