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[clang-tidy] Provide fix-its for downcasts in google-readability-casting #165411

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[clang-tidy] Provide fix-its for downcasts in google-readability-casting #165411

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6 changes: 6 additions & 0 deletions clang-tools-extra/clang-tidy/google/AvoidCStyleCastsCheck.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Comment on lines +272 to +277
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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.

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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?)

default:
break;
}
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4 changes: 4 additions & 0 deletions clang-tools-extra/docs/ReleaseNotes.rst
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Expand Up @@ -334,6 +334,10 @@ Changes in existing checks
adding an option to allow pointer arithmetic via prefix/postfix increment or
decrement operators.

- Improved :doc:`google-readability-casting
<clang-tidy/checks/google/readability-casting>` check by adding a fix-it
for downcasts.

- Improved :doc:`llvm-prefer-isa-or-dyn-cast-in-conditionals
<clang-tidy/checks/llvm/prefer-isa-or-dyn-cast-in-conditionals>` check:

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6 changes: 4 additions & 2 deletions clang-tools-extra/test/clang-tidy/checkers/google/readability-casting.cpp
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Expand Up @@ -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 [
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