Use underline suggestions for purely 'additive' replacements

Author: compiler-errors

compiler/rustc_errors/src/emitter.rs

@@ -1982,7 +1982,8 @@ impl HumanEmitter {
         {
             debug!(?complete, ?parts, ?highlights);
 
-            let has_deletion = parts.iter().any(|p| p.is_deletion(sm) || p.is_replacement(sm));
+            let has_deletion =
+                parts.iter().any(|p| p.is_deletion(sm) || p.is_destructive_replacement(sm));
             let is_multiline = complete.lines().count() > 1;
 
             if i == 0 {

compiler/rustc_errors/src/lib.rs

@@ -230,6 +230,17 @@ impl SubstitutionPart {
         !self.snippet.is_empty() && self.replaces_meaningful_content(sm)
     }
 
+    /// Whether this is a replacement that overwrites source with a snippet
+    /// in a way that isn't a superset of the original string. For example,
+    /// replacing "abc" with "abcde" is not destructive, but replacing it
+    /// it with "abx" is, since the "c" character is lost.
+    pub fn is_destructive_replacement(&self, sm: &SourceMap) -> bool {
+        self.is_replacement(sm)
+            && !sm
+                .span_to_snippet(self.span)
+                .is_ok_and(|snippet| self.snippet.trim_start().starts_with(snippet.trim_start()))
+    }
+
     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())

tests/ui/associated-types/defaults-suitability.current.stderr

@@ -134,9 +134,8 @@ LL |     type Baz = T;
    |          --- required by a bound in this associated type
 help: consider further restricting type parameter `T` with trait `Clone`
    |
-LL -     Self::Baz: Clone,
-LL +     Self::Baz: Clone, T: std::clone::Clone
-   |
+LL |     Self::Baz: Clone, T: std::clone::Clone
+   |                     ~~~~~~~~~~~~~~~~~~~~~~
 
 error: aborting due to 8 previous errors
 

tests/ui/associated-types/defaults-suitability.next.stderr

@@ -134,9 +134,8 @@ LL |     type Baz = T;
    |          --- required by a bound in this associated type
 help: consider further restricting type parameter `T` with trait `Clone`
    |
-LL -     Self::Baz: Clone,
-LL +     Self::Baz: Clone, T: std::clone::Clone
-   |
+LL |     Self::Baz: Clone, T: std::clone::Clone
+   |                     ~~~~~~~~~~~~~~~~~~~~~~
 
 error: aborting due to 8 previous errors
 

tests/ui/associated-types/issue-38821.stderr

@@ -13,9 +13,8 @@ LL | impl<T: NotNull> IntoNullable for T {
    |         unsatisfied trait bound introduced here
 help: consider extending the `where` clause, but there might be an alternative better way to express this requirement
    |
-LL -     Expr: Expression<SqlType=<Col::SqlType as IntoNullable>::Nullable>,
-LL +     Expr: Expression<SqlType=<Col::SqlType as IntoNullable>::Nullable>, <Col as Expression>::SqlType: NotNull
-   |
+LL |     Expr: Expression<SqlType=<Col::SqlType as IntoNullable>::Nullable>, <Col as Expression>::SqlType: NotNull
+   |                                                                       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 error[E0277]: the trait bound `<Col as Expression>::SqlType: NotNull` is not satisfied
   --> $DIR/issue-38821.rs:40:1
@@ -38,9 +37,8 @@ LL | impl<T: NotNull> IntoNullable for T {
    |         unsatisfied trait bound introduced here
 help: consider extending the `where` clause, but there might be an alternative better way to express this requirement
    |
-LL -     Expr: Expression<SqlType=<Col::SqlType as IntoNullable>::Nullable>,
-LL +     Expr: Expression<SqlType=<Col::SqlType as IntoNullable>::Nullable>, <Col as Expression>::SqlType: NotNull
-   |
+LL |     Expr: Expression<SqlType=<Col::SqlType as IntoNullable>::Nullable>, <Col as Expression>::SqlType: NotNull
+   |                                                                       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 error[E0277]: the trait bound `<Col as Expression>::SqlType: NotNull` is not satisfied
   --> $DIR/issue-38821.rs:23:10

tests/ui/associated-types/issue-54108.current.stderr

@@ -12,9 +12,8 @@ LL |     type Size: Add<Output = Self::Size>;
    |                ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Encoder::Size`
 help: consider further restricting the associated type
    |
-LL -     T: SubEncoder,
-LL +     T: SubEncoder, <T as SubEncoder>::ActualSize: Add
-   |
+LL |     T: SubEncoder, <T as SubEncoder>::ActualSize: Add
+   |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 error: aborting due to 1 previous error
 

tests/ui/associated-types/issue-54108.next.stderr

@@ -12,9 +12,8 @@ LL |     type Size: Add<Output = Self::Size>;
    |                    ^^^^^^^^^^^^^^^^^^^ required by this bound in `Encoder::Size`
 help: consider further restricting the associated type
    |
-LL -     T: SubEncoder,
-LL +     T: SubEncoder, <T as SubEncoder>::ActualSize: Add
-   |
+LL |     T: SubEncoder, <T as SubEncoder>::ActualSize: Add
+   |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 error: aborting due to 1 previous error
 

tests/ui/attributes/rustc_confusables.stderr

@@ -35,9 +35,8 @@ LL |     x.inser();
    |
 help: there is a method `insert` with a similar name
    |
-LL -     x.inser();
-LL +     x.insert();
-   |
+LL |     x.insert();
+   |       ~~~~~~
 
 error[E0599]: no method named `foo` found for struct `rustc_confusables_across_crate::BTreeSet` in the current scope
   --> $DIR/rustc_confusables.rs:15:7

tests/ui/attributes/rustc_confusables_std_cases.stderr

@@ -38,9 +38,8 @@ LL |     let mut x = VecDeque::new();
    |         ----- earlier `x` shadowed here with type `VecDeque`
 help: you might have meant to use `push_back`
    |
-LL -     x.push(1);
-LL +     x.push_back(1);
-   |
+LL |     x.push_back(1);
+   |       ~~~~~~~~~
 
 error[E0599]: no method named `length` found for struct `Vec<{integer}>` in the current scope
   --> $DIR/rustc_confusables_std_cases.rs:15:7
@@ -98,9 +97,8 @@ note: method defined here
   --> $SRC_DIR/alloc/src/string.rs:LL:COL
 help: you might have meant to use `push_str`
    |
-LL -     String::new().push("");
-LL +     String::new().push_str("");
-   |
+LL |     String::new().push_str("");
+   |                   ~~~~~~~~
 
 error[E0599]: no method named `append` found for struct `String` in the current scope
   --> $DIR/rustc_confusables_std_cases.rs:24:19

tests/ui/borrowck/issue-115259-suggest-iter-mut.stderr

@@ -8,9 +8,8 @@ LL |         self.layers.iter().fold(0, |result, mut layer| result + layer.proce
    |
 help: you may want to use `iter_mut` here
    |
-LL -         self.layers.iter().fold(0, |result, mut layer| result + layer.process())
-LL +         self.layers.iter_mut().fold(0, |result, mut layer| result + layer.process())
-   |
+LL |         self.layers.iter_mut().fold(0, |result, mut layer| result + layer.process())
+   |                     ~~~~~~~~
 
 error: aborting due to 1 previous error