From 6d2c0037fcf4b88c66e8d0f40be3b25c180b7fd3 Mon Sep 17 00:00:00 2001
From: Daniel Rosenwasser <Daniel.Rosenwasser@microsoft.com>
Date: Fri, 30 Nov 2018 16:42:14 -0800
Subject: [PATCH] Only count singleton unit types.

---
 src/compiler/checker.ts | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 8f1faaa368b..da22fecfb8d 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -11976,22 +11976,20 @@ namespace ts {
                         bestMatch = target;
                         matchingCount = Infinity;
                     }
-                    else if (isLiteralType(overlap)) {
+                    else if (overlap.flags & TypeFlags.Union) {
                         // We only want to account for literal types otherwise.
                         // If we have a union of index types, it seems likely that we
                         // needed to elaborate between two generic mapped types anyway.
-                        if (overlap.flags & TypeFlags.Union) {
-                            const len = length(filter((overlap as UnionType).types, isUnitType));
-                            if (len >= matchingCount) {
-                                bestMatch = target;
-                                matchingCount = len;
-                            }
-                        }
-                        else if (1 >= matchingCount) {
+                        const len = length(filter((overlap as UnionType).types, isUnitType));
+                        if (len >= matchingCount) {
                             bestMatch = target;
-                            matchingCount = 1;
+                            matchingCount = len;
                         }
                     }
+                    else if (isUnitType(overlap) && 1 >= matchingCount) {
+                        bestMatch = target;
+                        matchingCount = 1;
+                    }
                 }
                 return bestMatch;
             }