Structured suggestion for missing mut/const in raw pointer

compiler/rustc_parse/src/parser/ty.rs

@@ -397,10 +397,13 @@ impl<'a> Parser<'a> {
     fn parse_ty_ptr(&mut self) -> PResult<'a, TyKind> {
         let mutbl = self.parse_const_or_mut().unwrap_or_else(|| {
             let span = self.prev_token.span;
-            let msg = "expected mut or const in raw pointer type";
-            self.struct_span_err(span, msg)
-                .span_label(span, msg)
-                .help("use `*mut T` or `*const T` as appropriate")
+            self.struct_span_err(span, "expected `mut` or `const` keyword in raw pointer type")
+                .span_suggestions(
+                    span.shrink_to_hi(),
+                    "add `mut` or `const` here",
+                    ["mut ".to_string(), "const ".to_string()].into_iter(),
+                    Applicability::HasPlaceholders,
+                )
                 .emit();
             Mutability::Not
         });

src/test/ui/parser/bad-pointer-type.rs

@@ -1,5 +1,5 @@
 fn foo(_: *()) {
-    //~^ ERROR expected mut or const in raw pointer type
+    //~^ ERROR expected `mut` or `const` keyword in raw pointer type
 }
 
 fn main() {}

src/test/ui/parser/bad-pointer-type.stderr

@@ -1,10 +1,15 @@
-error: expected mut or const in raw pointer type
+error: expected `mut` or `const` keyword in raw pointer type
   --> $DIR/bad-pointer-type.rs:1:11
    |
 LL | fn foo(_: *()) {
-   |           ^ expected mut or const in raw pointer type
+   |           ^
    |
-   = help: use `*mut T` or `*const T` as appropriate
+help: add `mut` or `const` here
+   |
+LL | fn foo(_: *const ()) {
+   |            +++++
+LL | fn foo(_: *mut ()) {
+   |            +++
 
 error: aborting due to previous error
 

src/test/ui/parser/double-pointer.rs

@@ -0,0 +1,7 @@
+fn main() {
+    let x: i32 = 5;
+    let ptr: *const i32 = &x;
+    let dptr: **const i32 = &ptr;
+    //~^ ERROR expected `mut` or `const` keyword in raw pointer type
+    //~| HELP add `mut` or `const` here
+}

src/test/ui/parser/double-pointer.stderr

@@ -0,0 +1,15 @@
+error: expected `mut` or `const` keyword in raw pointer type
+  --> $DIR/double-pointer.rs:4:15
+   |
+LL |     let dptr: **const i32 = &ptr;
+   |               ^
+   |
+help: add `mut` or `const` here
+   |
+LL |     let dptr: *const *const i32 = &ptr;
+   |                +++++
+LL |     let dptr: *mut *const i32 = &ptr;
+   |                +++
+
+error: aborting due to previous error
+