Begin to use ConstArgKind::Path for all paths, not just params

Note that these test output changes are not desired.

compiler/rustc_ast_lowering/src/lib.rs

@@ -2357,53 +2357,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         ty_id: NodeId,
         span: Span,
     ) -> &'hir hir::ConstArg<'hir> {
-        let ct_kind = match res {
-            Res::Def(DefKind::ConstParam, _) => {
-                let qpath = self.lower_qpath(
-                    ty_id,
-                    &None,
-                    path,
-                    ParamMode::Optional,
-                    AllowReturnTypeNotation::No,
-                    ImplTraitContext::Disallowed(ImplTraitPosition::Path),
-                    None,
-                );
-                hir::ConstArgKind::Path(qpath)
-            }
-            _ => {
-                // Construct an AnonConst where the expr is the "ty"'s path.
-
-                let parent_def_id = self.current_def_id_parent;
-                let node_id = self.next_node_id();
-                let span = self.lower_span(span);
-
-                // Add a definition for the in-band const def.
-                let def_id =
-                    self.create_def(parent_def_id, node_id, kw::Empty, DefKind::AnonConst, span);
-                let hir_id = self.lower_node_id(node_id);
-
-                let path_expr = Expr {
-                    id: ty_id,
-                    kind: ExprKind::Path(None, path.clone()),
-                    span,
-                    attrs: AttrVec::new(),
-                    tokens: None,
-                };
-
-                let ct = self.with_new_scopes(span, |this| {
-                    self.arena.alloc(hir::AnonConst {
-                        def_id,
-                        hir_id,
-                        body: this.with_def_id_parent(def_id, |this| {
-                            this.lower_const_body(path_expr.span, Some(&path_expr))
-                        }),
-                        span,
-                    })
-                });
-                hir::ConstArgKind::Anon(ct)
-            }
-        };
-
+        let qpath = self.lower_qpath(
+            ty_id,
+            &None,
+            path,
+            ParamMode::Optional,
+            AllowReturnTypeNotation::No,
+            ImplTraitContext::Disallowed(ImplTraitPosition::Path),
+            None,
+        );
+        let ct_kind = hir::ConstArgKind::Path(qpath);
         self.arena.alloc(hir::ConstArg {
             hir_id: self.next_id(),
             kind: ct_kind,

compiler/rustc_middle/src/ty/consts.rs

@@ -215,10 +215,7 @@ impl<'tcx> Const<'tcx> {
         }
 
         match const_arg.kind {
-            hir::ConstArgKind::Path(qpath) => {
-                // FIXME(min_generic_const_args): for now only params are lowered to ConstArgKind::Path
-                Self::from_param(tcx, qpath, const_arg.hir_id)
-            }
+            hir::ConstArgKind::Path(qpath) => Self::from_path(tcx, qpath, const_arg.hir_id),
             hir::ConstArgKind::Anon(anon) => Self::from_anon_const(tcx, anon.def_id),
         }
     }
@@ -240,7 +237,7 @@ impl<'tcx> Const<'tcx> {
 
         let ty = tcx.type_of(def).no_bound_vars().expect("const parameter types cannot be generic");
 
-        match Self::try_from_lit_or_param(tcx, ty, expr) {
+        match Self::try_from_lit(tcx, ty, expr) {
             Some(v) => v,
             None => ty::Const::new_unevaluated(tcx, ty::UnevaluatedConst {
                 def: def.to_def_id(),
@@ -249,40 +246,54 @@ impl<'tcx> Const<'tcx> {
         }
     }
 
-    /// Lower a const param to a [`Const`].
-    ///
-    /// IMPORTANT: `qpath` must be a const param, otherwise this will panic
-    fn from_param(tcx: TyCtxt<'tcx>, qpath: hir::QPath<'tcx>, hir_id: HirId) -> Self {
-        let hir::QPath::Resolved(_, &hir::Path { res: Res::Def(DefKind::ConstParam, def_id), .. }) =
-            qpath
-        else {
-            span_bug!(qpath.span(), "non-param {qpath:?} passed to Const::from_param")
-        };
+    fn from_path(tcx: TyCtxt<'tcx>, qpath: hir::QPath<'tcx>, hir_id: HirId) -> Self {
+        match qpath {
+            hir::QPath::Resolved(_, &path) => match path.res {
+                Res::Def(DefKind::ConstParam, def_id) => Self::from_param(tcx, def_id, hir_id),
+                Res::Def(DefKind::Const, def_id) => {
+                    // FIXME: support parametrized consts (instead of empty list).
+                    let uv = ty::UnevaluatedConst::new(def_id, ty::List::empty());
+                    Self::new_unevaluated(tcx, uv)
+                }
+                r => Self::new_error(
+                    tcx,
+                    tcx.dcx().span_delayed_bug(
+                        tcx.hir().span(hir_id),
+                        format!("Const::from_path: invalid qpath res: {r:?}"),
+                    ),
+                ),
+            },
+            hir::QPath::TypeRelative(..) => todo!("associated const paths"),
+            // FIXME: use span_delayed_bug?
+            hir::QPath::LangItem(..) => span_bug!(
+                tcx.hir().span(hir_id),
+                "Const::from_path: invalid qpath provided: {qpath:?}"
+            ),
+        }
+    }
 
