Auto merge of #150786 - reddevilmidzy:mgca-array, r=BoxyUwU

mGCA: Support array expression as direct const arguments

tracking issue: rust-lang/rust#132980
resolve: rust-lang/rust#150612

Support array expression as direct const arguments (e. g. [1, 2, N]) in min_generic_const_args.

todo:
* [x] Rebase another mGCA PR
* [x] Add more test case
* [x] Modify clippy code

compiler/rustc_ast_lowering/src/lib.rs

@@ -2517,6 +2517,28 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     span,
                 }
             }
+            ExprKind::Array(elements) => {
+                let lowered_elems = self.arena.alloc_from_iter(elements.iter().map(|element| {
+                    let const_arg = if let ExprKind::ConstBlock(anon_const) = &element.kind {
+                        let def_id = self.local_def_id(anon_const.id);
+                        assert_eq!(DefKind::AnonConst, self.tcx.def_kind(def_id));
+                        self.lower_anon_const_to_const_arg(anon_const)
+                    } else {
+                        self.lower_expr_to_const_arg_direct(element)
+                    };
+                    &*self.arena.alloc(const_arg)
+                }));
+                let array_expr = self.arena.alloc(hir::ConstArgArrayExpr {
+                    span: self.lower_span(expr.span),
+                    elems: lowered_elems,
+                });
+
+                ConstArg {
+                    hir_id: self.next_id(),
+                    kind: hir::ConstArgKind::Array(array_expr),
+                    span,
+                }
+            }
             ExprKind::Underscore => ConstArg {
                 hir_id: self.lower_node_id(expr.id),
                 kind: hir::ConstArgKind::Infer(()),
@@ -2532,6 +2554,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             | ExprKind::Struct(..)
                             | ExprKind::Call(..)
                             | ExprKind::Tup(..)
+                            | ExprKind::Array(..)
                     )
                 {
                     return self.lower_expr_to_const_arg_direct(expr);

compiler/rustc_hir/src/hir.rs

@@ -513,6 +513,8 @@ pub enum ConstArgKind<'hir, Unambig = ()> {
     Struct(QPath<'hir>, &'hir [&'hir ConstArgExprField<'hir>]),
     /// Tuple constructor variant
     TupleCall(QPath<'hir>, &'hir [&'hir ConstArg<'hir>]),
+    /// Array literal argument
+    Array(&'hir ConstArgArrayExpr<'hir>),
     /// Error const
     Error(ErrorGuaranteed),
     /// This variant is not always used to represent inference consts, sometimes
@@ -529,6 +531,12 @@ pub struct ConstArgExprField<'hir> {
     pub expr: &'hir ConstArg<'hir>,
 }
 
+#[derive(Clone, Copy, Debug, HashStable_Generic)]
+pub struct ConstArgArrayExpr<'hir> {
+    pub span: Span,
+    pub elems: &'hir [&'hir ConstArg<'hir>],
+}
+
 #[derive(Clone, Copy, Debug, HashStable_Generic)]
 pub struct InferArg {
     #[stable_hasher(ignore)]

compiler/rustc_hir/src/intravisit.rs

@@ -1101,6 +1101,12 @@ pub fn walk_const_arg<'v, V: Visitor<'v>>(
             }
             V::Result::output()
         }
+        ConstArgKind::Array(array_expr) => {
+            for arg in array_expr.elems {
+                try_visit!(visitor.visit_const_arg_unambig(*arg));
+            }
+            V::Result::output()
+        }
         ConstArgKind::Path(qpath) => visitor.visit_qpath(qpath, *hir_id, qpath.span()),
         ConstArgKind::Anon(anon) => visitor.visit_anon_const(*anon),
         ConstArgKind::Error(_) => V::Result::output(), // errors and spans are not important

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -2389,6 +2389,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             hir::ConstArgKind::TupleCall(qpath, args) => {
                 self.lower_const_arg_tuple_call(hir_id, qpath, args, const_arg.span)
             }
+            hir::ConstArgKind::Array(array_expr) => self.lower_const_arg_array(array_expr, feed),
             hir::ConstArgKind::Anon(anon) => self.lower_const_arg_anon(anon),
             hir::ConstArgKind::Infer(()) => self.ct_infer(None, const_arg.span),
             hir::ConstArgKind::Error(e) => ty::Const::new_error(tcx, e),
@@ -2402,6 +2403,36 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         }
     }
 
