Add helper functions for detecting 'this' identifiers

Author: Andy Hanson

src/compiler/binder.ts

@@ -2432,8 +2432,7 @@ namespace ts {
         }
 
         // If the parameter's name is 'this', then it is TypeScript syntax.
-        if (subtreeFlags & TransformFlags.ContainsDecorators
-            || (name && isIdentifier(name) && name.originalKeywordKind === SyntaxKind.ThisKeyword)) {
+        if (subtreeFlags & TransformFlags.ContainsDecorators || isThisIdentifier(name)) {
             transformFlags |= TransformFlags.AssertTypeScript;
         }
 

src/compiler/checker.ts

@@ -9373,7 +9373,7 @@ namespace ts {
                 captureLexicalThis(node, container);
             }
             if (isFunctionLike(container) &&
-                (!isInParameterInitializerBeforeContainingFunction(node) || getFunctionLikeThisParameter(container))) {
+                (!isInParameterInitializerBeforeContainingFunction(node) || getThisParameter(container))) {
                 // Note: a parameter initializer should refer to class-this unless function-this is explicitly annotated.
 
                 // If this is a function in a JS file, it might be a class method. Check if it's the RHS
@@ -15557,10 +15557,6 @@ namespace ts {
             }
         }
 
-        function parameterIsThisKeyword(parameter: ParameterDeclaration) {
-            return parameter.name && (<Identifier>parameter.name).originalKeywordKind === SyntaxKind.ThisKeyword;
-        }
-
         function parameterNameStartsWithUnderscore(parameter: ParameterDeclaration) {
             return parameter.name && parameter.name.kind === SyntaxKind.Identifier && (<Identifier>parameter.name).text.charCodeAt(0) === CharacterCodes._;
         }
@@ -20141,18 +20137,8 @@ namespace ts {
         }
 
         function getAccessorThisParameter(accessor: AccessorDeclaration): ParameterDeclaration {
-            if (accessor.parameters.length === (accessor.kind === SyntaxKind.GetAccessor ? 1 : 2) &&
-                accessor.parameters[0].name.kind === SyntaxKind.Identifier &&
-                (<Identifier>accessor.parameters[0].name).originalKeywordKind === SyntaxKind.ThisKeyword) {
-                return accessor.parameters[0];
-            }
-        }
-
-        function getFunctionLikeThisParameter(func: FunctionLikeDeclaration) {
-            if (func.parameters.length &&
-                func.parameters[0].name.kind === SyntaxKind.Identifier &&
-                (<Identifier>func.parameters[0].name).originalKeywordKind === SyntaxKind.ThisKeyword) {
-                return func.parameters[0];
+            if (accessor.parameters.length === (accessor.kind === SyntaxKind.GetAccessor ? 1 : 2)) {
+                return getThisParameter(accessor);
             }
         }
 

src/compiler/transformers/ts.ts

@@ -2374,7 +2374,7 @@ namespace ts {
          * @param node The parameter declaration node.
          */
         function visitParameter(node: ParameterDeclaration) {
-            if (node.name && isIdentifier(node.name) && node.name.originalKeywordKind === SyntaxKind.ThisKeyword) {
+            if (parameterIsThisKeyword(node)) {
                 return undefined;
             }
 

src/compiler/utilities.ts

@@ -2707,15 +2707,35 @@ namespace ts {
         });
     }
 
-    export function getSetAccessorTypeAnnotationNode(accessor: AccessorDeclaration): TypeNode {
+    /** Get the type annotaion for the value parameter. */
+    export function getSetAccessorTypeAnnotationNode(accessor: SetAccessorDeclaration): TypeNode {
         if (accessor && accessor.parameters.length > 0) {
-            const hasThis = accessor.parameters.length === 2 &&
-                accessor.parameters[0].name.kind === SyntaxKind.Identifier &&
-                (accessor.parameters[0].name as Identifier).originalKeywordKind === SyntaxKind.ThisKeyword;
+            const hasThis = accessor.parameters.length === 2 && parameterIsThisKeyword(accessor.parameters[0]);
             return accessor.parameters[hasThis ? 1 : 0].type;
         }
     }
 
+    export function getThisParameter(signature: SignatureDeclaration): ParameterDeclaration | undefined {
+        if (signature.parameters.length) {
+            const thisParameter = signature.parameters[0];
+            if (parameterIsThisKeyword(thisParameter)) {
+                return thisParameter;
+            }
+        }
+    }
+
+    export function parameterIsThisKeyword(parameter: ParameterDeclaration): boolean {
+        return isThisIdentifier(parameter.name);
+    }
+
+    export function isThisIdentifier(node: Node | undefined): boolean {
+        return node && node.kind === SyntaxKind.Identifier && identifierIsThisKeyword(node as Identifier);
+    }
+
+    export function identifierIsThisKeyword(id: Identifier): boolean {
+        return id.originalKeywordKind === SyntaxKind.ThisKeyword;
+    }
+
     export interface AllAccessorDeclarations {
         firstAccessor: AccessorDeclaration;
         secondAccessor: AccessorDeclaration;

src/services/classifier.ts

@@ -954,8 +954,7 @@ namespace ts {
                             return;
                         case SyntaxKind.Parameter:
                             if ((<ParameterDeclaration>token.parent).name === token) {
-                                const isThis = token.kind === SyntaxKind.Identifier && (<Identifier>token).originalKeywordKind === SyntaxKind.ThisKeyword;
-                                return isThis ? ClassificationType.keyword : ClassificationType.parameterName;
+                                return isThisIdentifier(token) ? ClassificationType.keyword : ClassificationType.parameterName;
                             }
                             return;
                     }

src/services/utilities.ts

@@ -376,7 +376,7 @@ namespace ts {
                 return true;
             case SyntaxKind.Identifier:
                 // 'this' as a parameter
-                return (node as Identifier).originalKeywordKind === SyntaxKind.ThisKeyword && node.parent.kind === SyntaxKind.Parameter;
+                return identifierIsThisKeyword(node as Identifier) && node.parent.kind === SyntaxKind.Parameter;
             default:
                 return false;
         }