Practice good Self hygiene (#2127)
#2313
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This commit revises the `KnownLayout` derive on `repr(C)` target structs to
preserve the correct resolution of `Self` when constructing
`__ZerocopyKnownLayoutMaybeUninit`. This type contains a `MaybeUninit` version
of each of the target struct's field types. Previously, it achieved this by
simply copying the tokens corresponding to field types from the definition of
the target struct into the definition of `__ZerocopyKnownLayoutMaybeUninit`
However, on types like this:
#[repr(C)]
struct Struct([u8; Self::N]);
…this approach is insufficient. Pasted into `__ZerocopyKnownLayoutMaybeUninit`,
`Self` ceases to refer to the target struct and instead refers to
`__ZerocopyKnownLayoutMaybeUninit`.
To preserve `Self` hygiene, this commit defines a struct for projecting the
field types of the target struct based on their index:
pub unsafe trait Field<Index> {
type Type: ?Sized;
}
…then implements it for each of the field types of the target struct; e.g.:
struct Index<const N: usize>;
impl Field<Index<0>> for Struct {
type Type = [u8; Self::N];
}
With this, the fields of `__ZerocopyKnownLayoutMaybeUninit` can be defined
hygienically; e.g., as `<Struct as Field<0>>::Type`.
Fixes google#2116
jswrenn
approved these changes
Feb 6, 2025
Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## main #2313 +/- ##
=======================================
Coverage 89.27% 89.27%
=======================================
Files 16 16
Lines 5976 5976
=======================================
Hits 5335 5335
Misses 641 641 ☔ View full report in Codecov by Sentry. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Automated changes by create-pull-request GitHub action