Implement pathOf function for extracting property paths from lambda expressions

src/lib/object.spec.ts

@@ -1,4 +1,4 @@
-import { isObject, convertNullToUndefined } from "./object";
+import { isObject, convertNullToUndefined, pathOf } from "./object";
 
 describe("object tests", () => {
   test.each([
@@ -40,4 +40,73 @@ describe("object tests", () => {
     convertNullToUndefined(obj);
     expect(obj).toStrictEqual(expected);
   });
+
+  describe("pathOf", () => {
+    interface TestObject {
+      prop1: string;
+      nested: {
+        prop2: string;
+        deepNested: {
+          prop3: string;
+        };
+      };
+      Recursion: {
+        Recursion: {
+          Recursion: {
+            Recursion: string;
+          };
+        };
+      };
+    }
+
+    test("should return correct path for simple property access", () => {
+      expect(pathOf((x: TestObject) => x.prop1)).toBe("prop1");
+    });
+
+    test("should return correct path for nested property access", () => {
+      expect(pathOf((x: TestObject) => x.nested.prop2)).toBe("nested.prop2");
+    });
+
+    test("should return correct path for deep nested property access", () => {
+      expect(pathOf((x: TestObject) => x.nested.deepNested.prop3)).toBe("nested.deepNested.prop3");
+    });
+
+    test("should return correct path for recursive property access (matching C# example)", () => {
+      expect(pathOf((x: TestObject) => x.Recursion.Recursion.Recursion.Recursion)).toBe("Recursion.Recursion.Recursion.Recursion");
+    });
+
+    test("should handle different property types", () => {
+      expect(pathOf((x: { id: number }) => x.id)).toBe("id");
+      expect(pathOf((x: { name: string }) => x.name)).toBe("name");
+    });
+
+    test("should return empty string for expression that doesn't access properties", () => {
+      expect(pathOf(() => "constant")).toBe("");
+    });
+
+    test("should handle expressions that access properties on returned values", () => {
+      interface ComplexObject {
+        getData: {
+          value: string;
+        };
+      }
+
+      // This should work as it's accessing a property, not calling a function
+      const path = pathOf((x: ComplexObject) => x.getData.value);
+      expect(path).toBe("getData.value");
+    });
+
+    test("should handle expressions that may throw errors", () => {
+      interface TestObject {
+        prop: string;
+      }
+
+      // This expression might throw an error during execution, but the path should still be captured
+      const path = pathOf((x: TestObject) => {
+        // This would throw in normal execution, but we want to capture the path
+        return x.prop.toString();
+      });
+      expect(path).toBe("prop.toString");
+    });
+  });
 });

src/lib/object.ts

@@ -24,3 +24,44 @@ export const convertNullToUndefined = (obj: object): void => {
     }
   }
 };
+
+/**
+ * Get the full path of a nested object property from a lambda expression
+ * @param expression A function that accesses properties on an object
+ * @returns The property path as a string (e.g., "prop1.prop2.prop3")
+ */
+export const pathOf = <T extends object>(expression: (obj: T) => unknown): string => {
+  const path: string[] = [];
+
+  /**
+   * Create a proxy that tracks property access
+   * @param currentPath The current path being tracked
+   * @returns A proxy object that captures property access
+   */
+  const createProxy = (currentPath: string[] = []): T => {
+    return new Proxy({} as T, {
+      /**
+       * Intercept property access and build the path
+       * @param _target The proxy target (unused)
+       * @param prop The property being accessed
+       * @returns A new proxy for continued property access
+       */
+      get(_target, prop) {
+        if (typeof prop === "string") {
+          const newPath = [...currentPath, prop];
+          path.splice(0, path.length, ...newPath);
+          return createProxy(newPath);
+        }
+        return;
+      },
+    });
+  };
+
+  try {
+    expression(createProxy());
+  } catch {
+    // Ignore errors that might occur during property access
+  }
+
+  return path.join(".");
+};