From dbd126901ac7d6ee886e0a234e630b1fbfec9afd Mon Sep 17 00:00:00 2001 From: Jonas Schievink Date: Sun, 18 Jul 2021 03:34:50 +0200 Subject: [PATCH] Add feature gates for `for` and `?` in consts --- compiler/rustc_feature/src/active.rs | 6 +++ compiler/rustc_passes/src/check_const.rs | 9 +++-- compiler/rustc_span/src/symbol.rs | 2 + src/test/ui/consts/const-for-feature-gate.rs | 8 ++++ .../ui/consts/const-for-feature-gate.stderr | 11 ++++++ src/test/ui/consts/const-try-feature-gate.rs | 9 +++++ .../ui/consts/const-try-feature-gate.stderr | 11 ++++++ src/test/ui/consts/const-try.rs | 39 +++++++++++++++++++ 8 files changed, 91 insertions(+), 4 deletions(-) create mode 100644 src/test/ui/consts/const-for-feature-gate.rs create mode 100644 src/test/ui/consts/const-for-feature-gate.stderr create mode 100644 src/test/ui/consts/const-try-feature-gate.rs create mode 100644 src/test/ui/consts/const-try-feature-gate.stderr create mode 100644 src/test/ui/consts/const-try.rs diff --git a/compiler/rustc_feature/src/active.rs b/compiler/rustc_feature/src/active.rs index bf99d2988178d..9faed49c88bb2 100644 --- a/compiler/rustc_feature/src/active.rs +++ b/compiler/rustc_feature/src/active.rs @@ -677,6 +677,12 @@ declare_features! ( /// Allows `#[derive(Default)]` and `#[default]` on enums. (active, derive_default_enum, "1.56.0", Some(86985), None), + /// Allows `for _ in _` loops in const contexts. + (active, const_for, "1.55.0", None, None), + + /// Allows the `?` operator in const contexts. + (active, const_try, "1.55.0", None, None), + // ------------------------------------------------------------------------- // feature-group-end: actual feature gates // ------------------------------------------------------------------------- diff --git a/compiler/rustc_passes/src/check_const.rs b/compiler/rustc_passes/src/check_const.rs index 6ee54cfe37f30..f6a93f5e02d5f 100644 --- a/compiler/rustc_passes/src/check_const.rs +++ b/compiler/rustc_passes/src/check_const.rs @@ -40,13 +40,14 @@ impl NonConstExpr { use hir::MatchSource::*; let gates: &[_] = match self { - // A `for` loop's desugaring contains a call to `IntoIterator::into_iter`, - // so they are not yet allowed. - // Likewise, `?` desugars to a call to `Try::into_result`. - Self::Loop(ForLoop) | Self::Match(ForLoopDesugar | TryDesugar | AwaitDesugar) => { + Self::Match(AwaitDesugar) => { return None; } + Self::Loop(ForLoop) | Self::Match(ForLoopDesugar) => &[sym::const_for], + + Self::Match(TryDesugar) => &[sym::const_try], + Self::Match(IfLetGuardDesugar) => bug!("`if let` guard outside a `match` expression"), // All other expressions are allowed. diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs index 114750d9b7b3a..295e53aba3542 100644 --- a/compiler/rustc_span/src/symbol.rs +++ b/compiler/rustc_span/src/symbol.rs @@ -410,6 +410,7 @@ symbols! { const_fn_transmute, const_fn_union, const_fn_unsize, + const_for, const_format_args, const_generic_defaults, const_generics, @@ -432,6 +433,7 @@ symbols! { const_trait_bound_opt_out, const_trait_impl, const_transmute, + const_try, constant, constructor, contents, diff --git a/src/test/ui/consts/const-for-feature-gate.rs b/src/test/ui/consts/const-for-feature-gate.rs new file mode 100644 index 0000000000000..bec7b80890536 --- /dev/null +++ b/src/test/ui/consts/const-for-feature-gate.rs @@ -0,0 +1,8 @@ +// gate-test-const_for + +const _: () = { + for _ in 0..5 {} + //~^ error: `for` is not allowed in a `const` +}; + +fn main() {} diff --git a/src/test/ui/consts/const-for-feature-gate.stderr b/src/test/ui/consts/const-for-feature-gate.stderr new file mode 100644 index 0000000000000..c1b46ef737614 --- /dev/null +++ b/src/test/ui/consts/const-for-feature-gate.stderr @@ -0,0 +1,11 @@ +error[E0658]: `for` is not allowed in a `const` + --> $DIR/const-for-feature-gate.rs:4:5 + | +LL | for _ in 0..5 {} + | ^^^^^^^^^^^^^^^^ + | + = help: add `#![feature(const_for)]` to the crate attributes to enable + +error: aborting due to previous error + +For more information about this error, try `rustc --explain E0658`. diff --git a/src/test/ui/consts/const-try-feature-gate.rs b/src/test/ui/consts/const-try-feature-gate.rs new file mode 100644 index 0000000000000..0839c23a0b99b --- /dev/null +++ b/src/test/ui/consts/const-try-feature-gate.rs @@ -0,0 +1,9 @@ +// gate-test-const_try + +const fn t() -> Option<()> { + Some(())?; + //~^ error: `?` is not allowed in a `const fn` + None +} + +fn main() {} diff --git a/src/test/ui/consts/const-try-feature-gate.stderr b/src/test/ui/consts/const-try-feature-gate.stderr new file mode 100644 index 0000000000000..9e3aa09ab00f5 --- /dev/null +++ b/src/test/ui/consts/const-try-feature-gate.stderr @@ -0,0 +1,11 @@ +error[E0658]: `?` is not allowed in a `const fn` + --> $DIR/const-try-feature-gate.rs:4:5 + | +LL | Some(())?; + | ^^^^^^^^^ + | + = help: add `#![feature(const_try)]` to the crate attributes to enable + +error: aborting due to previous error + +For more information about this error, try `rustc --explain E0658`. diff --git a/src/test/ui/consts/const-try.rs b/src/test/ui/consts/const-try.rs new file mode 100644 index 0000000000000..e199fd9ff8a1a --- /dev/null +++ b/src/test/ui/consts/const-try.rs @@ -0,0 +1,39 @@ +// check-pass + +// Demonstrates what's needed to make use of `?` in const contexts. + +#![crate_type = "lib"] +#![feature(try_trait_v2)] +#![feature(const_trait_impl)] +#![feature(const_try)] + +use std::ops::{ControlFlow, FromResidual, Try}; + +struct TryMe; +struct Error; + +impl const FromResidual for TryMe { + fn from_residual(residual: Error) -> Self { + TryMe + } +} + +impl const Try for TryMe { + type Output = (); + type Residual = Error; + fn from_output(output: Self::Output) -> Self { + TryMe + } + fn branch(self) -> ControlFlow { + ControlFlow::Break(Error) + } +} + +const fn t() -> TryMe { + TryMe?; + TryMe +} + +const _: () = { + t(); +};