Rollup merge of #104614 - Nilstrieb:type-ascribe!, r=TaKO8Ki

Add `type_ascribe!` macro as placeholder syntax for type ascription

This makes it still possible to test the internal semantics of type ascription even once the `:`-syntax is removed from the parser. The macro now gets used in a bunch of UI tests that test the semantics and not syntax of type ascription.

I might have forgotten a few tests but this should hopefully be most of them. The remaining ones will certainly be found once type ascription is removed from the parser altogether.

Part of #101728

compiler/rustc_builtin_macros/src/lib.rs

@@ -45,6 +45,7 @@ mod log_syntax;
 mod source_util;
 mod test;
 mod trace_macros;
+mod type_ascribe;
 mod util;
 
 pub mod asm;
@@ -92,6 +93,7 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
         unreachable: edition_panic::expand_unreachable,
         stringify: source_util::expand_stringify,
         trace_macros: trace_macros::expand_trace_macros,
+        type_ascribe: type_ascribe::expand_type_ascribe,
     }
 
     register_attr! {

compiler/rustc_builtin_macros/src/type_ascribe.rs

@@ -0,0 +1,35 @@
+use rustc_ast::ptr::P;
+use rustc_ast::tokenstream::TokenStream;
+use rustc_ast::{token, Expr, ExprKind, Ty};
+use rustc_errors::PResult;
+use rustc_expand::base::{self, DummyResult, ExtCtxt, MacEager};
+use rustc_span::Span;
+
+pub fn expand_type_ascribe(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'static> {
+    let (expr, ty) = match parse_ascribe(cx, tts) {
+        Ok(parsed) => parsed,
+        Err(mut err) => {
+            err.emit();
+            return DummyResult::any(span);
+        }
+    };
+
+    let asc_expr = cx.expr(span, ExprKind::Type(expr, ty));
+
+    return MacEager::expr(asc_expr);
+}
+
+fn parse_ascribe<'a>(cx: &mut ExtCtxt<'a>, stream: TokenStream) -> PResult<'a, (P<Expr>, P<Ty>)> {
+    let mut parser = cx.new_parser_from_tts(stream);
+
+    let expr = parser.parse_expr()?;
+    parser.expect(&token::Comma)?;
+
+    let ty = parser.parse_ty()?;
+
+    Ok((expr, ty))
+}

compiler/rustc_span/src/symbol.rs

@@ -1488,6 +1488,7 @@ symbols! {
         ty,
         type_alias_enum_variants,
         type_alias_impl_trait,
+        type_ascribe,
         type_ascription,
         type_changing_struct_update,
         type_id,

library/core/src/macros/mod.rs

@@ -1546,6 +1546,18 @@ pub(crate) mod builtin {
         /* compiler built-in */
     }
 
+    /// Unstable placeholder for type ascription.
+    #[rustc_builtin_macro]
+    #[unstable(
+        feature = "type_ascription",
+        issue = "23416",
+        reason = "placeholder syntax for type ascription"
+    )]
+    #[cfg(not(bootstrap))]
+    pub macro type_ascribe($expr:expr, $ty:ty) {
+        /* compiler built-in */
+    }
+
     /// Unstable implementation detail of the `rustc` compiler, do not use.
     #[rustc_builtin_macro]
     #[stable(feature = "rust1", since = "1.0.0")]

library/core/src/prelude/v1.rs

@@ -98,3 +98,11 @@ pub use crate::macros::builtin::cfg_accessible;
     reason = "`cfg_eval` is a recently implemented feature"
 )]
 pub use crate::macros::builtin::cfg_eval;
+
+#[unstable(
+    feature = "type_ascription",
+    issue = "23416",
+    reason = "placeholder syntax for type ascription"
+)]
+#[cfg(not(bootstrap))]
+pub use crate::macros::builtin::type_ascribe;

library/std/src/prelude/v1.rs

@@ -85,6 +85,15 @@ pub use core::prelude::v1::cfg_accessible;
 )]
 pub use core::prelude::v1::cfg_eval;
 
+// Do not `doc(no_inline)` either.
+#[unstable(
+    feature = "type_ascription",
+    issue = "23416",
+    reason = "placeholder syntax for type ascription"
+)]
+#[cfg(not(bootstrap))]
+pub use core::prelude::v1::type_ascribe;
+
 // The file so far is equivalent to src/libcore/prelude/v1.rs,
 // and below to src/liballoc/prelude.rs.
 // Those files are duplicated rather than using glob imports

src/test/ui/associated-consts/issue-93835.rs

@@ -1,9 +1,11 @@
+#![feature(type_ascription)]
+
 fn e() {
-    p:a<p:p<e=6>>
+    type_ascribe!(p, a<p:p<e=6>>);
-    //~^ ERROR comparison operators
+    //~^ ERROR cannot find type `a` in this scope
     //~| ERROR cannot find value
     //~| ERROR associated const equality
-    //~| ERROR associated const equality
+    //~| ERROR cannot find trait `p` in this scope
     //~| ERROR associated type bounds
 }
 

