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])
     }

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 => "`..=` range",
             DesugaringKind::BoundModifier => "trait bound modifier",
             DesugaringKind::Contract => "contract check",
         }