Label struct/enum constructor instead of fn item, mention that it should be called on type mismatch

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -5,7 +5,7 @@ use crate::method::probe::{IsSuggestion, Mode, ProbeScope};
 use rustc_ast::util::parser::{ExprPrecedence, PREC_POSTFIX};
 use rustc_errors::{Applicability, Diagnostic, MultiSpan};
 use rustc_hir as hir;
-use rustc_hir::def::{CtorOf, DefKind};
+use rustc_hir::def::{CtorKind, CtorOf, DefKind};
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::{
     Expr, ExprKind, GenericBound, Node, Path, QPath, Stmt, StmtKind, TyKind, WherePredicate,
@@ -417,10 +417,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         } else if self.suggest_else_fn_with_closure(err, expr, found, expected) {
             return true;
         } else if self.suggest_fn_call(err, expr, found, |output| self.can_coerce(output, expected))
-            && let ty::FnDef(def_id, ..) = &found.kind()
-            && let Some(sp) = self.tcx.hir().span_if_local(*def_id)
+            && let ty::FnDef(def_id, ..) = *found.kind()
+            && let Some(sp) = self.tcx.hir().span_if_local(def_id)
         {
-            err.span_label(sp, format!("{found} defined here"));
+            let name = self.tcx.item_name(def_id);
+            let kind = self.tcx.def_kind(def_id);
+            if let DefKind::Ctor(of, CtorKind::Fn) = kind {
+                err.span_label(sp, format!("`{name}` defines {} constructor here, which should be called", match of {
+                    CtorOf::Struct => "a struct",
+                    CtorOf::Variant => "an enum variant",
+                }));
+            } else {
+                let descr = kind.descr(def_id);
+                err.span_label(sp, format!("{descr} `{name}` defined here"));
+            }
             return true;
         } else if self.check_for_cast(err, expr, found, expected, expected_ty_expr) {
             return true;

compiler/rustc_middle/src/ty/error.rs

@@ -2,10 +2,10 @@ use crate::traits::{ObligationCause, ObligationCauseCode};
 use crate::ty::diagnostics::suggest_constraining_type_param;
 use crate::ty::print::{with_forced_trimmed_paths, FmtPrinter, Printer};
 use crate::ty::{self, BoundRegionKind, Region, Ty, TyCtxt};
-use hir::def::DefKind;
 use rustc_errors::Applicability::{MachineApplicable, MaybeIncorrect};
 use rustc_errors::{pluralize, Diagnostic, MultiSpan};
 use rustc_hir as hir;
+use rustc_hir::def::{CtorOf, DefKind};
 use rustc_hir::def_id::DefId;
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::{BytePos, Span};
@@ -319,7 +319,11 @@ impl<'tcx> Ty<'tcx> {
                     .into()
                 }
             }
-            ty::FnDef(..) => "fn item".into(),
+            ty::FnDef(def_id, ..) => match tcx.def_kind(def_id) {
+                DefKind::Ctor(CtorOf::Struct, _) => "struct constructor".into(),
+                DefKind::Ctor(CtorOf::Variant, _) => "enum constructor".into(),
+                _ => "fn item".into(),
+            },
             ty::FnPtr(_) => "fn pointer".into(),
             ty::Dynamic(ref inner, ..) if let Some(principal) = inner.principal() => {
                 format!("trait object `dyn {}`", tcx.def_path_str(principal.def_id())).into()
@@ -366,7 +370,11 @@ impl<'tcx> Ty<'tcx> {
                 _ => "reference",
             }
             .into(),
-            ty::FnDef(..) => "fn item".into(),
+            ty::FnDef(def_id, ..) => match tcx.def_kind(def_id) {
+                DefKind::Ctor(CtorOf::Struct, _) => "struct constructor".into(),
+                DefKind::Ctor(CtorOf::Variant, _) => "enum constructor".into(),
+                _ => "fn item".into(),
+            },
             ty::FnPtr(_) => "fn pointer".into(),
             ty::Dynamic(..) => "trait object".into(),
             ty::Closure(..) => "closure".into(),

