From e69fcea6094e89253e1412a99f890c6db5ea62ef Mon Sep 17 00:00:00 2001 From: Jonas Schievink Date: Sun, 22 Nov 2020 04:19:46 +0100 Subject: [PATCH] const fn: allow use of trait impls from bounds --- .../src/transform/check_consts/validation.rs | 40 +++++++++++++++++-- .../call-generic-method-fail.rs | 11 +++++ .../call-generic-method-fail.stderr | 9 +++++ .../call-generic-method-nonconst-opt-out.rs | 24 +++++++++++ .../call-generic-method-nonconst.rs | 26 ++++++++++++ .../call-generic-method-pass.rs | 23 +++++++++++ 6 files changed, 129 insertions(+), 4 deletions(-) create mode 100644 src/test/ui/rfc-2632-const-trait-impl/call-generic-method-fail.rs create mode 100644 src/test/ui/rfc-2632-const-trait-impl/call-generic-method-fail.stderr create mode 100644 src/test/ui/rfc-2632-const-trait-impl/call-generic-method-nonconst-opt-out.rs create mode 100644 src/test/ui/rfc-2632-const-trait-impl/call-generic-method-nonconst.rs create mode 100644 src/test/ui/rfc-2632-const-trait-impl/call-generic-method-pass.rs diff --git a/compiler/rustc_mir/src/transform/check_consts/validation.rs b/compiler/rustc_mir/src/transform/check_consts/validation.rs index e4893044a15..d00038f345c 100644 --- a/compiler/rustc_mir/src/transform/check_consts/validation.rs +++ b/compiler/rustc_mir/src/transform/check_consts/validation.rs @@ -4,6 +4,7 @@ use rustc_hir::def_id::DefId; use rustc_hir::{self as hir, HirId, LangItem}; use rustc_infer::infer::TyCtxtInferExt; +use rustc_infer::traits::{ImplSource, Obligation, ObligationCause}; use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor}; use rustc_middle::mir::*; use rustc_middle::ty::cast::CastTy; @@ -11,9 +12,10 @@ use rustc_middle::ty::{ self, adjustment::PointerCast, Instance, InstanceDef, Ty, TyCtxt, TypeAndMut, }; +use rustc_middle::ty::{Binder, TraitPredicate, TraitRef}; use rustc_span::{sym, Span, Symbol}; use rustc_trait_selection::traits::error_reporting::InferCtxtExt; -use rustc_trait_selection::traits::{self, TraitEngine}; +use rustc_trait_selection::traits::{self, SelectionContext, TraitEngine}; use std::mem; use std::ops::Deref; @@ -765,9 +767,39 @@ fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location } }; - // Resolve a trait method call to its concrete implementation, which may be in a - // `const` trait impl. - if self.tcx.features().const_trait_impl { + // Attempting to call a trait method? + if let Some(trait_id) = tcx.trait_of_item(callee) { + if !self.tcx.features().const_trait_impl { + self.check_op(ops::FnCallNonConst(callee)); + return; + } + + let trait_ref = TraitRef::from_method(tcx, trait_id, substs); + let obligation = Obligation::new( + ObligationCause::dummy(), + param_env, + Binder::bind(TraitPredicate { + trait_ref: TraitRef::from_method(tcx, trait_id, substs), + }), + ); + + let implsrc = tcx.infer_ctxt().enter(|infcx| { + let mut selcx = SelectionContext::new(&infcx); + selcx.select(&obligation).unwrap() + }); + + // If the method is provided via a where-clause that does not use the `?const` + // opt-out, the call is allowed. + if let Some(ImplSource::Param(_, hir::Constness::Const)) = implsrc { + debug!( + "const_trait_impl: provided {:?} via where-clause in {:?}", + trait_ref, param_env + ); + return; + } + + // Resolve a trait method call to its concrete implementation, which may be in a + // `const` trait impl. let instance = Instance::resolve(tcx, param_env, callee, substs); debug!("Resolving ({:?}) -> {:?}", callee, instance); if let Ok(Some(func)) = instance { diff --git a/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-fail.rs b/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-fail.rs new file mode 100644 index 00000000000..6d4bfe722de --- /dev/null +++ b/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-fail.rs @@ -0,0 +1,11 @@ +#![feature(const_fn)] +#![feature(const_trait_impl)] +#![feature(const_trait_bound_opt_out)] +#![allow(incomplete_features)] + +pub const fn equals_self(t: &T) -> bool { + *t == *t + //~^ ERROR calls in constant functions are limited to constant functions +} + +fn main() {} diff --git a/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-fail.stderr b/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-fail.stderr new file mode 100644 index 00000000000..4b2fc56aaa7 --- /dev/null +++ b/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-fail.stderr @@ -0,0 +1,9 @@ +error[E0015]: calls in constant functions are limited to constant functions, tuple structs and tuple variants + --> $DIR/call-generic-method-fail.rs:7:5 + | +LL | *t == *t + | ^^^^^^^^ + +error: aborting due to previous error + +For more information about this error, try `rustc --explain E0015`. diff --git a/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-nonconst-opt-out.rs b/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-nonconst-opt-out.rs new file mode 100644 index 00000000000..f0e32142221 --- /dev/null +++ b/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-nonconst-opt-out.rs @@ -0,0 +1,24 @@ +// check-pass + +#![feature(const_fn)] +#![feature(const_trait_impl)] +#![feature(const_trait_bound_opt_out)] +#![allow(incomplete_features)] + +struct S; + +impl PartialEq for S { + fn eq(&self, _: &S) -> bool { + true + } +} + +const fn equals_self(t: &T) -> bool { + true +} + +pub const EQ: bool = equals_self(&S); + +// Calling `equals_self` with a type that only has a non-const impl is fine, because we opted out. + +fn main() {} diff --git a/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-nonconst.rs b/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-nonconst.rs new file mode 100644 index 00000000000..2c8f6354dc6 --- /dev/null +++ b/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-nonconst.rs @@ -0,0 +1,26 @@ +// FIXME(jschievink): this is not rejected correctly (only when the non-const impl is actually used) +// ignore-test + +#![feature(const_fn)] +#![feature(const_trait_impl)] +#![allow(incomplete_features)] + +struct S; + +impl PartialEq for S { + fn eq(&self, _: &S) -> bool { + true + } +} + +const fn equals_self(t: &T) -> bool { + true +} + +// Calling `equals_self` with something that has a non-const impl should throw an error, despite +// it not using the impl. + +pub const EQ: bool = equals_self(&S); +//~^ ERROR + +fn main() {} diff --git a/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-pass.rs b/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-pass.rs new file mode 100644 index 00000000000..e968e6ec7bb --- /dev/null +++ b/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-pass.rs @@ -0,0 +1,23 @@ +//! Basic test for calling methods on generic type parameters in `const fn`. + +// check-pass + +#![feature(const_fn)] +#![feature(const_trait_impl)] +#![allow(incomplete_features)] + +struct S; + +impl const PartialEq for S { + fn eq(&self, _: &S) -> bool { + true + } +} + +const fn equals_self(t: &T) -> bool { + *t == *t +} + +pub const EQ: bool = equals_self(&S); + +fn main() {} -- 2.44.0