Only treat symbols as external if all declarations are external

Ref: #2844

Author: Gerrit0

CHANGELOG.md

@@ -15,6 +15,8 @@ title: Changelog
 -   Fixed an issue where TypeDoc would incorrectly ignore type arguments in references, #2823.
 -   Improved narrator support for labeling icons, #2832.
 -   Fixed an issue with `@class` incorrectly handling mapped types, #2842.
+-   TypeDoc will now consider symbols to be external only if all of their declarations are external
+    so that declaration merged members with global symbols can be documented, #2844.
 
 ### Thanks!
 

src/lib/converter/converter.ts

@@ -621,7 +621,19 @@ export class Converter extends AbstractComponent<Application, ConverterEvents> {
         this.externalPatternCache ??= createMinimatch(this.externalPattern);
         const cache = this.externalPatternCache;
 
-        return (symbol.getDeclarations() ?? []).some((node) =>
+        const declarations = symbol.getDeclarations();
+
+        // `undefined` has no declarations, if someone does `export default undefined`
+        // the symbol ends up as having no declarations (the export symbol does, but
+        // not the source symbol)
+        if (!declarations?.length) {
+            return false;
+        }
+
+        // If there are any non-external declarations, treat it as non-external
+        // This is possible with declaration merging against external namespaces
+        // (e.g. merging with HTMLElementTagNameMap)
+        return declarations.every((node) =>
             matchesAny(cache, node.getSourceFile().fileName),
         );
     }

src/test/converter2/issues/gh2844.ts

@@ -0,0 +1,9 @@
+export {};
+
+declare global {
+    namespace globalThis {
+        interface URL {
+            customMethod(): string;
+        }
+    }
+}

src/test/issues.c2.test.ts

@@ -2022,4 +2022,14 @@ describe("Issue Tests", () => {
         equal(hello.kind, ReflectionKind.Property);
         equal(hello.type?.toString(), "string");
     });
+
+    it("#2844 treats partially-external symbols as not external", () => {
+        app.options.setValue("excludeExternals", true);
+        const project = convert();
+        const url = query(project, "globalThis.URL");
+        equal(
+            url.children?.map((c) => c.name),
+            ["customMethod"],
+        );
+    });
 });