add release-notes output

Add a new `release-notes` output to the action containing the release
notes for the newly released versions, allowing consumers to leverage it
in their workflows (e.g. by passing it down to the GitHub Release API).

Author: nbusseneau

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Add a new `release-notes` output to the action containing the release notes for the newly released versions.
+
 ## [3.0.0] - 2024-04-08
 
 ### Fixed

__tests__/fixtures/empty_release/release-notes.expected.md

@@ -0,0 +1,3 @@
+### Added
+
+- Everything since the beginning!

__tests__/fixtures/first_release/release-notes.expected.md

@@ -0,0 +1,3 @@
+### Changed
+
+- Our main theme is now blue instead of red.

__tests__/fixtures/lowercase_link_reference/release-notes.expected.md

@@ -0,0 +1,3 @@
+### Changed
+
+- Our main theme is now blue instead of red.

__tests__/fixtures/standard/release-notes.expected.md

@@ -0,0 +1,3 @@
+### Changed
+
+- Our main theme is now blue instead of red.

__tests__/fixtures/tag_on_tag/release-notes.expected.md

@@ -0,0 +1,35 @@
+import getReleaseNotes from "../src/getReleaseNotes";
+import { read } from "to-vfile";
+
+interface Fixture {
+  tag: string;
+  version: string;
+  date: string;
+  genesisHash: string;
+  owner: string;
+  repo: string;
+}
+
+it.each(["empty_release", "standard", "first_release", "lowercase_link_reference", "tag_release", "tag_on_tag"])(
+  `should extract %s release-notes output`,
+  async function(testcase) {
+    const expectedChangelog = await read(
+      `./__tests__/fixtures/${testcase}/CHANGELOG.expected.md`,
+      {
+        encoding: "utf-8"
+      }
+    );
+    const release: Fixture = await import(
+      `./fixtures/${testcase}/fixture`
+    ).then(module => module.default);
+
+    const expectedReleaseNotes = await read(
+      `./__tests__/fixtures/${testcase}/release-notes.expected.md`,
+      {
+        encoding: "utf-8"
+      }
+    ).then(expected => expected.toString("utf-8"));
+    const actualReleaseNotes = getReleaseNotes(expectedChangelog, release.version);
+    expect(actualReleaseNotes).toEqual(expectedReleaseNotes);
+  }
+);

__tests__/fixtures/tag_release/release-notes.expected.md

@@ -17,6 +17,9 @@ inputs:
   changelogPath:
     description: 'The path to the changelog file. Defaults to `./CHANGELOG.md`'
     required: false
+outputs:
+  release-notes:
+    description: 'The release notes of the newly released version'
 runs:
   using: 'node20'
   main: 'dist/index.js'

__tests__/getReleaseNotes.test.ts

@@ -0,0 +1,55 @@
+import unified, { Transformer } from "unified";
+import markdown from "remark-parse";
+import stringify from "remark-stringify";
+import { VFile } from "vfile";
+import { Node } from "unist";
+import { MarkdownRootNode } from "markdown-nodes";
+
+function releaseNotesExtraction(version: string) {
+  return transformer as unknown as Transformer;
+
+  function transformer(tree: MarkdownRootNode, _file: VFile) {
+    const children = tree.children;
+
+    const firstNodeIndex = children.findIndex(
+      node => node.type === "heading" && node.depth === 2 &&
+        node.children.length > 1 && node.children[0].type === "linkReference" &&
+        node.children[0].identifier === version
+    ) + 1;
+    const firstNode = children.slice(firstNodeIndex);
+
+    let lastNodeIndex = firstNode.findIndex(
+      node => node.type === "heading" && node.depth === 2
+    );
+    // special case: release notes for first release will not end with another
+    // section, instead they end with the compare URLs
+    if (lastNodeIndex === -1) {
+      lastNodeIndex = firstNode.findIndex(
+        node => node.type === "definition" && node.identifier === "unreleased"
+      );
+    }
+  
+    const releaseNotesNodes = firstNode.slice(0, lastNodeIndex);
+    tree.children = releaseNotesNodes;
+    return tree as Node;
+  }
+}
+
+export default function getReleaseNotes(
+  file: VFile,
+  version: string
+): string {
+  // @ts-ignore
+  return unified()
+    .use(markdown)
+    .use(releaseNotesExtraction, version)
+    .data("settings", {
+      listItemIndent: "1",
+      tightDefinitions: true,
+      bullet: "-"
+    })
+    .use(stringify)
+    .processSync(file)
+    .toString("utf-8")
+    .trim();
+}

action.yml

@@ -1,8 +1,10 @@
 import { setFailed } from "@actions/core";
+import { setOutput } from "@actions/core/lib/core";
 import { read, write } from "to-vfile";
 import updateChangelog from "./updateChangelog";
 import getInputs from "./getInputs";
 import getGenesisHash from "./getGenesisHash";
+import getReleaseNotes from "./getReleaseNotes";
 
 async function run(): Promise<void> {
   try {
@@ -20,8 +22,10 @@ async function run(): Promise<void> {
       owner,
       repo
     );
-
     await write(newChangelog, { encoding: "utf-8" });
+
+    const releaseNotes = getReleaseNotes(newChangelog, version);
+    setOutput("release-notes", releaseNotes);
   } catch (error) {
     setFailed(error.message);
   }