[wip] Account for alignment directives on DSTs in derive(IntoBytes)#3064
[wip] Account for alignment directives on DSTs in derive(IntoBytes)#3064
derive(IntoBytes)#3064Conversation
TODO: Regression tests. Fixes #3063 gherrit-pr-id: Gf18655827d1c30e4421c83579b962bf7aa453969
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Code Review
This pull request aims to account for alignment directives on Dynamically Sized Types (DSTs) when deriving IntoBytes. The changes involve updating internal macros to accept alignment and packing parameters and modifying the procedural macro logic to extract and pass these values. While the overall direction is correct, there are several issues to address: the use of unwrap() in the procedural macro is risky and redundant, the current implementation causes a regression in MSRV tests due to how paths are passed to macros, and the use of TODO comments violates the repository's policy of using FIXME for non-blocking issues to avoid CI failures.
| let repr_align = | ||
| repr.get_align().map(|spanned| { | ||
| let n = spanned.t.get(); | ||
| quote_spanned! { spanned.span => #option::Some(#n) } | ||
| }).unwrap_or(none.clone()); | ||
| let repr_packed = | ||
| repr.get_packed().map(|packed| { | ||
| let n = packed.get(); | ||
| quote! { #option::Some(#n) } | ||
| }).unwrap_or(none); |
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The regression in union.msrv.stderr (error: no rules expected the token ::) is likely caused by passing paths starting with :: as expr arguments to macros on the MSRV toolchain. Parenthesizing these paths when they are passed as macro arguments usually resolves this ambiguity in the macro parser.
| let repr_align = | |
| repr.get_align().map(|spanned| { | |
| let n = spanned.t.get(); | |
| quote_spanned! { spanned.span => #option::Some(#n) } | |
| }).unwrap_or(none.clone()); | |
| let repr_packed = | |
| repr.get_packed().map(|packed| { | |
| let n = packed.get(); | |
| quote! { #option::Some(#n) } | |
| }).unwrap_or(none); | |
| let repr_align = | |
| repr.get_align().map(|spanned| { | |
| let n = spanned.t.get(); | |
| quote_spanned! { spanned.span => (#option::Some(#n)) } | |
| }).unwrap_or(quote! { (#none) }); | |
| let repr_packed = | |
| repr.get_packed().map(|packed| { | |
| let n = packed.get(); | |
| quote! { (#option::Some(#n)) } | |
| }).unwrap_or(quote! { (#none) }); |
| macro_rules! struct_padding { | ||
| ($t:ty, [$($ts:ty),*]) => { | ||
| ($t:ty, $align:expr, $packed:expr, [$($ts:ty),*]) => { | ||
| // TODO: Assert `$align` and `$packed` are `None`. |
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According to the project's coding guidelines in AGENTS.md, TODO comments should only be used if they are intended to block the PR, as CI is configured to fail on them. For non-blocking improvements, please use FIXME instead.
| // TODO: Assert `$align` and `$packed` are `None`. | |
| // FIXME: Assert `$align` and `$packed` are `None`. |
References
- The style guide explicitly forbids the use of
TODOcomments unless they are intended to block the PR, suggestingFIXMEfor non-blocking issues. (link)
| let repr = | ||
| Repr::<PrimitiveRepr, NonZeroU32>::from_attrs(&self.ctx.ast.attrs).unwrap(); |
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Using .unwrap() here is risky as it can cause the procedural macro to panic if the repr attribute parsing fails. While the repr is likely validated earlier in the derive process, it is better to handle the error or pass the already-parsed repr into the ImplBlockBuilder to avoid redundant parsing and potential panics.
| quote! { #zerocopy_crate::util::macro_util::core_reexport::option::Option }; | ||
| let none = quote! { #option::None }; |
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You can simplify the construction of the Option path by leveraging the existing core_path() method on Ctx.
| quote! { #zerocopy_crate::util::macro_util::core_reexport::option::Option }; | |
| let none = quote! { #option::None }; | |
| let core = self.ctx.core_path(); | |
| let option = quote! { #core::option::Option }; | |
| let none = quote! { #option::None }; |
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #3064 +/- ##
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Coverage 91.87% 91.87%
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Files 20 20
Lines 6057 6057
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Hits 5565 5565
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2 participants
TODO: Regression tests.
Fixes #3063
derive(IntoBytes)#3064⬇️ Download this PR
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git fetch origin refs/heads/Gf18655827d1c30e4421c83579b962bf7aa453969 && git checkout -b pr-Gf18655827d1c30e4421c83579b962bf7aa453969 FETCH_HEADCheckout
git fetch origin refs/heads/Gf18655827d1c30e4421c83579b962bf7aa453969 && git checkout FETCH_HEADCherry Pick
git fetch origin refs/heads/Gf18655827d1c30e4421c83579b962bf7aa453969 && git cherry-pick FETCH_HEADPull
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