+    fn lower_const_arg_array(
+        &self,
+        array_expr: &'tcx hir::ConstArgArrayExpr<'tcx>,
+        feed: FeedConstTy<'tcx>,
+    ) -> Const<'tcx> {
+        let tcx = self.tcx();
+
+        let FeedConstTy::WithTy(ty) = feed else {
+            return Const::new_error_with_message(tcx, array_expr.span, "unsupported const array");
+        };
+
+        let ty::Array(elem_ty, _) = ty.kind() else {
+            return Const::new_error_with_message(
+                tcx,
+                array_expr.span,
+                "const array must have an array type",
+            );
+        };
+
+        let elems = array_expr
+            .elems
+            .iter()
+            .map(|elem| self.lower_const_arg(elem, FeedConstTy::WithTy(*elem_ty)))
+            .collect::<Vec<_>>();
+
+        let valtree = ty::ValTree::from_branches(tcx, elems);
+
+        ty::Const::new_value(tcx, valtree, ty)
+    }
+
     fn lower_const_arg_tuple_call(
         &self,
         hir_id: HirId,

compiler/rustc_hir_pretty/src/lib.rs

@@ -1153,6 +1153,7 @@ impl<'a> State<'a> {
             }
             ConstArgKind::Struct(qpath, fields) => self.print_const_struct(qpath, fields),
             ConstArgKind::TupleCall(qpath, args) => self.print_const_ctor(qpath, args),
+            ConstArgKind::Array(..) => self.word("/* ARRAY EXPR */"),
             ConstArgKind::Path(qpath) => self.print_qpath(qpath, true),
             ConstArgKind::Anon(anon) => self.print_anon_const(anon),
             ConstArgKind::Error(_) => self.word("/*ERROR*/"),

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1441,6 +1441,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                         // Skip encoding defs for these as they should not have had a `DefId` created
                         hir::ConstArgKind::Error(..)
                         | hir::ConstArgKind::Struct(..)
+                        | hir::ConstArgKind::Array(..)
                         | hir::ConstArgKind::TupleCall(..)
                         | hir::ConstArgKind::Tup(..)
                         | hir::ConstArgKind::Path(..)

compiler/rustc_resolve/src/def_collector.rs

@@ -419,7 +419,7 @@ impl<'a, 'ra, 'tcx> visit::Visitor<'a> for DefCollector<'a, 'ra, 'tcx> {
 
             // Avoid overwriting `const_arg_context` as we may want to treat const blocks
             // as being anon consts if we are inside a const argument.
-            ExprKind::Struct(_) | ExprKind::Call(..) | ExprKind::Tup(..) => {
+            ExprKind::Struct(_) | ExprKind::Call(..) | ExprKind::Tup(..) | ExprKind::Array(..) => {
                 return visit::walk_expr(self, expr);
             }
             // FIXME(mgca): we may want to handle block labels in some manner

src/librustdoc/clean/mod.rs

@@ -330,6 +330,9 @@ pub(crate) fn clean_const<'tcx>(constant: &hir::ConstArg<'tcx>) -> ConstantKind
             // FIXME(mgca): proper printing :3
             ConstantKind::Path { path: "/* TUPLE EXPR */".to_string().into() }
         }
+        hir::ConstArgKind::Array(..) => {
+            ConstantKind::Path { path: "/* ARRAY EXPR */".to_string().into() }
+        }
         hir::ConstArgKind::Anon(anon) => ConstantKind::Anonymous { body: anon.body },
         hir::ConstArgKind::Infer(..) | hir::ConstArgKind::Error(..) => ConstantKind::Infer,
         hir::ConstArgKind::Literal(..) => {
@@ -1818,6 +1821,7 @@ pub(crate) fn clean_ty<'tcx>(ty: &hir::Ty<'tcx>, cx: &mut DocContext<'tcx>) -> T
                 | hir::ConstArgKind::Path(..)
                 | hir::ConstArgKind::TupleCall(..)
                 | hir::ConstArgKind::Tup(..)
+                | hir::ConstArgKind::Array(..)
                 | hir::ConstArgKind::Literal(..) => {
                     let ct = lower_const_arg_for_rustdoc(cx.tcx, const_arg, FeedConstTy::No);
                     print_const(cx, ct)

