JS: Add TemplateLiteralTypeExpr

javascript/ql/src/semmle/javascript/TypeScript.qll

@@ -1213,6 +1213,29 @@ class InferTypeExpr extends @infer_typeexpr, TypeParameterized, TypeExpr {
   override string getAPrimaryQlClass() { result = "InferTypeExpr" }
 }
 
+/**
+ * A template literal used as a type.
+ */
+class TemplateLiteralTypeExpr extends @template_literal_typeexpr, TypeExpr {
+  /**
+   * Gets the `i`th element of this template literal, which may either
+   * be a type expression or a constant template element.
+   */
+  ExprOrType getElement(int i) { result = getChild(i) }
+
+  /**
+   * Gets an element of this template literal.
+   */
+  ExprOrType getAnElement() { result = getElement(_) }
+
+  /**
+   * Gets the number of elements of this template literal.
+   */
+  int getNumElement() { result = count(getAnElement()) }
+
+  override string getAPrimaryQlClass() { result = "TemplateLiteralTypeExpr" }
+}
+
 /**
  * A scope induced by a conditional type expression whose `extends` type
  * contains `infer` types.

javascript/ql/src/semmlecode.javascript.dbscheme

@@ -584,6 +584,7 @@ case @typeexpr.kind of
 | 34 = @rest_typeexpr
 | 35 = @bigint_literal_typeexpr
 | 36 = @readonly_typeexpr
+| 37 = @template_literal_typeexpr
 ;
 
 @typeref = @typeaccess | @type_decl;

javascript/ql/test/library-tests/TypeScript/TemplateLiteralTypes/templateLiteralTypes.ts

@@ -0,0 +1,57 @@
+// Based on snippets in https://devblogs.microsoft.com/typescript/announcing-typescript-4-1-beta/
+
+type World = "world";
+type Greeting = `hello ${World}`;
+
+
+type Color = "red" | "blue";
+type Quantity = "one" | "two";
+type SeussFish = `${Quantity | Color} fish`;
+
+
+type VerticalAlignment = "top" | "middle" | "bottom";
+type HorizontalAlignment = "left" | "center" | "right";
+declare function setAlignment(value: `${VerticalAlignment}-${HorizontalAlignment}`): void;
+
+
+type PropEventSource<T> = {
+    on<K extends string & keyof T>(eventName: `${K}Changed`, callback: (newValue: T[K]) => void ): void;
+};
+
+declare function makeWatchedObject<T>(obj: T): T & PropEventSource<T>;
+
+let person = makeWatchedObject({
+    firstName: "Homer",
+    age: 42,
+    location: "Springfield",
+});
+
+
+// Can no longer be parsed by TypeScript:
+// type EnthusiasticGreeting<T extends string> = `${uppercase T}`
+
+type HELLO = EnthusiasticGreeting<"hello">;
+
+// Can no longer be parsed by TypeScript:
+// type Getters<T> = {
+//     [K in keyof T as `get${capitalize K}`]: () => T[K]
+// };
+
+interface Person {
+    name: string;
+    age: number;
+    location: string;
+}
+
+type LazyPerson = Getters<Person>;
+
+type RemoveKindField<T> = {
+    [K in keyof T as Exclude<K, "kind">]: T[K]
+};
+
+interface Circle {
+    kind: "circle";
+    radius: number;
+}
+
+type KindlessCircle = RemoveKindField<Circle>;

javascript/ql/test/library-tests/TypeScript/TemplateLiteralTypes/test.expected

@@ -0,0 +1,9 @@
+| templateLiteralTypes.ts:4:17:4:32 | `hello ${World}` | 0 | templateLiteralTypes.ts:4:18:4:23 | hello  |
+| templateLiteralTypes.ts:4:17:4:32 | `hello ${World}` | 1 | templateLiteralTypes.ts:4:26:4:30 | World |
+| templateLiteralTypes.ts:9:18:9:43 | `${Quan ... } fish` | 0 | templateLiteralTypes.ts:9:21:9:36 | Quantity \| Color |
+| templateLiteralTypes.ts:9:18:9:43 | `${Quan ... } fish` | 1 | templateLiteralTypes.ts:9:38:9:42 |  fish |
+| templateLiteralTypes.ts:14:38:14:82 | `${Vert ... nment}` | 0 | templateLiteralTypes.ts:14:41:14:57 | VerticalAlignment |
+| templateLiteralTypes.ts:14:38:14:82 | `${Vert ... nment}` | 1 | templateLiteralTypes.ts:14:59:14:59 | - |
+| templateLiteralTypes.ts:14:38:14:82 | `${Vert ... nment}` | 2 | templateLiteralTypes.ts:14:62:14:80 | HorizontalAlignment |
+| templateLiteralTypes.ts:18:47:18:59 | `${K}Changed` | 0 | templateLiteralTypes.ts:18:50:18:50 | K |
+| templateLiteralTypes.ts:18:47:18:59 | `${K}Changed` | 1 | templateLiteralTypes.ts:18:52:18:58 | Changed |

javascript/ql/test/library-tests/TypeScript/TemplateLiteralTypes/test.ql

@@ -0,0 +1,5 @@
+import javascript
+
+query ExprOrType getElement(TemplateLiteralTypeExpr e, int i) {
+  result = e.getElement(i)
+}

javascript/ql/test/query-tests/Declarations/UnusedVariable/importtype.ts

@@ -3,4 +3,8 @@ import SomeInterface from 'somewhere';
 
 class SomeClass implements SomeInterface {
 }
-new SomeClass();
+new SomeClass();
+
+import SomethingElse from 'somewhere'; // OK: SomethingElse is used in a type
+
+type T = `Now for ${SomethingElse}`;