From 43bac20b83cd7ebe2a972e482ebbc87936d83c61 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Sat, 16 Jun 2018 13:30:17 -0700
Subject: [PATCH] Array literals contextually typed by tuple types with rest
 elements

---
 src/compiler/checker.ts | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index edeb4424d1d..3b85e7ab053 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -15993,7 +15993,7 @@ namespace ts {
 
         function checkArrayLiteral(node: ArrayLiteralExpression, checkMode: CheckMode | undefined): Type {
             const elements = node.elements;
-            let hasSpreadElement = false;
+            let hasNonEndingSpreadElement = false;
             const elementTypes: Type[] = [];
             const inDestructuringPattern = isAssignmentTarget(node);
             const contextualType = getApparentTypeOfContextualType(node);
@@ -16024,9 +16024,9 @@ namespace ts {
                     const type = checkExpressionForMutableLocation(e, checkMode, elementContextualType);
                     elementTypes.push(type);
                 }
-                hasSpreadElement = hasSpreadElement || e.kind === SyntaxKind.SpreadElement;
+                hasNonEndingSpreadElement = hasNonEndingSpreadElement || (index < elements.length - 1 && e.kind === SyntaxKind.SpreadElement);
             }
-            if (!hasSpreadElement) {
+            if (!hasNonEndingSpreadElement) {
                 // If array literal is actually a destructuring pattern, mark it as an implied type. We do this such
                 // that we get the same behavior for "var [x, y] = []" and "[x, y] = []".
                 if (inDestructuringPattern && elementTypes.length) {
@@ -16053,7 +16053,8 @@ namespace ts {
                             }
                         }
                     }
-                    return createTupleType(elementTypes);
+                    const hasSpreadElement = elements.length > 0 && elements[elements.length - 1].kind === SyntaxKind.SpreadElement;
+                    return createTupleType(elementTypes, elementTypes.length - (hasSpreadElement ? 1 : 0), hasSpreadElement);
                 }
             }
             return createArrayType(elementTypes.length ?