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

Summary:
Previoly, the added test failed with the fillowing 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)

Reviewers: alexfh, klimek

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D22069

llvm-svn: 276111

clang-tools-extra/clang-tidy/modernize/LoopConvertCheck.cpp

@@ -517,7 +517,17 @@ void LoopConvertCheck::doConversion(
   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();

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

@@ -1060,3 +1060,15 @@ void f() {
 }
 
 } // namespace InitLists
+
+void bug28341() {
+  char v[5];
+  for(int i = 0; i < 5; ++i) {
+      unsigned char value = v[i];
+      if (value > 127)
+        ;
+  // CHECK-MESSAGES: :[[@LINE-4]]:3: warning: use range-based for loop instead
+  // CHECK-FIXES: for(unsigned char value : v)
+  // CHECK-FIXES-NEXT: if (value > 127)
+  }
+}