A SubstitutionPart is not considered a deletion if it replaces nothing with nothing

compiler/rustc_errors/src/emitter.rs

@@ -1704,7 +1704,7 @@ impl EmitterWriter {
         {
             notice_capitalization |= only_capitalization;
 
-            let has_deletion = parts.iter().any(|p| p.is_deletion());
+            let has_deletion = parts.iter().any(|p| p.is_deletion(sm));
             let is_multiline = complete.lines().count() > 1;
 
             if let Some(span) = span.primary_span() {
@@ -1880,16 +1880,23 @@ impl EmitterWriter {
                     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
-                        .snippet
-                        .trim()
-                        .chars()
-                        .map(|ch| unicode_width::UnicodeWidthChar::width(ch).unwrap_or(1))
-                        .sum();
+                    let sub_len: usize =
+                        if is_whitespace_addition { &part.snippet } else { part.snippet.trim() }
+                            .chars()
+                            .map(|ch| unicode_width::UnicodeWidthChar::width(ch).unwrap_or(1))
+                            .sum();
 
                     let offset: isize = offsets
                         .iter()
@@ -2130,7 +2137,7 @@ impl EmitterWriter {
     }
 }
 
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, Debug)]
 enum DisplaySuggestion {
     Underline,
     Diff,

compiler/rustc_errors/src/lib.rs

@@ -150,21 +150,20 @@ pub struct SubstitutionHighlight {
 
 impl SubstitutionPart {
     pub fn is_addition(&self, sm: &SourceMap) -> bool {
-        !self.snippet.is_empty()
-            && sm
-                .span_to_snippet(self.span)
-                .map_or(self.span.is_empty(), |snippet| snippet.trim().is_empty())
+        !self.snippet.is_empty() && !self.replaces_meaningful_content(sm)
     }
 
-    pub fn is_deletion(&self) -> bool {
-        self.snippet.trim().is_empty()
+    pub fn is_deletion(&self, sm: &SourceMap) -> bool {
+        self.snippet.trim().is_empty() && self.replaces_meaningful_content(sm)
     }
 
     pub fn is_replacement(&self, sm: &SourceMap) -> bool {
-        !self.snippet.is_empty()
-            && sm
-                .span_to_snippet(self.span)
-                .map_or(!self.span.is_empty(), |snippet| !snippet.trim().is_empty())
+        !self.snippet.is_empty() && self.replaces_meaningful_content(sm)
+    }
+
+    fn replaces_meaningful_content(&self, sm: &SourceMap) -> bool {
+        sm.span_to_snippet(self.span)
+            .map_or(!self.span.is_empty(), |snippet| !snippet.trim().is_empty())
     }
 }
 

src/test/ui/dyn-keyword/dyn-2018-edition-lint.stderr

@@ -13,9 +13,8 @@ LL | #[deny(bare_trait_objects)]
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - fn function(x: &SomeTrait, y: Box<SomeTrait>) {
-LL + fn function(x: &dyn SomeTrait, y: Box<SomeTrait>) {
-   |
+LL | fn function(x: &dyn SomeTrait, y: Box<SomeTrait>) {
+   |                 +++
 
 error: trait objects without an explicit `dyn` are deprecated
   --> $DIR/dyn-2018-edition-lint.rs:4:35
@@ -27,9 +26,8 @@ LL | fn function(x: &SomeTrait, y: Box<SomeTrait>) {
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - fn function(x: &SomeTrait, y: Box<SomeTrait>) {
-LL + fn function(x: &SomeTrait, y: Box<dyn SomeTrait>) {
-   |
+LL | fn function(x: &SomeTrait, y: Box<dyn SomeTrait>) {
+   |                                   +++
 
 error: trait objects without an explicit `dyn` are deprecated
   --> $DIR/dyn-2018-edition-lint.rs:17:14
@@ -41,9 +39,8 @@ LL |     let _x: &SomeTrait = todo!();
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL -     let _x: &SomeTrait = todo!();
-LL +     let _x: &dyn SomeTrait = todo!();
-   |
+LL |     let _x: &dyn SomeTrait = todo!();
+   |              +++
 
 error: trait objects without an explicit `dyn` are deprecated
   --> $DIR/dyn-2018-edition-lint.rs:4:17
@@ -55,9 +52,8 @@ LL | fn function(x: &SomeTrait, y: Box<SomeTrait>) {
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - fn function(x: &SomeTrait, y: Box<SomeTrait>) {
-LL + fn function(x: &dyn SomeTrait, y: Box<SomeTrait>) {
-   |
+LL | fn function(x: &dyn SomeTrait, y: Box<SomeTrait>) {
+   |                 +++
 
