Mark desugaring of ..= as such when lowering

Author: samueltardieu

compiler/rustc_ast_lowering/src/expr.rs

@@ -1523,7 +1523,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
     fn lower_expr_range_closed(&mut self, span: Span, e1: &Expr, e2: &Expr) -> hir::ExprKind<'hir> {
         let e1 = self.lower_expr_mut(e1);
         let e2 = self.lower_expr_mut(e2);
-        let fn_path = hir::QPath::LangItem(hir::LangItem::RangeInclusiveNew, self.lower_span(span));
+        let span = self.mark_span_with_reason(DesugaringKind::Range, self.lower_span(span), None);
+        let fn_path = hir::QPath::LangItem(hir::LangItem::RangeInclusiveNew, span);
         let fn_expr = self.arena.alloc(self.expr(span, hir::ExprKind::Path(fn_path)));
         hir::ExprKind::Call(fn_expr, arena_vec![self; e1, e2])
     }
@@ -1581,14 +1582,21 @@ impl<'hir> LoweringContext<'_, 'hir> {
             e1.iter().map(|e| (sym::start, e)).chain(e2.iter().map(|e| (sym::end, e))).map(
                 |(s, e)| {
                     let expr = self.lower_expr(e);
-                    let ident = Ident::new(s, self.lower_span(e.span));
-                    self.expr_field(ident, expr, e.span)
+                    let field_span = self.mark_span_with_reason(
+                        DesugaringKind::Range,
+                        self.lower_span(e.span),
+                        None,
+                    );
+                    let ident = Ident::new(s, field_span);
+                    self.expr_field(ident, expr, field_span)
                 },
             ),
         );
 
+        let struct_span =
+            self.mark_span_with_reason(DesugaringKind::Range, self.lower_span(span), None);
         hir::ExprKind::Struct(
-            self.arena.alloc(hir::QPath::LangItem(lang_item, self.lower_span(span))),
+            self.arena.alloc(hir::QPath::LangItem(lang_item, struct_span)),
             fields,
             hir::StructTailExpr::None,
         )
@@ -2299,16 +2307,16 @@ impl<'hir> LoweringContext<'_, 'hir> {
         hir::Expr { hir_id, kind, span: self.lower_span(span) }
     }
 
-    pub(super) fn expr_field(
+    fn expr_field(
         &mut self,
         ident: Ident,
         expr: &'hir hir::Expr<'hir>,
-        span: Span,
+        lowered_span: Span,
     ) -> hir::ExprField<'hir> {
         hir::ExprField {
             hir_id: self.next_id(),
             ident,
-            span: self.lower_span(span),
+            span: lowered_span,
             expr,
             is_shorthand: false,
         }

compiler/rustc_span/src/hygiene.rs

@@ -1162,6 +1162,7 @@ pub enum DesugaringKind {
     Await,
     ForLoop,
     WhileLoop,
+    Range,
     /// `async Fn()` bound modifier
     BoundModifier,
     /// Calls to contract checks (`#[requires]` to precond, `#[ensures]` to postcond)
@@ -1181,6 +1182,7 @@ impl DesugaringKind {
             DesugaringKind::OpaqueTy => "`impl Trait`",
             DesugaringKind::ForLoop => "`for` loop",
             DesugaringKind::WhileLoop => "`while` loop",
+            DesugaringKind::Range => "`..` or `..=` range",
             DesugaringKind::BoundModifier => "trait bound modifier",
             DesugaringKind::Contract => "contract check",
         }