support pattern as const parents in type_of

compiler/rustc_hir/src/hir.rs

@@ -760,9 +760,9 @@ pub struct Pat<'hir> {
     pub default_binding_modes: bool,
 }
 
-impl Pat<'_> {
+impl<'hir> Pat<'hir> {
     // FIXME(#19596) this is a workaround, but there should be a better way
-    fn walk_short_(&self, it: &mut impl FnMut(&Pat<'_>) -> bool) -> bool {
+    fn walk_short_(&self, it: &mut impl FnMut(&Pat<'hir>) -> bool) -> bool {
         if !it(self) {
             return false;
         }
@@ -785,12 +785,12 @@ impl Pat<'_> {
     /// Note that when visiting e.g. `Tuple(ps)`,
     /// if visiting `ps[0]` returns `false`,
     /// then `ps[1]` will not be visited.
-    pub fn walk_short(&self, mut it: impl FnMut(&Pat<'_>) -> bool) -> bool {
+    pub fn walk_short(&self, mut it: impl FnMut(&Pat<'hir>) -> bool) -> bool {
         self.walk_short_(&mut it)
     }
 
     // FIXME(#19596) this is a workaround, but there should be a better way
-    fn walk_(&self, it: &mut impl FnMut(&Pat<'_>) -> bool) {
+    fn walk_(&self, it: &mut impl FnMut(&Pat<'hir>) -> bool) {
         if !it(self) {
             return;
         }
@@ -810,7 +810,7 @@ impl Pat<'_> {
     /// Walk the pattern in left-to-right order.
     ///
     /// If `it(pat)` returns `false`, the children are not visited.
-    pub fn walk(&self, mut it: impl FnMut(&Pat<'_>) -> bool) {
+    pub fn walk(&self, mut it: impl FnMut(&Pat<'hir>) -> bool) {
         self.walk_(&mut it)
     }
 

compiler/rustc_typeck/src/collect/type_of.rs

@@ -6,7 +6,7 @@ use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::intravisit;
 use rustc_hir::intravisit::Visitor;
-use rustc_hir::Node;
+use rustc_hir::{HirId, Node};
 use rustc_middle::hir::map::Map;
 use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts};
 use rustc_middle::ty::util::IntTypeExt;
@@ -22,7 +22,6 @@ use super::{bad_placeholder_type, is_suggestable_infer_ty};
 /// This should be called using the query `tcx.opt_const_param_of`.
 pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<DefId> {
     use hir::*;
-
     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
 
     if let Node::AnonConst(_) = tcx.hir().get(hir_id) {
@@ -62,9 +61,9 @@ pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<
             }
 
             Node::Ty(&Ty { kind: TyKind::Path(_), .. })
-            | Node::Expr(&Expr { kind: ExprKind::Struct(..), .. })
-            | Node::Expr(&Expr { kind: ExprKind::Path(_), .. })
-            | Node::TraitRef(..) => {
+            | Node::Expr(&Expr { kind: ExprKind::Path(_) | ExprKind::Struct(..), .. })
+            | Node::TraitRef(..)
+            | Node::Pat(_) => {
                 let path = match parent_node {
                     Node::Ty(&Ty { kind: TyKind::Path(QPath::Resolved(_, path)), .. })
                     | Node::TraitRef(&TraitRef { path, .. }) => &*path,
@@ -79,6 +78,20 @@ pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<
                         let _tables = tcx.typeck(body_owner);
                         &*path
                     }
+                    Node::Pat(pat) => {
+                        if let Some(path) = get_path_containing_arg_in_pat(pat, hir_id) {
+                            path
+                        } else {
+                            tcx.sess.delay_span_bug(
+                                tcx.def_span(def_id),
+                                &format!(
+                                    "unable to find const parent for {} in pat {:?}",
+                                    hir_id, pat
+                                ),
+                            );
+                            return None;
+                        }
+                    }
                     _ => {
                         tcx.sess.delay_span_bug(
                             tcx.def_span(def_id),
@@ -91,7 +104,6 @@ pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<
                 // We've encountered an `AnonConst` in some path, so we need to
                 // figure out which generic parameter it corresponds to and return
                 // the relevant type.
-
                 let (arg_index, segment) = path
                     .segments
                     .iter()
@@ -144,6 +156,34 @@ pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<
     }
 }
 
+fn get_path_containing_arg_in_pat<'hir>(
+    pat: &'hir hir::Pat<'hir>,
+    arg_id: HirId,
+) -> Option<&'hir hir::Path<'hir>> {
+    use hir::*;
+
+    let is_arg_in_path = |p: &hir::Path<'_>| {
+        p.segments
+            .iter()
+            .filter_map(|seg| seg.args)
+            .flat_map(|args| args.args)
+            .any(|arg| arg.id() == arg_id)
+    };
+    let mut arg_path = None;
+    pat.walk(|pat| match pat.kind {
+        PatKind::Struct(QPath::Resolved(_, path), _, _)
+        | PatKind::TupleStruct(QPath::Resolved(_, path), _, _)
+        | PatKind::Path(QPath::Resolved(_, path))
+            if is_arg_in_path(path) =>
+        {
+            arg_path = Some(path);
+            false
+        }
+        _ => true,
+    });
+    arg_path
+}
+
 pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
     let def_id = def_id.expect_local();
     use rustc_hir::*;

src/test/ui/const-generics/arg-in-pat-1.rs

@@ -0,0 +1,23 @@
+// check-pass
+enum ConstGenericEnum<const N: usize> {
+    Foo([i32; N]),
+    Bar,
+}
+
+fn foo<const N: usize>(val: &ConstGenericEnum<N>) {
+    if let ConstGenericEnum::<N>::Foo(field, ..) = val {}
+}
+
+fn bar<const N: usize>(val: &ConstGenericEnum<N>) {
+    match val {
+        ConstGenericEnum::<N>::Foo(field, ..) => (),
+        ConstGenericEnum::<N>::Bar => (),
+    }
+}
+
+fn main() {
+    match ConstGenericEnum::Bar {
+        ConstGenericEnum::<3>::Foo(field, ..) => (),
+        ConstGenericEnum::<3>::Bar => (),
+    }
+}

src/test/ui/const-generics/arg-in-pat-2.rs

@@ -0,0 +1,10 @@
+// check-pass
+enum Generic<const N: usize> {
+    Variant,
+}
+
+fn main() {
+    match todo!() {
+        Generic::<0usize>::Variant => todo!()
+    }
+}

src/test/ui/const-generics/arg-in-pat-3.rs

@@ -0,0 +1,43 @@
+// check-pass
+struct Foo<const N: usize>;
+
+fn bindingp() {
+    match Foo {
+        mut x @ Foo::<3> => {
+            let ref mut _x @ Foo::<3> = x;
+        }
+    }
+}
+
+struct Bar<const N: usize> {
+    field: Foo<N>,
+}
+
+fn structp() {
+    match todo!() {
+        Bar::<3> {
+            field: Foo::<3>,
+        } => (),
+    }
+}
+
+struct Baz<const N: usize>(Foo<N>);
+
+fn tuplestructp() {
+    match Baz(Foo) {
+        Baz::<3>(Foo::<3>) => (),
+    }
+}
+
+impl<const N: usize> Baz<N> {
+    const ASSOC: usize = 3;
+}
+
+fn pathp() {
+    match 3 {
+        Baz::<3>::ASSOC => (),
+        _ => (),
+    }
+}
+
+fn main() {}