src/tools/clippy/clippy_lints/src/utils/author.rs

@@ -321,6 +321,7 @@ impl<'a, 'tcx> PrintVisitor<'a, 'tcx> {
             },
             ConstArgKind::Struct(..) => chain!(self, "let ConstArgKind::Struct(..) = {const_arg}.kind"),
             ConstArgKind::TupleCall(..) => chain!(self, "let ConstArgKind::TupleCall(..) = {const_arg}.kind"),
+            ConstArgKind::Array(..) => chain!(self, "let ConstArgKind::Array(..) = {const_arg}.kind"),
             ConstArgKind::Infer(..) => chain!(self, "let ConstArgKind::Infer(..) = {const_arg}.kind"),
             ConstArgKind::Error(..) => chain!(self, "let ConstArgKind::Error(..) = {const_arg}.kind"),
             ConstArgKind::Tup(..) => chain!(self, "let ConstArgKind::Tup(..) = {const_arg}.kind"),

src/tools/clippy/clippy_utils/src/consts.rs

@@ -1144,6 +1144,7 @@ pub fn const_item_rhs_to_expr<'tcx>(tcx: TyCtxt<'tcx>, ct_rhs: ConstItemRhs<'tcx
             | ConstArgKind::Tup(..)
             | ConstArgKind::Literal(..)
             | ConstArgKind::TupleCall(..)
+            | ConstArgKind::Array(..)
             | ConstArgKind::Path(_)
             | ConstArgKind::Error(..)
             | ConstArgKind::Infer(..) => None,

src/tools/clippy/clippy_utils/src/hir_utils.rs

@@ -687,6 +687,11 @@ impl HirEqInterExpr<'_, '_, '_> {
                         .all(|(arg_a, arg_b)| self.eq_const_arg(arg_a, arg_b))
             },
             (ConstArgKind::Literal(kind_l), ConstArgKind::Literal(kind_r)) => kind_l == kind_r,
+            (ConstArgKind::Array(l_arr), ConstArgKind::Array(r_arr)) => {
+                l_arr.elems.len() == r_arr.elems.len()
+                && l_arr.elems.iter().zip(r_arr.elems.iter())
+                    .all(|(l_elem, r_elem)| self.eq_const_arg(l_elem, r_elem))
+            }
             // Use explicit match for now since ConstArg is undergoing flux.
             (
                 ConstArgKind::Path(..)
@@ -696,6 +701,7 @@ impl HirEqInterExpr<'_, '_, '_> {
                 | ConstArgKind::Infer(..)
                 | ConstArgKind::Struct(..)
                 | ConstArgKind::Literal(..)
+                | ConstArgKind::Array(..)
                 | ConstArgKind::Error(..),
                 _,
             ) => false,
@@ -1575,6 +1581,11 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
                     self.hash_const_arg(arg);
                 }
             },
+            ConstArgKind::Array(array_expr) => {
+                for elem in array_expr.elems {
+                    self.hash_const_arg(elem);
+                }
+            },
             ConstArgKind::Infer(..) | ConstArgKind::Error(..) => {},
             ConstArgKind::Literal(lit) => lit.hash(&mut self.s),
         }

tests/ui/const-generics/mgca/array-expr-complex.rs

@@ -0,0 +1,16 @@
+#![expect(incomplete_features)]
+#![feature(min_generic_const_args, adt_const_params)]
+
+fn takes_array<const A: [u32; 3]>() {}
+
+fn generic_caller<const X: u32, const Y: usize>() {
+    // not supported yet
+    takes_array::<{ [1, 2, 1 + 2] }>();
+    //~^ ERROR: complex const arguments must be placed inside of a `const` block
+    takes_array::<{ [X; 3] }>();
+    //~^ ERROR: complex const arguments must be placed inside of a `const` block
+    takes_array::<{ [0; Y] }>();
+    //~^ ERROR: complex const arguments must be placed inside of a `const` block
+}
+
+fn main() {}

tests/ui/const-generics/mgca/array-expr-complex.stderr

@@ -0,0 +1,20 @@
+error: complex const arguments must be placed inside of a `const` block
+  --> $DIR/array-expr-complex.rs:8:28
+   |
+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
+   |
+LL |     takes_array::<{ [X; 3] }>();
+   |                   ^^^^^^^^^^
+
+error: complex const arguments must be placed inside of a `const` block
+  --> $DIR/array-expr-complex.rs:12:19
+   |
+LL |     takes_array::<{ [0; Y] }>();
+   |                   ^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+

tests/ui/const-generics/mgca/array-expr-empty.rs

@@ -0,0 +1,9 @@
+#![expect(incomplete_features)]
+#![feature(min_generic_const_args)]
+
+fn takes_empty_array<const A: []>() {}
+//~^ ERROR: expected type, found `]`
+
+fn main() {
+    takes_empty_array::<{ [] }>();
+}

