From e9215bb7a97d61b5368f58fa299474a8606655d4 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Sun, 22 May 2022 21:42:01 -0700
Subject: [PATCH] Do writeback of child expressions before parent expression

---
 compiler/rustc_typeck/src/check/writeback.rs  |  3 +-
 .../type-check/unknown_type_for_closure.rs    | 18 ++++++++++--
 .../unknown_type_for_closure.stderr           | 29 +++++++++++++++++--
 3 files changed, 43 insertions(+), 7 deletions(-)

diff --git a/compiler/rustc_typeck/src/check/writeback.rs b/compiler/rustc_typeck/src/check/writeback.rs
index 16096ea3d74..4fe5b26dc05 100644
--- a/compiler/rustc_typeck/src/check/writeback.rs
+++ b/compiler/rustc_typeck/src/check/writeback.rs
@@ -263,8 +263,6 @@ impl<'cx, 'tcx> Visitor<'tcx> for WritebackCx<'cx, 'tcx> {
         self.fix_scalar_builtin_expr(e);
         self.fix_index_builtin_expr(e);
 
-        self.visit_node_id(e.span, e.hir_id);
-
         match e.kind {
             hir::ExprKind::Closure(_, _, body, _, _) => {
                 let body = self.fcx.tcx.hir().body(body);
@@ -291,6 +289,7 @@ impl<'cx, 'tcx> Visitor<'tcx> for WritebackCx<'cx, 'tcx> {
             _ => {}
         }
 
+        self.visit_node_id(e.span, e.hir_id);
         intravisit::walk_expr(self, e);
     }
 
diff --git a/src/test/ui/type/type-check/unknown_type_for_closure.rs b/src/test/ui/type/type-check/unknown_type_for_closure.rs
index 0dbf82453a2..0089d86e340 100644
--- a/src/test/ui/type/type-check/unknown_type_for_closure.rs
+++ b/src/test/ui/type/type-check/unknown_type_for_closure.rs
@@ -1,3 +1,17 @@
-fn main() {
-    let x = |_| {    }; //~ ERROR type annotations needed
+fn infer_in_arg() {
+    let x = |b: Vec<_>| {}; //~ ERROR E0282
 }
+
+fn empty_pattern() {
+    let x = |_| {}; //~ ERROR type annotations needed
+}
+
+fn infer_ty() {
+    let x = |k: _| {}; //~ ERROR type annotations needed
+}
+
+fn ambig_return() {
+    let x = || -> Vec<_> { Vec::new() }; //~ ERROR type annotations needed for the closure `fn() -> Vec<_>`
+}
+
+fn main() {}
diff --git a/src/test/ui/type/type-check/unknown_type_for_closure.stderr b/src/test/ui/type/type-check/unknown_type_for_closure.stderr
index 5971f56c97f..c3accad5f25 100644
--- a/src/test/ui/type/type-check/unknown_type_for_closure.stderr
+++ b/src/test/ui/type/type-check/unknown_type_for_closure.stderr
@@ -1,9 +1,32 @@
-error[E0282]: type annotations needed
+error[E0282]: type annotations needed for `Vec<_>`
   --> $DIR/unknown_type_for_closure.rs:2:14
    |
-LL |     let x = |_| {    };
+LL |     let x = |b: Vec<_>| {};
    |              ^ consider giving this closure parameter a type
 
-error: aborting due to previous error
+error[E0282]: type annotations needed
+  --> $DIR/unknown_type_for_closure.rs:6:14
+   |
+LL |     let x = |_| {};
+   |              ^ consider giving this closure parameter a type
+
+error[E0282]: type annotations needed
+  --> $DIR/unknown_type_for_closure.rs:10:14
+   |
+LL |     let x = |k: _| {};
+   |              ^ consider giving this closure parameter a type
+
+error[E0282]: type annotations needed for the closure `fn() -> Vec<_>`
+  --> $DIR/unknown_type_for_closure.rs:14:28
+   |
+LL |     let x = || -> Vec<_> { Vec::new() };
+   |                            ^^^^^^^^ cannot infer type for type parameter `T`
+   |
+help: give this closure an explicit return type without `_` placeholders
+   |
+LL |     let x = || -> Vec<_> { Vec::new() };
+   |                   ~~~~~~
+
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0282`.