[clang-tidy] Fix cppcoreguidelines-init-variables for invalid vardecl

https://godbolt.org/z/n4cK4fo3o
The checker missed a check for invalid vardecl and this could cause a false positive.

Reviewed By: carlosgalvezp

Differential Revision: https://reviews.llvm.org/D138655

Author: Sockke

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

@@ -59,6 +59,10 @@ void InitVariablesCheck::check(const MatchFinder::MatchResult &Result) {
   const ASTContext &Context = *Result.Context;
   const SourceManager &Source = Context.getSourceManager();
 
+  // Clang diagnostic error may cause the variable to be an invalid int vardecl
+  if (MatchedDecl->isInvalidDecl())
+    return;
+
   // We want to warn about cases where the type name
   // comes from a macro like this:
   //

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

@@ -1,4 +1,4 @@
-// RUN: %check_clang_tidy %s cppcoreguidelines-init-variables %t -- -- -fno-delayed-template-parsing -fexceptions
+// RUN: %check_clang_tidy %s cppcoreguidelines-init-variables -fix-errors %t -- -- -fno-delayed-template-parsing -fexceptions
 // CHECK-FIXES: {{^}}#include <math.h>
 
 // Ensure that function declarations are not changed.
@@ -124,3 +124,13 @@ void uninitialized_enum() {
   Fruit fruit;
   // CHECK-MESSAGES: :[[@LINE-1]]:9: warning: variable 'fruit' is not initialized [cppcoreguidelines-init-variables]
 }
+
+void test_clang_diagnostic_error() {
+  int a;
+  // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: variable 'a' is not initialized [cppcoreguidelines-init-variables]
+  // CHECK-FIXES: {{^}}  int a = 0;{{$}}
+
+  UnknownType b;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: error: unknown type name 'UnknownType' [clang-diagnostic-error]
+  // CHECK-FIXES-NOT: {{^}}  UnknownType b = 0;{{$}}
+}