Fix mispositioned span in suggestions with wide characters

src/librustc_errors/emitter.rs

@@ -1187,7 +1187,7 @@ impl EmitterWriter {
                     let sub_len = parts[0].snippet.trim().chars().fold(0, |acc, ch| {
                         acc + unicode_width::UnicodeWidthChar::width(ch).unwrap_or(0)
                     });
-                    let underline_start = span_start_pos.col.0 + start;
+                    let underline_start = span_start_pos.col_display + start;
                     let underline_end = span_start_pos.col.0 + start + sub_len;
                     for p in underline_start..underline_end {
                         buffer.putc(row_num,

src/test/ui/lint/use_suggestion_json.stderr

@@ -2,72 +2,7 @@
   "message": "cannot find type `Iter` in this scope",
   "code": {
     "code": "E0412",
-    "explanation": "
-The type name used is not in scope.
-
-Erroneous code examples:
-
-```compile_fail,E0412
-impl Something {} // error: type name `Something` is not in scope
-
-// or:
-
-trait Foo {
-    fn bar(N); // error: type name `N` is not in scope
-}
-
-// or:
-
-fn foo(x: T) {} // type name `T` is not in scope
-```
-
-To fix this error, please verify you didn't misspell the type name, you did
-declare it or imported it into the scope. Examples:
-
-```
-struct Something;
-
-impl Something {} // ok!
-
-// or:
-
-trait Foo {
-    type N;
-
-    fn bar(_: Self::N); // ok!
-}
-
-// or:
-
-fn foo<T>(x: T) {} // ok!
-```
-
-Another case that causes this error is when a type is imported into a parent
-module. To fix this, you can follow the suggestion and use File directly or
-`use super::File;` which will import the types from the parent namespace. An
-example that causes this error is below:
-
-```compile_fail,E0412
-use std::fs::File;
-
-mod foo {
-    fn some_function(f: File) {}
-}
-```
-
-```
-use std::fs::File;
-
-mod foo {
-    // either
-    use super::File;
-    // or
-    // use std::fs::File;
-    fn foo(f: File) {}
-}
-# fn main() {} // don't insert it for us; that'll break imports
-```
-"
+    "explanation": null
   },
   "level": "error",
   "spans": [