tools: add metadata JSON readiness output

Expose stable PR readiness reason codes from PRChecker and add
git node metadata --json for machine-readable metadata readiness
results.

The JSON output includes readiness classification, reserved exit-code
categories, generated metadata, unique reason codes, and detailed
reasons.

Signed-off-by: Filip Skokan <panva.ip@gmail.com>

Author: panva

components/git/metadata.js

@@ -36,6 +36,10 @@ const options = {
     describe: 'Check for \'LGTM\' in comments',
     type: 'boolean'
   },
+  json: {
+    describe: 'Print metadata and PR readiness result as JSON',
+    type: 'boolean'
+  },
   'max-commits': {
     describe: 'Number of commits to warn',
     type: 'number',
@@ -45,6 +49,29 @@ const options = {
 
 let yargsInstance;
 
+function writeStdout(text) {
+  return new Promise((resolve, reject) => {
+    process.stdout.write(text, (error) => {
+      if (error) {
+        reject(error);
+      } else {
+        resolve();
+      }
+    });
+  });
+}
+
+export async function writeMetadataJsonResult(metadataPromise) {
+  try {
+    const { json } = await metadataPromise;
+    await writeStdout(`${JSON.stringify(json, null, 2)}\n`);
+    process.exitCode = json.exitCode;
+  } catch (error) {
+    console.error(error);
+    process.exitCode = 1;
+  }
+}
+
 export function builder(yargs) {
   yargsInstance = yargs;
   return yargs
@@ -81,10 +108,16 @@ export function handler(argv) {
     return yargsInstance.showHelp();
   }
 
-  const logStream = process.stdout.isTTY ? process.stdout : process.stderr;
+  const logStream = argv.json || !process.stdout.isTTY
+    ? process.stderr
+    : process.stdout;
   const cli = new CLI(logStream);
 
   const merged = Object.assign({}, argv, parsed, config);
+  if (argv.json) {
+    return writeMetadataJsonResult(getMetadata(merged, false, cli));
+  }
+
   return runPromise(getMetadata(merged, false, cli)
     .then(({ status }) => {
       if (status === false) {

components/metadata.js

@@ -4,9 +4,73 @@ import Request from '../lib/request.js';
 import auth from '../lib/auth.js';
 import PRData from '../lib/pr_data.js';
 import PRSummary from '../lib/pr_summary.js';
-import PRChecker from '../lib/pr_checker.js';
+import PRChecker, {
+  PR_CHECK_REASON_CODES
+} from '../lib/pr_checker.js';
 import MetadataGenerator from '../lib/metadata_gen.js';
 
+export const METADATA_READINESS = Object.freeze({
+  READY: 'ready',
+  DEFERRABLE: 'deferrable',
+  FAILED: 'failed'
+});
+
+export const METADATA_EXIT_CODES = Object.freeze({
+  READY: 0,
+  DEFERRABLE: 20,
+  FAILED: 40
+});
+
+const DEFERRABLE_REASON_CODES = new Set([
+  PR_CHECK_REASON_CODES.MISSING_APPROVAL,
+  PR_CHECK_REASON_CODES.MISSING_TSC_APPROVAL,
+  PR_CHECK_REASON_CODES.WAIT_TIME
+]);
+
+export function classifyMetadataReadiness(ready, reasonCodes) {
+  if (ready) {
+    return METADATA_READINESS.READY;
+  }
+
+  if (reasonCodes.length > 0 &&
+      reasonCodes.every((code) => DEFERRABLE_REASON_CODES.has(code))) {
+    return METADATA_READINESS.DEFERRABLE;
+  }
+
+  return METADATA_READINESS.FAILED;
+}
+
+export function getMetadataExitCode(readiness) {
+  switch (readiness) {
+    case METADATA_READINESS.READY:
+      return METADATA_EXIT_CODES.READY;
+    case METADATA_READINESS.DEFERRABLE:
+      return METADATA_EXIT_CODES.DEFERRABLE;
+    default:
+      return METADATA_EXIT_CODES.FAILED;
+  }
+}
+
+export function formatMetadataResult({ status, data, metadata, checker }) {
+  const reasonCodes = [...new Set(checker.reasons.map(({ code }) => code))];
+  const readiness = classifyMetadataReadiness(status, reasonCodes);
+  const exitCode = getMetadataExitCode(readiness);
+  return {
+    ready: status,
+    readiness,
+    exitCode,
+    pullRequest: {
+      owner: data.owner,
+      repo: data.repo,
+      number: data.prid,
+      url: data.pr.url
+    },
+    metadata,
+    reasonCodes,
+    reasons: checker.reasons
+  };
+}
+
 export async function getMetadata(argv, skipRefs, cli) {
   const credentials = await auth({
     github: true,
@@ -22,7 +86,7 @@ export async function getMetadata(argv, skipRefs, cli) {
   summary.display();
 
