Don't trim substitution if it's only whitespace

compiler/rustc_errors/src/emitter.rs

@@ -268,7 +268,10 @@ fn primary_span_formatted<'a>(
                     SuggestionStyle::ShowAlways,
                ].contains(&sugg.style)
             {
-                let substitution = &sugg.substitutions[0].parts[0].snippet.trim();
+                // Don't trim the substitution if it's only whitespace changes
+                let substitution = &sugg.substitutions[0].parts[0].snippet;
+                let substitution =
+                    if substitution.trim().is_empty() { substitution } else { substitution.trim() };
                 let msg = if substitution.is_empty() || sugg.style.hide_inline() {
                     // This substitution is only removal OR we explicitly don't want to show the
                     // code inline (`hide_inline`). Therefore, we don't show the substitution.
@@ -1880,16 +1883,23 @@ fn emit_suggestion_default(
                     let span_start_pos = sm.lookup_char_pos(part.span.lo()).col_display;
                     let span_end_pos = sm.lookup_char_pos(part.span.hi()).col_display;
 
+                    // If this addition is _only_ whitespace, then don't trim it,
+                    // or else we're just not rendering anything.
+                    let is_whitespace_addition = part.snippet.trim().is_empty();
+
                     // Do not underline the leading...
-                    let start = part.snippet.len().saturating_sub(part.snippet.trim_start().len());
+                    let start = if is_whitespace_addition {
+                        0
+                    } else {
+                        part.snippet.len().saturating_sub(part.snippet.trim_start().len())
+                    };
                     // ...or trailing spaces. Account for substitutions containing unicode
                     // characters.
-                    let sub_len: usize = part
+                    let sub_len: usize =
-                        .snippet
+                        if is_whitespace_addition { &part.snippet } else { part.snippet.trim() }
-                        .trim()
+                            .chars()
-                        .chars()
+                            .map(|ch| unicode_width::UnicodeWidthChar::width(ch).unwrap_or(1))
-                        .map(|ch| unicode_width::UnicodeWidthChar::width(ch).unwrap_or(1))
+                            .sum();
-                        .sum();
 
                     let offset: isize = offsets
                         .iter()
@@ -2130,7 +2140,7 @@ fn draw_code_line(
     }
 }
 
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, Debug)]
 enum DisplaySuggestion {
     Underline,
     Diff,

src/test/ui/rust-2021/reserved-prefixes-migration.stderr

@@ -14,7 +14,7 @@ LL | #![warn(rust_2021_prefixes_incompatible_syntax)]
 help: insert whitespace here to avoid this being parsed as a prefix in Rust 2021
    |
 LL |     m2!(z "hey");
-   |
+   |          +
 
 warning: prefix `prefix` is unknown
   --> $DIR/reserved-prefixes-migration.rs:19:9
@@ -27,7 +27,7 @@ LL |     m2!(prefix"hey");
 help: insert whitespace here to avoid this being parsed as a prefix in Rust 2021
    |
 LL |     m2!(prefix "hey");
-   |
+   |               +
 
 warning: prefix `hey` is unknown
   --> $DIR/reserved-prefixes-migration.rs:22:9
@@ -40,7 +40,7 @@ LL |     m3!(hey#123);
 help: insert whitespace here to avoid this being parsed as a prefix in Rust 2021
    |
 LL |     m3!(hey #123);
-   |
+   |            +
 
 warning: prefix `hey` is unknown
   --> $DIR/reserved-prefixes-migration.rs:25:9
@@ -53,7 +53,7 @@ LL |     m3!(hey#hey);
 help: insert whitespace here to avoid this being parsed as a prefix in Rust 2021
    |
 LL |     m3!(hey #hey);
-   |
+   |            +
 
 warning: prefix `kind` is unknown
   --> $DIR/reserved-prefixes-migration.rs:35:14
@@ -66,7 +66,7 @@ LL |     #name = #kind#value
 help: insert whitespace here to avoid this being parsed as a prefix in Rust 2021
    |
 LL |     #name = #kind #value
-   |
+   |                  +
 
 warning: 5 warnings emitted
 

src/test/ui/rust-2021/reserved-prefixes.stderr

@@ -8,7 +8,7 @@ LL |     demo3!(foo#bar);
 help: consider inserting whitespace here
    |
 LL |     demo3!(foo #bar);
-   |
+   |               +
 
 error: prefix `foo` is unknown
   --> $DIR/reserved-prefixes.rs:17:12
@@ -20,7 +20,7 @@ LL |     demo2!(foo"bar");
 help: consider inserting whitespace here
    |
 LL |     demo2!(foo "bar");
-   |
+   |               +
 
 error: prefix `foo` is unknown
   --> $DIR/reserved-prefixes.rs:18:12
@@ -32,7 +32,7 @@ LL |     demo2!(foo'b');
 help: consider inserting whitespace here
    |
 LL |     demo2!(foo 'b');
-   |
+   |               +
 
 error: prefix `foo` is unknown
   --> $DIR/reserved-prefixes.rs:20:12
@@ -44,7 +44,7 @@ LL |     demo2!(foo'b);
 help: consider inserting whitespace here
    |
 LL |     demo2!(foo 'b);
-   |
+   |               +
 
 error: prefix `foo` is unknown
   --> $DIR/reserved-prefixes.rs:21:12
@@ -56,7 +56,7 @@ LL |     demo3!(foo# bar);
 help: consider inserting whitespace here
    |
 LL |     demo3!(foo # bar);
-   |
+   |               +
 
 error: prefix `foo` is unknown
   --> $DIR/reserved-prefixes.rs:22:12
@@ -68,7 +68,7 @@ LL |     demo4!(foo#! bar);
 help: consider inserting whitespace here
    |
 LL |     demo4!(foo #! bar);
-   |
+   |               +
 
 error: prefix `foo` is unknown
   --> $DIR/reserved-prefixes.rs:23:12
@@ -80,7 +80,7 @@ LL |     demo4!(foo## bar);
 help: consider inserting whitespace here
    |
 LL |     demo4!(foo ## bar);
-   |
+   |               +
 
 error: prefix `foo` is unknown
   --> $DIR/reserved-prefixes.rs:25:12
@@ -92,7 +92,7 @@ LL |     demo4!(foo#bar#);
 help: consider inserting whitespace here
    |
 LL |     demo4!(foo #bar#);
-   |
+   |               +
 
 error: prefix `bar` is unknown
   --> $DIR/reserved-prefixes.rs:25:16
@@ -104,7 +104,7 @@ LL |     demo4!(foo#bar#);
 help: consider inserting whitespace here
    |
 LL |     demo4!(foo#bar #);
-   |
+   |                   +
 
 error: aborting due to 9 previous errors