diff --git a/clippy_utils/src/qualify_min_const_fn.rs b/clippy_utils/src/qualify_min_const_fn.rs index 5d0401010db6..48d208966bc6 100644 --- a/clippy_utils/src/qualify_min_const_fn.rs +++ b/clippy_utils/src/qualify_min_const_fn.rs @@ -18,7 +18,7 @@ use rustc_middle::mir::{ }; use rustc_middle::traits::{BuiltinImplSource, ImplSource, ObligationCause}; use rustc_middle::ty::adjustment::PointerCoercion; -use rustc_middle::ty::{self, GenericArgKind, TraitRef, Ty, TyCtxt}; +use rustc_middle::ty::{self, GenericArgKind, Instance, TraitRef, Ty, TyCtxt}; use rustc_span::Span; use rustc_span::symbol::sym; use rustc_trait_selection::traits::{ObligationCtxt, SelectionContext}; @@ -349,7 +349,15 @@ fn check_terminator<'tcx>( } | TerminatorKind::TailCall { func, args, fn_span: _ } => { let fn_ty = func.ty(body, cx.tcx); - if let ty::FnDef(fn_def_id, _) = *fn_ty.kind() { + if let ty::FnDef(fn_def_id, fn_substs) = fn_ty.kind() { + // FIXME: when analyzing a function with generic parameters, we may not have enough information to + // resolve to an instance. However, we could check if a host effect predicate can guarantee that + // this can be made a `const` call. + let fn_def_id = match Instance::try_resolve(cx.tcx, cx.typing_env(), *fn_def_id, fn_substs) { + Ok(Some(fn_inst)) => fn_inst.def_id(), + Ok(None) => return Err((span, format!("cannot resolve instance for {func:?}").into())), + Err(_) => return Err((span, format!("error during instance resolution of {func:?}").into())), + }; if !is_stable_const_fn(cx, fn_def_id, msrv) { return Err(( span, diff --git a/tests/ui/missing_const_for_fn/const_trait.fixed b/tests/ui/missing_const_for_fn/const_trait.fixed new file mode 100644 index 000000000000..7e0d4fccaae2 --- /dev/null +++ b/tests/ui/missing_const_for_fn/const_trait.fixed @@ -0,0 +1,36 @@ +#![feature(const_trait_impl)] +#![warn(clippy::missing_const_for_fn)] + +// Reduced test case from https://github.com/rust-lang/rust-clippy/issues/14658 + +#[const_trait] +trait ConstTrait { + fn method(self); +} + +impl ConstTrait for u32 { + fn method(self) {} +} + +impl const ConstTrait for u64 { + fn method(self) {} +} + +fn cannot_be_const() { + 0u32.method(); +} + +//~v missing_const_for_fn +const fn can_be_const() { + 0u64.method(); +} + +// False negative, see FIXME comment in `clipy_utils::qualify_min_const` +fn could_be_const_but_does_not_trigger(t: T) +where + T: const ConstTrait, +{ + t.method(); +} + +fn main() {} diff --git a/tests/ui/missing_const_for_fn/const_trait.rs b/tests/ui/missing_const_for_fn/const_trait.rs new file mode 100644 index 000000000000..439da4622d7e --- /dev/null +++ b/tests/ui/missing_const_for_fn/const_trait.rs @@ -0,0 +1,36 @@ +#![feature(const_trait_impl)] +#![warn(clippy::missing_const_for_fn)] + +// Reduced test case from https://github.com/rust-lang/rust-clippy/issues/14658 + +#[const_trait] +trait ConstTrait { + fn method(self); +} + +impl ConstTrait for u32 { + fn method(self) {} +} + +impl const ConstTrait for u64 { + fn method(self) {} +} + +fn cannot_be_const() { + 0u32.method(); +} + +//~v missing_const_for_fn +fn can_be_const() { + 0u64.method(); +} + +// False negative, see FIXME comment in `clipy_utils::qualify_min_const` +fn could_be_const_but_does_not_trigger(t: T) +where + T: const ConstTrait, +{ + t.method(); +} + +fn main() {} diff --git a/tests/ui/missing_const_for_fn/const_trait.stderr b/tests/ui/missing_const_for_fn/const_trait.stderr new file mode 100644 index 000000000000..b994b88fac68 --- /dev/null +++ b/tests/ui/missing_const_for_fn/const_trait.stderr @@ -0,0 +1,17 @@ +error: this could be a `const fn` + --> tests/ui/missing_const_for_fn/const_trait.rs:24:1 + | +LL | / fn can_be_const() { +LL | | 0u64.method(); +LL | | } + | |_^ + | + = note: `-D clippy::missing-const-for-fn` implied by `-D warnings` + = help: to override `-D warnings` add `#[allow(clippy::missing_const_for_fn)]` +help: make the function `const` + | +LL | const fn can_be_const() { + | +++++ + +error: aborting due to 1 previous error +