Actually use TAIT instead of emulating it #125362
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r? @Nilstrieb rustbot has assigned @Nilstrieb. Use |
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It was actually quite a simple fix: The clippy lint checks that the TAIT's destructor is insignificant, but it can't/shouldn't be able to figure that out as the TAIT is opaque. Using |
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…llaumeGomez Rollup of 6 pull requests Successful merges: - rust-lang#125263 (rust-lld: fallback to rustc's sysroot if there's no path to the linker in the target sysroot) - rust-lang#125345 (rustc_codegen_llvm: add support for writing summary bitcode) - rust-lang#125362 (Actually use TAIT instead of emulating it) - rust-lang#125412 (Don't suggest adding the unexpected cfgs to the build-script it-self) - rust-lang#125445 (Migrate `run-make/rustdoc-with-short-out-dir-option` to `rmake.rs`) - rust-lang#125452 (Cleanup check-cfg handling in core and std) r? `@ghost` `@rustbot` modify labels: rollup
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…llaumeGomez Rollup of 6 pull requests Successful merges: - rust-lang#125263 (rust-lld: fallback to rustc's sysroot if there's no path to the linker in the target sysroot) - rust-lang#125345 (rustc_codegen_llvm: add support for writing summary bitcode) - rust-lang#125362 (Actually use TAIT instead of emulating it) - rust-lang#125412 (Don't suggest adding the unexpected cfgs to the build-script it-self) - rust-lang#125445 (Migrate `run-make/rustdoc-with-short-out-dir-option` to `rmake.rs`) - rust-lang#125452 (Cleanup check-cfg handling in core and std) r? `@ghost` `@rustbot` modify labels: rollup
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Rollup merge of rust-lang#125362 - joboet:tait_hack, r=Nilstrieb Actually use TAIT instead of emulating it `core`'s `impl_fn_for_zst` macro is just a hacky way of emulating TAIT. TAIT has become stable enough to be used [in other places](https://github.com/rust-lang/rust/blob/e8fbd991287f637f95016a71ddc13438415bbe59/library/std/src/backtrace.rs#L431) inside the standard library, so let's use it in `core` as well.
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Is there a reason not to use TAIT for the full iterator type? e.g. |
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…in_sig, r=lcnr Tait must be constrained if in sig r? `@compiler-errors` kind of reverts rust-lang#62423, but that PR only removed cycles in cases that we want to forbid now anyway. see https://rust-lang.zulipchat.com/#narrow/stream/315482-t-compiler.2Fetc.2Fopaque-types/topic/lcnr.20oli.20meeting/near/370712246 for related discussion and motivating example a TAIT showing up in a signature doesn't just mean it can register a hidden type, but that it must. This is the [design the types team decided upon](https://hackmd.io/QOsEaEJtQK-XDS_xN4UyQA#Proposal-preferred) for the following reasons * avoids a hypothetical situation where getting smarter in trait solving could cause new cycle errors or new inference errors to show up, where today something is treated as opaque. * avoids having the situation where a (minor?) change to a function body causes an error, because its TAIT usage suddenly isn't "opaque enough" anymore. * avoids having to explain why in some cases you need to put a Tait into a tiny module together with its defining usages. Now you basically gotta always do this, the moment a Tait is in a signature that isn't in the defining scope. * avoids false-cycle errors * anything diverging from this pattern needs to either * move the TAIT declaration and defining function into their own helper sub module * use the attributes we'll provide in the future to explicitly opt in or out of being in the defining scope fixes rust-lang#117861 reverts rust-lang#125362 cc `@Nilstrieb` `@joboet`
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core'simpl_fn_for_zstmacro is just a hacky way of emulating TAIT. TAIT has become stable enough to be used in other places inside the standard library, so let's use it incoreas well.