diff --git a/compiler/rustc_typeck/src/collect/type_of.rs b/compiler/rustc_typeck/src/collect/type_of.rs index 29a87b18a9eb7..abe5d69a3b3c1 100644 --- a/compiler/rustc_typeck/src/collect/type_of.rs +++ b/compiler/rustc_typeck/src/collect/type_of.rs @@ -9,7 +9,7 @@ use rustc_hir::{HirId, Node}; use rustc_middle::hir::map::Map; use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts}; use rustc_middle::ty::util::IntTypeExt; -use rustc_middle::ty::{self, DefIdTree, Ty, TyCtxt, TypeFoldable}; +use rustc_middle::ty::{self, DefIdTree, Ty, TyCtxt, TypeFoldable, TypeFolder}; use rustc_span::symbol::Ident; use rustc_span::{Span, DUMMY_SP}; @@ -749,6 +749,40 @@ fn infer_placeholder_type( span: Span, item_ident: Ident, ) -> Ty<'_> { + // Attempts to make the type nameable by turning FnDefs into FnPtrs. + struct MakeNameable<'tcx> { + success: bool, + tcx: TyCtxt<'tcx>, + } + + impl<'tcx> MakeNameable<'tcx> { + fn new(tcx: TyCtxt<'tcx>) -> Self { + MakeNameable { success: true, tcx } + } + } + + impl TypeFolder<'tcx> for MakeNameable<'tcx> { + fn tcx(&self) -> TyCtxt<'tcx> { + self.tcx + } + + fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> { + if !self.success { + return ty; + } + + match ty.kind() { + ty::FnDef(def_id, _) => self.tcx.mk_fn_ptr(self.tcx.fn_sig(*def_id)), + // FIXME: non-capturing closures should also suggest a function pointer + ty::Closure(..) | ty::Generator(..) => { + self.success = false; + ty + } + _ => ty.super_fold_with(self), + } + } + } + let ty = tcx.diagnostic_only_typeck(def_id).node_type(body_id.hir_id); // If this came from a free `const` or `static mut?` item, @@ -760,24 +794,47 @@ fn infer_placeholder_type( // The parser provided a sub-optimal `HasPlaceholders` suggestion for the type. // We are typeck and have the real type, so remove that and suggest the actual type. err.suggestions.clear(); - err.span_suggestion( - span, - "provide a type for the item", - format!("{}: {}", item_ident, ty), - Applicability::MachineApplicable, - ) - .emit_unless(ty.references_error()); + + // Suggesting unnameable types won't help. + let mut mk_nameable = MakeNameable::new(tcx); + let ty = mk_nameable.fold_ty(ty); + let sugg_ty = if mk_nameable.success { Some(ty) } else { None }; + if let Some(sugg_ty) = sugg_ty { + err.span_suggestion( + span, + "provide a type for the item", + format!("{}: {}", item_ident, sugg_ty), + Applicability::MachineApplicable, + ); + } else { + err.span_note( + tcx.hir().body(body_id).value.span, + &format!("however, the inferred type `{}` cannot be named", ty.to_string()), + ); + } + + err.emit_unless(ty.references_error()); } None => { let mut diag = bad_placeholder_type(tcx, vec![span]); if !ty.references_error() { - diag.span_suggestion( - span, - "replace with the correct type", - ty.to_string(), - Applicability::MaybeIncorrect, - ); + let mut mk_nameable = MakeNameable::new(tcx); + let ty = mk_nameable.fold_ty(ty); + let sugg_ty = if mk_nameable.success { Some(ty) } else { None }; + if let Some(sugg_ty) = sugg_ty { + diag.span_suggestion( + span, + "replace with the correct type", + sugg_ty.to_string(), + Applicability::MaybeIncorrect, + ); + } else { + diag.span_note( + tcx.hir().body(body_id).value.span, + &format!