Rollup merge of rust-lang#153075 - reddevilmidzy:mgca-neg, r=BoxyUwU

JonathanBrouwer · web-flow · commit 63fd1cd1e8ae · 2026-02-25T13:53:27.000+01:00
mGCA: Lower negated literals directly and reject non-integer negations follow up rust-lang#152001 resolve: rust-lang#152246 r? BoxyUwU
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
@@ -2521,16 +2521,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             ExprKind::Block(block, _) => {
                 if let [stmt] = block.stmts.as_slice()
                     && let StmtKind::Expr(expr) = &stmt.kind
-                    && matches!(
-                        expr.kind,
-                        ExprKind::Block(..)
-                            | ExprKind::Path(..)
-                            | ExprKind::Struct(..)
-                            | ExprKind::Call(..)
-                            | ExprKind::Tup(..)
-                            | ExprKind::Array(..)
-                            | ExprKind::ConstBlock(..)
-                    )
                 {
                     return self.lower_expr_to_const_arg_direct(expr);
                 }
@@ -2553,6 +2543,17 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 let span = expr.span;
                 let literal = self.lower_lit(literal, span);
 
+                if !matches!(literal.node, LitKind::Int(..)) {
+                    let err =
+                        self.dcx().struct_span_err(expr.span, "negated literal must be an integer");
+
+                    return ConstArg {
+                        hir_id: self.next_id(),
+                        kind: hir::ConstArgKind::Error(err.emit()),
+                        span,
+                    };
+                }
+
                 ConstArg {
                     hir_id: self.lower_node_id(expr.id),
                     kind: hir::ConstArgKind::Literal { lit: literal.node, negated: true },
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
@@ -1628,8 +1628,7 @@ impl<'a> Parser<'a> {
             let first_expr = self.parse_expr()?;
             if self.eat(exp!(Semi)) {
                 // Repeating array syntax: `[ 0; 512 ]`
-                let count =
-                    self.parse_expr_anon_const(|this, expr| this.mgca_direct_lit_hack(expr))?;
+                let count = self.parse_expr_anon_const(|_, _| MgcaDisambiguation::Direct)?;
                 self.expect(close)?;
                 ExprKind::Repeat(first_expr, count)
             } else if self.eat(exp!(Comma)) {
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
@@ -1587,9 +1587,7 @@ impl<'a> Parser<'a> {
 
         let rhs = match (self.eat(exp!(Eq)), const_arg) {
             (true, true) => ConstItemRhsKind::TypeConst {
-                rhs: Some(
-                    self.parse_expr_anon_const(|this, expr| this.mgca_direct_lit_hack(expr))?,
-                ),
+                rhs: Some(self.parse_expr_anon_const(|_, _| MgcaDisambiguation::Direct)?),
             },
             (true, false) => ConstItemRhsKind::Body { rhs: Some(self.parse_expr()?) },
             (false, true) => ConstItemRhsKind::TypeConst { rhs: None },
diff --git a/compiler/rustc_parse/src/parser/path.rs b/compiler/rustc_parse/src/parser/path.rs
@@ -915,28 +915,7 @@ impl<'a> Parser<'a> {
             });
         }
 
-        let mgca_disambiguation = self.mgca_direct_lit_hack(&expr);
-        Ok((expr, mgca_disambiguation))
-    }
-
-    /// Under `min_generic_const_args` we still allow *some* anon consts to be written without
-    /// a `const` block as it makes things quite a lot nicer. This function is useful for contexts
-    /// where we would like to use `MgcaDisambiguation::Direct` but need to fudge it to be `AnonConst`
-    /// in the presence of literals.
-    //
-    /// FIXME(min_generic_const_args): In the long term it would be nice to have a way to directly
-    /// represent literals in `hir::ConstArgKind` so that we can remove this special case by not
-    /// needing an anon const.
-    pub fn mgca_direct_lit_hack(&self, expr: &Expr) -> MgcaDisambiguation {
-        match &expr.kind {
-            ast::ExprKind::Lit(_) => MgcaDisambiguation::AnonConst,
-            ast::ExprKind::Unary(ast::UnOp::Neg, expr)
-                if matches!(expr.kind, ast::ExprKind::Lit(_)) =>
-            {
-                MgcaDisambiguation::AnonConst
-            }
-            _ => MgcaDisambiguation::Direct,
-        }
+        Ok((expr, MgcaDisambiguation::Direct))
     }
 
