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

The test error changes are undesired and need to be investigated.

compiler/rustc_ast_lowering/src/lib.rs

@@ -2298,56 +2298,19 @@ 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,
+        );
 
         self.arena.alloc(hir::ConstArg {
             hir_id: self.next_id(),
-            kind: ct_kind,
+            kind: hir::ConstArgKind::Path(qpath),
             is_desugared_from_effects: false,
         })
     }

compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs

@@ -115,17 +115,12 @@ fn generic_arg_mismatch_err(
             }
         }
         (GenericArg::Const(cnst), GenericParamDefKind::Type { .. }) => {
-            // FIXME(min_generic_const_args): once ConstArgKind::Path is used for non-params too,
-            // this should match against that instead of ::Anon
-            if let hir::ConstArgKind::Anon(anon) = cnst.kind
-                && let body = tcx.hir().body(anon.body)
-                && let rustc_hir::ExprKind::Path(rustc_hir::QPath::Resolved(_, path)) =
-                    body.value.kind
+            if let hir::ConstArgKind::Path(qpath) = cnst.kind
+                && let rustc_hir::QPath::Resolved(_, path) = qpath
+                && let Res::Def(DefKind::Fn { .. }, id) = path.res
             {
-                if let Res::Def(DefKind::Fn { .. }, id) = path.res {
-                    err.help(format!("`{}` is a function item, not a type", tcx.item_name(id)));
-                    err.help("function item types cannot be named directly");
-                }
+                err.help(format!("`{}` is a function item, not a type", tcx.item_name(id)));
+                err.help("function item types cannot be named directly");
             }
         }
         _ => {}

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -2010,41 +2010,62 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         }
 
         match const_arg.kind {
-            hir::ConstArgKind::Path(qpath) => {
-                // FIXME(min_generic_const_args): for now only params are lowered to ConstArgKind::Path
-                self.lower_const_arg_param(qpath, const_arg.hir_id)
-            }
+            hir::ConstArgKind::Path(qpath) => self.lower_const_arg_path(qpath, const_arg.hir_id),
             hir::ConstArgKind::Anon(anon) => Const::from_anon_const(tcx, anon.def_id),
         }
     }
 
-    /// Lower a use of a const param to a [`Const`].
-    ///
-    /// IMPORTANT: `qpath` must be a const param, otherwise this will panic
-    fn lower_const_arg_param(&self, qpath: hir::QPath<'tcx>, hir_id: HirId) -> Const<'tcx> {
+    /// Lower a const path to a [`Const`].
+    fn lower_const_arg_path(&self, qpath: hir::QPath<'tcx>, hir_id: HirId) -> Const<'tcx> {
         let tcx = self.tcx();
 
-        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")
-        };
+        // TODO: handle path args properly
+        match qpath {
+            hir::QPath::Resolved(_, &hir::Path { res: Res::Def(DefKind::ConstParam, did), .. }) => {
+                self.lower_const_arg_param(did, hir_id)
+            }
+            hir::QPath::Resolved(
+                _,
+                &hir::Path { res: Res::Def(DefKind::Fn | DefKind::AssocFn, _), .. },
+            ) => ty::Const::new_error_with_message(
+                tcx,
+                qpath.span(),
+                "fn's cannot be used as const args",
+            ),
+            hir::QPath::Resolved(_, path @ &hir::Path { res: Res::Def(_, did), .. }) => {
+                let (item_segment, _) = path.segments.split_last().unwrap();
+                let args = self.lower_generic_args_of_path_segment(path.span, did, item_segment);
+                ty::Const::new_unevaluated(tcx, ty::UnevaluatedConst::new(did, args))
+            }
+            // TODO: type-relative paths
+            _ => ty::Const::new_error_with_message(
+                tcx,
+                qpath.span(),
+                "Const::lower_const_arg_path: invalid qpath",
+            ),
+        }
+    }
 
-        match tcx.named_bound_var(hir_id) {
+    /// Lower a const param to a [`Const`]. This is only meant as a helper for [`Self::lower_const_arg_path`].
+    /// FIXME: dedup with lower_const_param
+    fn lower_const_arg_param(&self, param_def_id: DefId, path_hir_id: HirId) -> Const<'tcx> {
+        let tcx = self.tcx();
+
+        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),
         }
     }
 

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 +72,33 @@ help: add `#![feature(adt_const_params)]` to the crate attributes to enable more
 LL + #![feature(adt_const_params)]
    |
 
+<<<<<<< HEAD
 error: maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#0}
   --> $DIR/unevaluated-const-ice-119731.rs:28:37
-   |
-LL |     impl<const v10: usize> v17<v10, v2> {
-   |                                     ^^
+||||||| parent of 883a4baff18 (Begin to use `ConstArgKind::Path` for all paths, not just 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
+>>>>>>> 883a4baff18 (Begin to use `ConstArgKind::Path` for all paths, not just params)
+   |
+LL |     const v2: v11 = [[256; v4]; v4];
+   |     ^^^^^^^^^^^^^
 
+<<<<<<< HEAD
 error: maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#0}
   --> $DIR/unevaluated-const-ice-119731.rs:28:37
-   |
-LL |     impl<const v10: usize> v17<v10, v2> {
-   |                                     ^^
+||||||| parent of 883a4baff18 (Begin to use `ConstArgKind::Path` for all paths, not just 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
+>>>>>>> 883a4baff18 (Begin to use `ConstArgKind::Path` for all paths, not just params)
+   |
+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`.