🐛 Support factory function apps when entrypoint is configured (#101)

Author: savannahostrowski

src/core/routerResolver.ts

@@ -113,6 +113,25 @@ async function buildRouterGraphInternal(
     }
   }
 
+  // Factory function: if the entrypoint variable (e.g. "app" from "main:app")
+  // is assigned via a factory function (`app = create_app()`) rather than a direct
+  // FastAPI() constructor call, static analysis can't determine the type. If routes
+  // are decorated with @app.get(...) etc. though, we know it must be a FastAPI instance.
+  if (
+    !appRouter &&
+    targetVariable &&
+    analysis.routes.some((r) => r.owner === targetVariable)
+  ) {
+    appRouter = {
+      variableName: targetVariable,
+      type: "FastAPI",
+      prefix: "",
+      tags: [],
+      line: 0,
+      column: 0,
+    }
+  }
+
   if (!appRouter || !analysis) {
     return null
   }

src/test/core/routerResolver.test.ts

@@ -538,5 +538,37 @@ suite("routerResolver", () => {
       assert.strictEqual(result.children[0].router.prefix, "/users")
       assert.ok(result.children[0].router.routes.length >= 2)
     })
+
+    test("infers FastAPI app when assigned via factory function (app = get_fastapi_app())", async () => {
+      const result = await buildRouterGraph(
+        fixtures.factoryFunc.mainPy,
+        parser,
+        fixtures.factoryFunc.root,
+        nodeFileSystem,
+        "app",
+      )
+
+      assert.ok(
+        result,
+        "Should find app even when assigned via factory function",
+      )
+      assert.strictEqual(result.type, "FastAPI")
+      assert.strictEqual(result.variableName, "app")
+      assert.strictEqual(result.routes.length, 2)
+      const paths = result.routes.map((r) => r.path)
+      assert.ok(paths.includes("/1"))
+      assert.ok(paths.includes("/2"))
+    })
+
+    test("returns null without targetVariable when app is a factory function", async () => {
+      const result = await buildRouterGraph(
+        fixtures.factoryFunc.mainPy,
+        parser,
+        fixtures.factoryFunc.root,
+        nodeFileSystem,
+      )
+
+      assert.strictEqual(result, null)
+    })
   })
 })

src/test/fixtures/factory-func/app.py

@@ -0,0 +1,5 @@
+from fastapi import FastAPI
+
+
+def get_fastapi_app() -> FastAPI:
+    return FastAPI()

src/test/fixtures/factory-func/main.py

@@ -0,0 +1,13 @@
+from app import get_fastapi_app
+
+app = get_fastapi_app()
+
+
+@app.get("/1")
+def one():
+    return "Route one"
+
+
+@app.get("/2")
+def two():
+    return "Route two"

src/test/testUtils.ts

@@ -83,6 +83,10 @@ export const fixtures = {
     projectRoot: uri(join(fixturesPath, "monorepo", "service")),
     mainPy: uri(join(fixturesPath, "monorepo", "service", "myapp", "main.py")),
   },
+  factoryFunc: {
+    root: uri(join(fixturesPath, "factory-func")),
+    mainPy: uri(join(fixturesPath, "factory-func", "main.py")),
+  },
 }
 
 /**