src/test/ui/associated-consts/issue-93835.stderr

@@ -1,65 +1,40 @@
-error: comparison operators cannot be chained
-  --> $DIR/issue-93835.rs:2:8
-   |
-LL | fn e() {
-   |        - while parsing this struct
-LL |     p:a<p:p<e=6>>
-   |        ^        ^
-   |
-   = help: use `::<...>` instead of `<...>` to specify lifetime, type, or const arguments
-   = help: or use `(...)` if you meant to specify fn arguments
-
 error[E0425]: cannot find value `p` in this scope
-  --> $DIR/issue-93835.rs:2:5
+  --> $DIR/issue-93835.rs:4:19
    |
-LL |     p:a<p:p<e=6>>
+LL |     type_ascribe!(p, a<p:p<e=6>>);
-   |     ^ not found in this scope
+   |                   ^ not found in this scope
+
+error[E0412]: cannot find type `a` in this scope
+  --> $DIR/issue-93835.rs:4:22
    |
-help: you might have meant to write a `struct` literal
+LL |     type_ascribe!(p, a<p:p<e=6>>);
+   |                      ^ not found in this scope
+
+error[E0405]: cannot find trait `p` in this scope
+  --> $DIR/issue-93835.rs:4:26
    |
-LL ~ fn e() { SomeStruct {
+LL |     type_ascribe!(p, a<p:p<e=6>>);
-LL |     p:a<p:p<e=6>>
+   |                          ^ not found in this scope
- ...
-LL |
-LL ~ }}
-   |
-help: maybe you meant to write a path separator here
-   |
-LL |     p::a<p:p<e=6>>
-   |      ~~
-help: maybe you meant to write an assignment here
-   |
-LL |     let p:a<p:p<e=6>>
-   |     ~~~~~
 
 error[E0658]: associated const equality is incomplete
-  --> $DIR/issue-93835.rs:2:13
+  --> $DIR/issue-93835.rs:4:28
    |
-LL |     p:a<p:p<e=6>>
+LL |     type_ascribe!(p, a<p:p<e=6>>);
-   |             ^^^
+   |                            ^^^
-   |
-   = note: see issue #92827 <https://github.com/rust-lang/rust/issues/92827> for more information
-   = help: add `#![feature(associated_const_equality)]` to the crate attributes to enable
-
-error[E0658]: associated const equality is incomplete
-  --> $DIR/issue-93835.rs:2:13
-   |
-LL |     p:a<p:p<e=6>>
-   |             ^^^
    |
    = note: see issue #92827 <https://github.com/rust-lang/rust/issues/92827> for more information
    = help: add `#![feature(associated_const_equality)]` to the crate attributes to enable
 
 error[E0658]: associated type bounds are unstable
-  --> $DIR/issue-93835.rs:2:9
+  --> $DIR/issue-93835.rs:4:24
    |
-LL |     p:a<p:p<e=6>>
+LL |     type_ascribe!(p, a<p:p<e=6>>);
-   |         ^^^^^^^^
+   |                        ^^^^^^^^
    |
    = note: see issue #52662 <https://github.com/rust-lang/rust/issues/52662> for more information
    = help: add `#![feature(associated_type_bounds)]` to the crate attributes to enable
 
 error: aborting due to 5 previous errors
 
-Some errors have detailed explanations: E0425, E0658.
+Some errors have detailed explanations: E0405, E0412, E0425, E0658.
-For more information about an error, try `rustc --explain E0425`.
+For more information about an error, try `rustc --explain E0405`.

src/test/ui/closures/issue-90871.rs

@@ -1,5 +1,7 @@
+#![feature(type_ascription)]
+
 fn main() {
-    2: n([u8; || 1])
+    type_ascribe!(2, n([u8; || 1]))
     //~^ ERROR cannot find type `n` in this scope
     //~| ERROR mismatched types
 }

src/test/ui/closures/issue-90871.stderr

@@ -1,21 +1,26 @@
 error[E0412]: cannot find type `n` in this scope
-  --> $DIR/issue-90871.rs:2:8
+  --> $DIR/issue-90871.rs:4:22
    |
-LL |     2: n([u8; || 1])
+LL |     type_ascribe!(2, n([u8; || 1]))
-   |        ^ expecting a type here because of type ascription
+   |                      ^ help: a trait with a similar name exists: `Fn`
+   |
+  ::: $SRC_DIR/core/src/ops/function.rs:LL:COL
+   |
+LL | pub trait Fn<Args: Tuple>: FnMut<Args> {
+   | -------------------------------------- similarly named trait `Fn` defined here
 
 error[E0308]: mismatched types
-  --> $DIR/issue-90871.rs:2:15
+  --> $DIR/issue-90871.rs:4:29
    |
-LL |     2: n([u8; || 1])
+LL |     type_ascribe!(2, n([u8; || 1]))
-   |               ^^^^ expected `usize`, found closure
+   |                             ^^^^ expected `usize`, found closure
    |
    = note: expected type `usize`
-           found closure `[closure@$DIR/issue-90871.rs:2:15: 2:17]`
+           found closure `[closure@$DIR/issue-90871.rs:4:29: 4:31]`
 help: use parentheses to call this closure
    |
-LL |     2: n([u8; (|| 1)()])
+LL |     type_ascribe!(2, n([u8; (|| 1)()]))
-   |               +    +++
+   |                             +    +++
 
 error: aborting due to 2 previous errors
 

src/test/ui/coercion/coerce-expect-unsized-ascribed.rs

@@ -6,27 +6,27 @@
 use std::fmt::Debug;
 