tests/ui/associated-types/substs-ppaux.normal.stderr

@@ -2,7 +2,7 @@ error[E0308]: mismatched types
   --> $DIR/substs-ppaux.rs:16:17
    |
 LL |     fn bar<'a, T>() where T: 'a {}
-   |     --------------------------- fn() {<i8 as Foo<'static, 'static, u8>>::bar::<'static, char>} defined here
+   |     --------------------------- associated function `bar` defined here
 ...
 LL |     let x: () = <i8 as Foo<'static, 'static,  u8>>::bar::<'static, char>;
    |            --   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found fn item
@@ -20,7 +20,7 @@ error[E0308]: mismatched types
   --> $DIR/substs-ppaux.rs:25:17
    |
 LL |     fn bar<'a, T>() where T: 'a {}
-   |     --------------------------- fn() {<i8 as Foo<'static, 'static>>::bar::<'static, char>} defined here
+   |     --------------------------- associated function `bar` defined here
 ...
 LL |     let x: () = <i8 as Foo<'static, 'static,  u32>>::bar::<'static, char>;
    |            --   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found fn item
@@ -38,7 +38,7 @@ error[E0308]: mismatched types
   --> $DIR/substs-ppaux.rs:33:17
    |
 LL |     fn baz() {}
-   |     -------- fn() {<i8 as Foo<'static, 'static, u8>>::baz} defined here
+   |     -------- associated function `baz` defined here
 ...
 LL |     let x: () = <i8 as Foo<'static, 'static,  u8>>::baz;
    |            --   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found fn item
@@ -56,7 +56,7 @@ error[E0308]: mismatched types
   --> $DIR/substs-ppaux.rs:41:17
    |
 LL | fn foo<'z>() where &'z (): Sized {
-   | -------------------------------- fn() {foo::<'static>} defined here
+   | -------------------------------- function `foo` defined here
 ...
 LL |     let x: () = foo::<'static>;
    |            --   ^^^^^^^^^^^^^^ expected `()`, found fn item

tests/ui/associated-types/substs-ppaux.verbose.stderr

@@ -2,7 +2,7 @@ error[E0308]: mismatched types
   --> $DIR/substs-ppaux.rs:16:17
    |
 LL |     fn bar<'a, T>() where T: 'a {}
-   |     --------------------------- fn() {<i8 as Foo<ReStatic, ReStatic, u8>>::bar::<ReStatic, char>} defined here
+   |     --------------------------- associated function `bar` defined here
 ...
 LL |     let x: () = <i8 as Foo<'static, 'static,  u8>>::bar::<'static, char>;
    |            --   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found fn item
@@ -20,7 +20,7 @@ error[E0308]: mismatched types
   --> $DIR/substs-ppaux.rs:25:17
    |
 LL |     fn bar<'a, T>() where T: 'a {}
-   |     --------------------------- fn() {<i8 as Foo<ReStatic, ReStatic>>::bar::<ReStatic, char>} defined here
+   |     --------------------------- associated function `bar` defined here
 ...
 LL |     let x: () = <i8 as Foo<'static, 'static,  u32>>::bar::<'static, char>;
    |            --   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found fn item
@@ -38,7 +38,7 @@ error[E0308]: mismatched types
   --> $DIR/substs-ppaux.rs:33:17
    |
 LL |     fn baz() {}
-   |     -------- fn() {<i8 as Foo<ReStatic, ReStatic, u8>>::baz} defined here
+   |     -------- associated function `baz` defined here
 ...
 LL |     let x: () = <i8 as Foo<'static, 'static,  u8>>::baz;
    |            --   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found fn item
@@ -56,7 +56,7 @@ error[E0308]: mismatched types
   --> $DIR/substs-ppaux.rs:41:17
    |
 LL | fn foo<'z>() where &'z (): Sized {
-   | -------------------------------- fn() {foo::<ReStatic>} defined here
+   | -------------------------------- function `foo` defined here
 ...
 LL |     let x: () = foo::<'static>;
    |            --   ^^^^^^^^^^^^^^ expected `()`, found fn item

