clang-tidy modernize-loop-convert: preserve type of alias declaration (bug 28341)

[mgehre]

Summary

Previously, the added test failed with the following fixit:

     char v[5];

-    for(size_t i = 0; i < 5; ++i)
+    for(char value : v)
     {
-        unsigned char value = v[i];
         if (value > 127)

i.e. the variable 'value' changes from unsigned char to signed char. And
thus the following 'if' does not work anymore.

With this commit, the fixit is changed to:

char v[5];

-    for(size_t i = 0; i < 5; ++i)
+    for(unsigned char value : v)
     {
-        unsigned char value = v[i];
         if (value > 127)

[alexfh]

Thank you for fixing the bug! One comment below.

clang-tidy/modernize/LoopConvertCheck.cpp

525

1. Can the AliasVar->getType().isNull() condition be true?
2. If it can, consider !Descriptor.ElemType.isNull().isNull() and AliasVar->getType().isNull(). In this case setting Descriptor.ElemType to AliasVar->getType() (which is null) doesn't make much sense.

I'd probably just wrap the added code in if (!AliasVar->getType().isNull()).

[mgehre]

clang-tidy/modernize/LoopConvertCheck.cpp

525

Thanks for you fast review.

I copied the block from isAliasDecl(). I don't see any reason why the types can be Null, but I'm also not an expert in llvm.

When would a VarDecl have no type? Maybe I should put an assert instead?

[alexfh]

clang-tidy/modernize/LoopConvertCheck.cpp

525

You can try to add an assert and run the check on llvm, for example.

Alternatively, wrap the added code in if (!AliasVar->getType().isNull())

[mgehre]

Added assert.
Runs on llvm code-base without triggering the assert.

[mgehre]

I additionally have run the check on blender and ITK and the assert did not fire.

[mgehre]

Friendly ping

[alexfh]

LG

test/clang-tidy/modernize-loop-convert-extra.cpp

1070

I'd just CHECK-FIXES-NEXT: if (value > 127)

clang-tidy/modernize/LoopConvertCheck.cpp

void LoopConvertCheck::doConversion(
   std::string VarName;
   bool VarNameFromAlias = (Usages.size() == 1) && AliasDecl;
   bool AliasVarIsRef = false;
   bool CanCopy = true;
 
   if (VarNameFromAlias) {
     const auto *AliasVar = cast<VarDecl>(AliasDecl->getSingleDecl());
     VarName = AliasVar->getName().str();
-    AliasVarIsRef = AliasVar->getType()->isReferenceType();
+
+    // Use the type of the alias if it's not the same
+    QualType AliasVarType = AliasVar->getType();
+    assert(!AliasVarType.isNull() && "Type in VarDecl is null");
+    if (AliasVarType->isReferenceType()) {
+      AliasVarType = AliasVarType.getNonReferenceType();
+      AliasVarIsRef = true;
+    }
+    if (Descriptor.ElemType.isNull() ||
+        !Context->hasSameUnqualifiedType(AliasVarType, Descriptor.ElemType))
+      Descriptor.ElemType = AliasVarType;
 
     // We keep along the entire DeclStmt to keep the correct range here.
     SourceRange ReplaceRange = AliasDecl->getSourceRange();
 
     std::string ReplacementText;
     if (AliasUseRequired) {
       ReplacementText = VarName;
     } else if (AliasFromForInit) {

test/clang-tidy/modernize-loop-convert-extra.cpp

void f() {
   // CHECK-FIXES-NEXT: int A{ I };
   // CHECK-FIXES-NEXT: int B{ g(I) };
   // CHECK-FIXES-NEXT: int C{ g( { I } ) };
   // CHECK-FIXES-NEXT: D Dd{ { g( { I } ) } };
   // CHECK-FIXES-NEXT: E Ee{ { { g( { I } ) } } };
 }
 
 } // namespace InitLists
+
+void bug28341() {
+  char v[5];
+  for(int i = 0; i < 5; ++i) {
+      unsigned char value = v[i];
+  // CHECK-MESSAGES: :[[@LINE-2]]:3: warning: use range-based for loop instead
+  // CHECK-FIXES: for(unsigned char value : v)
+  // CHECK-FIXES-NOT: unsigned char value = v[i];
+      if (value > 127)
+        ;
+  }
+}