From fca46bb7061ff5f8c6875e589faf8a8b35ef720c Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Tue, 26 Mar 2019 07:00:19 -0700
Subject: [PATCH] Compute per-element contextual type in getSpreadArgumentType

---
 src/compiler/checker.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 26727e82c63..2fd72ed40ef 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -20264,15 +20264,15 @@ namespace ts {
                         getArrayifiedType(checkExpressionWithContextualType((<SpreadElement>arg).expression, restType, context, CheckMode.Normal));
                 }
             }
-            const contextualType = getIndexedAccessType(restType, numberType);
-            const hasPrimitiveContextualType = maybeTypeOfKind(contextualType, TypeFlags.Primitive | TypeFlags.Index);
             const types = [];
             let spreadIndex = -1;
             for (let i = index; i < argCount; i++) {
+                const contextualType = getIndexedAccessType(restType, getLiteralType(i - index));
                 const argType = checkExpressionWithContextualType(args[i], contextualType, context, CheckMode.Normal);
                 if (spreadIndex < 0 && isSpreadArgument(args[i])) {
                     spreadIndex = i - index;
                 }
+                const hasPrimitiveContextualType = maybeTypeOfKind(contextualType, TypeFlags.Primitive | TypeFlags.Index);
                 types.push(hasPrimitiveContextualType ? getRegularTypeOfLiteralType(argType) : getWidenedLiteralType(argType));
             }
             return spreadIndex < 0 ?