     /// Parse a generic argument in a path segment.
diff --git a/compiler/rustc_parse/src/parser/ty.rs b/compiler/rustc_parse/src/parser/ty.rs
@@ -658,8 +658,7 @@ impl<'a> Parser<'a> {
         };
 
         let ty = if self.eat(exp!(Semi)) {
-            let mut length =
-                self.parse_expr_anon_const(|this, expr| this.mgca_direct_lit_hack(expr))?;
+            let mut length = self.parse_expr_anon_const(|_, _| MgcaDisambiguation::Direct)?;
 
             if let Err(e) = self.expect(exp!(CloseBracket)) {
                 // Try to recover from `X<Y, ...>` when `X::<Y, ...>` works
diff --git a/tests/ui/const-generics/associated-const-bindings/dyn-compat-self-const-projections-in-assoc-const-ty.stderr b/tests/ui/const-generics/associated-const-bindings/dyn-compat-self-const-projections-in-assoc-const-ty.stderr
@@ -1,27 +1,14 @@
-error[E0277]: the trait bound `FreshTy(0): A` is not satisfied
+error: type annotations needed for the literal
   --> $DIR/dyn-compat-self-const-projections-in-assoc-const-ty.rs:32:33
    |
 LL |     let _: dyn A<Ty = i32, CT = 0>;
-   |                                 ^ the trait `A` is not implemented for `FreshTy(0)`
-   |
-help: the trait `A` is implemented for `()`
-  --> $DIR/dyn-compat-self-const-projections-in-assoc-const-ty.rs:20:1
-   |
-LL | impl A for () {
-   | ^^^^^^^^^^^^^
+   |                                 ^
 
-error[E0277]: the trait bound `FreshTy(0): A` is not satisfied
+error: type annotations needed for the literal
   --> $DIR/dyn-compat-self-const-projections-in-assoc-const-ty.rs:34:34
    |
 LL |     let _: &dyn A<Ty = i32, CT = 0> = &();
-   |                                  ^ the trait `A` is not implemented for `FreshTy(0)`
-   |
-help: the trait `A` is implemented for `()`
-  --> $DIR/dyn-compat-self-const-projections-in-assoc-const-ty.rs:20:1
-   |
-LL | impl A for () {
-   | ^^^^^^^^^^^^^
+   |                                  ^
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/const-generics/mgca/array-expr-complex.stderr b/tests/ui/const-generics/mgca/array-expr-complex.stderr
@@ -5,16 +5,16 @@ LL |     takes_array::<{ [1, 2, 1 + 2] }>();
    |                            ^^^^^
 
 error: complex const arguments must be placed inside of a `const` block
-  --> $DIR/array-expr-complex.rs:10:19
+  --> $DIR/array-expr-complex.rs:10:21
    |
 LL |     takes_array::<{ [X; 3] }>();
-   |                   ^^^^^^^^^^
+   |                     ^^^^^^
 
 error: complex const arguments must be placed inside of a `const` block
-  --> $DIR/array-expr-complex.rs:12:19
+  --> $DIR/array-expr-complex.rs:12:21
    |
 LL |     takes_array::<{ [0; Y] }>();
-   |                   ^^^^^^^^^^
+   |                     ^^^^^^
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/const-generics/mgca/array-expr-type-mismatch-in-where-bound.rs b/tests/ui/const-generics/mgca/array-expr-type-mismatch-in-where-bound.rs
@@ -14,7 +14,7 @@ where
 
 fn bar<T>()
 where
-    T: Trait2<3>, //~ ERROR: mismatched types
+    T: Trait2<3>, //~ ERROR: type annotations needed for the literal
 {
 }
 
diff --git a/tests/ui/const-generics/mgca/array-expr-type-mismatch-in-where-bound.stderr b/tests/ui/const-generics/mgca/array-expr-type-mismatch-in-where-bound.stderr
@@ -4,12 +4,11 @@ error: expected `usize`, found const array
 LL |     T: Trait1<{ [] }>,
    |                 ^^
 