   const metadata = new MetadataGenerator({ skipRefs, ...data }).getMetadata();
-  if (!process.stdout.isTTY) {
+  if (!argv.json && !process.stdout.isTTY) {
     process.stdout.write(metadata);
   }
 
@@ -33,17 +97,23 @@ export async function getMetadata(argv, skipRefs, cli) {
     cli.stopSpinner(`Done writing metadata to ${argv.file}`);
   }
 
-  cli.separator('Generated metadata');
-  cli.write(metadata);
-  cli.separator();
+  if (!argv.json) {
+    cli.separator('Generated metadata');
+    cli.write(metadata);
+    cli.separator();
+  }
 
   const checker = new PRChecker(cli, data, request, argv);
   const status = await checker.checkAll(argv.checkComments, argv.checkCI);
-  return {
+  const result = {
     status,
     request,
     data,
     metadata,
     checker
   };
+  return {
+    ...result,
+    json: formatMetadataResult(result)
+  };
 };

docs/git-node.md

@@ -291,6 +291,7 @@ Options:
   --file, -f        File to write the metadata in                                 [string]
   --readme          Path to file that contains collaborator contacts              [string]
   --check-comments  Check for 'LGTM' in comments                                 [boolean]
+  --json            Print metadata and PR readiness result as JSON               [boolean]
   --max-commits     Number of commits to warn                        [number] [default: 3]
 ```
 
@@ -309,6 +310,9 @@ $ git node metadata $PRID -o nodejs -r node
 # Or, redirect the metadata to a file while see the checks in stderr
 $ git node metadata $PRID > msg.txt
 
+# Or, get machine-readable metadata and readiness reason codes
+$ git node metadata $PRID --json
+
 # Using it to amend commit messages:
 $ git node metadata $PRID -f msg.txt
 $ echo -e "$(git show -s --format=%B)\n\n$(cat msg.txt)" > msg.txt
@@ -319,6 +323,27 @@ $ git commit --amend -F msg.txt
 git node metadata 167 --repo llnode --readme ../node/README.md
 ```
 
+When `--json` is used, stdout contains a JSON object and progress/check output
+is written to stderr. The command still exits non-zero when the pull request is
+not ready to land. The JSON includes `ready`, `readiness`, `exitCode`,
+`metadata`, `reasonCodes`, and `reasons`. `reasonCodes` is a de-duplicated list
+of stable machine-readable codes such as `missing-approval`,
+`missing-tsc-approval`, `wait-time`, `missing-github-ci`, `pending-github-ci`,
+`conflict`, `requested-changes`, and `stale-review`.
+
+The metadata JSON exit-code contract is:
+
+- `0`: the pull request is ready
+- `20`: the pull request is not ready, but only for deferrable metadata reasons
+  currently owned by the lightweight queue selector: `missing-approval`,
+  `missing-tsc-approval`, and `wait-time`
+- `40`: the pull request is not ready for a hard or mixed reason and should be
+  handled by the existing landing/failure path
+
+Exit codes `20`-`29` are reserved for future deferrable metadata states, and
+`40`-`49` are reserved for future hard metadata failure states. Unexpected tool
+or runtime failures continue to use exit code `1`.
+
 <a id="git-node-metadata-optional-settings"></a>
 
 ### Optional Settings