From 527292a1a697c8831fc1ec01b1047ecebc10f809 Mon Sep 17 00:00:00 2001
From: Takayuki Maeda <takoyaki0316@gmail.com>
Date: Fri, 16 Sep 2022 11:24:14 +0900
Subject: [PATCH] do not suggest a placeholder to const and static without a
 type

---
 compiler/rustc_errors/src/lib.rs              |  4 ++++
 compiler/rustc_typeck/src/collect.rs          |  8 +++++---
 ...laceholder-to-const-static-without-type.rs |  8 ++++++++
 ...holder-to-const-static-without-type.stderr | 20 +++++++++++++++++++
 4 files changed, 37 insertions(+), 3 deletions(-)
 create mode 100644 src/test/ui/typeck/do-not-suggest-placeholder-to-const-static-without-type.rs
 create mode 100644 src/test/ui/typeck/do-not-suggest-placeholder-to-const-static-without-type.stderr

diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index 68abdd0bad1..d89b3da049c 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -637,6 +637,10 @@ pub fn steal_diagnostic(&self, span: Span, key: StashKey) -> Option<DiagnosticBu
         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()
diff --git a/compiler/rustc_typeck/src/collect.rs b/compiler/rustc_typeck/src/collect.rs
index 6236ad370df..8f5b4815cf8 100644
--- a/compiler/rustc_typeck/src/collect.rs
+++ b/compiler/rustc_typeck/src/collect.rs
@@ -25,7 +25,7 @@
 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(_)) => {
diff --git a/src/test/ui/typeck/do-not-suggest-placeholder-to-const-static-without-type.rs b/src/test/ui/typeck/do-not-suggest-placeholder-to-const-static-without-type.rs
new file mode 100644
index 00000000000..97e0b213f2e
--- /dev/null
+++ b/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() {}
diff --git a/src/test/ui/typeck/do-not-suggest-placeholder-to-const-static-without-type.stderr b/src/test/ui/typeck/do-not-suggest-placeholder-to-const-static-without-type.stderr
new file mode 100644
index 00000000000..8982d628561
--- /dev/null
+++ b/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
+