-error[E0308]: mismatched types
+error: type annotations needed for the literal
   --> $DIR/array-expr-type-mismatch-in-where-bound.rs:17:15
    |
 LL |     T: Trait2<3>,
-   |               ^ expected `[u8; 3]`, found integer
+   |               ^
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0308`.
diff --git a/tests/ui/const-generics/mgca/explicit_anon_consts.stderr b/tests/ui/const-generics/mgca/explicit_anon_consts.stderr
@@ -1,8 +1,8 @@
 error: complex const arguments must be placed inside of a `const` block
-  --> $DIR/explicit_anon_consts.rs:13:33
+  --> $DIR/explicit_anon_consts.rs:13:35
    |
 LL | type Adt4<const N: usize> = Foo<{ 1 + 1 }>;
-   |                                 ^^^^^^^^^
+   |                                   ^^^^^
 
 error: complex const arguments must be placed inside of a `const` block
   --> $DIR/explicit_anon_consts.rs:21:34
@@ -17,22 +17,22 @@ LL |     let _4 = [(); 1 + 1];
    |                   ^^^^^
 
 error: complex const arguments must be placed inside of a `const` block
-  --> $DIR/explicit_anon_consts.rs:45:43
+  --> $DIR/explicit_anon_consts.rs:45:45
    |
 LL | type const ITEM4<const N: usize>: usize = { 1 + 1 };
-   |                                           ^^^^^^^^^
+   |                                             ^^^^^
 
 error: complex const arguments must be placed inside of a `const` block
-  --> $DIR/explicit_anon_consts.rs:62:23
+  --> $DIR/explicit_anon_consts.rs:62:25
    |
 LL |     T4: Trait<ASSOC = { 1 + 1 }>,
-   |                       ^^^^^^^^^
+   |                         ^^^^^
 
 error: complex const arguments must be placed inside of a `const` block
-  --> $DIR/explicit_anon_consts.rs:71:50
+  --> $DIR/explicit_anon_consts.rs:71:52
    |
 LL | struct Default4<const N: usize, const M: usize = { 1 + 1 }>;
-   |                                                  ^^^^^^^^^
+   |                                                    ^^^^^
 
 error: generic parameters may not be used in const operations
   --> $DIR/explicit_anon_consts.rs:42:51
diff --git a/tests/ui/const-generics/mgca/nonsensical-negated-literal.rs b/tests/ui/const-generics/mgca/nonsensical-negated-literal.rs
@@ -1,4 +1,4 @@
-#![feature(adt_const_params, min_generic_const_args)]
+#![feature(adt_const_params, min_generic_const_args, unsized_const_params)]
 #![expect(incomplete_features)]
 