 error: trait objects without an explicit `dyn` are deprecated
   --> $DIR/dyn-2018-edition-lint.rs:4:17
@@ -69,9 +65,8 @@ LL | fn function(x: &SomeTrait, y: Box<SomeTrait>) {
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - fn function(x: &SomeTrait, y: Box<SomeTrait>) {
-LL + fn function(x: &dyn SomeTrait, y: Box<SomeTrait>) {
-   |
+LL | fn function(x: &dyn SomeTrait, y: Box<SomeTrait>) {
+   |                 +++
 
 error: trait objects without an explicit `dyn` are deprecated
   --> $DIR/dyn-2018-edition-lint.rs:4:35
@@ -83,9 +78,8 @@ LL | fn function(x: &SomeTrait, y: Box<SomeTrait>) {
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - fn function(x: &SomeTrait, y: Box<SomeTrait>) {
-LL + fn function(x: &SomeTrait, y: Box<dyn SomeTrait>) {
-   |
+LL | fn function(x: &SomeTrait, y: Box<dyn SomeTrait>) {
+   |                                   +++
 
 error: trait objects without an explicit `dyn` are deprecated
   --> $DIR/dyn-2018-edition-lint.rs:4:35
@@ -97,9 +91,8 @@ LL | fn function(x: &SomeTrait, y: Box<SomeTrait>) {
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - fn function(x: &SomeTrait, y: Box<SomeTrait>) {
-LL + fn function(x: &SomeTrait, y: Box<dyn SomeTrait>) {
-   |
+LL | fn function(x: &SomeTrait, y: Box<dyn SomeTrait>) {
+   |                                   +++
 
 error: aborting due to 7 previous errors
 

src/test/ui/dyn-keyword/dyn-2021-edition-error.stderr

@@ -6,9 +6,8 @@ LL | fn function(x: &SomeTrait, y: Box<SomeTrait>) {
    |
 help: add `dyn` keyword before this trait
    |
-LL - fn function(x: &SomeTrait, y: Box<SomeTrait>) {
-LL + fn function(x: &dyn SomeTrait, y: Box<SomeTrait>) {
-   |
+LL | fn function(x: &dyn SomeTrait, y: Box<SomeTrait>) {
+   |                 +++
 
 error[E0782]: trait objects must include the `dyn` keyword
   --> $DIR/dyn-2021-edition-error.rs:3:35
@@ -18,9 +17,8 @@ LL | fn function(x: &SomeTrait, y: Box<SomeTrait>) {
    |
 help: add `dyn` keyword before this trait
    |
-LL - fn function(x: &SomeTrait, y: Box<SomeTrait>) {
-LL + fn function(x: &SomeTrait, y: Box<dyn SomeTrait>) {
-   |
+LL | fn function(x: &SomeTrait, y: Box<dyn SomeTrait>) {
+   |                                   +++
 
 error: aborting due to 2 previous errors
 

src/test/ui/dyn-keyword/dyn-angle-brackets.stderr

@@ -13,9 +13,8 @@ LL | #![deny(bare_trait_objects)]
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL -         <fmt::Debug>::fmt(self, f)
-LL +         <dyn fmt::Debug>::fmt(self, f)
-   |
+LL |         <dyn fmt::Debug>::fmt(self, f)
+   |          +++
 
 error: aborting due to previous error
 

src/test/ui/impl-trait/generic-with-implicit-hrtb-without-dyn.edition2021.stderr

@@ -6,9 +6,8 @@ LL | fn ice() -> impl AsRef<Fn(&())> {
    |
 help: add `dyn` keyword before this trait
    |
-LL - fn ice() -> impl AsRef<Fn(&())> {
-LL + fn ice() -> impl AsRef<dyn Fn(&())> {
-   |
+LL | fn ice() -> impl AsRef<dyn Fn(&())> {
+   |                        +++
 
 error[E0277]: the trait bound `(): AsRef<(dyn for<'r> Fn(&'r ()) + 'static)>` is not satisfied
   --> $DIR/generic-with-implicit-hrtb-without-dyn.rs:6:13

src/test/ui/issues/issue-86756.stderr

@@ -25,9 +25,8 @@ LL |     eq::<dyn, Foo>
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL -     eq::<dyn, Foo>
-LL +     eq::<dyn, dyn Foo>
-   |
+LL |     eq::<dyn, dyn Foo>
+   |               +++
 
 error[E0107]: missing generics for trait `Foo`
   --> $DIR/issue-86756.rs:5:15

src/test/ui/lint/force-warn/allowed-group-warn-by-default-lint.stderr

@@ -9,9 +9,8 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - pub fn function(_x: Box<SomeTrait>) {}
-LL + pub fn function(_x: Box<dyn SomeTrait>) {}
-   |
+LL | pub fn function(_x: Box<dyn SomeTrait>) {}
+   |                         +++
 