tests/ui/issues/issue-35241.stderr

@@ -2,15 +2,15 @@ error[E0308]: mismatched types
   --> $DIR/issue-35241.rs:3:20
    |
 LL | struct Foo(u32);
-   | ---------- fn(u32) -> Foo {Foo} defined here
+   | ---------- `Foo` defines a struct constructor here, which should be called
 LL |
 LL | fn test() -> Foo { Foo }
-   |              ---   ^^^ expected struct `Foo`, found fn item
+   |              ---   ^^^ expected struct `Foo`, found struct constructor
    |              |
    |              expected `Foo` because of return type
    |
-   = note: expected struct `Foo`
-             found fn item `fn(u32) -> Foo {Foo}`
+   = note:          expected struct `Foo`
+           found struct constructor `fn(u32) -> Foo {Foo}`
 help: use parentheses to construct this tuple struct
    |
 LL | fn test() -> Foo { Foo(/* u32 */) }

tests/ui/resolve/privacy-enum-ctor.stderr

@@ -264,15 +264,15 @@ error[E0308]: mismatched types
   --> $DIR/privacy-enum-ctor.rs:27:20
    |
 LL |             Fn(u8),
-   |             -- fn(u8) -> Z {Z::Fn} defined here
+   |             -- `Fn` defines an enum variant constructor here, which should be called
 ...
 LL |         let _: Z = Z::Fn;
-   |                -   ^^^^^ expected enum `Z`, found fn item
+   |                -   ^^^^^ expected enum `Z`, found enum constructor
    |                |
    |                expected due to this
    |
-   = note: expected enum `Z`
-           found fn item `fn(u8) -> Z {Z::Fn}`
+   = note:          expected enum `Z`
+           found enum constructor `fn(u8) -> Z {Z::Fn}`
 help: use parentheses to construct this tuple variant
    |
 LL |         let _: Z = Z::Fn(/* u8 */);
@@ -305,15 +305,15 @@ error[E0308]: mismatched types
   --> $DIR/privacy-enum-ctor.rs:43:16
    |
 LL |         Fn(u8),
-   |         -- fn(u8) -> E {E::Fn} defined here
+   |         -- `Fn` defines an enum variant constructor here, which should be called
 ...
 LL |     let _: E = m::E::Fn;
-   |            -   ^^^^^^^^ expected enum `E`, found fn item
+   |            -   ^^^^^^^^ expected enum `E`, found enum constructor
    |            |
    |            expected due to this
    |
-   = note: expected enum `E`
-           found fn item `fn(u8) -> E {E::Fn}`
+   = note:          expected enum `E`
+           found enum constructor `fn(u8) -> E {E::Fn}`
 help: use parentheses to construct this tuple variant
    |
 LL |     let _: E = m::E::Fn(/* u8 */);
@@ -346,15 +346,15 @@ error[E0308]: mismatched types
   --> $DIR/privacy-enum-ctor.rs:51:16
    |
 LL |         Fn(u8),
-   |         -- fn(u8) -> E {E::Fn} defined here
+   |         -- `Fn` defines an enum variant constructor here, which should be called
 ...
 LL |     let _: E = E::Fn;
-   |            -   ^^^^^ expected enum `E`, found fn item
+   |            -   ^^^^^ expected enum `E`, found enum constructor
    |            |
    |            expected due to this
    |
-   = note: expected enum `E`
-           found fn item `fn(u8) -> E {E::Fn}`
+   = note:          expected enum `E`
+           found enum constructor `fn(u8) -> E {E::Fn}`
 help: use parentheses to construct this tuple variant
    |
 LL |     let _: E = E::Fn(/* u8 */);