("however, the inferred type `{}` cannot be named", ty.to_string()), + ); + } } diag.emit(); diff --git a/src/test/ui/suggestions/unnamable-types.rs b/src/test/ui/suggestions/unnamable-types.rs new file mode 100644 index 0000000000000..5d0616443e5ac --- /dev/null +++ b/src/test/ui/suggestions/unnamable-types.rs @@ -0,0 +1,39 @@ +// Test that we do not suggest to add type annotations for unnamable types. + +#![crate_type="lib"] +#![feature(generators)] + +const A = 5; +//~^ ERROR: missing type for `const` item +//~| HELP: provide a type for the item + +static B: _ = "abc"; +//~^ ERROR: the type placeholder `_` is not allowed within types on item signatures +//~| NOTE: not allowed in type signatures +//~| HELP: replace with the correct type + + +// FIXME: this should also suggest a function pointer, as the closure is non-capturing +const C: _ = || 42; +//~^ ERROR: the type placeholder `_` is not allowed within types on item signatures +//~| NOTE: not allowed in type signatures +//~| NOTE: however, the inferred type + +struct S { t: T } +const D = S { t: { let i = 0; move || -> i32 { i } } }; +//~^ ERROR: missing type for `const` item +//~| NOTE: however, the inferred type + + +fn foo() -> i32 { 42 } +const E = foo; +//~^ ERROR: missing type for `const` item +//~| HELP: provide a type for the item +const F = S { t: foo }; +//~^ ERROR: missing type for `const` item +//~| HELP: provide a type for the item + + +const G = || -> i32 { yield 0; return 1; }; +//~^ ERROR: missing type for `const` item +//~| NOTE: however, the inferred type diff --git a/src/test/ui/suggestions/unnamable-types.stderr b/src/test/ui/suggestions/unnamable-types.stderr new file mode 100644 index 0000000000000..2c8166781bfdc --- /dev/null +++ b/src/test/ui/suggestions/unnamable-types.stderr @@ -0,0 +1,66 @@ +error: missing type for `const` item + --> $DIR/unnamable-types.rs:6:7 + | +LL | const A = 5; + | ^ help: provide a type for the item: `A: i32` + +error[E0121]: the type placeholder `_` is not allowed within types on item signatures + --> $DIR/unnamable-types.rs:10:11 + | +LL | static B: _ = "abc"; + | ^ + | | + | not allowed in type signatures + | help: replace with the correct type: `&str` + +error[E0121]: the type placeholder `_` is not allowed within types on item signatures + --> $DIR/unnamable-types.rs:17:10 + | +LL | const C: _ = || 42; + | ^ not allowed in type signatures + | +note: however, the inferred type `[closure@$DIR/unnamable-types.rs:17:14: 17:19]` cannot be named + --> $DIR/unnamable-types.rs:17:14 + | +LL | const C: _ = || 42; + | ^^^^^ + +error: missing type for `const` item + --> $DIR/unnamable-types.rs:23:7 + | +LL | const D = S { t: { let i = 0; move || -> i32 { i } } }; + | ^ + | +note: however, the inferred type `S<[closure@$DIR/unnamable-types.rs:23:31: 23:51]>` cannot be named + --> $DIR/unnamable-types.rs:23:11 + | +LL | const D = S { t: { let i = 0; move || -> i32 { i } } }; + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: missing type for `const` item + --> $DIR/unnamable-types.rs:29:7 + | +LL | const E = foo; + | ^ help: provide a type for the item: `E: fn() -> i32` + +error: missing type for `const` item + --> $DIR/unnamable-types.rs:32:7 + | +LL | const F = S { t: foo }; + | ^ help: provide a type for the item: `F: S i32>` + +error: missing type for `const` item + --> $DIR/unnamable-types.rs:37:7 + | +LL | const G = || -> i32 { yield 0; return 1; }; + | ^ + | +note: however, the inferred type `[generator@$DIR/unnamable-types.rs:37:11: 37:43 {i32, ()}]` cannot be named + --> $DIR/unnamable-types.rs:37:11 + | +LL | const G = || -> i32 { yield 0; return 1; }; + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: aborting due to 7 previous errors + +For more information about this error, try `rustc --explain E0121`.