-        match tcx.named_bound_var(hir_id) {
+    /// Lower a const param to a [`Const`]. This is only meant as a helper for [`Self::from_path`].
+    fn from_param(tcx: TyCtxt<'tcx>, param_def_id: DefId, path_hir_id: HirId) -> Self {
+        match tcx.named_bound_var(path_hir_id) {
             Some(rbv::ResolvedArg::EarlyBound(_)) => {
                 // Find the name and index of the const parameter by indexing the generics of
                 // the parent item and construct a `ParamConst`.
-                let item_def_id = tcx.parent(def_id);
+                let item_def_id = tcx.parent(param_def_id);
                 let generics = tcx.generics_of(item_def_id);
-                let index = generics.param_def_id_to_index[&def_id];
-                let name = tcx.item_name(def_id);
+                let index = generics.param_def_id_to_index[&param_def_id];
+                let name = tcx.item_name(param_def_id);
                 ty::Const::new_param(tcx, ty::ParamConst::new(index, name))
             }
             Some(rbv::ResolvedArg::LateBound(debruijn, index, _)) => {
                 ty::Const::new_bound(tcx, debruijn, ty::BoundVar::from_u32(index))
             }
             Some(rbv::ResolvedArg::Error(guar)) => ty::Const::new_error(tcx, guar),
-            arg => bug!("unexpected bound var resolution for {:?}: {arg:?}", hir_id),
+            arg => bug!("unexpected bound var resolution for {:?}: {arg:?}", path_hir_id),
         }
     }
 
     #[instrument(skip(tcx), level = "debug")]
-    fn try_from_lit_or_param(
-        tcx: TyCtxt<'tcx>,
-        ty: Ty<'tcx>,
-        expr: &'tcx hir::Expr<'tcx>,
-    ) -> Option<Self> {
+    fn try_from_lit(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, expr: &'tcx hir::Expr<'tcx>) -> Option<Self> {
         // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
         // currently have to be wrapped in curly brackets, so it's necessary to special-case.
         let expr = match &expr.kind {

tests/ui/const-generics/fn-const-param-infer.adt_const_params.stderr

@@ -13,18 +13,7 @@ LL |     let _ = Checked::<{ generic_arg::<u32> }>;
    = note: expected fn pointer `fn(usize) -> _`
                  found fn item `fn(u32) -> _ {generic_arg::<u32>}`
 
-error[E0282]: type annotations needed
-  --> $DIR/fn-const-param-infer.rs:35:23
-   |
-LL |     let _ = Checked::<generic>;
-   |                       ^^^^^^^ cannot infer type of the type parameter `T` declared on the function `generic`
-   |
-help: consider specifying the generic argument
-   |
-LL |     let _ = Checked::<generic::<T>>;
-   |                              +++++
-
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0282, E0308, E0741.
-For more information about an error, try `rustc --explain E0282`.
+Some errors have detailed explanations: E0308, E0741.
+For more information about an error, try `rustc --explain E0308`.

tests/ui/const-generics/fn-const-param-infer.full.stderr

@@ -13,18 +13,7 @@ LL |     let _ = Checked::<{ generic_arg::<u32> }>;
    = note: expected fn pointer `fn(usize) -> _`
                  found fn item `fn(u32) -> _ {generic_arg::<u32>}`
 
-error[E0282]: type annotations needed
-  --> $DIR/fn-const-param-infer.rs:35:23
-   |
-LL |     let _ = Checked::<generic>;
-   |                       ^^^^^^^ cannot infer type of the type parameter `T` declared on the function `generic`
-   |
-help: consider specifying the generic argument
-   |
-LL |     let _ = Checked::<generic::<T>>;
-   |                              +++++
-
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0282, E0308, E0741.
-For more information about an error, try `rustc --explain E0282`.
+Some errors have detailed explanations: E0308, E0741.
+For more information about an error, try `rustc --explain E0308`.

tests/ui/const-generics/fn-const-param-infer.min.stderr

@@ -15,18 +15,6 @@ LL |     let _ = Checked::<{ generic_arg::<u32> }>;
    = note: expected fn pointer `fn(usize) -> _`
                  found fn item `fn(u32) -> _ {generic_arg::<u32>}`
 
-error[E0282]: type annotations needed
-  --> $DIR/fn-const-param-infer.rs:35:23
-   |
-LL |     let _ = Checked::<generic>;
-   |                       ^^^^^^^ cannot infer type of the type parameter `T` declared on the function `generic`
-   |
-help: consider specifying the generic argument
-   |
-LL |     let _ = Checked::<generic::<T>>;
-   |                              +++++
-
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0282, E0308.
-For more information about an error, try `rustc --explain E0282`.
+For more information about this error, try `rustc --explain E0308`.

