From 3e6b84474d7cd813bda0956568966024915d0ea8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Sat, 21 Sep 2019 16:31:27 -0700
Subject: [PATCH] Propagate `types.err` in locals further to avoid spurious
 knock-down errors

---
 src/librustc_typeck/check/coercion.rs |  8 ++++++--
 src/librustc_typeck/check/mod.rs      | 23 ++++++++++++++++++++++-
 src/test/ui/issues/issue-33575.rs     |  4 ++++
 src/test/ui/issues/issue-33575.stderr |  9 +++++++++
 4 files changed, 41 insertions(+), 3 deletions(-)
 create mode 100644 src/test/ui/issues/issue-33575.rs
 create mode 100644 src/test/ui/issues/issue-33575.stderr

diff --git a/src/librustc_typeck/check/coercion.rs b/src/librustc_typeck/check/coercion.rs
index ee4f0a868c1..ac1bf8e91a1 100644
--- a/src/librustc_typeck/check/coercion.rs
+++ b/src/librustc_typeck/check/coercion.rs
@@ -163,7 +163,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
 
         // Just ignore error types.
         if a.references_error() || b.references_error() {
-            return success(vec![], b, vec![]);
+            return success(vec![], self.fcx.tcx.types.err, vec![]);
         }
 
         if a.is_never() {
@@ -821,7 +821,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         let (adjustments, _) = self.register_infer_ok_obligations(ok);
         self.apply_adjustments(expr, adjustments);
-        Ok(target)
+        if expr_ty.references_error() {
+            Ok(self.tcx.types.err)
+        } else {
+            Ok(target)
+        }
     }
 
     /// Same as `try_coerce()`, but without side-effects.
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index 0eeeee01c82..75942731d87 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -153,7 +153,7 @@ use self::method::{MethodCallee, SelfSource};
 use self::TupleArgumentsFlag::*;
 
 /// The type of a local binding, including the revealed type for anon types.
-#[derive(Copy, Clone)]
+#[derive(Copy, Clone, Debug)]
 pub struct LocalTy<'tcx> {
     decl_ty: Ty<'tcx>,
     revealed_ty: Ty<'tcx>
@@ -3752,14 +3752,35 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         if let Some(ref init) = local.init {
             let init_ty = self.check_decl_initializer(local, &init);
             if init_ty.references_error() {
+                // Override the types everywhere with `types.err` to avoid knock down errors.
                 self.write_ty(local.hir_id, init_ty);
+                self.write_ty(local.pat.hir_id, init_ty);
+                self.locals.borrow_mut().insert(local.hir_id, LocalTy {
+                    decl_ty: t,
+                    revealed_ty: init_ty,
+                });
+                self.locals.borrow_mut().insert(local.pat.hir_id, LocalTy {
+                    decl_ty: t,
+                    revealed_ty: init_ty,
+                });
             }
         }
 
         self.check_pat_top(&local.pat, t, None);
         let pat_ty = self.node_ty(local.pat.hir_id);
+        debug!("check_decl_local pat_ty {:?}", pat_ty);
         if pat_ty.references_error() {
+            // Override the types everywhere with `types.err` to avoid knock down errors.
             self.write_ty(local.hir_id, pat_ty);
+            self.write_ty(local.pat.hir_id, pat_ty);
+            self.locals.borrow_mut().insert(local.hir_id, LocalTy {
+                decl_ty: t,
+                revealed_ty: pat_ty,
+            });
+            self.locals.borrow_mut().insert(local.pat.hir_id, LocalTy {
+                decl_ty: t,
+                revealed_ty: pat_ty,
+            });
         }
     }
 
diff --git a/src/test/ui/issues/issue-33575.rs b/src/test/ui/issues/issue-33575.rs
new file mode 100644
index 00000000000..d97afc3d31d
--- /dev/null
+++ b/src/test/ui/issues/issue-33575.rs
@@ -0,0 +1,4 @@
+fn main() {
+    let baz = ().foo(); //~ ERROR no method named `foo` found for type `()` in the current scope
+    <i32 as std::str::FromStr>::from_str(&baz); // No complains about `str` being unsized
+}
diff --git a/src/test/ui/issues/issue-33575.stderr b/src/test/ui/issues/issue-33575.stderr
new file mode 100644
index 00000000000..e6b74d262c3
--- /dev/null
+++ b/src/test/ui/issues/issue-33575.stderr
@@ -0,0 +1,9 @@
+error[E0599]: no method named `foo` found for type `()` in the current scope
+  --> $DIR/issue-33575.rs:2:18
+   |
+LL |     let baz = ().foo();
+   |                  ^^^ method not found in `()`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0599`.