From d1338354ca7afae7088f84756ed103ea94ce82f9 Mon Sep 17 00:00:00 2001
From: Josh Mcguigan <joshmcg88@gmail.com>
Date: Fri, 10 Apr 2020 20:14:53 -0700
Subject: fix match arm false positive

---
 crates/ra_hir_ty/src/_match.rs | 15 +++++++++------
 crates/ra_hir_ty/src/expr.rs   | 13 +++++++------
 2 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/crates/ra_hir_ty/src/_match.rs b/crates/ra_hir_ty/src/_match.rs
index 9e9a9d047..342a78b45 100644
--- a/crates/ra_hir_ty/src/_match.rs
+++ b/crates/ra_hir_ty/src/_match.rs
@@ -1315,8 +1315,9 @@ mod tests {
             }
         ";
 
-        // Match arms with the incorrect type are filtered out.
-        check_diagnostic(content);
+        // Match statements with arms that don't match the
+        // expression pattern do not fire this diagnostic.
+        check_no_diagnostic(content);
     }
 
     #[test]
@@ -1330,8 +1331,9 @@ mod tests {
             }
         ";
 
-        // Match arms with the incorrect type are filtered out.
-        check_diagnostic(content);
+        // Match statements with arms that don't match the
+        // expression pattern do not fire this diagnostic.
+        check_no_diagnostic(content);
     }
 
     #[test]
@@ -1344,8 +1346,9 @@ mod tests {
             }
         ";
 
-        // Match arms with the incorrect type are filtered out.
-        check_diagnostic(content);
+        // Match statements with arms that don't match the
+        // expression pattern do not fire this diagnostic.
+        check_no_diagnostic(content);
     }
 
     #[test]
diff --git a/crates/ra_hir_ty/src/expr.rs b/crates/ra_hir_ty/src/expr.rs
index 827b687de..03ef488b9 100644
--- a/crates/ra_hir_ty/src/expr.rs
+++ b/crates/ra_hir_ty/src/expr.rs
@@ -163,12 +163,6 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
 
         let mut seen = Matrix::empty();
         for pat in pats {
-            // We skip any patterns whose type we cannot resolve.
-            //
-            // This could lead to false positives in this diagnostic, so
-            // it might be better to skip the entire diagnostic if we either
-            // cannot resolve a match arm or determine that the match arm has
-            // the wrong type.
             if let Some(pat_ty) = infer.type_of_pat.get(pat) {
                 // We only include patterns whose type matches the type
                 // of the match expression. If we had a InvalidMatchArmPattern
@@ -191,8 +185,15 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
                     // to the matrix here.
                     let v = PatStack::from_pattern(pat);
                     seen.push(&cx, v);
+                    continue;
                 }
             }
+
+            // If we can't resolve the type of a pattern, or the pattern type doesn't
+            // fit the match expression, we skip this diagnostic. Skipping the entire
+            // diagnostic rather than just not including this match arm is preferred
+            // to avoid the chance of false positives.
+            return;
         }
 
         match is_useful(&cx, &seen, &PatStack::from_wild()) {
-- 
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