 pub fn main() {
-    let _ = box { [1, 2, 3] }: Box<[i32]>; //~ ERROR mismatched types
+    let _ = type_ascribe!(box { [1, 2, 3] }, Box<[i32]>); //~ ERROR mismatched types
-    let _ = box if true { [1, 2, 3] } else { [1, 3, 4] }: Box<[i32]>; //~ ERROR mismatched types
+    let _ = type_ascribe!(box if true { [1, 2, 3] } else { [1, 3, 4] }, Box<[i32]>); //~ ERROR mismatched types
-    let _ = box match true { true => [1, 2, 3], false => [1, 3, 4] }: Box<[i32]>;
+    let _ = type_ascribe!(box match true { true => [1, 2, 3], false => [1, 3, 4] }, Box<[i32]>);
     //~^ ERROR mismatched types
-    let _ = box { |x| (x as u8) }: Box<dyn Fn(i32) -> _>; //~ ERROR mismatched types
+    let _ = type_ascribe!(box { |x| (x as u8) }, Box<dyn Fn(i32) -> _>); //~ ERROR mismatched types
-    let _ = box if true { false } else { true }: Box<dyn Debug>; //~ ERROR mismatched types
+    let _ = type_ascribe!(box if true { false } else { true }, Box<dyn Debug>); //~ ERROR mismatched types
-    let _ = box match true { true => 'a', false => 'b' }: Box<dyn Debug>; //~ ERROR mismatched types
+    let _ = type_ascribe!(box match true { true => 'a', false => 'b' }, Box<dyn Debug>); //~ ERROR mismatched types
 
-    let _ = &{ [1, 2, 3] }: &[i32]; //~ ERROR mismatched types
+    let _ = type_ascribe!(&{ [1, 2, 3] }, &[i32]); //~ ERROR mismatched types
-    let _ = &if true { [1, 2, 3] } else { [1, 3, 4] }: &[i32]; //~ ERROR mismatched types
+    let _ = type_ascribe!(&if true { [1, 2, 3] } else { [1, 3, 4] }, &[i32]); //~ ERROR mismatched types
-    let _ = &match true { true => [1, 2, 3], false => [1, 3, 4] }: &[i32];
+    let _ = type_ascribe!(&match true { true => [1, 2, 3], false => [1, 3, 4] }, &[i32]);
     //~^ ERROR mismatched types
-    let _ = &{ |x| (x as u8) }: &dyn Fn(i32) -> _; //~ ERROR mismatched types
+    let _ = type_ascribe!(&{ |x| (x as u8) }, &dyn Fn(i32) -> _); //~ ERROR mismatched types
-    let _ = &if true { false } else { true }: &dyn Debug; //~ ERROR mismatched types
+    let _ = type_ascribe!(&if true { false } else { true }, &dyn Debug); //~ ERROR mismatched types
-    let _ = &match true { true => 'a', false => 'b' }: &dyn Debug; //~ ERROR mismatched types
+    let _ = type_ascribe!(&match true { true => 'a', false => 'b' }, &dyn Debug); //~ ERROR mismatched types
 
-    let _ = Box::new([1, 2, 3]): Box<[i32]>; //~ ERROR mismatched types
+    let _ = type_ascribe!(Box::new([1, 2, 3]), Box<[i32]>); //~ ERROR mismatched types
-    let _ = Box::new(|x| (x as u8)): Box<dyn Fn(i32) -> _>; //~ ERROR mismatched types
+    let _ = type_ascribe!(Box::new(|x| (x as u8)), Box<dyn Fn(i32) -> _>); //~ ERROR mismatched types
 
-    let _ = vec![
+    let _ = type_ascribe!(vec![
         Box::new(|x| (x as u8)),
         box |x| (x as i16 as u8),
-    ]: Vec<Box<dyn Fn(i32) -> _>>;
+    ], Vec<Box<dyn Fn(i32) -> _>>);
 }

src/test/ui/coercion/coerce-expect-unsized-ascribed.stderr

@@ -1,128 +1,128 @@
 error[E0308]: mismatched types
-  --> $DIR/coerce-expect-unsized-ascribed.rs:9:13
+  --> $DIR/coerce-expect-unsized-ascribed.rs:9:27
    |
-LL |     let _ = box { [1, 2, 3] }: Box<[i32]>;
+LL |     let _ = type_ascribe!(box { [1, 2, 3] }, Box<[i32]>);
-   |             ^^^^^^^^^^^^^^^^^ expected slice `[i32]`, found array `[i32; 3]`
+   |                           ^^^^^^^^^^^^^^^^^ expected slice `[i32]`, found array `[i32; 3]`
    |
    = note: expected struct `Box<[i32]>`
               found struct `Box<[i32; 3]>`
 
 error[E0308]: mismatched types
-  --> $DIR/coerce-expect-unsized-ascribed.rs:10:13
+  --> $DIR/coerce-expect-unsized-ascribed.rs:10:27
    |
-LL |     let _ = box if true { [1, 2, 3] } else { [1, 3, 4] }: Box<[i32]>;
+LL |     let _ = type_ascribe!(box if true { [1, 2, 3] } else { [1, 3, 4] }, Box<[i32]>);
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected slice `[i32]`, found array `[i32; 3]`
+   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected slice `[i32]`, found array `[i32; 3]`
    |
    = note: expected struct `Box<[i32]>`
               found struct `Box<[i32; 3]>`
 
 error[E0308]: mismatched types
-  --> $DIR/coerce-expect-unsized-ascribed.rs:11:13
+  --> $DIR/coerce-expect-unsized-ascribed.rs:11:27
    |
-LL |     let _ = box match true { true => [1, 2, 3], false => [1, 3, 4] }: Box<[i32]>;
+LL |     let _ = type_ascribe!(box match true { true => [1, 2, 3], false => [1, 3, 4] }, Box<[i32]>);
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected slice `[i32]`, found array `[i32; 3]`
+   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected slice `[i32]`, found array `[i32; 3]`
    |
    = note: expected struct `Box<[i32]>`
               found struct `Box<[i32; 3]>`
 
