Use inner ctxt when lowering ExprKind::Paren

Author: camsteffen

compiler/rustc_ast_lowering/src/expr.rs

@@ -272,8 +272,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 ExprKind::Paren(ref ex) => {
                     let mut ex = self.lower_expr_mut(ex);
                     // Include parens in span, but only if it is a super-span.
+                    // Use the inner ctxt to maintain desugaring marker for `(a..b)`
                     if e.span.contains(ex.span) {
-                        ex.span = self.lower_span(e.span);
+                        ex.span = self.lower_span(e.span.with_ctxt(ex.span.ctxt()));
                     }
                     // Merge attributes into the inner expression.
                     if !e.attrs.is_empty() {

src/test/ui/iterators/collect-into-array.stderr

@@ -1,10 +1,10 @@
 error[E0277]: an array of type `[u32; 10]` cannot be built directly from an iterator
-  --> $DIR/collect-into-array.rs:3:31
+  --> $DIR/collect-into-array.rs:3:32
    |
 LL |     let whatever: [u32; 10] = (0..10).collect();
-   |                               ^^^^^^^ ------- required by a bound introduced by this call
-   |                               |
-   |                               try collecting into a `Vec<{integer}>`, then using `.try_into()`
+   |                                ^^^^^  ------- required by a bound introduced by this call
+   |                                |
+   |                                try collecting into a `Vec<{integer}>`, then using `.try_into()`
    |
    = help: the trait `FromIterator<{integer}>` is not implemented for `[u32; 10]`
 note: required by a bound in `collect`

src/test/ui/iterators/collect-into-slice.stderr

@@ -22,12 +22,12 @@ LL |     fn collect<B: FromIterator<Self::Item>>(self) -> B
    |                ^ required by this bound in `collect`
 
 error[E0277]: a slice of type `[i32]` cannot be built since `[i32]` has no definite size
-  --> $DIR/collect-into-slice.rs:8:30
+  --> $DIR/collect-into-slice.rs:8:31
    |
 LL |     let some_generated_vec = (0..10).collect();
-   |                              ^^^^^^^ ------- required by a bound introduced by this call
-   |                              |
-   |                              try explicitly collecting into a `Vec<{integer}>`
+   |                               ^^^^^  ------- required by a bound introduced by this call
+   |                               |
+   |                               try explicitly collecting into a `Vec<{integer}>`
    |
    = help: the trait `FromIterator<{integer}>` is not implemented for `[i32]`
 note: required by a bound in `collect`