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…=JonathanBrouwer stabilize `cfg_select!` *[View all comments](https://triagebot.infra.rust-lang.org/gh-comments/rust-lang/rust/pull/149783)* tracking issue: rust-lang#115585 closes rust-lang#115585 reference PR: - rust-lang/reference#2103 # Request for Stabilization ## Summary The `cfg_select!` macro picks the expansion corresponding to the first `cfg` condition that evaluates to `true`. It simplifies complex conditional expressions. ```rust cfg_select! { unix => { fn foo() { /* unix specific functionality */ } } target_pointer_width = "32" => { fn foo() { /* non-unix, 32-bit functionality */ } } _ => { fn foo() { /* fallback implementation */ } } } let is_unix_str = cfg_select! { unix => "unix", _ => "not unix", }; println!("{is_unix_str}"); ``` ## Semantics The expansion of a `cfg_select!` call is the right-hand side of the first `cfg` rule that evaluates to true. This can be roughly expressed using this macro: ```rust macro_rules! cfg_select { ({ $($tt:tt)* }) => {{ $crate::cfg_select! { $($tt)* } }}; (_ => { $($output:tt)* }) => { $($output)* }; ( $cfg:meta => $output:tt $($( $rest:tt )+)? ) => { #[cfg($cfg)] $crate::cfg_select! { _ => $output } $( #[cfg(not($cfg))] $crate::cfg_select! { $($rest)+ } )? } } ``` The actual implementation uses a builtin macro so that `cfg_select!` can be used both in item and expression position. ## Documentation reference PR: - rust-lang/reference#2103 ## Tests The `cfg_select!` macro is already used extensively in the rust compiler codebase. It has several dedicated tests: - [`tests/ui/check-cfg/cfg-select.rs`](https://github.com/rust-lang/rust/blob/main/tests/ui/check-cfg/cfg-select.rs)tests that warnings are emitted when an unexpected `cfg` condition is used. - [`tests/ui/macros/cfg_select.rs`](https://github.com/rust-lang/rust/blob/main/tests/ui/macros/cfg_select.rs) tests that `cfg_select!` has the expected expansion, and tests that the expected syntax is accepted. ## History - rust-lang#115416 - rust-lang#117162 - rust-lang#133720 - rust-lang#135625 - rust-lang#137198 - rust-lang#138993 - rust-lang#138996 - rust-lang#143461 - rust-lang#143941 - rust-lang#145233 - rust-lang#148712 - rust-lang#149380 - rust-lang#149925 # Resolved questions # Unresolved questions The style team has decided on how to format `cfg_select!`, but this formatting has not yet been implemented. See rust-lang#144323. r? @traviscross <!-- TRIAGEBOT_START --> <!-- TRIAGEBOT_CONCERN-ISSUE_START --> > [!NOTE] > # Concerns (0 active) > > - ~~[allowing-comma-after-closing-brace](rust-lang#149783 (comment) resolved in [this comment](rust-lang#149783 (comment)) > > *Managed by `@rustbot`—see [help](https://forge.rust-lang.org/triagebot/concern.html) for details.* <!-- TRIAGEBOT_CONCERN-ISSUE_END --> <!-- TRIAGEBOT_END -->
…rtn, r=davidtwco fix refining_impl_trait suggestion with return_type_notation using `#![feature(return_type_notation)] `on top of `refining_impl_trait` made the lint suggest a pretty wild “wrap the body in `<Self as Trait>::f(..)”` fix instead of the simple “just copy the return type from the trait”. this patch makes the lint always suggest the plain return-type replacement based on the trait signature (by grabbing the original snippet when possible), so you don’t get RTN-style desugarings in the help new test here fixes rust-lang#151663
… r=jhpratt Revert "Stabilize `str_as_str`" Reverts rust-lang#151603, clean revert. Fixes rust-lang#152961
…e-check, r=JonathanBrouwer Remove redundant call to `check_codegen_attributes_extra` in Inliner Inside `try_inlining`, `check_codegen_attributes` is called first. This function internally invokes `check_codegen_attributes_extra`. However, immediately after that returns, `try_inlining` calls `check_codegen_attributes_extra` again. First call: https://github.com/rust-lang/rust/blob/7ec34defe9e62a1a6946d3e700b5903d8dc89ece/compiler/rustc_mir_transform/src/inline.rs#L800-L814 Second call: https://github.com/rust-lang/rust/blob/7ec34defe9e62a1a6946d3e700b5903d8dc89ece/compiler/rustc_mir_transform/src/inline.rs#L598-L612 ```rust // Inside try_inlining: check_codegen_attributes(inliner, callsite, callee_attrs)?; // Internally calls `check_codegen_attributes_extra` inliner.check_codegen_attributes_extra(callee_attrs)?; // Called again here ``` In `try_inlining`, inliner is held as a shared reference (`&I`). Since `check_codegen_attributes_extra` takes `&self` and does not rely on interior mutability or external state, there does not seem to be any state change between the two calls. Therefore, the second call appears to be redundant. Currently, `check_codegen_attributes` is only called from `try_inlining`, and `check_codegen_attributes_extra` appears to be called only from these two locations. It seems reasonable for the `check_codegen_attributes` wrapper to handle the hook automatically.
…nBrouwer Use `HashStable` derive in more places This applies `HashStable` derive in a couple more places. Also `stable_hasher` is declared for `HashStable_NoContext`.
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Successful merges:
cfg_select!#149783 (stabilizecfg_select!)str_as_str" #152963 (Revert "Stabilizestr_as_str")check_codegen_attributes_extrain Inliner #152984 (Remove redundant call tocheck_codegen_attributes_extrain Inliner)HashStablederive in more places #152987 (UseHashStablederive in more places)r? @ghost
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