When a vector is instantiated with a pointer type (`T` being `const
Foo*`), the inferred annotation becomes `push_back(const Foo*& value
[[clang::lifetime_capture_by(this)]])`.
For reference parameters, the `lifetime_capture_by` attribute treats the
lifetime as referring to the referenced object -- in this case, the
**pointer** itself, not the pointee object. In the `push_back`, we copy
the pointer's value, which does not establish a reference to the
pointer. This behavior is safe and does not capture the pointer's
lifetime.
The annotation should not be inferred for cases where `T` is a pointer
type, as the intended semantics do not align with the annotation.
Fixes#121391
With this change, the lifetime_capture_by code path will not handle the
constructor decl to avoid bogus diagnostics (see the testcase).
Instead, we reuse the lifetimebound code as the
lifetime_capture_by(this) has the same semantic as lifetimebound in
constructor. The downside is that the lifetimebound diagnostic is reused
for the capture case (I think it is not a big issue).
Fixes#117680
This PR uses the existing lifetime analysis for the `capture_by`
attribute.
The analysis is behind `-Wdangling-capture` warning and is disabled by
default for now. Once it is found to be stable, it will be default
enabled.
Planned followup:
- add implicit inference of this attribute on STL container methods like
`std::vector::push_back`.
- (consider) warning if capturing `X` cannot capture anything. It should
be a reference, pointer or a view type.
- refactoring temporary visitors and other related handlers.
- start discussing `__global` vs `global` in the annotation in a
separate PR.
---------
Co-authored-by: Boaz Brickner <brickner@google.com>
