address review comments + better tests

2 files changed, 20 insertions, 4 deletions

diff --git a/compiler/rustc_ast_lowering/src/item.rs b/compiler/rustc_ast_lowering/src/item.rs
index bda914d2888..294ffec8a5e 100644
--- a/compiler/rustc_ast_lowering/src/item.rs
+++ b/compiler/rustc_ast_lowering/src/item.rs
@@ -1316,6 +1316,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 param.id,
                 &param.kind,
                 &param.bounds,
+                param.colon_span,
+                generics.span,
                 itctx,
                 PredicateOrigin::GenericParam,
             )
@@ -1365,6 +1367,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
         id: NodeId,
         kind: &GenericParamKind,
         bounds: &[GenericBound],
+        colon_span: Option<Span>,
+        parent_span: Span,
         itctx: &ImplTraitContext,
         origin: PredicateOrigin,
     ) -> Option<hir::WherePredicate<'hir>> {
@@ -1377,8 +1381,17 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
         let ident = self.lower_ident(ident);
         let param_span = ident.span;
-        let span =
-            bounds.iter().fold(param_span.shrink_to_hi(), |span, bound| span.to(bound.span()));
+
+        // Reconstruct the span of the entire predicate from the individual generic bounds.
+        let span_start = colon_span.unwrap_or_else(|| param_span.shrink_to_hi());
+        let span = bounds.iter().fold(span_start, |span_accum, bound| {
+            match bound.span().find_ancestor_inside(parent_span) {
+                Some(bound_span) => span_accum.to(bound_span),
+                None => span_accum,
+            }
+        });
+        let span = self.lower_span(span);
+
         match kind {
             GenericParamKind::Const { .. } => None,
             GenericParamKind::Type { .. } => {
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index 0ef784a4453..a2b0f112e3b 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -2247,6 +2247,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     ) -> (hir::GenericParam<'hir>, Option<hir::WherePredicate<'hir>>, hir::TyKind<'hir>) {
         // Add a definition for the in-band `Param`.
         let def_id = self.local_def_id(node_id);
+        let span = self.lower_span(span);
 
         // Set the name to `impl Bound1 + Bound2`.
         let param = hir::GenericParam {
@@ -2254,7 +2255,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             def_id,
             name: ParamName::Plain(self.lower_ident(ident)),
             pure_wrt_drop: false,
-            span: self.lower_span(span),
+            span,
             kind: hir::GenericParamKind::Type { default: None, synthetic: true },
             colon_span: None,
         };
@@ -2264,6 +2265,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             node_id,
             &GenericParamKind::Type { default: None },
             bounds,
+            /* colon_span */ None,
+            span,
             &ImplTraitContext::Universal,
             hir::PredicateOrigin::ImplTrait,
         );
@@ -2273,7 +2276,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         let ty = hir::TyKind::Path(hir::QPath::Resolved(
             None,
             self.arena.alloc(hir::Path {
-                span: self.lower_span(span),
+                span,
                 res,
                 segments:
                     arena_vec![self; hir::PathSegment::new(self.lower_ident(ident), hir_id, res)],