Using index's span when inference of recv failed when calling method on result of index op

Author: mu001999

compiler/rustc_hir_typeck/src/expr.rs

@@ -1330,7 +1330,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ) -> Ty<'tcx> {
         let rcvr_t = self.check_expr(rcvr);
         // no need to check for bot/err -- callee does that
-        let rcvr_t = self.structurally_resolve_type(rcvr.span, rcvr_t);
+        let rcvr_t = if let ExprKind::Index(_, index, _) = rcvr.kind {
+            self.structurally_resolve_type(index.span, rcvr_t)
+        } else {
+            self.structurally_resolve_type(rcvr.span, rcvr_t)
+        };
         let span = segment.ident.span;
 
         let method = match self.lookup_method(rcvr_t, segment, span, expr, rcvr, args) {

tests/ui/inference/need_type_info/calling-method-on-result-of-index-op-issue-125924.rs

@@ -0,0 +1,13 @@
+struct Foo;
+
+impl Foo {
+    fn foo(&self) {}
+}
+
+fn main() {
+    let thing: Vec<Foo> = vec![];
+
+    let foo = |i| {
+        thing[i].foo(); //~ ERROR type annotations needed
+    };
+}

tests/ui/inference/need_type_info/calling-method-on-result-of-index-op-issue-125924.stderr

@@ -0,0 +1,9 @@
+error[E0282]: type annotations needed
+  --> $DIR/calling-method-on-result-of-index-op-issue-125924.rs:11:15
+   |
+LL |         thing[i].foo();
+   |               ^ cannot infer type
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0282`.