tests/ui/const-generics/generic_const_exprs/unevaluated-const-ice-119731.stderr

@@ -72,17 +72,17 @@ help: add `#![feature(adt_const_params)]` to the crate attributes to enable more
 LL + #![feature(adt_const_params)]
    |
 
-error: maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#0}
-  --> $DIR/unevaluated-const-ice-119731.rs:27:37
+error: maximum number of nodes exceeded in constant v20::v2
+  --> $DIR/unevaluated-const-ice-119731.rs:11:5
    |
-LL |     impl<const v10: usize> v17<v10, v2> {
-   |                                     ^^
+LL |     const v2: v11 = [[256; v4]; v4];
+   |     ^^^^^^^^^^^^^
 
-error: maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#0}
-  --> $DIR/unevaluated-const-ice-119731.rs:27:37
+error: maximum number of nodes exceeded in constant v20::v2
+  --> $DIR/unevaluated-const-ice-119731.rs:11:5
    |
-LL |     impl<const v10: usize> v17<v10, v2> {
-   |                                     ^^
+LL |     const v2: v11 = [[256; v4]; v4];
+   |     ^^^^^^^^^^^^^
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 

tests/ui/const-generics/opaque_types2.stderr

@@ -1,15 +1,50 @@
-error[E0308]: mismatched types
-  --> $DIR/opaque_types2.rs:13:11
+error[E0391]: cycle detected when computing type of `Foo::{opaque#0}`
+  --> $DIR/opaque_types2.rs:3:12
    |
 LL | type Foo = impl Sized;
-   |            ---------- the found opaque type
-...
-LL |     foo::<C>();
-   |           ^ expected `u32`, found opaque type
+   |            ^^^^^^^^^^
    |
-   = note:     expected type `u32`
-           found opaque type `Foo`
+note: ...which requires computing type of opaque `Foo::{opaque#0}`...
+  --> $DIR/opaque_types2.rs:3:12
+   |
+LL | type Foo = impl Sized;
+   |            ^^^^^^^^^^
+note: ...which requires type-checking `bar`...
+  --> $DIR/opaque_types2.rs:9:1
+   |
+LL | / fn bar()
+LL | | where
+LL | |     Foo:,
+   | |_________^
+note: ...which requires evaluating type-level constant...
+  --> $DIR/opaque_types2.rs:7:1
+   |
+LL | const C: Foo = 42;
+   | ^^^^^^^^^^^^
+note: ...which requires const-evaluating + checking `C`...
+  --> $DIR/opaque_types2.rs:7:1
+   |
+LL | const C: Foo = 42;
+   | ^^^^^^^^^^^^
+note: ...which requires caching mir of `C` for CTFE...
+  --> $DIR/opaque_types2.rs:7:1
+   |
+LL | const C: Foo = 42;
+   | ^^^^^^^^^^^^
+note: ...which requires elaborating drops for `C`...
+  --> $DIR/opaque_types2.rs:7:1
+   |
+LL | const C: Foo = 42;
+   | ^^^^^^^^^^^^
+   = note: ...which requires normalizing `Foo`...
+   = note: ...which again requires computing type of `Foo::{opaque#0}`, completing the cycle
+note: cycle used when checking that `Foo::{opaque#0}` is well-formed
+  --> $DIR/opaque_types2.rs:3:12
+   |
+LL | type Foo = impl Sized;
+   |            ^^^^^^^^^^
+   = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0308`.
+For more information about this error, try `rustc --explain E0391`.

tests/ui/generics/generic-function-item-where-type.stderr

@@ -3,9 +3,6 @@ error[E0747]: constant provided when a type was expected
    |
 LL |     foo::<main>()
    |           ^^^^
-   |
-   = help: `main` is a function item, not a type
-   = help: function item types cannot be named directly
 
 error: aborting due to 1 previous error
 

tests/ui/privacy/privacy-ns1.stderr

@@ -57,9 +57,6 @@ error[E0747]: constant provided when a type was expected
    |
 LL |     let _x: Box<Bar>;
    |                 ^^^
-   |
-   = help: `Bar` is a function item, not a type
-   = help: function item types cannot be named directly
 
 error: aborting due to 4 previous errors
 

tests/ui/privacy/privacy-ns2.stderr

@@ -83,18 +83,12 @@ error[E0747]: constant provided when a type was expected
    |
 LL |     let _x : Box<Bar>;
    |                  ^^^
-   |
-   = help: `Bar` is a function item, not a type
-   = help: function item types cannot be named directly
 
 error[E0747]: constant provided when a type was expected
   --> $DIR/privacy-ns2.rs:48:17
    |
 LL |     let _x: Box<Bar>;
    |                 ^^^
-   |
-   = help: `Bar` is a function item, not a type
-   = help: function item types cannot be named directly
 
 error: aborting due to 8 previous errors