 error[E0308]: mismatched types
-  --> $DIR/coerce-expect-unsized-ascribed.rs:13:13
+  --> $DIR/coerce-expect-unsized-ascribed.rs:13:27
    |
-LL |     let _ = box { |x| (x as u8) }: Box<dyn Fn(i32) -> _>;
+LL |     let _ = type_ascribe!(box { |x| (x as u8) }, Box<dyn Fn(i32) -> _>);
-   |             ^^^^^^^^^^^^^^^^^^^^^ expected trait object `dyn Fn`, found closure
+   |                           ^^^^^^^^^^^^^^^^^^^^^ expected trait object `dyn Fn`, found closure
    |
    = note: expected struct `Box<dyn Fn(i32) -> u8>`
-              found struct `Box<[closure@$DIR/coerce-expect-unsized-ascribed.rs:13:19: 13:22]>`
+              found struct `Box<[closure@$DIR/coerce-expect-unsized-ascribed.rs:13:33: 13:36]>`
 
 error[E0308]: mismatched types
-  --> $DIR/coerce-expect-unsized-ascribed.rs:14:13
+  --> $DIR/coerce-expect-unsized-ascribed.rs:14:27
    |
-LL |     let _ = box if true { false } else { true }: Box<dyn Debug>;
+LL |     let _ = type_ascribe!(box if true { false } else { true }, Box<dyn Debug>);
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected trait object `dyn Debug`, found `bool`
+   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected trait object `dyn Debug`, found `bool`
    |
    = note: expected struct `Box<dyn Debug>`
               found struct `Box<bool>`
 
 error[E0308]: mismatched types
-  --> $DIR/coerce-expect-unsized-ascribed.rs:15:13
+  --> $DIR/coerce-expect-unsized-ascribed.rs:15:27
    |
-LL |     let _ = box match true { true => 'a', false => 'b' }: Box<dyn Debug>;
+LL |     let _ = type_ascribe!(box match true { true => 'a', false => 'b' }, Box<dyn Debug>);
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected trait object `dyn Debug`, found `char`
+   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected trait object `dyn Debug`, found `char`
    |
    = note: expected struct `Box<dyn Debug>`
               found struct `Box<char>`
 
 error[E0308]: mismatched types
-  --> $DIR/coerce-expect-unsized-ascribed.rs:17:13
+  --> $DIR/coerce-expect-unsized-ascribed.rs:17:27
    |
-LL |     let _ = &{ [1, 2, 3] }: &[i32];
+LL |     let _ = type_ascribe!(&{ [1, 2, 3] }, &[i32]);
-   |             ^^^^^^^^^^^^^^ expected slice `[i32]`, found array `[i32; 3]`
+   |                           ^^^^^^^^^^^^^^ expected slice `[i32]`, found array `[i32; 3]`
    |
    = note: expected reference `&[i32]`
               found reference `&[i32; 3]`
 
 error[E0308]: mismatched types
-  --> $DIR/coerce-expect-unsized-ascribed.rs:18:13
+  --> $DIR/coerce-expect-unsized-ascribed.rs:18:27
    |
-LL |     let _ = &if true { [1, 2, 3] } else { [1, 3, 4] }: &[i32];
+LL |     let _ = type_ascribe!(&if true { [1, 2, 3] } else { [1, 3, 4] }, &[i32]);
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected slice `[i32]`, found array `[i32; 3]`
+   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected slice `[i32]`, found array `[i32; 3]`
    |
    = note: expected reference `&[i32]`
               found reference `&[i32; 3]`
 
 error[E0308]: mismatched types
-  --> $DIR/coerce-expect-unsized-ascribed.rs:19:13
+  --> $DIR/coerce-expect-unsized-ascribed.rs:19:27
    |
-LL |     let _ = &match true { true => [1, 2, 3], false => [1, 3, 4] }: &[i32];
+LL |     let _ = type_ascribe!(&match true { true => [1, 2, 3], false => [1, 3, 4] }, &[i32]);
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected slice `[i32]`, found array `[i32; 3]`
+   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected slice `[i32]`, found array `[i32; 3]`
    |
    = note: expected reference `&[i32]`
               found reference `&[i32; 3]`
 
 error[E0308]: mismatched types
-  --> $DIR/coerce-expect-unsized-ascribed.rs:21:13
+  --> $DIR/coerce-expect-unsized-ascribed.rs:21:27
    |
-LL |     let _ = &{ |x| (x as u8) }: &dyn Fn(i32) -> _;
+LL |     let _ = type_ascribe!(&{ |x| (x as u8) }, &dyn Fn(i32) -> _);
-   |             ^^^^^^^^^^^^^^^^^^ expected trait object `dyn Fn`, found closure
+   |                           ^^^^^^^^^^^^^^^^^^ expected trait object `dyn Fn`, found closure
    |
    = note: expected reference `&dyn Fn(i32) -> u8`
-              found reference `&[closure@$DIR/coerce-expect-unsized-ascribed.rs:21:16: 21:19]`
+              found reference `&[closure@$DIR/coerce-expect-unsized-ascribed.rs:21:30: 21:33]`
 
 error[E0308]: mismatched types
-  --> $DIR/coerce-expect-unsized-ascribed.rs:22:13
+  --> $DIR/coerce-expect-unsized-ascribed.rs:22:27
    |
-LL |     let _ = &if true { false } else { true }: &dyn Debug;
+LL |     let _ = type_ascribe!(&if true { false } else { true }, &dyn Debug);
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected trait object `dyn Debug`, found `bool`
+   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected trait object `dyn Debug`, found `bool`
    |
    = note: expected reference `&dyn Debug`
               found reference `&bool`
 
