Allow returning a value and having Danger execute the code

.travis.yml

@@ -29,7 +29,7 @@ matrix:
      - node scripts/run-fixtures.js
 
   # Does the real danger run
-  - node_js: node
+  - node_js: '9'
     script:
     - yarn jest --outputFile test-results.json --json --runInBand
     - yarn run link

CHANGELOG.md

@@ -14,6 +14,7 @@
 ## Master
 
 * Prints a link to the comment in the build log [@orta][]
+* A Dangerfile can return a default export, and then Danger will handle the execution of that code [@orta][]
 
 ## 3.5.0 - 3.5.1
 

scripts/run-fixtures.js

@@ -1,5 +1,5 @@
 // Note: Keep this ES6 only, want to be able to run this directly via node
-// to ensur that something like ts-node doesn't mess up paths etc
+// to ensure that something like ts-node doesn't mess up paths etc
 
 // yarn build; cat source/_tests/fixtures/danger-js-pr-395.json | env DANGER_FAKE_CI="YEP" DANGER_TEST_REPO='danger/danger-js' DANGER_TEST_PR='395' node --inspect distribution/commands/danger-runner.js --text-only --dangerfile /Users/orta/dev/projects/danger/danger-js/source/runner/_tests/fixtures/__DangerfileAsync.js
 

source/runner/_tests/fixtures/__DangerfileDefaultExport.js

@@ -0,0 +1 @@
+export default () => warn("Synchronous Warning")

source/runner/_tests/fixtures/__DangerfileDefaultExportAsync.js

@@ -0,0 +1,7 @@
+export default async () =>
+  new Promise(res => {
+    setTimeout(() => {
+      warn("Asynchronous Warning")
+      res()
+    }, 10)
+  })

source/runner/_tests/fixtures/results/__DangerfileDefaultExport.js.json

@@ -0,0 +1,11 @@
+{
+  "fails": [],
+  "warnings": [
+    {
+      "message": "Synchronous Warning"
+    }
+  ],
+  "messages": [],
+  "markdowns": [],
+  "scheduled": []
+}

source/runner/_tests/fixtures/results/__DangerfileDefaultExportAsync.js.json

@@ -0,0 +1,11 @@
+{
+  "fails": [],
+  "warnings": [
+    {
+      "message": "Asynchronous Warning"
+    }
+  ],
+  "messages": [],
+  "markdowns": [],
+  "scheduled": []
+}

source/runner/runners/_tests/vm2.test.ts

@@ -269,6 +269,38 @@ runners.forEach(run => {
         expect(results.fails[0].message).toContain("Danger failed to run")
         expect(results.markdowns[0].message).toContain("Error: failure")
       })
+
+      it("handles running default export code", async () => {
+        const context = await setupDangerfileContext()
+        const runtime = await exec.runner.createDangerfileRuntimeEnvironment(context)
+        const results = await exec.runner.runDangerfileEnvironment(
+          resolve(fixtures, "__DangerfileDefaultExport.js"),
+          undefined,
+          runtime
+        )
+        expect(results).toEqual({
+          fails: [],
+          messages: [],
+          markdowns: [],
+          warnings: [{ message: "Synchronous Warning" }],
+        })
+      })
+
+      it("handles running default export async code", async () => {
+        const context = await setupDangerfileContext()
+        const runtime = await exec.runner.createDangerfileRuntimeEnvironment(context)
+        const results = await exec.runner.runDangerfileEnvironment(
+          resolve(fixtures, "__DangerfileDefaultExportAsync.js"),
+          undefined,
+          runtime
+        )
+        expect(results).toEqual({
+          fails: [],
+          messages: [],
+          markdowns: [],
+          warnings: [{ message: "Asynchronous Warning" }],
+        })
+      })
     })
   })
 })

source/runner/runners/inline.ts

@@ -29,17 +29,20 @@ export async function createDangerfileRuntimeEnvironment(dangerfileContext: Dang
  * The values inside a Danger context are applied as globals to the Dangerfiles runtime.
  *
  * @param {string} filename the file path for the dangerfile
- * @param {any} environment the results of createDangerfileRuntimeEnvironment
+ * @param {string} originalContents optional, the JS pre-compiled
+ * @param {DangerContext} environment the results of createDangerfileRuntimeEnvironment
+ * @param {any | undefined} injectedObjectToExport an optional object for passing into default exports
  * @returns {DangerResults} the results of the run
  */
 export async function runDangerfileEnvironment(
   filename: string,
   originalContents: string | undefined,
-  environment: DangerContext
+  environment: DangerContext,
+  injectedObjectToExport: any | undefined = undefined
 ): Promise<DangerResults> {
   // We need to change the local runtime to support running JavaScript
-  // and TypeScript through babel first. This is a simple implmentation
-  // and if we need more nuance, then we can look at other implementations
+  // and TypeScript through babel first. This is a simple implementation
+  // and if we need more nuance, then we can look at other options
   const customModuleHandler = (module: any, filename: string) => {
     if (!filename.includes("node_modules")) {
       d("Handling custom module: ", filename)
@@ -70,7 +73,12 @@ export async function runDangerfileEnvironment(
     }
 
     d("Started parsing Dangerfile: ", filename)
-    _require(compiled, filename, {})
+    const optionalExport = _require(compiled, filename, {})
+
+    if (typeof optionalExport.default === "function") {
+      d("Running default export from Dangerfile", filename)
+      await optionalExport.default(injectedObjectToExport)
+    }
     d("Finished running dangerfile: ", filename)
     // Don't stop all current async code from breaking,
     // however new code (without Peril support) can run

source/runner/runners/runner.ts

@@ -7,14 +7,16 @@ export interface DangerRunner {
    * The values inside a Danger context are applied as globals to the Dangerfiles runtime.
    *
    * @param {string} filename the file path for the dangerfile
-   * @param {string | undefined} originalContents the contents of the Dangerfile, or undefined to use fs.readFileSync
-   * @param {any} environment the resuts of createDangerfileRuntimeEnvironment
+   * @param {string} originalContents optional, the JS pre-compiled
+   * @param {DangerContext} environment the results of createDangerfileRuntimeEnvironment
+   * @param {any | undefined} injectedObjectToExport an optional object for passing into default exports
    * @returns {DangerResults} the results of the run
    */
   runDangerfileEnvironment: (
     filename: string,
     originalContents: string | undefined,
-    environment: any
+    environment: any,
+    injectedObjectToExport?: any
   ) => Promise<DangerResults>
 
   /**

source/runner/runners/vm2.ts

@@ -39,7 +39,8 @@ export async function createDangerfileRuntimeEnvironment(dangerfileContext: Dang
 export async function runDangerfileEnvironment(
   filename: string,
   originalContents: string | undefined,
-  environment: NodeVMOptions
+  environment: NodeVMOptions,
+  injectedObjectToExport: any | undefined = undefined
 ) {
   const vm = new NodeVM(environment)
 
@@ -48,7 +49,10 @@ export async function runDangerfileEnvironment(
   let content = cleanDangerfile(originalContents)
 
   try {
-    vm.run(content, filename)
+    const optionalExport = vm.run(content, filename)
+    if (typeof optionalExport.default === "function") {
+      await optionalExport.default(injectedObjectToExport)
+    }
 
     const results = environment.sandbox!.results!
     await Promise.all(