chore(ci): Build modified backends on PR (#6086)

* chore(stablediffusion-ggml): rm redundant comment

Signed-off-by: Richard Palethorpe <io@richiejp.com>

* chore(ci): Build modified backends on PR

Signed-off-by: Richard Palethorpe <io@richiejp.com>

---------

Signed-off-by: Richard Palethorpe <io@richiejp.com>

scripts/changed-backends.js

@@ -0,0 +1,79 @@
+import fs from "fs";
+import yaml from "js-yaml";
+import { Octokit } from "@octokit/core";
+
+// Load backend.yml and parse matrix.include
+const backendYml = yaml.load(fs.readFileSync(".github/workflows/backend.yml", "utf8"));
+const jobs = backendYml.jobs;
+const backendJob = jobs["backend-jobs"];
+const strategy = backendJob.strategy;
+const matrix = strategy.matrix;
+const includes = matrix.include;
+
+// Set up Octokit for PR changed files
+const token = process.env.GITHUB_TOKEN;
+const octokit = new Octokit({ auth: token });
+
+const eventPath = process.env.GITHUB_EVENT_PATH;
+const event = JSON.parse(fs.readFileSync(eventPath, "utf8"));
+
+let prNumber, repo, owner;
+if (event.pull_request) {
+  prNumber = event.pull_request.number;
+  repo = event.repository.name;
+  owner = event.repository.owner.login;
+} else {
+  throw new Error("This workflow must be triggered by a pull_request event.");
+}
+
+async function getChangedFiles() {
+  let files = [];
+  let page = 1;
+  while (true) {
+    const res = await octokit.request('GET /repos/{owner}/{repo}/pulls/{pull_number}/files', {
+      owner,
+      repo,
+      pull_number: prNumber,
+      per_page: 100,
+      page
+    });
+    files = files.concat(res.data.map(f => f.filename));
+    if (res.data.length < 100) break;
+    page++;
+  }
+  return files;
+}
+
+// Infer backend path
+function inferBackendPath(item) {
+  if (item.dockerfile.endsWith("python")) {
+    return `backend/python/${item.backend}`;
+  }
+  if (item.dockerfile.endsWith("golang")) {
+    return `backend/go/${item.backend}`;
+  }
+  if (item.dockerfile.endsWith("llama-cpp")) {
+    return `backend/cpp/llama-cpp`;
+  }
+  return null;
+}
+
+(async () => {
+  const changedFiles = await getChangedFiles();
+
+  console.log("Changed files:", changedFiles);
+
+  const filtered = includes.filter(item => {
+    const backendPath = inferBackendPath(item);
+    if (!backendPath) return false;
+    return changedFiles.some(file => file.startsWith(backendPath));
+  });
+
+  console.log("Filtered files:", filtered);
+
+  const hasBackends = filtered.length > 0 ? 'true' : 'false';
+  console.log("Has backends?:", hasBackends);
+
+  fs.appendFileSync(process.env.GITHUB_OUTPUT, `has-backends=${hasBackends}\n`);
+  fs.appendFileSync(process.env.GITHUB_OUTPUT, `matrix=${JSON.stringify({ include: filtered })}\n`);
+})();