[clang] Warn [[clang::lifetimebound]] misusages on types #118281

emaxx-google · 2024-12-02T10:48:45Z

Emit the "cannot be applied to types" warning instead of silently ignoring the attribute when it's attempted to be used on a type (instead of a function argument or the function definition).

Before this commit, the warning has been printed when the attribute was (mis)used on a decl-specifier, but not in other places in a declarator.

Examples where the warning starts being emitted with this commit:

  int * [[clang::lifetimebound]] x;

  void f(int * [[clang::lifetimebound]] x);

  void g(int * [[clang::lifetimebound]]);

Note that the last example is the case of an unnamed function parameter. While in theory Clang could've supported the [[clang::lifetimebound]] analysis for unnamed parameters, it doesn't currently, so the commit at least makes the situation better by highlighting this as a warning instead of a silent ignore - which was reported at #96034.

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github-actions · 2024-12-02T10:49:04Z

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llvmbot · 2024-12-02T12:11:36Z

@llvm/pr-subscribers-clang

Author: Maksim Ivanov (emaxx-google)

Changes

Emit the "cannot be applied to types" warning instead of silently ignoring the attribute when it's attempted to be used on a type (instead of a function argument or the function definition).

Before this commit, the warning has been printed when the attribute was (mis)used on a decl-specifier, but not in other places in a declarator.

Examples where the warning starts being emitted with this commit:

  int * [[clang::lifetimebound]] x;

  void f(int * [[clang::lifetimebound]] x);

  void g(int * [[clang::lifetimebound]]);

Note that the last example is the case of an unnamed function parameter. While in theory Clang could've supported the [[clang::lifetimebound]], it doesn't currently, so the commit at least makes the situation better by highlighting this as a warning instead of a silent ignore.

Full diff: https://github.com/llvm/llvm-project/pull/118281.diff

2 Files Affected:

(modified) clang/lib/Sema/SemaType.cpp (+2)
(modified) clang/test/SemaCXX/attr-lifetimebound.cpp (+11-2)

diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index f32edc5ac06440..200056bddc9b70 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -8612,7 +8612,9 @@ static void HandleLifetimeBoundAttr(TypeProcessingState &State,
     CurType = State.getAttributedType(
         createSimpleAttr<LifetimeBoundAttr>(State.getSema().Context, Attr),
         CurType, CurType);
+    return;
   }
+  State.getSema().Diag(Attr.getLoc(), diag::err_attribute_not_type_attr) << Attr << Attr.isRegularKeywordAttribute();
 }
 
 static void HandleLifetimeCaptureByAttr(TypeProcessingState &State,
diff --git a/clang/test/SemaCXX/attr-lifetimebound.cpp b/clang/test/SemaCXX/attr-lifetimebound.cpp
index f89b556f5bba08..5f10dea97c29b4 100644
--- a/clang/test/SemaCXX/attr-lifetimebound.cpp
+++ b/clang/test/SemaCXX/attr-lifetimebound.cpp
@@ -9,11 +9,20 @@ namespace usage_invalid {
     ~A() [[clang::lifetimebound]]; // expected-error {{cannot be applied to a destructor}}
     static int *static_class_member() [[clang::lifetimebound]]; // expected-error {{static member function has no implicit object parameter}}
     int *explicit_object(this A&) [[clang::lifetimebound]]; // expected-error {{explicit object member function has no implicit object parameter}}
-    int not_function [[clang::lifetimebound]]; // expected-error {{only applies to parameters and implicit object parameters}}
-    int [[clang::lifetimebound]] also_not_function; // expected-error {{cannot be applied to types}}
+    int attr_on_var [[clang::lifetimebound]]; // expected-error {{only applies to parameters and implicit object parameters}}
+    int [[clang::lifetimebound]] attr_on_int; // expected-error {{cannot be applied to types}}
+    int * [[clang::lifetimebound]] attr_on_int_ptr; // expected-error {{cannot be applied to types}}
+    int * [[clang::lifetimebound]] * attr_on_int_ptr_ptr; // expected-error {{cannot be applied to types}}
+    int (* [[clang::lifetimebound]] attr_on_func_ptr)(); // expected-error {{cannot be applied to types}}
     void void_return_member() [[clang::lifetimebound]]; // expected-error {{'lifetimebound' attribute cannot be applied to an implicit object parameter of a function that returns void; did you mean 'lifetime_capture_by(X)'}}
   };
   int *attr_with_param(int &param [[clang::lifetimebound(42)]]); // expected-error {{takes no arguments}}
+
+  void attr_on_ptr_arg(int * [[clang::lifetimebound]] ptr); // expected-error {{cannot be applied to types}}
+  static_assert((int [[clang::lifetimebound]]) 12); // expected-error {{cannot be applied to types}}
+  int* attr_on_unnamed_arg(const int& [[clang::lifetimebound]]); // expected-error {{cannot be applied to types}}
+  template <typename T>
+  int* attr_on_template_ptr_arg(T * [[clang::lifetimebound]] ptr); // expected-error {{cannot be applied to types}}
 }
 
 namespace usage_ok {

Emit the "cannot be applied to types" warning instead of silently ignoring the attribute when it's attempted to be used on a type (instead of a function argument or the function definition). Before this commit, the warning has been printed when the attribute was (mis)used on a decl-specifier, but not in other places in a declarator. Examples where the warning starts being emitted with this commit: int * [[clang::lifetimebound]] x; void f(int * [[clang::lifetimebound]] x); void g(int * [[clang::lifetimebound]]); Note that the last example is the case of an unnamed function parameter. While in theory Clang could've supported the [[clang::lifetimebound]], it doesn't currently, so the commit at least makes the situation better by highlighting this as a warning instead of a silent ignore.

ilya-biryukov

Thanks for digging through that! This clearly looks like a good improvement and I wanted to mention that we had users genuinely confused about this before.