 use std::marker::ConstParamTy;
@@ -10,17 +10,22 @@ struct Foo {
 
 fn foo<const F: Foo>() {}
 
+fn bar<const B: &'static str>() {}
+
 fn main() {
     foo::<{ Foo { field: -1_usize } }>();
     //~^ ERROR: type annotations needed for the literal
     foo::<{ Foo { field: { -1_usize } } }>();
-    //~^ ERROR: complex const arguments must be placed inside of a `const` block
+    //~^ ERROR: type annotations needed for the literal
     foo::<{ Foo { field: -true } }>();
-    //~^ ERROR: the constant `true` is not of type `isize`
+    //~^ ERROR negated literal must be an integer
     foo::<{ Foo { field: { -true } } }>();
-    //~^ ERROR: complex const arguments must be placed inside of a `const` block
+    //~^ ERROR negated literal must be an integer
     foo::<{ Foo { field: -"<3" } }>();
-    //~^ ERROR: the constant `"<3"` is not of type `isize`
+    //~^ ERROR negated literal must be an integer
     foo::<{ Foo { field: { -"<3" } } }>();
-    //~^ ERROR: complex const arguments must be placed inside of a `const` block
+    //~^ ERROR negated literal must be an integer
+
+    bar::<{ -"hi" }>();
+    //~^ ERROR: negated literal must be an integer
 }
diff --git a/tests/ui/const-generics/mgca/nonsensical-negated-literal.stderr b/tests/ui/const-generics/mgca/nonsensical-negated-literal.stderr
@@ -1,38 +1,44 @@
-error: complex const arguments must be placed inside of a `const` block
-  --> $DIR/nonsensical-negated-literal.rs:16:26
+error: negated literal must be an integer
+  --> $DIR/nonsensical-negated-literal.rs:20:26
    |
-LL |     foo::<{ Foo { field: { -1_usize } } }>();
-   |                          ^^^^^^^^^^^^
+LL |     foo::<{ Foo { field: -true } }>();
+   |                          ^^^^^
 
-error: complex const arguments must be placed inside of a `const` block
-  --> $DIR/nonsensical-negated-literal.rs:20:26
+error: negated literal must be an integer
+  --> $DIR/nonsensical-negated-literal.rs:22:28
    |
 LL |     foo::<{ Foo { field: { -true } } }>();
-   |                          ^^^^^^^^^
+   |                            ^^^^^
 
-error: complex const arguments must be placed inside of a `const` block
+error: negated literal must be an integer
   --> $DIR/nonsensical-negated-literal.rs:24:26
    |
+LL |     foo::<{ Foo { field: -"<3" } }>();
+   |                          ^^^^^
+
+error: negated literal must be an integer
+  --> $DIR/nonsensical-negated-literal.rs:26:28
+   |
 LL |     foo::<{ Foo { field: { -"<3" } } }>();
-   |                          ^^^^^^^^^
+   |                            ^^^^^
+
+error: negated literal must be an integer
+  --> $DIR/nonsensical-negated-literal.rs:29:13
+   |
+LL |     bar::<{ -"hi" }>();
+   |             ^^^^^
 
 error: type annotations needed for the literal
-  --> $DIR/nonsensical-negated-literal.rs:14:26
+  --> $DIR/nonsensical-negated-literal.rs:16:26
    |
 LL |     foo::<{ Foo { field: -1_usize } }>();
    |                          ^^^^^^^^
 
-error: the constant `true` is not of type `isize`
-  --> $DIR/nonsensical-negated-literal.rs:18:13
-   |
-LL |     foo::<{ Foo { field: -true } }>();
-   |             ^^^^^^^^^^^^^^^^^^^^ expected `isize`, found `bool`
-
-error: the constant `"<3"` is not of type `isize`
-  --> $DIR/nonsensical-negated-literal.rs:22:13
+error: type annotations needed for the literal
+  --> $DIR/nonsensical-negated-literal.rs:18:28
    |
-LL |     foo::<{ Foo { field: -"<3" } }>();
-   |             ^^^^^^^^^^^^^^^^^^^^ expected `isize`, found `&'static str`
+LL |     foo::<{ Foo { field: { -1_usize } } }>();
+   |                            ^^^^^^^^
 
-error: aborting due to 6 previous errors
+error: aborting due to 7 previous errors
 
diff --git a/tests/ui/const-generics/mgca/type_const-inherent-const-omitted-type.rs b/tests/ui/const-generics/mgca/type_const-inherent-const-omitted-type.rs
@@ -6,6 +6,7 @@ struct A;
 impl A {
     type const B = 4;
     //~^ ERROR: missing type for `const` item
+    //~| ERROR: type annotations needed for the literal
 }
 
 fn main() {}
diff --git a/tests/ui/const-generics/mgca/type_const-inherent-const-omitted-type.stderr b/tests/ui/const-generics/mgca/type_const-inherent-const-omitted-type.stderr
@@ -9,5 +9,11 @@ help: provide a type for the item
 LL |     type const B: <type> = 4;
    |                 ++++++++
 
