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Unrolled build for #133607
Rollup merge of #133607 - WaffleLapkin:tail-call-checks, r=compiler-errors implement checks for tail calls Quoting the [RFC draft](https://github.com/phi-go/rfcs/blob/guaranteed-tco/text/0000-explicit-tail-calls.md): > The argument to become is a function (or method) call, that exactly matches the function signature and calling convention of the callee. The intent is to ensure a matching ABI. Note that lifetimes may differ as long as they pass borrow checking, see [below](https://github.com/phi-go/rfcs/blob/guaranteed-tco/text/0000-explicit-tail-calls.md#return-type-coercion) for specifics on the return type. > Tail calling closures and tail calling from closures is not allowed. This is due to the high implementation effort, see below, this restriction can be lifted by a future RFC. > Invocations of operators were considered as valid targets but were rejected on grounds of being too error-prone. In any case, these can still be called as methods. > Tail calling [variadic functions](https://doc.rust-lang.org/beta/unstable-book/language-features/c-variadic.html) and tail calling from variadic functions is not allowed. As support for variadic function is stabilized on a per target level, support for tail-calls regarding variadic functions would need to follow a similar approach. To avoid this complexity and to minimize implementation effort for backends, this interaction is currently not allowed but support can be added with a future RFC. ----- The checks are implemented as a query, similarly to `check_unsafety`. The code is cherry-picked straight out of #112657 which was written more than a year ago, so I expect we might need to change some things ^^"
2 parents c94848c + 144d6cc commit 08d46c5

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‎compiler/rustc_middle/src/query/mod.rs

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@@ -916,6 +916,12 @@ rustc_queries! {
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cache_on_disk_if { true }
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}
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/// Checks well-formedness of tail calls (`become f()`).
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query check_tail_calls(key: LocalDefId) -> Result<(), rustc_errors::ErrorGuaranteed> {
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desc { |tcx| "tail-call-checking `{}`", tcx.def_path_str(key) }
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cache_on_disk_if { true }
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}
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/// Returns the types assumed to be well formed while "inside" of the given item.
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///
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/// Note that we've liberated the late bound regions of function signatures, so

‎compiler/rustc_mir_build/src/build/mod.rs

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@@ -50,6 +50,10 @@ pub(crate) fn mir_build<'tcx>(tcx: TyCtxtAt<'tcx>, def: LocalDefId) -> Body<'tcx
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return construct_error(tcx, def, e);
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}
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if let Err(err) = tcx.check_tail_calls(def) {
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return construct_error(tcx, def, err);
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}
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let body = match tcx.thir_body(def) {
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Err(error_reported) => construct_error(tcx, def, error_reported),
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Ok((thir, expr)) => {

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