Use underline suggestions for purely 'additive' replacements

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
 

tests/ui/borrowck/issue-62387-suggest-iter-mut-2.stderr

@@ -8,9 +8,8 @@ LL | vec.iter().flat_map(|container| container.things()).cloned().co
  |
 help: you may want to use `iter_mut` here
  |
-LL - vec.iter().flat_map(|container| container.things()).cloned().collect::<Vec<PathBuf>>();
-LL + vec.iter_mut().flat_map(|container| container.things()).cloned().collect::<Vec<PathBuf>>();
- |
+LL | vec.iter_mut().flat_map(|container| container.things()).cloned().collect::<Vec<PathBuf>>();
+ | ~~~~~~~~
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/issue-62387-suggest-iter-mut.stderr

@@ -8,9 +8,8 @@ LL | v.iter().for_each(|a| a.double());
  |
 help: you may want to use `iter_mut` here
  |
-LL - v.iter().for_each(|a| a.double());
-LL + v.iter_mut().for_each(|a| a.double());
- |
+LL | v.iter_mut().for_each(|a| a.double());
+ | ~~~~~~~~
 
 error[E0596]: cannot borrow `*a` as mutable, as it is behind a `&` reference
  --> $DIR/issue-62387-suggest-iter-mut.rs:25:39
@@ -22,9 +21,8 @@ LL | v.iter().rev().rev().for_each(|a| a.double());
  |
 help: you may want to use `iter_mut` here
  |
-LL - v.iter().rev().rev().for_each(|a| a.double());
-LL + v.iter_mut().rev().rev().for_each(|a| a.double());
- |
+LL | v.iter_mut().rev().rev().for_each(|a| a.double());
+ | ~~~~~~~~
 
 error: aborting due to 2 previous errors
 

tests/ui/c-variadic/issue-86053-1.stderr

@@ -63,9 +63,8 @@ LL | self , ... , self , self , ... ) where F : FnOnce ( & 'a & 'b usize
  |
 help: a trait with a similar name exists
  |
-LL - self , ... , self , self , ... ) where F : FnOnce ( & 'a & 'b usize ) {
-LL + self , ... , self , self , ... ) where Fn : FnOnce ( & 'a & 'b usize ) {
- |
+LL | self , ... , self , self , ... ) where Fn : FnOnce ( & 'a & 'b usize ) {
+ | ~~
 help: you might be missing a type parameter
  |
 LL | fn ordering4 < 'a , 'b, F > ( a : , self , self , self ,

tests/ui/cfg/cfg-method-receiver.stderr

@@ -16,9 +16,8 @@ LL | cbor_map! { #[cfg(test)] 4};
  = note: this error originates in the macro `cbor_map` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: you must specify a concrete type for this numeric value, like `i32`
  |
-LL - cbor_map! { #[cfg(test)] 4};
-LL + cbor_map! { #[cfg(test)] 4_i32};
- |
+LL | cbor_map! { #[cfg(test)] 4_i32};
+ | ~~~~~
 
 error: aborting due to 2 previous errors
 

tests/ui/check-cfg/diagnotics.cargo.stderr

@@ -17,9 +17,8 @@ LL | #[cfg(featur = "foo")]
  = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration
 help: there is a config with a similar name and value
  |
-LL - #[cfg(featur = "foo")]
-LL + #[cfg(feature = "foo")]
- |
+LL | #[cfg(feature = "foo")]
+ | ~~~~~~~
 
 warning: unexpected `cfg` condition name: `featur`
  --> $DIR/diagnotics.rs:17:7

tests/ui/check-cfg/diagnotics.rustc.stderr

@@ -19,9 +19,8 @@ LL | #[cfg(featur = "foo")]
  = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
 help: there is a config with a similar name and value
  |
-LL - #[cfg(featur = "foo")]
-LL + #[cfg(feature = "foo")]
- |
+LL | #[cfg(feature = "foo")]
+ | ~~~~~~~
 
 warning: unexpected `cfg` condition name: `featur`
  --> $DIR/diagnotics.rs:17:7

tests/ui/closures/2229_closure_analysis/bad-pattern.stderr

@@ -108,9 +108,8 @@ LL | let PAT = v1;
  = note: the matched value is of type `u32`
 help: introduce a variable instead
  |
-LL - let PAT = v1;
-LL + let PAT_var = v1;
- |
+LL | let PAT_var = v1;
+ | ~~~~~~~
 
 error: aborting due to 7 previous errors
 

tests/ui/closures/issue-78720.stderr

@@ -15,9 +15,8 @@ LL | _func: F,
  |
 help: a trait with a similar name exists
  |
-LL - _func: F,
-LL + _func: Fn,
- |
+LL | _func: Fn,
+ | ~~
 help: you might be missing a type parameter
  |
 LL | struct Map2<Segment2, F> {

tests/ui/compare-method/bad-self-type.stderr

@@ -8,9 +8,8 @@ LL | fn poll(self, _: &mut Context<'_>) -> Poll<()> {
  found signature `fn(MyFuture, &mut Context<'_>) -> Poll<_>`
 help: change the self-receiver type to match the trait
  |
-LL - fn poll(self, _: &mut Context<'_>) -> Poll<()> {
-LL + fn poll(self: Pin<&mut MyFuture>, _: &mut Context<'_>) -> Poll<()> {
- |
+LL | fn poll(self: Pin<&mut MyFuture>, _: &mut Context<'_>) -> Poll<()> {
+ | ~~~~~~~~~~~~~~~~~~~~~~~~
 
 error[E0053]: method `foo` has an incompatible type for trait
  --> $DIR/bad-self-type.rs:22:18

