Account for suggestions for complete removal of lines

Fix  #94192.

compiler/rustc_errors/src/emitter.rs

@@ -1657,6 +1657,31 @@ impl EmitterWriter {
             let line_start = sm.lookup_char_pos(parts[0].span.lo()).line;
             draw_col_separator_no_space(&mut buffer, 1, max_line_num_len + 1);
             let mut lines = complete.lines();
+            if lines.clone().next().is_none() {
+                // Account for a suggestion to completely remove a line(s) with whitespace (#94192).
+                let line_end = sm.lookup_char_pos(parts[0].span.hi()).line;
+                for line in line_start..=line_end {
+                    buffer.puts(
+                        row_num - 1 + line - line_start,
+                        0,
+                        &self.maybe_anonymized(line),
+                        Style::LineNumber,
+                    );
+                    buffer.puts(
+                        row_num - 1 + line - line_start,
+                        max_line_num_len + 1,
+                        "- ",
+                        Style::Removal,
+                    );
+                    buffer.puts(
+                        row_num - 1 + line - line_start,
+                        max_line_num_len + 3,
+                        &normalize_whitespace(&*file_lines.file.get_line(line - 1).unwrap()),
+                        Style::Removal,
+                    );
+                }
+                row_num += line_end - line_start;
+            }
             for (line_pos, (line, highlight_parts)) in
                 lines.by_ref().zip(highlights).take(MAX_SUGGESTION_HIGHLIGHT_LINES).enumerate()
             {

src/test/ui/suggestions/removal-of-multiline-trait-bound-in-where-clause.rs

@@ -0,0 +1,30 @@
+struct Wrapper<T>(T);
+
+fn foo<T>(foo: Wrapper<T>)
+//~^ ERROR the size for values of type `T` cannot be known at compilation time
+where
+    T
+    :
+    ?
+    Sized
+{
+    //
+}
+
+fn bar<T>(foo: Wrapper<T>)
+//~^ ERROR the size for values of type `T` cannot be known at compilation time
+where T: ?Sized
+{
+    //
+}
+
+fn qux<T>(foo: Wrapper<T>)
+//~^ ERROR the size for values of type `T` cannot be known at compilation time
+where
+    T: ?Sized
+{
+    //
+}
+
+
+fn main() {}

src/test/ui/suggestions/removal-of-multiline-trait-bound-in-where-clause.stderr

@@ -0,0 +1,83 @@
+error[E0277]: the size for values of type `T` cannot be known at compilation time
+  --> $DIR/removal-of-multiline-trait-bound-in-where-clause.rs:3:16
+   |
+LL | fn foo<T>(foo: Wrapper<T>)
+   |        -       ^^^^^^^^^^ doesn't have a size known at compile-time
+   |        |
+   |        this type parameter needs to be `std::marker::Sized`
+   |
+note: required by a bound in `Wrapper`
+  --> $DIR/removal-of-multiline-trait-bound-in-where-clause.rs:1:16
+   |
+LL | struct Wrapper<T>(T);
+   |                ^ required by this bound in `Wrapper`
+help: you could relax the implicit `Sized` bound on `T` if it were used through indirection like `&T` or `Box<T>`
+  --> $DIR/removal-of-multiline-trait-bound-in-where-clause.rs:1:16
+   |
+LL | struct Wrapper<T>(T);
+   |                ^  - ...if indirection were used here: `Box<T>`
+   |                |
+   |                this could be changed to `T: ?Sized`...
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL - where
+LL -     T
+LL -     :
+LL -     ?
+LL -     Sized
+   | 
+
+error[E0277]: the size for values of type `T` cannot be known at compilation time
+  --> $DIR/removal-of-multiline-trait-bound-in-where-clause.rs:14:16
+   |
+LL | fn bar<T>(foo: Wrapper<T>)
+   |        -       ^^^^^^^^^^ doesn't have a size known at compile-time
+   |        |
+   |        this type parameter needs to be `std::marker::Sized`
+   |
+note: required by a bound in `Wrapper`
+  --> $DIR/removal-of-multiline-trait-bound-in-where-clause.rs:1:16
+   |
+LL | struct Wrapper<T>(T);
+   |                ^ required by this bound in `Wrapper`
+help: you could relax the implicit `Sized` bound on `T` if it were used through indirection like `&T` or `Box<T>`
+  --> $DIR/removal-of-multiline-trait-bound-in-where-clause.rs:1:16
+   |
+LL | struct Wrapper<T>(T);
+   |                ^  - ...if indirection were used here: `Box<T>`
+   |                |
+   |                this could be changed to `T: ?Sized`...
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL - where T: ?Sized
+   | 
+
+error[E0277]: the size for values of type `T` cannot be known at compilation time
+  --> $DIR/removal-of-multiline-trait-bound-in-where-clause.rs:21:16
+   |
+LL | fn qux<T>(foo: Wrapper<T>)
+   |        -       ^^^^^^^^^^ doesn't have a size known at compile-time
+   |        |
+   |        this type parameter needs to be `std::marker::Sized`
+   |
+note: required by a bound in `Wrapper`
+  --> $DIR/removal-of-multiline-trait-bound-in-where-clause.rs:1:16
+   |
+LL | struct Wrapper<T>(T);
+   |                ^ required by this bound in `Wrapper`
+help: you could relax the implicit `Sized` bound on `T` if it were used through indirection like `&T` or `Box<T>`
+  --> $DIR/removal-of-multiline-trait-bound-in-where-clause.rs:1:16
+   |
+LL | struct Wrapper<T>(T);
+   |                ^  - ...if indirection were used here: `Box<T>`
+   |                |
+   |                this could be changed to `T: ?Sized`...
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL - where
+LL -     T: ?Sized
+   | 
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0277`.