 error[E0308]: mismatched types
-  --> $DIR/coerce-expect-unsized-ascribed.rs:23:13
+  --> $DIR/coerce-expect-unsized-ascribed.rs:23:27
    |
-LL |     let _ = &match true { true => 'a', false => 'b' }: &dyn Debug;
+LL |     let _ = type_ascribe!(&match true { true => 'a', false => 'b' }, &dyn Debug);
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected trait object `dyn Debug`, found `char`
+   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected trait object `dyn Debug`, found `char`
    |
    = note: expected reference `&dyn Debug`
               found reference `&char`
 
 error[E0308]: mismatched types
-  --> $DIR/coerce-expect-unsized-ascribed.rs:25:13
+  --> $DIR/coerce-expect-unsized-ascribed.rs:25:27
    |
-LL |     let _ = Box::new([1, 2, 3]): Box<[i32]>;
+LL |     let _ = type_ascribe!(Box::new([1, 2, 3]), Box<[i32]>);
-   |             ^^^^^^^^^^^^^^^^^^^ expected slice `[i32]`, found array `[i32; 3]`
+   |                           ^^^^^^^^^^^^^^^^^^^ expected slice `[i32]`, found array `[i32; 3]`
    |
    = note: expected struct `Box<[i32]>`
               found struct `Box<[i32; 3]>`
 
 error[E0308]: mismatched types
-  --> $DIR/coerce-expect-unsized-ascribed.rs:26:13
+  --> $DIR/coerce-expect-unsized-ascribed.rs:26:27
    |
-LL |     let _ = Box::new(|x| (x as u8)): Box<dyn Fn(i32) -> _>;
+LL |     let _ = type_ascribe!(Box::new(|x| (x as u8)), Box<dyn Fn(i32) -> _>);
-   |             ^^^^^^^^^^^^^^^^^^^^^^^ expected trait object `dyn Fn`, found closure
+   |                           ^^^^^^^^^^^^^^^^^^^^^^^ expected trait object `dyn Fn`, found closure
    |
    = note: expected struct `Box<dyn Fn(i32) -> u8>`
-              found struct `Box<[closure@$DIR/coerce-expect-unsized-ascribed.rs:26:22: 26:25]>`
+              found struct `Box<[closure@$DIR/coerce-expect-unsized-ascribed.rs:26:36: 26:39]>`
 
 error: aborting due to 14 previous errors
 

src/test/ui/consts/const_in_pattern/accept_structural.rs

@@ -45,7 +45,7 @@ fn main() {
     const TUPLE: (OND, OND) = (None, None);
     match (None, None) { TUPLE => dbg!(TUPLE), _ => panic!("whoops"), };
 
-    const TYPE_ASCRIPTION: OND = None: OND;
+    const TYPE_ASCRIPTION: OND = type_ascribe!(None, OND);
     match None { TYPE_ASCRIPTION => dbg!(TYPE_ASCRIPTION), _ => panic!("whoops"), };
 
     const ARRAY: [OND; 2] = [None, None];

src/test/ui/consts/const_in_pattern/reject_non_structural.rs

@@ -53,7 +53,7 @@ fn main() {
     match (None, Some(NoDerive)) { TUPLE => dbg!(TUPLE), _ => panic!("whoops"), };
     //~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]`
 
-    const TYPE_ASCRIPTION: OND = Some(NoDerive): OND;
+    const TYPE_ASCRIPTION: OND = type_ascribe!(Some(NoDerive), OND);
     match Some(NoDerive) { TYPE_ASCRIPTION => dbg!(TYPE_ASCRIPTION), _ => panic!("whoops"), };
     //~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]`
 

src/test/ui/enum/issue-67945-2.rs

@@ -1,7 +1,7 @@
 #![feature(type_ascription)]
 
 enum Bug<S> { //~ ERROR parameter `S` is never used
-    Var = 0: S,
+    Var = type_ascribe!(0, S),
     //~^ ERROR generic parameters may not be used
 }
 

src/test/ui/enum/issue-67945-2.stderr

@@ -1,8 +1,8 @@
 error: generic parameters may not be used in const operations
-  --> $DIR/issue-67945-2.rs:4:14
+  --> $DIR/issue-67945-2.rs:4:28
    |
-LL |     Var = 0: S,
+LL |     Var = type_ascribe!(0, S),
-   |              ^ cannot perform const operation using `S`
+   |                            ^ cannot perform const operation using `S`
    |
    = note: type parameters may not be used in const expressions
    = help: use `#![feature(generic_const_exprs)]` to allow generic const expressions

src/test/ui/lint/unused/issue-88519-unused-paren.rs

@@ -51,22 +51,13 @@ mod casts {
 
 mod typeascription {
     fn outside() -> u8 {
-        ({ 0 }): u8
+        type_ascribe!(({ 0 }), u8)
-    }
-    fn inside() -> u8 {
-        ({ 0 }: u8)
     }
     fn outside_match() -> u8 {
-        (match 0 { x => x }): u8
+        type_ascribe!((match 0 { x => x }), u8)
-    }
-    fn inside_match() -> u8 {
-        (match 0 { x => x }: u8)
     }
     fn outside_if() -> u8 {
-        (if false { 0 } else { 0 }): u8
+        type_ascribe!((if false { 0 } else { 0 }), u8)
-    }
-    fn inside_if() -> u8 {
-        (if false { 0 } else { 0 }: u8)
     }
 }
 

src/test/ui/mir/mir_ascription_coercion.rs

@@ -6,5 +6,5 @@
 fn main() {
     let x = [1, 2, 3];
     // The RHS should coerce to &[i32]
-    let _y : &[i32] = &x : &[i32; 3];
+    let _y : &[i32] = type_ascribe!(&x, &[i32; 3]);
 }