tests/ui/const-generics/ensure_is_evaluatable.stderr

@@ -14,9 +14,8 @@ LL | [(); N + 1]:,
  | ^^^^^ required by this bound in `bar`
 help: try adding a `where` bound
  |
-LL - [(); M + 1]:,
-LL + [(); M + 1]:, [(); N + 1]:
- |
+LL | [(); M + 1]:, [(); N + 1]:
+ | ~~~~~~~~~~~~~~
 
 error: aborting due to 1 previous error
 

tests/ui/const-generics/fn_with_two_const_inputs.stderr

@@ -14,9 +14,8 @@ LL | [(); N + 1]:,
  | ^^^^^ required by this bound in `bar`
 help: try adding a `where` bound
  |
-LL - [(); both(N + 1, M + 1)]:,
-LL + [(); both(N + 1, M + 1)]:, [(); N + 1]:
- |
+LL | [(); both(N + 1, M + 1)]:, [(); N + 1]:
+ | ~~~~~~~~~~~~~~
 
 error: aborting due to 1 previous error
 

tests/ui/const-generics/generic_const_exprs/abstract-const-as-cast-3.stderr

@@ -16,9 +16,8 @@ LL | fn assert_impl<T: Trait>() {}
  | ^^^^^ required by this bound in `assert_impl`
 help: try adding a `where` bound
  |
-LL - EvaluatableU128<{N as u128}>:, {
-LL + EvaluatableU128<{N as u128}>:, [(); { O as u128 } as usize]: {
- |
+LL | EvaluatableU128<{N as u128}>:, [(); { O as u128 } as usize]: {
+ | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 error[E0308]: mismatched types
  --> $DIR/abstract-const-as-cast-3.rs:17:5
@@ -52,9 +51,8 @@ LL | fn assert_impl<T: Trait>() {}
  | ^^^^^ required by this bound in `assert_impl`
 help: try adding a `where` bound
  |
-LL - EvaluatableU128<{N as u128}>:, {
-LL + EvaluatableU128<{N as u128}>:, [(); { O as u128 } as usize]: {
- |
+LL | EvaluatableU128<{N as u128}>:, [(); { O as u128 } as usize]: {
+ | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 error[E0308]: mismatched types
  --> $DIR/abstract-const-as-cast-3.rs:20:5
@@ -116,9 +114,8 @@ LL | fn assert_impl<T: Trait>() {}
  | ^^^^^ required by this bound in `assert_impl`
 help: try adding a `where` bound
  |
-LL - EvaluatableU128<{N as _}>:, {
-LL + EvaluatableU128<{N as _}>:, [(); { O as u128 } as usize]: {
- |
+LL | EvaluatableU128<{N as _}>:, [(); { O as u128 } as usize]: {
+ | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 error[E0308]: mismatched types
  --> $DIR/abstract-const-as-cast-3.rs:35:5
@@ -152,9 +149,8 @@ LL | fn assert_impl<T: Trait>() {}
  | ^^^^^ required by this bound in `assert_impl`
 help: try adding a `where` bound
  |
-LL - EvaluatableU128<{N as _}>:, {
-LL + EvaluatableU128<{N as _}>:, [(); { O as u128 } as usize]: {
- |
+LL | EvaluatableU128<{N as _}>:, [(); { O as u128 } as usize]: {
+ | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 error[E0308]: mismatched types
  --> $DIR/abstract-const-as-cast-3.rs:38:5

tests/ui/const-generics/generic_const_exprs/assoc_const_unification/doesnt_unify_evaluatable.stderr

@@ -6,9 +6,8 @@ LL | bar::<{ T::ASSOC }>();
  |
 help: try adding a `where` bound
  |
-LL - fn foo<T: Trait, U: Trait>() where [(); U::ASSOC]:, {
-LL + fn foo<T: Trait, U: Trait>() where [(); U::ASSOC]:, [(); { T::ASSOC }]: {
- |
+LL | fn foo<T: Trait, U: Trait>() where [(); U::ASSOC]:, [(); { T::ASSOC }]: {
+ | ~~~~~~~~~~~~~~~~~~~~~
 
 error: aborting due to 1 previous error
 

tests/ui/const-generics/generic_const_exprs/const_kind_expr/issue_114151.stderr

@@ -26,9 +26,8 @@ LL | foo::<_, L>([(); L + 1 + L]);
  |
 help: try adding a `where` bound
  |
-LL - [(); (L - 1) + 1 + L]:,
-LL + [(); (L - 1) + 1 + L]:, [(); L + 1 + L]:
- |
+LL | [(); (L - 1) + 1 + L]:, [(); L + 1 + L]:
+ | ~~~~~~~~~~~~~~~~~~
 
 error: unconstrained generic constant
  --> $DIR/issue_114151.rs:17:17

tests/ui/const-generics/generic_const_exprs/const_kind_expr/wf_obligation.stderr

@@ -15,9 +15,8 @@ LL | foo::<_, L>([(); L + 1 + L]);
  |
 help: try adding a `where` bound
  |
-LL - [(); (L - 1) + 1 + L]:,
-LL + [(); (L - 1) + 1 + L]:, [(); L + 1 + L]:
- |
+LL | [(); (L - 1) + 1 + L]:, [(); L + 1 + L]:
+ | ~~~~~~~~~~~~~~~~~~
 
 error: aborting due to 2 previous errors
 

tests/ui/const-generics/generic_const_exprs/expected-type-of-closure-body-to-be-a-closure-or-coroutine-ice-113776.stderr

@@ -9,9 +9,8 @@ LL | let f: F = async { 1 };
  |
 help: a trait with a similar name exists
  |
-LL - let f: F = async { 1 };
-LL + let f: Fn = async { 1 };
- |
+LL | let f: Fn = async { 1 };
+ | ~~
 help: you might be missing a type parameter
  |
 LL | fn f<T, F>(