perf(dev): skip unchanged process-host package rebuilds (#29317)

Co-authored-by: OrcaWin <293788423+OrcaWin@users.noreply.github.com>

config/build-plugins/process-host-dev-rebuild.ts

@@ -49,13 +49,22 @@ export function createProcessHostDevRebuildPlugin(root = process.cwd()): Plugin
   let signalDirectory: string | undefined
   let signalFile: string | undefined
   let signalVersion = 0
+  let packageDirty = true
+  let packageFiles = new Set<string>()
   return {
     name: 'orca-process-host-dev-rebuild',
+    watchChange(id) {
+      const file = resolve(id)
+      if (packageFiles.has(file) || file === signalFile) {
+        packageDirty = true
+      }
+    },
     buildStart() {
       if (!this.meta.watchMode) {
         return
       }
       const inputs = processHostInputs(root)
+      packageFiles = new Set(inputs.files.map((file) => resolve(file)))
       for (const file of inputs.files) {
         this.addWatchFile(file)
       }
@@ -87,6 +96,7 @@ export function createProcessHostDevRebuildPlugin(root = process.cwd()): Plugin
         const watcher = ts.sys.watchDirectory(
           directory,
           () => {
+            packageDirty = true
             if (signalFile) {
               writeFileSync(signalFile, String(++signalVersion))
             }
@@ -96,6 +106,9 @@ export function createProcessHostDevRebuildPlugin(root = process.cwd()): Plugin
         )
         directoryWatchers.set(directory, { recursive, watcher })
       }
+      if (!packageDirty) {
+        return
+      }
       // The external package must finish emitting before electron-vite restarts the app. The
       // package's own build keeps its compiler and per-file atomic dist sync identical to build:packages.
       const result = runProcessSync({
@@ -113,6 +126,7 @@ export function createProcessHostDevRebuildPlugin(root = process.cwd()): Plugin
           `[process-host-dev-rebuild] Package compilation failed: ${result.stderr || result.stdout || result.signal || result.code}`
         )
       }
+      packageDirty = false
     },
     closeWatcher() {
       signalFile = undefined

config/scripts/process-host-dev-rebuild.test.ts

@@ -38,7 +38,7 @@ function fixture(): { root: string; packageDir: string; main: string } {
   // Runs the real package build against this fixture package.
   writeFileSync(
     join(packageDir, 'scripts', 'build-dist.mjs'),
-    `const { buildPackageDist } = await import(${JSON.stringify(pathToFileURL(resolve(realPackageDir, 'scripts', 'build-dist.mjs')).href)})\nawait buildPackageDist(${JSON.stringify(packageDir)})\n`
+    `import { appendFileSync } from 'node:fs'\nappendFileSync(${JSON.stringify(join(packageDir, 'builds.txt'))}, 'build\\n')\nconst { buildPackageDist } = await import(${JSON.stringify(pathToFileURL(resolve(realPackageDir, 'scripts', 'build-dist.mjs')).href)})\nawait buildPackageDist(${JSON.stringify(packageDir)})\n`
   )
   mkdirSync(join(root, 'node_modules', '@orca'), { recursive: true })
   const packageRequire = createRequire(join(realPackageDir, 'package.json'))
@@ -127,6 +127,29 @@ function readEmittedVersion(root: string): number {
 }
 
 describe('External process-host development rebuilds', () => {
+  it('skips package compilation when only application code changes', async () => {
+    const { root, packageDir, main } = fixture()
+    const watcher = watch({
+      input: main,
+      external: ['@orca/process-host'],
+      plugins: [createProcessHostDevRebuildPlugin(root)],
+      output: { file: join(root, 'out', 'main.cjs'), format: 'cjs' }
+    })
+    watchers.push(watcher)
+    closeSuccessfulBundles(watcher)
+    await nextEvent(watcher, 'END')
+    const builds = join(packageDir, 'builds.txt')
+    expect(readFileSync(builds, 'utf8')).toBe('build\n')
+
+    const rebuilt = nextEvent(watcher, 'END')
+    writeFileSync(main, "module.exports = { ...require('@orca/process-host'), changed: true }\n")
+    await rebuilt
+
+    expect(readEmittedVersion(root)).toBe(1)
+    expect(readFileSync(join(root, 'out', 'main.cjs'), 'utf8')).toContain('changed')
+    expect(readFileSync(builds, 'utf8')).toBe('build\n')
+  })
+
   it('emits private source edits and new imports before the Electron reload hook', async () => {
     const { root, packageDir, main } = fixture()
     const loadedVersions: number[] = []