[Clang] Fix -Wunused-private-field false negative with defaulted comparison operators #116871
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@llvm/pr-subscribers-clang Author: Chris White (whiteio) ChangesFix -Wunused-private-field incorrectly suppressing warnings for friend defaulted comparison operators. The warning should only be suppressed when the defaulted comparison is a class member function. Fixes #116270 Full diff: https://github.com/llvm/llvm-project/pull/116871.diff 2 Files Affected:
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 26041e53de5061..e115eb0a3d7e10 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -7535,7 +7535,7 @@ void Sema::CheckExplicitlyDefaultedFunction(Scope *S, FunctionDecl *FD) {
return;
}
- if (DefKind.isComparison())
+ if (DefKind.isComparison() && isa<CXXRecordDecl>(FD->getDeclContext()))
UnusedPrivateFields.clear();
if (DefKind.isSpecialMember()
diff --git a/clang/test/SemaCXX/warn-unused-private-field.cpp b/clang/test/SemaCXX/warn-unused-private-field.cpp
index 1128eacc309d9f..bdd66807dca35f 100644
--- a/clang/test/SemaCXX/warn-unused-private-field.cpp
+++ b/clang/test/SemaCXX/warn-unused-private-field.cpp
@@ -20,6 +20,17 @@ class SpaceShipDefaultCompare {
int operator<=>(const SpaceShipDefaultCompare &) const = default;
};
+class UnusedConstPrivateField {
+ public:
+ UnusedConstPrivateField() : unused_(0) {}
+ private:
+ const int unused_; // expected-warning{{private field 'unused_' is not used}}
+};
+
+class FriendEqDefaultCompare {
+ friend auto operator==(FriendEqDefaultCompare, FriendEqDefaultCompare) -> bool = default;
+};
+
#endif
class NotFullyDefined {
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I'll update my changes to fix the other tests that are failing this evening, sorry about that, should have ran the rest of them after making the change. |
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LGTM Thanks!. Can you add a note in the clang release notes here:
llvm-project/clang/docs/ReleaseNotes.rst
Line 559 in d8a1c6d
I think this should be good for the text:
- Fixed a bug where Clang would not emit ``-Wunused-private-field`` warnings when an unrelated class
defined a defaulted comparison operator (#GH116270).
.. code-block:: c++
class A {
private:
int a; // warning: private field 'a' is not used, no diagnostic previously
};
class C {
bool operator==(const C&) = default;
};
(If you want to build the clang documentation to check locally, you can follow https://github.com/llvm/llvm-project/blob/main/llvm/docs/README.txt#L11 and replace docs-llvm-html with docs-clang-html.)
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Thanks for that @Maetveis! I've updated the release notes. |
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Thanks! I added @AaronBallman, as a reviewer just to make sure I didn't miss anything, as I don't consider myself an expert when it comes to frontend. @AaronBallman I think you can merge if everything looks okay, I'm pretty sure @whiteio does not have commit rights. |
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Hey, @whiteio I'm sorry the review is taking long, Aaron was off for the holidays. In the meantime it looks like some conflicts came up, are you comfortable resolving those or do you need help? I'll ping Aaron or find some other front-end reviewer once the conflicts are resolved. |
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@Maetveis Thanks for letting me know, I'll resolve the conflicts and let you know once they're resolved. |
…arison operators Fix -Wunused-private-field suppressing warnings when defaulted comparison operators are declared as friend functions. The warning should only be suppressed for comparison operators that are class members. Fixes llvm#116270
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Hey @Maetveis, I've addressed the conflicts 👍 |
Thanks, ping @AaronBallman or @erichkeane I would appreciate a second look from someone closer to frontend. |
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@whiteio You seem to have the Keep my email addresses private setting enabled in your account. This will make the merged commit reference |
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@Maetveis I've disabled that setting now. Thanks! |
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/30/builds/11645 Here is the relevant piece of the build log for the reference |
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Thanks for this fix! In our codebase, one example where this warning used to not fire (mostly by coincidence) was a class that did this: While it's true that (You could make the bitfield unnamed and memset the bitfield area to 0, but then you'd have to do that from the class ctor body, meaning you'd have to initialize all member variables there too instead of in the initializer list, and it's pretty awkward, and memsetting member vars is questionable, etc.) Is there a better way to deal with this particular case that I'm not seeing? Or should this warning maybe not fire for member variables that are part of a bitfield, where other parts are used? |
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There are a few ways around this: if you are using c++17 or later, there is #pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wunused-private-field"
// your code for which the warning gets suppressed
#pragma clang diagnostic pop
// not suppressed here |
Note you can also spell the standard attribute as |
Fix -Wunused-private-field incorrectly suppressing warnings for friend defaulted comparison operators. The warning should only be suppressed when the defaulted comparison is a class member function.
Fixes #116270