[clang-tidy] Do not lint on attribute macros (#164806)

`cppcoreguidelines-macro-usage` lint incorrectly identifies these macros
as candidates for rewrite into template arguments. There are no,
variadic or not, equivalent to these macros using templated functions.

In short, we should not suggest code writers to rewrite this macro with
`constexpr` functions.

```c
#define FORMAT_STR(format_msg, first_idx) __attribute__((format(printf, format_msg, first_idx)))
```

Signed-off-by: Xiangfei Ding <dingxiangfei2009@protonmail.ch>

clang-tools-extra/clang-tidy/cppcoreguidelines/MacroUsageCheck.cpp

@@ -82,6 +82,15 @@ void MacroUsageCheck::registerPPCallbacks(const SourceManager &SM,
 void MacroUsageCheck::warnMacro(const MacroDirective *MD, StringRef MacroName) {
   const MacroInfo *Info = MD->getMacroInfo();
   StringRef Message;
+  bool MacroBodyExpressionLike;
+  if (Info->getNumTokens() > 0) {
+    const Token &Tok = Info->getReplacementToken(0);
+    // Now notice that keywords like `__attribute` cannot be a leading
+    // token in an expression.
+    MacroBodyExpressionLike = !Tok.is(tok::kw___attribute);
+  } else {
+    MacroBodyExpressionLike = true;
+  }
 
   if (llvm::all_of(Info->tokens(), std::mem_fn(&Token::isLiteral)))
     Message = "macro '%0' used to declare a constant; consider using a "
@@ -89,10 +98,10 @@ void MacroUsageCheck::warnMacro(const MacroDirective *MD, StringRef MacroName) {
   // A variadic macro is function-like at the same time. Therefore variadic
   // macros are checked first and will be excluded for the function-like
   // diagnostic.
-  else if (Info->isVariadic())
+  else if (Info->isVariadic() && MacroBodyExpressionLike)
     Message = "variadic macro '%0' used; consider using a 'constexpr' "
               "variadic template function";
-  else if (Info->isFunctionLike())
+  else if (Info->isFunctionLike() && MacroBodyExpressionLike)
     Message = "function-like macro '%0' used; consider a 'constexpr' template "
               "function";
 

clang-tools-extra/docs/ReleaseNotes.rst

@@ -325,6 +325,12 @@ Changes in existing checks
   <clang-tidy/checks/cppcoreguidelines/init-variables>` check by fixing the
   insertion location for function pointers with multiple parameters.
 
+- Improved :doc:`cppcoreguidelines-macro-usage
+  <clang-tidy/checks/cppcoreguidelines/macro-usage>` check by excluding macro
+  bodies that starts with ``__attribute__((..))`` keyword.
+  Such a macro body is unlikely a proper expression and so suggesting users
+  an impossible rewrite into a template function should be avoided.
+
 - Improved :doc:`cppcoreguidelines-prefer-member-initializer
   <clang-tidy/checks/cppcoreguidelines/prefer-member-initializer>` check to
   avoid false positives on inherited members in class templates.

clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/macro-usage.cpp

@@ -47,4 +47,6 @@
 #define DLLEXPORTS __declspec(dllimport)
 #endif
 
+#define ATTRIBUTE_MACRO(...) __attribute__(__VA_ARGS__)
+
 #endif