From 24fddb15e86a46e6057c8c0f2f0fb18844f50049 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Wed, 1 May 2019 14:57:24 -0700
Subject: [PATCH] Resolve match arm ty when arms diverge

---
 src/librustc/infer/error_reporting/mod.rs     |  2 +-
 src/test/ui/match/match-type-err-first-arm.rs | 24 ++++++++-----
 .../ui/match/match-type-err-first-arm.stderr  | 35 ++++++++++++++-----
 3 files changed, 43 insertions(+), 18 deletions(-)

diff --git a/src/librustc/infer/error_reporting/mod.rs b/src/librustc/infer/error_reporting/mod.rs
index c20a08fc5aea6..95b566d4a1b69 100644
--- a/src/librustc/infer/error_reporting/mod.rs
+++ b/src/librustc/infer/error_reporting/mod.rs
@@ -644,7 +644,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                         for sp in prior_arms {
                             err.span_label(*sp, format!(
                                 "this is found to be of type `{}`",
-                                last_ty,
+                                self.resolve_type_vars_if_possible(&last_ty),
                             ));
                         }
                     } else if let Some(sp) = prior_arms.last() {
diff --git a/src/test/ui/match/match-type-err-first-arm.rs b/src/test/ui/match/match-type-err-first-arm.rs
index b4b84ef8f1cec..8dfbf1019e9a4 100644
--- a/src/test/ui/match/match-type-err-first-arm.rs
+++ b/src/test/ui/match/match-type-err-first-arm.rs
@@ -3,8 +3,7 @@ fn main() {
     let _ = test_func2(1);
 }
 
-fn test_func1(n: i32) -> i32 {
-    //~^ NOTE expected `i32` because of return type
+fn test_func1(n: i32) -> i32 { //~ NOTE expected `i32` because of return type
     match n {
         12 => 'b',
         //~^ ERROR mismatched types
@@ -14,10 +13,8 @@ fn test_func1(n: i32) -> i32 {
 }
 
 fn test_func2(n: i32) -> i32 {
-    let x = match n {
-    //~^ NOTE `match` arms have incompatible types
-        12 => 'b',
-        //~^ NOTE this is found to be of type `char`
+    let x = match n { //~ NOTE `match` arms have incompatible types
+        12 => 'b', //~ NOTE this is found to be of type `char`
         _ => 42,
         //~^ ERROR match arms have incompatible types
         //~| NOTE expected char, found integer
@@ -27,8 +24,7 @@ fn test_func2(n: i32) -> i32 {
 }
 
 fn test_func3(n: i32) -> i32 {
-    let x = match n {
-    //~^ NOTE `match` arms have incompatible types
+    let x = match n { //~ NOTE `match` arms have incompatible types
         1 => 'b',
         2 => 'b',
         3 => 'b',
@@ -43,3 +39,15 @@ fn test_func3(n: i32) -> i32 {
     };
     x
 }
+
+fn test_func4() {
+    match Some(0u32) { //~ NOTE `match` arms have incompatible types
+        Some(x) => {
+            x //~ NOTE this is found to be of type `u32`
+        },
+        None => {}
+        //~^ ERROR match arms have incompatible types
+        //~| NOTE expected u32, found ()
+        //~| NOTE expected type `u32`
+    };
+}
diff --git a/src/test/ui/match/match-type-err-first-arm.stderr b/src/test/ui/match/match-type-err-first-arm.stderr
index a318e6cffb937..e0553fca683a5 100644
--- a/src/test/ui/match/match-type-err-first-arm.stderr
+++ b/src/test/ui/match/match-type-err-first-arm.stderr
@@ -1,24 +1,23 @@
 error[E0308]: mismatched types
-  --> $DIR/match-type-err-first-arm.rs:9:15
+  --> $DIR/match-type-err-first-arm.rs:8:15
    |
 LL | fn test_func1(n: i32) -> i32 {
    |                          --- expected `i32` because of return type
-...
+LL |     match n {
 LL |         12 => 'b',
    |               ^^^ expected i32, found char
 
 error[E0308]: match arms have incompatible types
-  --> $DIR/match-type-err-first-arm.rs:21:14
+  --> $DIR/match-type-err-first-arm.rs:18:14
    |
 LL |       let x = match n {
    |  _____________-
-LL | |
 LL | |         12 => 'b',
    | |               --- this is found to be of type `char`
-LL | |
 LL | |         _ => 42,
    | |              ^^ expected char, found integer
-...  |
+LL | |
+LL | |
 LL | |
 LL | |     };
    | |_____- `match` arms have incompatible types
@@ -27,13 +26,13 @@ LL | |     };
               found type `{integer}`
 
 error[E0308]: match arms have incompatible types
-  --> $DIR/match-type-err-first-arm.rs:39:14
+  --> $DIR/match-type-err-first-arm.rs:35:14
    |
 LL |       let x = match n {
    |  _____________-
-LL | |
 LL | |         1 => 'b',
 LL | |         2 => 'b',
+LL | |         3 => 'b',
 ...  |
 LL | |         6 => 'b',
    | |              --- this and all prior arms are found to be of type `char`
@@ -48,6 +47,24 @@ LL | |     };
    = note: expected type `char`
               found type `{integer}`
 
-error: aborting due to 3 previous errors
+error[E0308]: match arms have incompatible types
+  --> $DIR/match-type-err-first-arm.rs:48:17
+   |
+LL | /     match Some(0u32) {
+LL | |         Some(x) => {
+LL | |             x
+   | |             - this is found to be of type `u32`
+LL | |         },
+LL | |         None => {}
+   | |                 ^^ expected u32, found ()
+...  |
+LL | |
+LL | |     };
+   | |_____- `match` arms have incompatible types
+   |
+   = note: expected type `u32`
+              found type `()`
+
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0308`.