[clang-tidy] fix insertion location for function pointers in cppcoreguidelines-init-variables (#112091)

Previously, the insertion location for the `= nullptr` fix would be
after the variable name. However, if the variable is of type function
pointer that is not an alias, then the insertion would happen inside the
type specification: `void (*a1)(void*);` -> `void (*a1 =
nullptr)(void*);`.
With this change, the insertion location will be at the next
'terminator'. That is, at the next `,` or `;`, as that will finish the
current declaration: `void (a1)(void*) = nullptr;`.

Fixes #112089

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

@@ -8,9 +8,10 @@
 
 #include "InitVariablesCheck.h"
 
+#include "../utils/LexerUtils.h"
 #include "clang/AST/ASTContext.h"
+#include "clang/AST/Type.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
-#include "clang/Lex/PPCallbacks.h"
 #include "clang/Lex/Preprocessor.h"
 #include <optional>
 
@@ -107,8 +108,9 @@ void InitVariablesCheck::check(const MatchFinder::MatchResult &Result) {
         << MatchedDecl;
     if (*InitializationString != nullptr)
       Diagnostic << FixItHint::CreateInsertion(
-          MatchedDecl->getLocation().getLocWithOffset(
-              MatchedDecl->getName().size()),
+          utils::lexer::findNextTerminator(MatchedDecl->getLocation(),
+                                           *Result.SourceManager,
+                                           Result.Context->getLangOpts()),
           *InitializationString);
     if (AddMathInclude) {
       Diagnostic << IncludeInserter.createIncludeInsertion(

clang-tools-extra/docs/ReleaseNotes.rst

@@ -194,6 +194,10 @@ Changes in existing checks
   fix false positive that floating point variable is only used in increment
   expression.
 
+- Improved :doc:`cppcoreguidelines-init-variables
+  <clang-tidy/checks/cppcoreguidelines/init-variables>` check by fixing the
+  insertion location for function pointers.
+
 - Improved :doc:`cppcoreguidelines-prefer-member-initializer
   <clang-tidy/checks/cppcoreguidelines/prefer-member-initializer>` check to
   avoid false positive when member initialization depends on a structured
@@ -212,9 +216,9 @@ Changes in existing checks
   false positive for C++23 deducing this.
 
 - Improved :doc:`modernize-avoid-c-arrays
-  <clang-tidy/checks/modernize/avoid-c-arrays>` check to suggest using ``std::span``
-  as a replacement for parameters of incomplete C array type in C++20 and 
-  ``std::array`` or ``std::vector`` before C++20.
+  <clang-tidy/checks/modernize/avoid-c-arrays>` check to suggest using 
+  ``std::span`` as a replacement for parameters of incomplete C array type in
+  C++20 and ``std::array`` or ``std::vector`` before C++20.
 
 - Improved :doc:`modernize-loop-convert
   <clang-tidy/checks/modernize/loop-convert>` check to fix false positive when

clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/init-variables.cpp

@@ -134,3 +134,17 @@ void test_clang_diagnostic_error() {
   // CHECK-MESSAGES: :[[@LINE-1]]:3: error: unknown type name 'UnknownType' [clang-diagnostic-error]
   // CHECK-FIXES-NOT: {{^}}  UnknownType b = 0;{{$}}
 }
+
+namespace gh112089 {
+    void foo(void*);
+    using FPtr = void(*)(void*);
+    void test() {
+        void(*a1)(void*);
+  // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: variable 'a1' is not initialized [cppcoreguidelines-init-variables]
+  // CHECK-FIXES: void(*a1)(void*) = nullptr;
+        FPtr a2;
+  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: variable 'a2' is not initialized [cppcoreguidelines-init-variables]
+  // CHECK-FIXES: FPtr a2 = nullptr;
+    }
+} // namespace gh112089
+