src/test/ui/nll/user-annotations/issue-57731-ascibed-coupled-types.rs

@@ -8,17 +8,17 @@ type PairCoupledTypes<T> = (T, T);
 type PairCoupledRegions<'a, T> = (&'a T, &'a T);
 
 fn uncoupled_wilds_rhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
-    let ((y, _z),) = ((s, _x),): (PairUncoupled<_>,);
+    let ((y, _z),) = type_ascribe!(((s, _x),), (PairUncoupled<_>,));
     y // OK
 }
 
 fn coupled_wilds_rhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
-    let ((y, _z),) = ((s, _x),): (PairCoupledTypes<_>,);
+    let ((y, _z),) = type_ascribe!(((s, _x),), (PairCoupledTypes<_>,));
     y //~ ERROR lifetime may not live long enough
 }
 
 fn coupled_regions_rhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
-    let ((y, _z),) = ((s, _x),): (PairCoupledRegions<_>,);
+    let ((y, _z),) = type_ascribe!(((s, _x),), (PairCoupledRegions<_>,));
     y //~ ERROR lifetime may not live long enough
 }
 

src/test/ui/nll/user-annotations/issue-57731-ascibed-coupled-types.stderr

@@ -3,7 +3,7 @@ error: lifetime may not live long enough
    |
 LL | fn coupled_wilds_rhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
    |                      -- lifetime `'a` defined here
-LL |     let ((y, _z),) = ((s, _x),): (PairCoupledTypes<_>,);
+LL |     let ((y, _z),) = type_ascribe!(((s, _x),), (PairCoupledTypes<_>,));
 LL |     y
    |     ^ returning this value requires that `'a` must outlive `'static`
 
@@ -12,7 +12,7 @@ error: lifetime may not live long enough
    |
 LL | fn coupled_regions_rhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
    |                        -- lifetime `'a` defined here
-LL |     let ((y, _z),) = ((s, _x),): (PairCoupledRegions<_>,);
+LL |     let ((y, _z),) = type_ascribe!(((s, _x),), (PairCoupledRegions<_>,));
 LL |     y
    |     ^ returning this value requires that `'a` must outlive `'static`
 

src/test/ui/nll/user-annotations/type_ascription_static_lifetime.rs

@@ -3,5 +3,5 @@
 
 fn main() {
     let x = 22_u32;
-    let y: &u32 = &x: &'static u32; //~ ERROR E0597
+    let y: &u32 = type_ascribe!(&x, &'static u32); //~ ERROR E0597
 }

src/test/ui/nll/user-annotations/type_ascription_static_lifetime.stderr

@@ -1,10 +1,10 @@
 error[E0597]: `x` does not live long enough
-  --> $DIR/type_ascription_static_lifetime.rs:6:19
+  --> $DIR/type_ascription_static_lifetime.rs:6:33
    |
-LL |     let y: &u32 = &x: &'static u32;
+LL |     let y: &u32 = type_ascribe!(&x, &'static u32);
-   |                   ^^--------------
+   |                   --------------^^---------------
-   |                   |
+   |                   |             |
-   |                   borrowed value does not live long enough
+   |                   |             borrowed value does not live long enough
    |                   type annotation requires that `x` is borrowed for `'static`
 LL | }
    | - `x` dropped here while still borrowed

src/test/ui/raw-ref-op/raw-ref-temp-deref.rs

@@ -18,7 +18,7 @@ fn main() {
     let index_deref_ref = &raw const SLICE_REF[1];
 
     let x = 0;
-    let ascribe_ref = &raw const (x: i32);
+    let ascribe_ref = &raw const type_ascribe!(x, i32);
-    let ascribe_deref = &raw const (*ARRAY_REF: [i32; 2]);
+    let ascribe_deref = &raw const type_ascribe!(*ARRAY_REF, [i32; 2]);
-    let ascribe_index_deref = &raw const (ARRAY_REF[0]: i32);
+    let ascribe_index_deref = &raw const type_ascribe!(ARRAY_REF[0], i32);
 }

src/test/ui/raw-ref-op/raw-ref-temp.rs

@@ -8,24 +8,24 @@ const PAIR: (i32, i64) = (1, 2);
 const ARRAY: [i32; 2] = [1, 2];
 
 fn main() {
-    let ref_expr = &raw const 2;                        //~ ERROR cannot take address
+    let ref_expr = &raw const 2;                                    //~ ERROR cannot take address
-    let mut_ref_expr = &raw mut 3;                      //~ ERROR cannot take address
+    let mut_ref_expr = &raw mut 3;                                  //~ ERROR cannot take address
-    let ref_const = &raw const FOUR;                    //~ ERROR cannot take address
+    let ref_const = &raw const FOUR;                                //~ ERROR cannot take address
-    let mut_ref_const = &raw mut FOUR;                  //~ ERROR cannot take address
+    let mut_ref_const = &raw mut FOUR;                              //~ ERROR cannot take address
 
-    let field_ref_expr = &raw const (1, 2).0;           //~ ERROR cannot take address
+    let field_ref_expr = &raw const (1, 2).0;                       //~ ERROR cannot take address
-    let mut_field_ref_expr = &raw mut (1, 2).0;         //~ ERROR cannot take address
+    let mut_field_ref_expr = &raw mut (1, 2).0;                     //~ ERROR cannot take address
-    let field_ref = &raw const PAIR.0;                  //~ ERROR cannot take address
+    let field_ref = &raw const PAIR.0;                              //~ ERROR cannot take address
-    let mut_field_ref = &raw mut PAIR.0;                //~ ERROR cannot take address
+    let mut_field_ref = &raw mut PAIR.0;                            //~ ERROR cannot take address
 
