[clang-tidy] Keep parentheses when replacing index access in `sizeof` calls (#82166)

Fixes #56021.

3 files changed, 25 insertions, 3 deletions

diff --git a/clang-tools-extra/clang-tidy/modernize/LoopConvertCheck.cpp b/clang-tools-extra/clang-tidy/modernize/LoopConvertCheck.cpp
index f0791da..3229e30 100644
--- a/clang-tools-extra/clang-tidy/modernize/LoopConvertCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/LoopConvertCheck.cpp
@@ -706,13 +706,17 @@ void LoopConvertCheck::doConversion(
         ReplaceText = Usage.Kind == Usage::UK_MemberThroughArrow
                           ? VarNameOrStructuredBinding + "."
                           : VarNameOrStructuredBinding;
-        auto Parents = Context->getParents(*Usage.Expression);
+        const DynTypedNodeList Parents = Context->getParents(*Usage.Expression);
         if (Parents.size() == 1) {
           if (const auto *Paren = Parents[0].get<ParenExpr>()) {
             // Usage.Expression will be replaced with the new index variable,
             // and parenthesis around a simple DeclRefExpr can always be
-            // removed.
-            Range = Paren->getSourceRange();
+            // removed except in case of a `sizeof` operator call.
+            const DynTypedNodeList GrandParents = Context->getParents(*Paren);
+            if (GrandParents.size() != 1 ||
+                GrandParents[0].get<UnaryExprOrTypeTraitExpr>() == nullptr) {
+              Range = Paren->getSourceRange();
+            }
           } else if (const auto *UOP = Parents[0].get<UnaryOperator>()) {
             // If we are taking the address of the loop variable, then we must
             // not use a copy, as it would mean taking the address of the loop's
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 7ca7037..5862942 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -170,6 +170,11 @@ Changes in existing checks
   `AllowStringArrays` option, enabling the exclusion of array types with deduced
   length initialized from string literals.
 
+- Improved :doc:`modernize-loop-convert
+  <clang-tidy/checks/modernize/loop-convert>` check by ensuring that fix-its
+  don't remove parentheses used in ``sizeof`` calls when they have array index
+  accesses as arguments.
+
 - Improved :doc:`modernize-use-override
   <clang-tidy/checks/modernize/use-override>` check to also remove any trailing
   whitespace when deleting the ``virtual`` keyword.
diff --git a/clang-tools-extra/test/clang-tidy/checkers/modernize/loop-convert-basic.cpp b/clang-tools-extra/test/clang-tidy/checkers/modernize/loop-convert-basic.cpp
index c29fbc9f..695925a 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/modernize/loop-convert-basic.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/modernize/loop-convert-basic.cpp
@@ -88,6 +88,19 @@ void f() {
   // CHECK-FIXES-NEXT: printf("Fibonacci number %d has address %p\n", I, &I);
   // CHECK-FIXES-NEXT: Sum += I + 2;
 
+  int Matrix[N][12];
+  unsigned size = 0;
+  for (int I = 0; I < N; ++I) {
+      size += sizeof(Matrix[I]);
+      size += sizeof Matrix[I];
+      size += sizeof((Matrix[I]));
+  }
+  // CHECK-MESSAGES: :[[@LINE-5]]:3: warning: use range-based for loop instead
+  // CHECK-FIXES: for (auto & I : Matrix)
+  // CHECK-FIXES-NEXT: size += sizeof(I);
+  // CHECK-FIXES-NEXT: size += sizeof I;
+  // CHECK-FIXES-NEXT: size += sizeof(I);
+
   Val Teas[N];
   for (int I = 0; I < N; ++I) {
     Teas[I].g();