tests/ui/suggestions/fn-or-tuple-struct-without-args.stderr

@@ -2,7 +2,7 @@ error[E0308]: mismatched types
   --> $DIR/fn-or-tuple-struct-without-args.rs:29:20
    |
 LL | fn foo(a: usize, b: usize) -> usize { a }
-   | ----------------------------------- fn(usize, usize) -> usize {foo} defined here
+   | ----------------------------------- function `foo` defined here
 ...
 LL |     let _: usize = foo;
    |            -----   ^^^ expected `usize`, found fn item
@@ -20,15 +20,15 @@ error[E0308]: mismatched types
   --> $DIR/fn-or-tuple-struct-without-args.rs:30:16
    |
 LL | struct S(usize, usize);
-   | -------- fn(usize, usize) -> S {S} defined here
+   | -------- `S` defines a struct constructor here, which should be called
 ...
 LL |     let _: S = S;
-   |            -   ^ expected struct `S`, found fn item
+   |            -   ^ expected struct `S`, found struct constructor
    |            |
    |            expected due to this
    |
-   = note: expected struct `S`
-             found fn item `fn(usize, usize) -> S {S}`
+   = note:          expected struct `S`
+           found struct constructor `fn(usize, usize) -> S {S}`
 help: use parentheses to construct this tuple struct
    |
 LL |     let _: S = S(/* usize */, /* usize */);
@@ -38,7 +38,7 @@ error[E0308]: mismatched types
   --> $DIR/fn-or-tuple-struct-without-args.rs:31:20
    |
 LL | fn bar() -> usize { 42 }
-   | ----------------- fn() -> usize {bar} defined here
+   | ----------------- function `bar` defined here
 ...
 LL |     let _: usize = bar;
    |            -----   ^^^ expected `usize`, found fn item
@@ -56,15 +56,15 @@ error[E0308]: mismatched types
   --> $DIR/fn-or-tuple-struct-without-args.rs:32:16
    |
 LL | struct V();
-   | -------- fn() -> V {V} defined here
+   | -------- `V` defines a struct constructor here, which should be called
 ...
 LL |     let _: V = V;
-   |            -   ^ expected struct `V`, found fn item
+   |            -   ^ expected struct `V`, found struct constructor
    |            |
    |            expected due to this
    |
-   = note: expected struct `V`
-             found fn item `fn() -> V {V}`
+   = note:          expected struct `V`
+           found struct constructor `fn() -> V {V}`
 help: use parentheses to construct this tuple struct
    |
 LL |     let _: V = V();
@@ -74,7 +74,7 @@ error[E0308]: mismatched types
   --> $DIR/fn-or-tuple-struct-without-args.rs:33:20
    |
 LL |     fn baz(x: usize, y: usize) -> usize { x }
-   |     ----------------------------------- fn(usize, usize) -> usize {<_ as T>::baz} defined here
+   |     ----------------------------------- associated function `baz` defined here
 ...
 LL |     let _: usize = T::baz;
    |            -----   ^^^^^^ expected `usize`, found fn item
@@ -92,7 +92,7 @@ error[E0308]: mismatched types
   --> $DIR/fn-or-tuple-struct-without-args.rs:34:20
    |
 LL |     fn bat(x: usize) -> usize { 42 }
-   |     ------------------------- fn(usize) -> usize {<_ as T>::bat} defined here
+   |     ------------------------- associated function `bat` defined here
 ...
 LL |     let _: usize = T::bat;
    |            -----   ^^^^^^ expected `usize`, found fn item
@@ -110,15 +110,15 @@ error[E0308]: mismatched types
   --> $DIR/fn-or-tuple-struct-without-args.rs:35:16
    |
 LL |     A(usize),
-   |     - fn(usize) -> E {E::A} defined here
+   |     - `A` defines an enum variant constructor here, which should be called
 ...
 LL |     let _: E = E::A;
-   |            -   ^^^^ expected enum `E`, found fn item
+   |            -   ^^^^ expected enum `E`, found enum constructor
    |            |
    |            expected due to this
    |
-   = note: expected enum `E`
-           found fn item `fn(usize) -> E {E::A}`
+   = note:          expected enum `E`
+           found enum constructor `fn(usize) -> E {E::A}`
 help: use parentheses to construct this tuple variant
    |
 LL |     let _: E = E::A(/* usize */);
@@ -134,7 +134,7 @@ error[E0308]: mismatched types
   --> $DIR/fn-or-tuple-struct-without-args.rs:37:20
    |
 LL |     fn baz(x: usize, y: usize) -> usize { x }
-   |     ----------------------------------- fn(usize, usize) -> usize {<X as T>::baz} defined here
+   |     ----------------------------------- associated function `baz` defined here
 ...
 LL |     let _: usize = X::baz;
    |            -----   ^^^^^^ expected `usize`, found fn item
@@ -152,7 +152,7 @@ error[E0308]: mismatched types
   --> $DIR/fn-or-tuple-struct-without-args.rs:38:20
    |
 LL |     fn bat(x: usize) -> usize { 42 }
-   |     ------------------------- fn(usize) -> usize {<X as T>::bat} defined here
+   |     ------------------------- associated function `bat` defined here
 ...
 LL |     let _: usize = X::bat;
    |            -----   ^^^^^^ expected `usize`, found fn item
@@ -170,7 +170,7 @@ error[E0308]: mismatched types
   --> $DIR/fn-or-tuple-struct-without-args.rs:39:20
    |
 LL |     fn bax(x: usize) -> usize { 42 }
-   |     ------------------------- fn(usize) -> usize {<X as T>::bax} defined here
+   |     ------------------------- associated function `bax` defined here
 ...
 LL |     let _: usize = X::bax;
    |            -----   ^^^^^^ expected `usize`, found fn item
@@ -188,7 +188,7 @@ error[E0308]: mismatched types
   --> $DIR/fn-or-tuple-struct-without-args.rs:40:20
    |
 LL |     fn bach(x: usize) -> usize;
-   |     --------------------------- fn(usize) -> usize {<X as T>::bach} defined here
+   |     --------------------------- associated function `bach` defined here
 ...
 LL |     let _: usize = X::bach;
    |            -----   ^^^^^^^ expected `usize`, found fn item
@@ -206,7 +206,7 @@ error[E0308]: mismatched types
   --> $DIR/fn-or-tuple-struct-without-args.rs:41:20
    |
 LL |     fn ban(&self) -> usize { 42 }
-   |     ---------------------- for<'a> fn(&'a X) -> usize {<X as T>::ban} defined here
+   |     ---------------------- associated function `ban` defined here
 ...
 LL |     let _: usize = X::ban;
    |            -----   ^^^^^^ expected `usize`, found fn item
@@ -224,7 +224,7 @@ error[E0308]: mismatched types
   --> $DIR/fn-or-tuple-struct-without-args.rs:42:20
    |
 LL |     fn bal(&self) -> usize;
-   |     ----------------------- for<'a> fn(&'a X) -> usize {<X as T>::bal} defined here
+   |     ----------------------- associated function `bal` defined here
 ...
 LL |     let _: usize = X::bal;
    |            -----   ^^^^^^ expected `usize`, found fn item

