TS: Support const type assertions

javascript/extractor/src/com/semmle/js/parser/TypeScriptASTConverter.java

@@ -345,7 +345,7 @@ public class TypeScriptASTConverter {
       case "ArrowFunction":
         return convertArrowFunction(node, loc);
       case "AsExpression":
-        return convertAsExpression(node, loc);
+        return convertTypeAssertionExpression(node, loc);
       case "AwaitExpression":
         return convertAwaitExpression(node, loc);
       case "BigIntKeyword":
@@ -797,11 +797,6 @@ public class TypeScriptASTConverter {
         convertChildAsType(node, "type"));
   }
 
-  private Node convertAsExpression(JsonObject node, SourceLocation loc) throws ParseError {
-    return new TypeAssertion(
-        loc, convertChild(node, "expression"), convertChildAsType(node, "type"), true);
-  }
-
   private Node convertAwaitExpression(JsonObject node, SourceLocation loc) throws ParseError {
     return new AwaitExpression(loc, convertChild(node, "expression"));
   }
@@ -2115,8 +2110,12 @@ public class TypeScriptASTConverter {
 
   private Node convertTypeAssertionExpression(JsonObject node, SourceLocation loc)
       throws ParseError {
-    return new TypeAssertion(
-        loc, convertChild(node, "expression"), convertChildAsType(node, "type"), false);
+    ITypeExpression type = convertChildAsType(node, "type");
+    // `T as const` is extracted as a cast to the keyword type `const`.
+    if (type instanceof Identifier && ((Identifier) type).getName().equals("const")) {
+      type = new KeywordTypeExpr(type.getLoc(), "const");
+    }
+    return new TypeAssertion(loc, convertChild(node, "expression"), type, false);
   }
 
   private Node convertTypeLiteral(JsonObject obj, SourceLocation loc) throws ParseError {

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

@@ -585,6 +585,9 @@ class TypeExpr extends ExprOrType, @typeexpr {
   /** Holds if this is the `bigint` type. */
   predicate isBigInt() { none() }
 
+  /** Holds if this is the `const` keyword, occurding in a type assertion such as `x as const`. */
+  predicate isConstKeyword() { none() }
+
   /** Gets this type expression, with any surrounding parentheses removed. */
   override TypeExpr stripParens() { result = this }
 
@@ -638,6 +641,8 @@ private class KeywordTypeExpr extends @keywordtypeexpr, TypeExpr {
   override predicate isUnknownKeyword() { getName() = "unknown" }
 
   override predicate isBigInt() { getName() = "bigint" }
+
+  override predicate isConstKeyword() { getName() = "const" }
 }
 
 /**

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

@@ -0,0 +1,6 @@
+test_ConstKeyword
+| tst.ts:1:19:1:23 | const |
+| tst.ts:2:10:2:14 | const |
+test_ConstTypeAssertion
+| tst.ts:1:9:1:23 | [1, 2] as const |
+| tst.ts:2:9:2:21 | <const>[1, 2] |

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

@@ -0,0 +1,9 @@
+import javascript
+
+query predicate test_ConstKeyword(TypeExpr t) {
+  t.isConstKeyword()
+}
+
+query predicate test_ConstTypeAssertion(TypeAssertion t) {
+  t.getTypeAnnotation().isConstKeyword()
+}

javascript/ql/test/library-tests/TypeScript/ConstKeyword/tst.ts

@@ -0,0 +1,2 @@
+var x = [1, 2] as const;
+var x = <const>[1, 2];

javascript/ql/test/library-tests/TypeScript/Types/GetExprType.expected

@@ -80,6 +80,16 @@
 | tst.ts:38:5:38:24 | tupleWithRestElement | [number, ...string[]] |
 | tst.ts:39:5:39:36 | tupleWi ... lements | [number, string?, ...number[]] |
 | tst.ts:40:5:40:15 | unknownType | unknown |
+| tst.ts:42:5:42:21 | constArrayLiteral | readonly [1, 2] |
+| tst.ts:42:25:42:30 | [1, 2] | readonly [1, 2] |
+| tst.ts:42:25:42:39 | [1, 2] as const | readonly [1, 2] |
+| tst.ts:42:26:42:26 | 1 | 1 |
+| tst.ts:42:29:42:29 | 2 | 2 |
+| tst.ts:43:5:43:22 | constObjectLiteral | { readonly foo: "foo"; } |
+| tst.ts:43:26:43:39 | { foo: "foo" } | { readonly foo: "foo"; } |
+| tst.ts:43:26:43:48 | { foo:  ... s const | { readonly foo: "foo"; } |
+| tst.ts:43:28:43:30 | foo | "foo" |
+| tst.ts:43:33:43:37 | "foo" | "foo" |
 | type_alias.ts:3:5:3:5 | b | boolean |
 | type_definition_objects.ts:1:13:1:17 | dummy | typeof dummy.ts |
 | type_definition_objects.ts:1:24:1:32 | "./dummy" | any |

javascript/ql/test/library-tests/TypeScript/Types/GetTypeExprType.expected

@@ -68,6 +68,8 @@
 | tst.ts:39:60:39:65 | number | number |
 | tst.ts:39:60:39:67 | number[] | number[] |
 | tst.ts:40:18:40:24 | unknown | unknown |
+| tst.ts:42:35:42:39 | const | any |
+| tst.ts:43:44:43:48 | const | any |
 | type_alias.ts:1:6:1:6 | B | boolean |
 | type_alias.ts:1:10:1:16 | boolean | boolean |
 | type_alias.ts:3:8:3:8 | B | boolean |

javascript/ql/test/library-tests/TypeScript/Types/TupleTypes.expected

@@ -8,3 +8,9 @@
 | tst.ts:39:5:39:36 | tupleWi ... lements | [number, string?, ...number[]] | 0 | number | 1 | number |
 | tst.ts:39:5:39:36 | tupleWi ... lements | [number, string?, ...number[]] | 1 | string | 1 | number |
 | tst.ts:39:5:39:36 | tupleWi ... lements | [number, string?, ...number[]] | 2 | number | 1 | number |
+| tst.ts:42:5:42:21 | constArrayLiteral | readonly [1, 2] | 0 | 1 | 2 | no-rest |
+| tst.ts:42:5:42:21 | constArrayLiteral | readonly [1, 2] | 1 | 2 | 2 | no-rest |
+| tst.ts:42:25:42:30 | [1, 2] | readonly [1, 2] | 0 | 1 | 2 | no-rest |
+| tst.ts:42:25:42:30 | [1, 2] | readonly [1, 2] | 1 | 2 | 2 | no-rest |
+| tst.ts:42:25:42:39 | [1, 2] as const | readonly [1, 2] | 0 | 1 | 2 | no-rest |
+| tst.ts:42:25:42:39 | [1, 2] as const | readonly [1, 2] | 1 | 2 | 2 | no-rest |

javascript/ql/test/library-tests/TypeScript/Types/tst.ts

@@ -37,4 +37,7 @@ let tupleWithOptionalElement: [number, string, number?];
 let emptyTuple: [];
 let tupleWithRestElement: [number, ...string[]];
 let tupleWithOptionalAndRestElements: [number, string?, ...number[]];
-let unknownType: unknown;
+let unknownType: unknown;
+
+let constArrayLiteral = [1, 2] as const;
+let constObjectLiteral = { foo: "foo" } as const;