From 604631881cfe883fe32e62a780315ad8f73ea7d2 Mon Sep 17 00:00:00 2001
From: Nathan Shively-Sanders <nathansa@microsoft.com>
Date: Fri, 16 Dec 2016 13:38:29 -0800
Subject: [PATCH] Add `| undefined` in .d.ts for initialised params

---
 src/compiler/declarationEmitter.ts | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/src/compiler/declarationEmitter.ts b/src/compiler/declarationEmitter.ts
index 23122d05612..9c8cd96280f 100644
--- a/src/compiler/declarationEmitter.ts
+++ b/src/compiler/declarationEmitter.ts
@@ -319,12 +319,12 @@ namespace ts {
             }
         }
 
-            function writeTypeOfDeclaration(declaration: AccessorDeclaration | VariableLikeDeclaration, type: TypeNode, getSymbolAccessibilityDiagnostic: GetSymbolAccessibilityDiagnostic, addUndefined?: boolean) {
+            function writeTypeOfDeclaration(declaration: AccessorDeclaration | VariableLikeDeclaration, type: TypeNode, getSymbolAccessibilityDiagnostic: GetSymbolAccessibilityDiagnostic) {
             writer.getSymbolAccessibilityDiagnostic = getSymbolAccessibilityDiagnostic;
             write(": ");
             if (type) {
                 // Write the type
-                emitType(type, addUndefined);
+                emitType(type);
             }
             else {
                 errorNameNode = declaration.name;
@@ -384,7 +384,7 @@ namespace ts {
             emitType(type);
         }
 
-        function emitType(type: TypeNode | Identifier | QualifiedName, addUndefined?: boolean) {
+        function emitType(type: TypeNode | Identifier | QualifiedName) {
             switch (type.kind) {
                 case SyntaxKind.AnyKeyword:
                 case SyntaxKind.StringKeyword:
@@ -1593,7 +1593,10 @@ namespace ts {
                 emitTypeOfVariableDeclarationFromTypeLiteral(node);
             }
             else if (!hasModifier(node.parent, ModifierFlags.Private)) {
-                writeTypeOfDeclaration(node, node.type, getParameterDeclarationTypeVisibilityError, !!node.initializer && !(getModifierFlags(node) & ModifierFlags.ParameterPropertyModifier));
+                // use the checker's type, not the declared type, for an initialized parameter (that isn't a parameter property)
+                const isInitializedParameter = node.initializer && !(getModifierFlags(node) & ModifierFlags.ParameterPropertyModifier);
+                const typeNode = isInitializedParameter ? undefined : node.type;
+                writeTypeOfDeclaration(node, typeNode, getParameterDeclarationTypeVisibilityError);
             }
 
             function getParameterDeclarationTypeVisibilityError(symbolAccessibilityResult: SymbolAccessibilityResult): SymbolAccessibilityDiagnostic {