From a636bd5f4848cccb8b8d1928970c9079f88724a0 Mon Sep 17 00:00:00 2001
From: Gerrit Birkeland <gerrit@gerritbirkeland.com>
Date: Wed, 27 Dec 2023 11:49:07 -0700
Subject: [PATCH] Fix #2451

---
 CHANGELOG.md                         |  1 +
 scripts/testcase.js                  |  2 ++
 src/lib/converter/types.ts           | 21 +++++++++++----------
 src/test/converter2/issues/gh2451.ts | 15 +++++++++++++++
 src/test/issues.c2.test.ts           |  9 ++++++++-
 5 files changed, 37 insertions(+), 11 deletions(-)
 create mode 100644 src/test/converter2/issues/gh2451.ts

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4524b60ae..93a124933 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@
 
 ### Bug Fixes
 
+-   Fix crash when converting some complicated union/intersection types, #2451.
 -   Navigation triangle markers should no longer display on a separate line with some font settings, #2457.
 -   `@group` and `@category` organization is now applied later to allow inherited comments to create groups/categories, #2459.
 -   Keyword syntax highlighting introduced in 0.25.4 was not always applied to keywords.
diff --git a/scripts/testcase.js b/scripts/testcase.js
index 64c28e729..b531d9529 100644
--- a/scripts/testcase.js
+++ b/scripts/testcase.js
@@ -57,6 +57,8 @@ async function main() {
     );
     if (!code) {
         console.log("No codeblock found");
+        const file = `src/test/converter2/issues/gh${issue}.ts`;
+        await exec(`code ${file}`);
         return;
     }
 
diff --git a/src/lib/converter/types.ts b/src/lib/converter/types.ts
index 1d5ae1e11..a54fab61c 100644
--- a/src/lib/converter/types.ts
+++ b/src/lib/converter/types.ts
@@ -132,6 +132,17 @@ export function convertType(
         return requestBugReport(context, typeOrNode);
     }
 
+    // TS 4.2 added this to enable better tracking of type aliases.
+    // We need to check it here, not just in the union checker, because typeToTypeNode
+    // will use the origin when serializing
+    if (
+        typeOrNode.isUnion() &&
+        typeOrNode.origin &&
+        !typeOrNode.origin.isUnion()
+    ) {
+        return convertType(context, typeOrNode.origin);
+    }
+
     // IgnoreErrors is important, without it, we can't assert that we will get a node.
     const node = context.checker.typeToTypeNode(
         typeOrNode,
@@ -1011,11 +1022,6 @@ const typeOperatorConverter: TypeConverter<ts.TypeOperatorNode> = {
         // keyof will only show up with generic functions, otherwise it gets eagerly
         // resolved to a union of strings.
         if (node.operator === ts.SyntaxKind.KeyOfKeyword) {
-            // TS 4.2 added this to enable better tracking of type aliases.
-            if (type.isUnion() && type.origin) {
-                return convertType(context, type.origin);
-            }
-
             // There's probably an interface for this somewhere... I couldn't find it.
             const targetType = (type as ts.Type & { type: ts.Type }).type;
             return new TypeOperatorType(
@@ -1038,11 +1044,6 @@ const unionConverter: TypeConverter<ts.UnionTypeNode, ts.UnionType> = {
         );
     },
     convertType(context, type) {
-        // TS 4.2 added this to enable better tracking of type aliases.
-        if (type.origin) {
-            return convertType(context, type.origin);
-        }
-
         return new UnionType(
             type.types.map((type) => convertType(context, type)),
         );
diff --git a/src/test/converter2/issues/gh2451.ts b/src/test/converter2/issues/gh2451.ts
new file mode 100644
index 000000000..aaf4af3e0
--- /dev/null
+++ b/src/test/converter2/issues/gh2451.ts
@@ -0,0 +1,15 @@
+export type Foo = FooA | FooB;
+
+export interface BaseFoo<T extends string> {
+    type: T;
+
+    is<Type extends string>(
+        type: Type,
+    ): this is Foo & {
+        type: Type;
+    };
+}
+
+export interface FooA extends BaseFoo<"A"> {}
+
+export interface FooB extends BaseFoo<"B"> {}
diff --git a/src/test/issues.c2.test.ts b/src/test/issues.c2.test.ts
index 5ca72e39d..6a299b9a9 100644
--- a/src/test/issues.c2.test.ts
+++ b/src/test/issues.c2.test.ts
@@ -27,7 +27,7 @@ import {
     getConverter2Program,
 } from "./programs";
 import { TestLogger } from "./TestLogger";
-import { getComment, getLinks, query } from "./utils";
+import { getComment, getLinks, query, querySig } from "./utils";
 
 const base = getConverter2Base();
 const app = getConverter2App();
@@ -1225,4 +1225,11 @@ describe("Issue Tests", () => {
         equal(boolEq.signatures![0].parameters![0].type?.toString(), "boolean");
         equal(numEq.signatures![0].parameters![0].type?.toString(), "number");
     });
+
+    it("Handles unions created due to union within intersection, #2451", () => {
+        const project = convert();
+
+        const is = querySig(project, "FooA.is");
+        equal(is.type?.toString(), "this is Foo & Object");
+    });
 });