[clang-tidy] Provide fix-its for downcasts in google-readability-casting

[ckandeler]

No description provided.

[llvmbot]

@llvm/pr-subscribers-clang-tools-extra

@llvm/pr-subscribers-clang-tidy

Author: Christian Kandeler (ckandeler)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/165411.diff

2 Files Affected:

• (modified) clang-tools-extra/clang-tidy/google/AvoidCStyleCastsCheck.cpp (+6)
• (modified) clang-tools-extra/test/clang-tidy/checkers/google/readability-casting.cpp (+4-2)

diff --git a/clang-tools-extra/clang-tidy/google/AvoidCStyleCastsCheck.cpp b/clang-tools-extra/clang-tidy/google/AvoidCStyleCastsCheck.cpp
index 174ecb0ed7b77..80c53de0cf237 100644
--- a/clang-tools-extra/clang-tidy/google/AvoidCStyleCastsCheck.cpp
+++ b/clang-tools-extra/clang-tidy/google/AvoidCStyleCastsCheck.cpp
@@ -269,6 +269,12 @@ void AvoidCStyleCastsCheck::check(const MatchFinder::MatchResult &Result) {
       return;
     }
     break;
+  case CK_BaseToDerived:
+    if (!needsConstCast(SourceType, DestType)) {
+      ReplaceWithNamedCast("static_cast");
+      return;
+    }
+    break;
   default:
     break;
   }
diff --git a/clang-tools-extra/test/clang-tidy/checkers/google/readability-casting.cpp b/clang-tools-extra/test/clang-tidy/checkers/google/readability-casting.cpp
index 7ccdf705e8399..f9feb8854249b 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/google/readability-casting.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/google/readability-casting.cpp
@@ -102,9 +102,11 @@ void f(int a, double b, const char *cpc, const void *cpv, X *pX) {
   // CHECK-FIXES: b1 = static_cast<int>(b);
 
   Y *pB = (Y*)pX;
-  // CHECK-MESSAGES: :[[@LINE-1]]:11: warning: {{.*}}; use static_cast/const_cast/reinterpret_cast [
+  // CHECK-MESSAGES: :[[@LINE-1]]:11: warning: {{.*}}; use static_cast {{.*}}
+  // CHECK-FIXES: Y *pB = static_cast<Y*>(pX);
   Y &rB = (Y&)*pX;
-  // CHECK-MESSAGES: :[[@LINE-1]]:11: warning: {{.*}}; use static_cast/const_cast/reinterpret_cast [
+  // CHECK-MESSAGES: :[[@LINE-1]]:11: warning: {{.*}}; use static_cast {{.*}}
+  // CHECK-FIXES: Y &rB = static_cast<Y&>(*pX);
 
   const char *pc3 = (const char*)cpv;
   // CHECK-MESSAGES: :[[@LINE-1]]:21: warning: {{.*}}; use static_cast [

[HerrCai0907]

Is it a best practice to use static_cast for base to derived always?
I think under RTTI, we should use dynamic_cast and under non-RTTI, static_cast could be used also.

[ckandeler]

The fact that the code uses an unchecked cast implies a priori knowledge about the safety to do so, so static_cast seems to be the correct equivalent. Using dynamic_cast would likely incur unwanted overhead.
(I'm not too familiar with the clang-tidy code base: Is it possible/recommended to suggest competing fixes? If so, what happens to the respective code if --fix is used?)

[EugeneZelenko]

Please update Release Notes.