-    let index_ref_expr = &raw const [1, 2][0];          //~ ERROR cannot take address
+    let index_ref_expr = &raw const [1, 2][0];                      //~ ERROR cannot take address
-    let mut_index_ref_expr = &raw mut [1, 2][0];        //~ ERROR cannot take address
+    let mut_index_ref_expr = &raw mut [1, 2][0];                    //~ ERROR cannot take address
-    let index_ref = &raw const ARRAY[0];                //~ ERROR cannot take address
+    let index_ref = &raw const ARRAY[0];                            //~ ERROR cannot take address
-    let mut_index_ref = &raw mut ARRAY[1];              //~ ERROR cannot take address
+    let mut_index_ref = &raw mut ARRAY[1];                          //~ ERROR cannot take address
 
-    let ref_ascribe = &raw const (2: i32);              //~ ERROR cannot take address
+    let ref_ascribe = &raw const type_ascribe!(2, i32);             //~ ERROR cannot take address
-    let mut_ref_ascribe = &raw mut (3: i32);            //~ ERROR cannot take address
+    let mut_ref_ascribe = &raw mut type_ascribe!(3, i32);           //~ ERROR cannot take address
 
-    let ascribe_field_ref = &raw const (PAIR.0: i32);   //~ ERROR cannot take address
+    let ascribe_field_ref = &raw const type_ascribe!(PAIR.0, i32);  //~ ERROR cannot take address
-    let ascribe_index_ref = &raw mut (ARRAY[0]: i32);   //~ ERROR cannot take address
+    let ascribe_index_ref = &raw mut type_ascribe!(ARRAY[0], i32);  //~ ERROR cannot take address
 }

src/test/ui/raw-ref-op/raw-ref-temp.stderr

@@ -73,26 +73,26 @@ LL |     let mut_index_ref = &raw mut ARRAY[1];
 error[E0745]: cannot take address of a temporary
   --> $DIR/raw-ref-temp.rs:26:34
    |
-LL |     let ref_ascribe = &raw const (2: i32);
+LL |     let ref_ascribe = &raw const type_ascribe!(2, i32);
-   |                                  ^^^^^^^^ temporary value
+   |                                  ^^^^^^^^^^^^^^^^^^^^^ temporary value
 
 error[E0745]: cannot take address of a temporary
   --> $DIR/raw-ref-temp.rs:27:36
    |
-LL |     let mut_ref_ascribe = &raw mut (3: i32);
+LL |     let mut_ref_ascribe = &raw mut type_ascribe!(3, i32);
-   |                                    ^^^^^^^^ temporary value
+   |                                    ^^^^^^^^^^^^^^^^^^^^^ temporary value
 
 error[E0745]: cannot take address of a temporary
   --> $DIR/raw-ref-temp.rs:29:40
    |
-LL |     let ascribe_field_ref = &raw const (PAIR.0: i32);
+LL |     let ascribe_field_ref = &raw const type_ascribe!(PAIR.0, i32);
-   |                                        ^^^^^^^^^^^^^ temporary value
+   |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^ temporary value
 
 error[E0745]: cannot take address of a temporary
   --> $DIR/raw-ref-temp.rs:30:38
    |
-LL |     let ascribe_index_ref = &raw mut (ARRAY[0]: i32);
+LL |     let ascribe_index_ref = &raw mut type_ascribe!(ARRAY[0], i32);
-   |                                      ^^^^^^^^^^^^^^^ temporary value
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ temporary value
 
 error: aborting due to 16 previous errors
 

src/test/ui/reachable/expr_type.rs

@@ -6,7 +6,7 @@
 
 fn a() {
     // the cast is unreachable:
-    let x = {return}: !; //~ ERROR unreachable
+    let x = type_ascribe!({return}, !); //~ ERROR unreachable
 }
 
 fn main() { }

src/test/ui/reachable/expr_type.stderr

@@ -1,10 +1,10 @@
 error: unreachable expression
   --> $DIR/expr_type.rs:9:13
    |
-LL |     let x = {return}: !;
+LL |     let x = type_ascribe!({return}, !);
-   |             ^------^^^^
+   |             ^^^^^^^^^^^^^^^------^^^^^
-   |             ||
+   |             |              |
-   |             |any code following this expression is unreachable
+   |             |              any code following this expression is unreachable
    |             unreachable expression
    |
 note: the lint level is defined here

src/test/ui/type/type-ascription-soundness.rs

@@ -4,10 +4,10 @@
 
 fn main() {
     let arr = &[1u8, 2, 3];
-    let ref x = arr: &[u8]; //~ ERROR mismatched types
+    let ref x = type_ascribe!(arr, &[u8]);      //~ ERROR mismatched types
-    let ref mut x = arr: &[u8]; //~ ERROR mismatched types
+    let ref mut x = type_ascribe!(arr, &[u8]);  //~ ERROR mismatched types
-    match arr: &[u8] { //~ ERROR mismatched types
+    match type_ascribe!(arr, &[u8]) {           //~ ERROR mismatched types
         ref x => {}
     }
-    let _len = (arr: &[u8]).len(); //~ ERROR mismatched types
+    let _len = type_ascribe!(arr, &[u8]).len();              //~ ERROR mismatched types
 }