-error: aborting due to 1 previous error
+error: type annotations needed for the literal
+  --> $DIR/type_const-inherent-const-omitted-type.rs:7:20
+   |
+LL |     type const B = 4;
+   |                    ^
+
+error: aborting due to 2 previous errors
 
diff --git a/tests/ui/const-generics/mgca/type_const-mismatched-types.rs b/tests/ui/const-generics/mgca/type_const-mismatched-types.rs
@@ -3,7 +3,6 @@
 
 type const FREE: u32 = 5_usize;
 //~^ ERROR the constant `5` is not of type `u32`
-//~| ERROR mismatched types
 
 type const FREE2: isize = FREE;
 //~^ ERROR the constant `5` is not of type `isize`
@@ -14,7 +13,7 @@ trait Tr {
 
 impl Tr for () {
     type const N: usize = false;
-    //~^ ERROR mismatched types
+    //~^ ERROR the constant `false` is not of type `usize`
 }
 
 fn main() {}
diff --git a/tests/ui/const-generics/mgca/type_const-mismatched-types.stderr b/tests/ui/const-generics/mgca/type_const-mismatched-types.stderr
@@ -5,29 +5,16 @@ LL | type const FREE: u32 = 5_usize;
    | ^^^^^^^^^^^^^^^^^^^^ expected `u32`, found `usize`
 
 error: the constant `5` is not of type `isize`
-  --> $DIR/type_const-mismatched-types.rs:8:1
+  --> $DIR/type_const-mismatched-types.rs:7:1
    |
 LL | type const FREE2: isize = FREE;
    | ^^^^^^^^^^^^^^^^^^^^^^^ expected `isize`, found `usize`
 
-error[E0308]: mismatched types
-  --> $DIR/type_const-mismatched-types.rs:16:27
+error: the constant `false` is not of type `usize`
+  --> $DIR/type_const-mismatched-types.rs:15:5
    |
 LL |     type const N: usize = false;
-   |                           ^^^^^ expected `usize`, found `bool`
+   |     ^^^^^^^^^^^^^^^^^^^ expected `usize`, found `bool`
 
-error[E0308]: mismatched types
-  --> $DIR/type_const-mismatched-types.rs:4:24
-   |
-LL | type const FREE: u32 = 5_usize;
-   |                        ^^^^^^^ expected `u32`, found `usize`
-   |
-help: change the type of the numeric literal from `usize` to `u32`
-   |
-LL - type const FREE: u32 = 5_usize;
-LL + type const FREE: u32 = 5_u32;
-   |
-
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
-For more information about this error, try `rustc --explain E0308`.
diff --git a/tests/ui/const-generics/mgca/type_const-only-in-impl-omitted-type.rs b/tests/ui/const-generics/mgca/type_const-only-in-impl-omitted-type.rs
@@ -10,6 +10,7 @@ struct GoodS;
 impl BadTr for GoodS {
     type const NUM: = 84;
     //~^ ERROR: missing type for `const` item
+    //~| ERROR: type annotations needed for the literal
 
 }
 
diff --git a/tests/ui/const-generics/mgca/type_const-only-in-impl-omitted-type.stderr b/tests/ui/const-generics/mgca/type_const-only-in-impl-omitted-type.stderr

Original file line number	Diff line number	Diff line change
`@@ -14,7 +14,7 @@ where`
`14`	`14`
`15`	`15`	`fn bar<T>()`
`16`	`16`	`where`
`17`		`- T: Trait2<3>, //~ ERROR: mismatched types`
	`17`	`+ T: Trait2<3>, //~ ERROR: type annotations needed for the literal`
`18`	`18`	`{`
`19`	`19`	`}`
`20`	`20`