TS: Avoid infinite recursion in stringifyType

Author: asger-semmle

javascript/extractor/lib/typescript/src/type_table.ts

@@ -436,7 +436,10 @@ export class TypeTable {
     let toStringValue: string;
     // Some types can't be stringified. Just discard the type if we can't stringify it.
     try {
-      toStringValue = this.typeChecker.typeToString(type);
+      toStringValue = this.typeChecker.typeToString(
+            type,
+            undefined,
+            ts.TypeFormatFlags.UseAliasDefinedOutsideCurrentScope);
     } catch (e) {
       console.warn("Recovered from a compiler crash while stringifying a type. Discarding the type.");
       console.warn(e.stack);
@@ -454,7 +457,11 @@ export class TypeTable {
     // Some types can't be stringified. Just discard the type if we can't stringify it.
     try {
       toStringValue =
-          this.typeChecker.signatureToString(signature, signature.declaration, ts.TypeFormatFlags.None, kind);
+          this.typeChecker.signatureToString(
+              signature,
+              signature.declaration,
+              ts.TypeFormatFlags.UseAliasDefinedOutsideCurrentScope,
+              kind);
     } catch (e) {
       console.warn("Recovered from a compiler crash while stringifying a signature. Discarding the signature.");
       console.warn(e.stack);

javascript/ql/test/library-tests/TypeScript/RegressionTests/RecursiveTypeAlias/Test.expected

@@ -0,0 +1,2 @@
+| test.ts:3:1:7:6 | type Di ... \\n    T; | Disjunction<T> |
+| test.ts:9:8:9:65 | type Tr ... n<T>>>; | Disjunction<Disjunction<Disjunction<T>>> |

javascript/ql/test/library-tests/TypeScript/RegressionTests/RecursiveTypeAlias/Test.ql

@@ -0,0 +1,4 @@
+import javascript
+
+from TypeAliasDeclaration decl
+select decl, decl.getDefinition().getType()

javascript/ql/test/library-tests/TypeScript/RegressionTests/RecursiveTypeAlias/test.ts

@@ -0,0 +1,9 @@
+import { ArrayBox, Box } from 'somewhere';
+
+type Disjunction<T> =
+    T extends ArrayBox<infer U1> ? U1[] :
+    T extends Box<infer U2> ? U2 :
+    T extends ({[P in keyof T]: T[P]} & {p: any}) ? {[P in Exclude<keyof T, 'p'>]: Disjunction<T[P]>} :
+    T;
+
+export type Triple<T> = Disjunction<Disjunction<Disjunction<T>>>;

javascript/ql/test/library-tests/TypeScript/RegressionTests/RecursiveTypeAlias/tsconfig.json

@@ -0,0 +1 @@
+{}