Merge pull request #12921 from asgerf/js/typescript-compiler-crash

JS: Fix extractor crash related to recursive generic type alias

Author: asgerf

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

@@ -43,6 +43,9 @@ function isTypeAlwaysSafeToExpand(type: ts.Type): boolean {
       return false;
     }
   }
+  if (type.aliasSymbol != null) {
+    return false;
+  }
   return true;
 }
 
@@ -447,7 +450,7 @@ export class TypeTable {
         this.isInShallowTypeContext ? TypeExtractionState.PendingShallow : TypeExtractionState.PendingFull);
       // If the type is the self-type for a named type (not a generic instantiation of it),
       // emit the self-type binding for that type.
-      if (content.startsWith("reference;") && !(isTypeReference(type) && type.target !== type)) {
+      if (content.startsWith("reference;") && isTypeSelfReference(type)) {
         this.selfTypes.symbols.push(this.getSymbolId(type.aliasSymbol || type.symbol));
         this.selfTypes.selfTypes.push(id);
       }
@@ -533,7 +536,7 @@ export class TypeTable {
         let enclosingType = getEnclosingTypeOfThisType(type);
         if (enclosingType != null) {
           return "this;" + this.getId(enclosingType, false);
-        } else if (symbol.parent == null) {
+        } else if (symbol.parent == null || isFunctionTypeOrTypeAlias(symbol.declarations?.[0])) {
           // The type variable is bound on a call signature. Only extract it by name.
           return "lextypevar;" + symbol.name;
         } else {
@@ -614,14 +617,14 @@ export class TypeTable {
         // cannot be written using TypeScript syntax - so we ignore them entirely.
         return null;
       }
-      return this.makeTypeStringVector("union", unionType.types);
+      return this.makeDeduplicatedTypeStringVector("union", unionType.types);
     }
     if (flags & ts.TypeFlags.Intersection) {
       let intersectionType = type as ts.IntersectionType;
       if (intersectionType.types.length === 0) {
         return null; // Ignore malformed type.
       }
-      return this.makeTypeStringVector("intersection", intersectionType.types);
+      return this.makeDeduplicatedTypeStringVector("intersection", intersectionType.types);
     }
     if (isTypeReference(type) && (type.target.objectFlags & ts.ObjectFlags.Tuple)) {
       // Encode the minimum length and presence of rest element in the first two parts of the type string.
@@ -784,6 +787,27 @@ export class TypeTable {
     return hash;
   }
 
+  /**
+   * Returns the given string with the IDs of the given types appended,
+   * ignoring duplicates, and each separated by `;`.
+   */
+  private makeDeduplicatedTypeStringVector(tag: string, types: ReadonlyArray<ts.Type>, length = types.length): string | null {
+    let seenIds = new Set<number>();
+    let numberOfSeenIds = 0;
+    let hash = tag;
+    for (let i = 0; i < length; ++i) {
+      let id = this.getId(types[i], false);
+      if (id == null) return null;
+      seenIds.add(id);
+      if (seenIds.size > numberOfSeenIds) {
+        // This ID was not seen before
+        ++numberOfSeenIds;
+        hash += ";" + id;
+      }
+    }
+    return hash;
+  }
+
   /** Returns the type of `symbol` or `null` if it could not be computed. */
   private tryGetTypeOfSymbol(symbol: ts.Symbol) {
     try {
@@ -1328,3 +1352,35 @@ export class TypeTable {
     }
   }
 }
+
+function isFunctionTypeOrTypeAlias(declaration: ts.Declaration | undefined) {
+  if (declaration == null) return false;
+  return declaration.kind === ts.SyntaxKind.FunctionType || declaration.kind === ts.SyntaxKind.TypeAliasDeclaration;
+}
+
+/**
+ * Given a `type` whose type-string is known to be a `reference`, returns true if this is the self-type for the referenced type.
+ *
+ * For example, for `type Foo<R> = ...` this returns true if `type` is `Foo<R>`.
+ */
+function isTypeSelfReference(type: ts.Type) {
+  if (type.aliasSymbol != null) {
+    const { aliasTypeArguments } = type;
+    if (aliasTypeArguments == null) return true;
+    let declaration = type.aliasSymbol.declarations?.[0];
+    if (declaration == null || declaration.kind !== ts.SyntaxKind.TypeAliasDeclaration) return false;
+    let alias = declaration as ts.TypeAliasDeclaration;
+    for (let i = 0; i < aliasTypeArguments.length; ++i) {
+      if (aliasTypeArguments[i].symbol?.declarations?.[0] !== alias.typeParameters[i]) {
+        return false;
+      }
+    }
+    return true;
+  } else if (isTypeReference(type)) {
+    return type.target === type;
+  } else {
+    // Return true because we know we have mapped this type to kind `reference`, and in the cases
+    // not covered above (i.e. generic types) it is always a self-reference.
+    return true;
+  }
+}

javascript/ql/src/change-notes/2023-04-26-typescript-compiler-crash.md

@@ -0,0 +1,5 @@
+---
+category: fix
+---
+* Fixes an issue that would cause TypeScript extraction to hang in rare cases when extracting
+  code containing recursive generic type aliases.

javascript/ql/test/library-tests/TypeScript/RegressionTests/GenericTypeAlias/test.expected

@@ -0,0 +1,15 @@
+typeAliases
+| tst.ts:1:8:1:41 | type Fo ... R \| A>; |
+| tst.ts:3:8:3:42 | type Ba ... R, A]>; |
+| tst.ts:5:8:5:47 | type Ba ...  => A>; |
+typeAliasType
+| tst.ts:1:8:1:41 | type Fo ... R \| A>; | Foo<R> |
+| tst.ts:3:8:3:42 | type Ba ... R, A]>; | Bar<R> |
+| tst.ts:5:8:5:47 | type Ba ...  => A>; | Baz<R> |
+getAliasedType
+| Bar<R> | <A>() => Bar<[R, A]> |
+| Bar<[R, A]> | <A>() => Bar<[[R, A], A]> |
+| Baz<(x: R) => A> | <A>() => Baz<(x: (x: R) => A) => A> |
+| Baz<R> | <A>() => Baz<(x: R) => A> |
+| Foo<R \| A> | <A>() => Foo<R \| A> |
+| Foo<R> | <A>() => Foo<R \| A> |

javascript/ql/test/library-tests/TypeScript/RegressionTests/GenericTypeAlias/test.ql

@@ -0,0 +1,8 @@
+import javascript
+
+// The extractor would hang on this test case, it doesn't matter too much what the output of the test is.
+query TypeAliasDeclaration typeAliases() { any() }
+
+query Type typeAliasType(TypeAliasDeclaration decl) { result = decl.getTypeName().getType() }
+
+query Type getAliasedType(TypeAliasReference ref) { result = ref.getAliasedType() }

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

@@ -0,0 +1,3 @@
+{
+    "include": ["."]
+}

javascript/ql/test/library-tests/TypeScript/RegressionTests/GenericTypeAlias/tst.ts

@@ -0,0 +1,5 @@
+export type Foo<R> = <A>() => Foo<R | A>;
+
+export type Bar<R> = <A>() => Bar<[R, A]>;
+
+export type Baz<R> = <A>() => Baz<(x: R) => A>;