From 8b12d5f42f98f50e5e47156eea343ea6d32b10db Mon Sep 17 00:00:00 2001
From: Andy Russell <arussell123@gmail.com>
Date: Sun, 22 Jan 2023 12:06:23 -0500
Subject: [PATCH] suggest qualifying bare associated constants

---
 compiler/rustc_resolve/src/late/diagnostics.rs  | 17 ++++++++++++-----
 .../ui/suggestions/assoc-const-without-self.rs  | 11 +++++++++++
 .../suggestions/assoc-const-without-self.stderr | 14 ++++++++++++++
 3 files changed, 37 insertions(+), 5 deletions(-)
 create mode 100644 tests/ui/suggestions/assoc-const-without-self.rs
 create mode 100644 tests/ui/suggestions/assoc-const-without-self.stderr

diff --git a/compiler/rustc_resolve/src/late/diagnostics.rs b/compiler/rustc_resolve/src/late/diagnostics.rs
index 6d448433ee6db..37beff37c1fb9 100644
--- a/compiler/rustc_resolve/src/late/diagnostics.rs
+++ b/compiler/rustc_resolve/src/late/diagnostics.rs
@@ -227,20 +227,27 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
                     && let Some(FnCtxt::Assoc(_)) = fn_kind.ctxt()
                     && let Some(items) = self.diagnostic_metadata.current_impl_items
                     && let Some(item) = items.iter().find(|i| {
-                        if let AssocItemKind::Fn(_) = &i.kind && i.ident.name == item_str.name
+                        if let AssocItemKind::Fn(..) | AssocItemKind::Const(..) = &i.kind
+                            && i.ident.name == item_str.name
                         {
                             debug!(?item_str.name);
                             return true
                         }
                         false
                     })
-                    && let AssocItemKind::Fn(fn_) = &item.kind
                 {
-                    debug!(?fn_);
-                    let self_sugg = if fn_.sig.decl.has_self() { "self." } else { "Self::" };
+                    let self_sugg = match &item.kind {
+                        AssocItemKind::Fn(fn_) if fn_.sig.decl.has_self() => "self.",
+                        _ => "Self::",
+                    };
+
                     Some((
                         item_span.shrink_to_lo(),
-                        "consider using the associated function",
+                        match &item.kind {
+                            AssocItemKind::Fn(..) => "consider using the associated function",
+                            AssocItemKind::Const(..) => "consider using the associated constant",
+                            _ => unreachable!("item kind was filtered above"),
+                        },
                         self_sugg.to_string()
                     ))
                 } else {
diff --git a/tests/ui/suggestions/assoc-const-without-self.rs b/tests/ui/suggestions/assoc-const-without-self.rs
new file mode 100644
index 0000000000000..95070ec601cd4
--- /dev/null
+++ b/tests/ui/suggestions/assoc-const-without-self.rs
@@ -0,0 +1,11 @@
+struct Foo;
+
+impl Foo {
+    const A_CONST: usize = 1;
+
+    fn foo() -> usize {
+        A_CONST //~ ERROR cannot find value `A_CONST` in this scope
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/suggestions/assoc-const-without-self.stderr b/tests/ui/suggestions/assoc-const-without-self.stderr
new file mode 100644
index 0000000000000..88d72da70cb9b
--- /dev/null
+++ b/tests/ui/suggestions/assoc-const-without-self.stderr
@@ -0,0 +1,14 @@
+error[E0425]: cannot find value `A_CONST` in this scope
+  --> $DIR/assoc-const-without-self.rs:7:9
+   |
+LL |         A_CONST
+   |         ^^^^^^^ not found in this scope
+   |
+help: consider using the associated constant
+   |
+LL |         Self::A_CONST
+   |         ++++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0425`.