From badfcbfb43f594710020481662fa2ae680ddfecd Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Tue, 16 May 2017 09:45:01 -0700
Subject: [PATCH] findAncestor: Add generic overload for use with type
 predicates

---
 src/compiler/checker.ts   | 4 ++--
 src/compiler/core.ts      | 2 ++
 src/compiler/utilities.ts | 4 ++++
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 7a22c841450..5b816656183 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -1300,7 +1300,7 @@ namespace ts {
                     return <ImportEqualsDeclaration>node;
                 }
 
-                return findAncestor(node, n => n.kind === SyntaxKind.ImportDeclaration) as ImportDeclaration;
+                return findAncestor(node, isImportDeclaration);
             }
         }
 
@@ -22638,7 +22638,7 @@ namespace ts {
                             const symbolIsUmdExport = symbolFile !== referenceFile;
                             return symbolIsUmdExport ? undefined : symbolFile;
                         }
-                        return findAncestor(node.parent, n => isModuleOrEnumDeclaration(n) && getSymbolOfNode(n) === parentSymbol) as ModuleDeclaration | EnumDeclaration;
+                        return findAncestor(node.parent, (n): n is ModuleDeclaration | EnumDeclaration => isModuleOrEnumDeclaration(n) && getSymbolOfNode(n) === parentSymbol);
                     }
                 }
             }
diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 5e4afce98c8..60553fdab01 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -230,6 +230,8 @@ namespace ts {
      * If no such value is found, it applies the callback until the parent pointer is undefined or the callback returns "quit"
      * At that point findAncestor returns undefined.
      */
+    export function findAncestor<T extends Node>(node: Node, callback: (element: Node) => element is T): T | undefined;
+    export function findAncestor(node: Node, callback: (element: Node) => boolean | "quit"): Node | undefined;
     export function findAncestor(node: Node, callback: (element: Node) => boolean | "quit"): Node {
         while (node) {
             const result = callback(node);
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index 5046b44d094..43a144f9045 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -4010,6 +4010,10 @@ namespace ts {
         return node.kind === SyntaxKind.ImportEqualsDeclaration;
     }
 
+    export function isImportDeclaration(node: Node): node is ImportDeclaration {
+        return node.kind === SyntaxKind.ImportDeclaration;
+    }
+
     export function isImportClause(node: Node): node is ImportClause {
         return node.kind === SyntaxKind.ImportClause;
     }