tests/ui/typeck/issue-87181/empty-tuple-method.rs

@@ -10,5 +10,5 @@ impl Foo {
 fn main() {
     let thing = Bar { bar: Foo };
     thing.bar.foo();
-    //~^ ERROR no method named `foo` found for fn item `fn() -> Foo {Foo}` in the current scope [E0599]
+    //~^ ERROR no method named `foo` found for struct constructor `fn() -> Foo {Foo}` in the current scope [E0599]
 }

tests/ui/typeck/issue-87181/empty-tuple-method.stderr

@@ -1,4 +1,4 @@
-error[E0599]: no method named `foo` found for fn item `fn() -> Foo {Foo}` in the current scope
+error[E0599]: no method named `foo` found for struct constructor `fn() -> Foo {Foo}` in the current scope
   --> $DIR/empty-tuple-method.rs:12:15
    |
 LL |     thing.bar.foo();

tests/ui/typeck/issue-87181/enum-variant.rs

@@ -12,5 +12,5 @@ impl Foo {
 fn main() {
     let thing = Bar { bar: Foo::Tup };
     thing.bar.foo();
-    //~^ ERROR no method named `foo` found for fn item `fn() -> Foo {Foo::Tup}` in the current scope [E0599]
+    //~^ ERROR no method named `foo` found for enum constructor `fn() -> Foo {Foo::Tup}` in the current scope [E0599]
 }

tests/ui/typeck/issue-87181/enum-variant.stderr

@@ -1,4 +1,4 @@
-error[E0599]: no method named `foo` found for fn item `fn() -> Foo {Foo::Tup}` in the current scope
+error[E0599]: no method named `foo` found for enum constructor `fn() -> Foo {Foo::Tup}` in the current scope
   --> $DIR/enum-variant.rs:14:15
    |
 LL |     thing.bar.foo();