tests/ui/const-generics/mgca/array-expr-empty.stderr

@@ -0,0 +1,8 @@
+error: expected type, found `]`
+  --> $DIR/array-expr-empty.rs:4:32
+   |
+LL | fn takes_empty_array<const A: []>() {}
+   |                                ^ expected type
+
+error: aborting due to 1 previous error
+

tests/ui/const-generics/mgca/array-expr-simple.rs

@@ -0,0 +1,25 @@
+//@ run-pass
+#![expect(incomplete_features)]
+#![feature(min_generic_const_args, adt_const_params)]
+#![allow(dead_code)]
+
+fn takes_array_u32<const A: [u32; 3]>() {}
+fn takes_array_bool<const A: [bool; 2]>() {}
+fn takes_nested_array<const A: [[u32; 2]; 2]>() {}
+fn takes_empty_array<const A: [u32; 0]>() {}
+
+fn generic_caller<const X: u32, const Y: u32>() {
+    takes_array_u32::<{ [X, Y, X] }>();
+    takes_array_u32::<{ [X, Y, const { 1 }] }>();
+    takes_array_u32::<{ [X, Y, const { 1 + 1 }] }>();
+    takes_array_u32::<{ [2_002, 2u32, 1_u32] }>();
+
+    takes_array_bool::<{ [true, false] }>();
+
+    takes_nested_array::<{ [[X, Y], [3, 4]] }>();
+    takes_nested_array::<{ [[1u32, 2_u32], [const { 3 }, 4]] }>();
+
+    takes_empty_array::<{ [] }>();
+}
+
+fn main() {}

tests/ui/const-generics/mgca/array-expr-with-assoc-const.rs

@@ -0,0 +1,18 @@
+//@ run-pass
+#![expect(incomplete_features)]
+#![feature(min_generic_const_args, adt_const_params)]
+#![allow(dead_code)]
+
+fn takes_array<const A: [u32; 3]>() {}
+
+trait Trait {
+    #[type_const]
+    const ASSOC: u32;
+}
+
+fn generic_caller<T: Trait, const N: u32>() {
+    takes_array::<{ [T::ASSOC, N, T::ASSOC] }>();
+    takes_array::<{ [1_u32, T::ASSOC, 2] }>();
+}
+
+fn main() {}

tests/ui/const-generics/mgca/array-expr-with-macro.rs

@@ -0,0 +1,18 @@
+//@ run-pass
+#![expect(incomplete_features)]
+#![feature(min_generic_const_args, adt_const_params)]
+#![allow(dead_code)]
+
+macro_rules! make_array {
+    ($n:expr, $m:expr, $p:expr) => {
+        [N, $m, $p]
+    };
+}
+
+fn takes_array<const A: [u32; 3]>() {}
+
+fn generic_caller<const N: u32>() {
+    takes_array::<{ make_array!(N, 2, 3) }>();
+}
+
+fn main() {}

tests/ui/const-generics/mgca/array-expr-with-struct.rs

@@ -0,0 +1,20 @@
+//@ run-pass
+#![feature(min_generic_const_args, adt_const_params)]
+#![expect(incomplete_features)]
+#![allow(dead_code)]
+
+use std::marker::ConstParamTy;
+
+#[derive(PartialEq, Eq, ConstParamTy)]
+struct Container {
+    values: [u32; 3],
+}
+
+fn takes_container<const C: Container>() {}
+
+fn generic_caller<const N: u32, const M: u32>() {
+    takes_container::<{ Container { values: [N, M, 1] } }>();
+    takes_container::<{ Container { values: [1, 2, 3] } }>();
+}
+
+fn main() {}

tests/ui/const-generics/mgca/array-expr-with-tuple.rs

@@ -0,0 +1,13 @@
+//@ run-pass
+#![feature(min_generic_const_args, adt_const_params, unsized_const_params)]
+#![expect(incomplete_features)]
+#![allow(dead_code)]
+
+fn takes_tuple<const T: ([u32; 2], u32, [u32; 2])>() {}
+
+fn generic_caller<const N: u32, const M: u32>() {
+    takes_tuple::<{ ([N, M], 5, [M, N]) }>();
+    takes_tuple::<{ ([1, 2], 3, [4, 5]) }>();
+}
+
+fn main() {}