I only have a few suggestions, otherwise very supportive of the patch.

clang/test/SemaCXX/attr-lifetimebound.cpp

clang/lib/Sema/SemaType.cpp

ilya-biryukov

LGTM!

clang/test/SemaCXX/attr-lifetimebound.cpp

clang/lib/Sema/SemaType.cpp

hokein

Can you add a note in llvm-project/clang/docs/ReleaseNotes.rst?

clang/lib/Sema/SemaType.cpp

clang/test/SemaCXX/attr-lifetimebound.cpp

emaxx-google · 2024-12-03T01:49:26Z

Can you add a note in llvm-project/clang/docs/ReleaseNotes.rst?

done - thanks for pointing this out.

hokein

Thanks, looks good.

emaxx-google · 2024-12-03T10:08:29Z

Thanks for the reviews! Please merge the PR (I don't have write access).

hokein · 2024-12-03T10:10:21Z

Thanks for the reviews! Please merge the PR (I don't have write access).

Done.

github-actions · 2024-12-03T10:10:33Z

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…8281)" Temporarily revert the patch to give downstream teams some time to clean up their codebases. This reverts commit 4849d59.

…18501) This relands #118281 as-is, after it got reverted in commit 356df2d. The reland can go in after we fixed some downstream codebases that had incorrectly placed attributes. Original commit description: > Emit the "cannot be applied to types" warning instead of silently ignoring the attribute when it's attempted to be used on a type (instead of a function argument or the function definition). > > Before this commit, the warning has been printed when the attribute was (mis)used on a decl-specifier, but not in other places in a declarator. > > Examples where the warning starts being emitted with this commit: > > ``` > int * [[clang::lifetimebound]] x; > > void f(int * [[clang::lifetimebound]] x); > > void g(int * [[clang::lifetimebound]]); > ``` > > Note that the last example is the case of an unnamed function parameter. While in theory Clang could've supported the `[[clang::lifetimebound]]` analysis for unnamed parameters, it doesn't currently, so the commit at least makes the situation better by highlighting this as a warning instead of a silent ignore - which was reported at #96034.

…vm#118501) This relands llvm#118281 as-is, after it got reverted in commit 356df2d. The reland can go in after we fixed some downstream codebases that had incorrectly placed attributes. Original commit description: > Emit the "cannot be applied to types" warning instead of silently ignoring the attribute when it's attempted to be used on a type (instead of a function argument or the function definition). > > Before this commit, the warning has been printed when the attribute was (mis)used on a decl-specifier, but not in other places in a declarator. > > Examples where the warning starts being emitted with this commit: > > ``` > int * [[clang::lifetimebound]] x; > > void f(int * [[clang::lifetimebound]] x); > > void g(int * [[clang::lifetimebound]]); > ``` > > Note that the last example is the case of an unnamed function parameter. While in theory Clang could've supported the `[[clang::lifetimebound]]` analysis for unnamed parameters, it doesn't currently, so the commit at least makes the situation better by highlighting this as a warning instead of a silent ignore - which was reported at llvm#96034.

emaxx-google marked this pull request as ready for review December 2, 2024 12:11

llvmbot added clang Clang issues not falling into any other category clang:frontend Language frontend issues, e.g. anything involving "Sema" labels Dec 2, 2024

emaxx-google force-pushed the lifetimebound-warn branch from 2ba52fc to ffba96a Compare December 2, 2024 12:27

emaxx-google mentioned this pull request Dec 2, 2024

[[clang::lifetimebound]] is ignored without warning if the function parameter doesn't have a name. #96034

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ilya-biryukov reviewed Dec 2, 2024

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emaxx-google added 2 commits December 2, 2024 15:47

change warning

8bd3f8d

test func types

b003a4d

emaxx-google requested a review from ilya-biryukov December 2, 2024 15:55

ilya-biryukov approved these changes Dec 2, 2024

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release notes

b8daefa

emaxx-google requested a review from hokein December 3, 2024 01:49

hokein approved these changes Dec 3, 2024

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hokein merged commit 4849d59 into llvm:main Dec 3, 2024
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hokein added a commit that referenced this pull request Dec 3, 2024

Revert "[clang] Warn [[clang::lifetimebound]] misusages on types (#11…

356df2d

…8281)" Temporarily revert the patch to give downstream teams some time to clean up their codebases. This reverts commit 4849d59.

emaxx-google mentioned this pull request Dec 3, 2024

(reland) [clang] Warn [[clang::lifetimebound]] misusages on types #118501

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