 warning: trait objects without an explicit `dyn` are deprecated
   --> $DIR/allowed-group-warn-by-default-lint.rs:10:25
@@ -23,9 +22,8 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - pub fn function(_x: Box<SomeTrait>) {}
-LL + pub fn function(_x: Box<dyn SomeTrait>) {}
-   |
+LL | pub fn function(_x: Box<dyn SomeTrait>) {}
+   |                         +++
 
 warning: trait objects without an explicit `dyn` are deprecated
   --> $DIR/allowed-group-warn-by-default-lint.rs:10:25
@@ -37,9 +35,8 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - pub fn function(_x: Box<SomeTrait>) {}
-LL + pub fn function(_x: Box<dyn SomeTrait>) {}
-   |
+LL | pub fn function(_x: Box<dyn SomeTrait>) {}
+   |                         +++
 
 warning: 3 warnings emitted
 

src/test/ui/lint/force-warn/cap-lints-allow.stderr

@@ -9,9 +9,8 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - pub fn function(_x: Box<SomeTrait>) {}
-LL + pub fn function(_x: Box<dyn SomeTrait>) {}
-   |
+LL | pub fn function(_x: Box<dyn SomeTrait>) {}
+   |                         +++
 
 warning: trait objects without an explicit `dyn` are deprecated
   --> $DIR/cap-lints-allow.rs:8:25
@@ -23,9 +22,8 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - pub fn function(_x: Box<SomeTrait>) {}
-LL + pub fn function(_x: Box<dyn SomeTrait>) {}
-   |
+LL | pub fn function(_x: Box<dyn SomeTrait>) {}
+   |                         +++
 
 warning: trait objects without an explicit `dyn` are deprecated
   --> $DIR/cap-lints-allow.rs:8:25
@@ -37,9 +35,8 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - pub fn function(_x: Box<SomeTrait>) {}
-LL + pub fn function(_x: Box<dyn SomeTrait>) {}
-   |
+LL | pub fn function(_x: Box<dyn SomeTrait>) {}
+   |                         +++
 
 warning: 3 warnings emitted
 

src/test/ui/lint/force-warn/lint-group-allowed-cli-warn-by-default-lint.stderr

@@ -9,9 +9,8 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - pub fn function(_x: Box<SomeTrait>) {}
-LL + pub fn function(_x: Box<dyn SomeTrait>) {}
-   |
+LL | pub fn function(_x: Box<dyn SomeTrait>) {}
+   |                         +++
 
 warning: trait objects without an explicit `dyn` are deprecated
   --> $DIR/lint-group-allowed-cli-warn-by-default-lint.rs:8:25
@@ -23,9 +22,8 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - pub fn function(_x: Box<SomeTrait>) {}
-LL + pub fn function(_x: Box<dyn SomeTrait>) {}
-   |
+LL | pub fn function(_x: Box<dyn SomeTrait>) {}
+   |                         +++
 
 warning: trait objects without an explicit `dyn` are deprecated
   --> $DIR/lint-group-allowed-cli-warn-by-default-lint.rs:8:25
@@ -37,9 +35,8 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - pub fn function(_x: Box<SomeTrait>) {}
-LL + pub fn function(_x: Box<dyn SomeTrait>) {}
-   |
+LL | pub fn function(_x: Box<dyn SomeTrait>) {}
+   |                         +++
 
 warning: 3 warnings emitted
 

src/test/ui/lint/force-warn/lint-group-allowed-lint-group.stderr

@@ -9,9 +9,8 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - pub fn function(_x: Box<SomeTrait>) {}
-LL + pub fn function(_x: Box<dyn SomeTrait>) {}
-   |
+LL | pub fn function(_x: Box<dyn SomeTrait>) {}
+   |                         +++
 
 warning: trait objects without an explicit `dyn` are deprecated
   --> $DIR/lint-group-allowed-lint-group.rs:10:25
@@ -23,9 +22,8 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - pub fn function(_x: Box<SomeTrait>) {}
-LL + pub fn function(_x: Box<dyn SomeTrait>) {}
-   |
+LL | pub fn function(_x: Box<dyn SomeTrait>) {}
+   |                         +++
 
 warning: trait objects without an explicit `dyn` are deprecated
   --> $DIR/lint-group-allowed-lint-group.rs:10:25
@@ -37,9 +35,8 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
 help: use `dyn`
    |
-LL - pub fn function(_x: Box<SomeTrait>) {}
-LL + pub fn function(_x: Box<dyn SomeTrait>) {}
-   |
+LL | pub fn function(_x: Box<dyn SomeTrait>) {}
+   |                         +++
 
 warning: 3 warnings emitted