src/test/ui/type/type-ascription-soundness.stderr

@@ -1,35 +1,35 @@
 error[E0308]: mismatched types
-  --> $DIR/type-ascription-soundness.rs:7:17
+  --> $DIR/type-ascription-soundness.rs:7:31
    |
-LL |     let ref x = arr: &[u8];
+LL |     let ref x = type_ascribe!(arr, &[u8]);
-   |                 ^^^ expected slice `[u8]`, found array `[u8; 3]`
+   |                               ^^^ expected slice `[u8]`, found array `[u8; 3]`
    |
    = note: expected reference `&[u8]`
               found reference `&[u8; 3]`
 
 error[E0308]: mismatched types
-  --> $DIR/type-ascription-soundness.rs:8:21
+  --> $DIR/type-ascription-soundness.rs:8:35
    |
-LL |     let ref mut x = arr: &[u8];
+LL |     let ref mut x = type_ascribe!(arr, &[u8]);
-   |                     ^^^ expected slice `[u8]`, found array `[u8; 3]`
+   |                                   ^^^ expected slice `[u8]`, found array `[u8; 3]`
    |
    = note: expected reference `&[u8]`
               found reference `&[u8; 3]`
 
 error[E0308]: mismatched types
-  --> $DIR/type-ascription-soundness.rs:9:11
+  --> $DIR/type-ascription-soundness.rs:9:25
    |
-LL |     match arr: &[u8] {
+LL |     match type_ascribe!(arr, &[u8]) {
-   |           ^^^ expected slice `[u8]`, found array `[u8; 3]`
+   |                         ^^^ expected slice `[u8]`, found array `[u8; 3]`
    |
    = note: expected reference `&[u8]`
               found reference `&[u8; 3]`
 
 error[E0308]: mismatched types
-  --> $DIR/type-ascription-soundness.rs:12:17
+  --> $DIR/type-ascription-soundness.rs:12:30
    |
-LL |     let _len = (arr: &[u8]).len();
+LL |     let _len = type_ascribe!(arr, &[u8]).len();
-   |                 ^^^ expected slice `[u8]`, found array `[u8; 3]`
+   |                              ^^^ expected slice `[u8]`, found array `[u8; 3]`
    |
    = note: expected reference `&[u8]`
               found reference `&[u8; 3]`

src/test/ui/type/type-ascription.rs

@@ -8,32 +8,32 @@
 
 use std::mem;
 
-const C1: u8 = 10: u8;
+const C1: u8 = type_ascribe!(10, u8);
-const C2: [u8; 1: usize] = [1];
+const C2: [u8; type_ascribe!(1, usize)] = [1];
 
 struct S {
     a: u8
 }
 
 fn main() {
-    assert_eq!(C1.into(): i32, 10);
+    assert_eq!(type_ascribe!(C1.into(), i32), 10);
     assert_eq!(C2[0], 1);
 
-    let s = S { a: 10: u8 };
+    let s = S { a: type_ascribe!(10, u8) };
     let arr = &[1u8, 2, 3];
 
-    let mut v = arr.iter().cloned().collect(): Vec<_>;
+    let mut v = type_ascribe!(arr.iter().cloned().collect(), Vec<_>);
     v.push(4);
     assert_eq!(v, [1, 2, 3, 4]);
 
-    let a = 1: u8;
+    let a = type_ascribe!(1, u8);
-    let b = a.into(): u16;
+    let b = type_ascribe!(a.into(), u16);
-    assert_eq!(v[a.into(): usize], 2);
+    assert_eq!(v[type_ascribe!(a.into(), usize)], 2);
     assert_eq!(mem::size_of_val(&a), 1);
     assert_eq!(mem::size_of_val(&b), 2);
-    assert_eq!(b, 1: u16);
+    assert_eq!(b, type_ascribe!(1, u16));
 
     let mut v = Vec::new();
-    v: Vec<u8> = vec![1, 2, 3]; // Place expression type ascription
+    type_ascribe!(v, Vec<u8>) = vec![1, 2, 3]; // Place expression type ascription
     assert_eq!(v, [1u8, 2, 3]);
 }

src/test/ui/typeck/issue-91267.rs

@@ -1,5 +1,7 @@
+#![feature(type_ascription)]
+
 fn main() {
-    0: u8<e<5>=e>
+    type_ascribe!(0, u8<e<5>=e>)
     //~^ ERROR: cannot find type `e` in this scope [E0412]
     //~| ERROR: associated type bindings are not allowed here [E0229]
     //~| ERROR: mismatched types [E0308]

src/test/ui/typeck/issue-91267.stderr

@@ -1,25 +1,22 @@
 error[E0412]: cannot find type `e` in this scope
-  --> $DIR/issue-91267.rs:2:16
+  --> $DIR/issue-91267.rs:4:30
    |
-LL |     0: u8<e<5>=e>
+LL |     type_ascribe!(0, u8<e<5>=e>)
-   |                ^
+   |                              ^ not found in this scope
-   |                |
-   |                not found in this scope
-   |                help: maybe you meant to write an assignment here: `let e`
 
 error[E0229]: associated type bindings are not allowed here
-  --> $DIR/issue-91267.rs:2:11
+  --> $DIR/issue-91267.rs:4:25
    |
-LL |     0: u8<e<5>=e>
+LL |     type_ascribe!(0, u8<e<5>=e>)
-   |           ^^^^^^ associated type not allowed here
+   |                         ^^^^^^ associated type not allowed here
 
 error[E0308]: mismatched types
-  --> $DIR/issue-91267.rs:2:5
+  --> $DIR/issue-91267.rs:4:5
    |
 LL | fn main() {
    |           - expected `()` because of default return type
-LL |     0: u8<e<5>=e>
+LL |     type_ascribe!(0, u8<e<5>=e>)
-   |     ^^^^^^^^^^^^^ expected `()`, found `u8`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found `u8`
 
 error: aborting due to 3 previous errors