Do not suggest a placeholder to const and static without a type

compiler/rustc_errors/src/lib.rs

@@ -637,6 +637,10 @@ impl Handler {
         inner.steal((span, key)).map(|diag| DiagnosticBuilder::new_diagnostic(self, diag))
     }
 
+    pub fn has_stashed_diagnostic(&self, span: Span, key: StashKey) -> bool {
+        self.inner.borrow().stashed_diagnostics.get(&(span, key)).is_some()
+    }
+
     /// Emit all stashed diagnostics.
     pub fn emit_stashed_diagnostics(&self) -> Option<ErrorGuaranteed> {
         self.inner.borrow_mut().emit_stashed_diagnostics()

compiler/rustc_typeck/src/collect.rs

@@ -25,7 +25,7 @@ use rustc_ast::{MetaItemKind, NestedMetaItem};
 use rustc_attr::{list_contains_name, InlineAttr, InstructionSetAttr, OptimizeAttr};
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
-use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed};
+use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed, StashKey};
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, DefKind};
 use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_ID, LOCAL_CRATE};
@@ -852,12 +852,14 @@ fn convert_trait_item(tcx: TyCtxt<'_>, trait_item_id: hir::TraitItemId) {
             tcx.ensure().type_of(trait_item_id.def_id);
         }
 
-        hir::TraitItemKind::Const(..) => {
+        hir::TraitItemKind::Const(hir_ty, _) => {
             tcx.ensure().type_of(trait_item_id.def_id);
             // Account for `const C: _;`.
             let mut visitor = HirPlaceholderCollector::default();
             visitor.visit_trait_item(trait_item);
-            placeholder_type_error(tcx, None, visitor.0, false, None, "constant");
+            if !tcx.sess.diagnostic().has_stashed_diagnostic(hir_ty.span, StashKey::ItemNoType) {
+                placeholder_type_error(tcx, None, visitor.0, false, None, "constant");
+            }
         }
 
         hir::TraitItemKind::Type(_, Some(_)) => {

src/test/ui/typeck/do-not-suggest-placeholder-to-const-static-without-type.rs

@@ -0,0 +1,8 @@
+trait Foo {
+    const A; //~ ERROR missing type for `const` item
+    static B;
+    //~^ ERROR associated `static` items are not allowed
+    //~| ERROR missing type for `static` item
+}
+
+fn main() {}

src/test/ui/typeck/do-not-suggest-placeholder-to-const-static-without-type.stderr

@@ -0,0 +1,20 @@
+error: associated `static` items are not allowed
+  --> $DIR/do-not-suggest-placeholder-to-const-static-without-type.rs:3:5
+   |
+LL |     static B;
+   |     ^^^^^^^^^
+
+error: missing type for `const` item
+  --> $DIR/do-not-suggest-placeholder-to-const-static-without-type.rs:2:12
+   |
+LL |     const A;
+   |            ^ help: provide a type for the item: `: <type>`
+
+error: missing type for `static` item
+  --> $DIR/do-not-suggest-placeholder-to-const-static-without-type.rs:3:13
+   |
+LL |     static B;
+   |             ^ help: provide a type for the item: `: <type>`
+
+error: aborting due to 3 previous errors
+