fix: paintWhenInitiallyHidden on Windows/Linux

script/lint-roller-chromium-changes.mjs

@@ -124,7 +124,7 @@ async function main () {
   // Get the merge base with the target branch
   let mergeBase;
   try {
-    mergeBase = execSync(`git merge-base HEAD origin/${targetBranch}`, {
+    mergeBase = execSync(`git merge-base ${currentBranch} origin/${targetBranch}`, {
       cwd: ELECTRON_DIR,
       encoding: 'utf8'
     }).trim();

script/release/uploaders/upload.py

@@ -368,9 +368,6 @@ def upload_io_to_github(release, filename, filepath, version):
       for c in iter(lambda: upload_process.stdout.read(1), b""):
         sys.stdout.buffer.write(c)
         sys.stdout.flush()
-    upload_process.wait()
-    if upload_process.returncode != 0:
-      sys.exit(upload_process.returncode)
 
   if "GITHUB_OUTPUT" in os.environ:
     output_path = os.environ["GITHUB_OUTPUT"]

shell/browser/api/electron_api_browser_window.cc

@@ -49,6 +49,7 @@ BrowserWindow::BrowserWindow(gin::Arguments* args,
   // when initially hidden
   bool paint_when_initially_hidden = true;
   options.Get(options::kPaintWhenInitiallyHidden, &paint_when_initially_hidden);
+  paint_when_initially_hidden_ = paint_when_initially_hidden;
   if (!paint_when_initially_hidden) {
     bool show = true;
     options.Get(options::kShow, &show);
@@ -288,6 +289,17 @@ void BrowserWindow::OnWindowHide() {
   BaseWindow::OnWindowHide();
 }
 
+void BrowserWindow::RenderViewReady() {
+  // When paintWhenInitiallyHidden is true and the native window has not been
+  // shown yet, tell the WebContents it is visible so the renderer's compositor
+  // starts producing frames.  Without this the renderer's LayerTreeHost stays
+  // hidden and no CompositorFrames (and therefore no presentation callbacks)
+  // are ever produced, which means PerformanceObserver paint-timing entries
+  // (first-paint / first-contentful-paint) never fire.
+  if (paint_when_initially_hidden_ && !window()->IsVisible())
+    web_contents()->WasShown();
+}
+
 void BrowserWindow::Show() {
   web_contents()->WasShown();
   BaseWindow::Show();

shell/browser/api/electron_api_browser_window.h

@@ -42,6 +42,7 @@ class BrowserWindow : public BaseWindow,
 
   // content::WebContentsObserver:
   void BeforeUnloadDialogCancelled() override;
+  void RenderViewReady() override;
   void WebContentsDestroyed() override;
 
   // ExtendedWebContentsObserver:
@@ -79,6 +80,12 @@ class BrowserWindow : public BaseWindow,
  private:
   // Helpers.
 
+  // When true and the window is created with show: false, the renderer is
+  // told it is visible as soon as it is ready so that PerformanceObserver
+  // paint‐timing entries (first-paint / first-contentful-paint) are
+  // produced even before the native window is shown.
+  bool paint_when_initially_hidden_ = false;
+
   v8::Global<v8::Value> web_contents_;
   v8::Global<v8::Value> web_contents_view_;
   base::WeakPtr<api::WebContents> api_web_contents_;

shell/browser/api/electron_api_msix_updater.cc

@@ -9,7 +9,6 @@
 #include "base/environment.h"
 #include "base/functional/bind.h"
 #include "base/logging.h"
-#include "base/strings/string_number_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/task/single_thread_task_runner.h"
 #include "content/public/browser/browser_task_traits.h"
@@ -280,8 +279,7 @@ void OnDeploymentCompleted(std::unique_ptr<DeploymentCallbackData> data,
         HRESULT error_code;
         hr = async_info->get_ErrorCode(&error_code);
         if (SUCCEEDED(hr)) {
-          error +=
-              " (" + base::NumberToString(static_cast<int>(error_code)) + ")";
+          error += " (" + std::to_string(static_cast<int>(error_code)) + ")";
         }
       }
     }
@@ -800,10 +798,10 @@ v8::Local<v8::Value> GetPackageInfo() {
         ABI::Windows::ApplicationModel::PackageVersion pkg_version;
         hr = package_id->get_Version(&pkg_version);
         if (SUCCEEDED(hr)) {
-          std::string version = base::NumberToString(pkg_version.Major) + "." +
-                                base::NumberToString(pkg_version.Minor) + "." +
-                                base::NumberToString(pkg_version.Build) + "." +
-                                base::NumberToString(pkg_version.Revision);
+          std::string version = std::to_string(pkg_version.Major) + "." +
+                                std::to_string(pkg_version.Minor) + "." +
+                                std::to_string(pkg_version.Build) + "." +
+                                std::to_string(pkg_version.Revision);
           result.Set("version", version);
         }
       }

shell/browser/api/electron_api_web_contents.cc

@@ -23,7 +23,6 @@
 #include "base/json/json_reader.h"
 #include "base/no_destructor.h"
 #include "base/strings/strcat.h"
-#include "base/strings/string_number_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/task/current_thread.h"
 #include "base/threading/scoped_blocking_call.h"
@@ -2660,7 +2659,7 @@ void WebContents::RestoreHistory(
       thrower.ThrowError(
           "Failed to restore navigation history: Invalid navigation entry at "
           "index " +
-          base::NumberToString(index) + ".");
+          std::to_string(index) + ".");
       return;
     }
 

shell/common/node_bindings.cc

@@ -18,7 +18,6 @@
 #include "base/environment.h"
 #include "base/path_service.h"
 #include "base/run_loop.h"
-#include "base/strings/string_number_conversions.h"
 #include "base/strings/string_split.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/task/single_thread_task_runner.h"
@@ -193,7 +192,7 @@ void V8OOMErrorCallback(const char* location, const v8::OOMDetails& details) {
 
 #if !IS_MAS_BUILD()
   electron::crash_keys::SetCrashKey("electron.v8-oom.is_heap_oom",
-                                    base::NumberToString(details.is_heap_oom));
+                                    std::to_string(details.is_heap_oom));
   if (location) {
     electron::crash_keys::SetCrashKey("electron.v8-oom.location", location);
   }

spec/api-browser-window-spec.ts

@@ -6721,28 +6721,35 @@ describe('BrowserWindow module', () => {
     w.loadFile(path.join(fixtures, 'pages', 'send-after-node.html'));
   });
 
-  // TODO(codebytere): fix on Windows and Linux too
-  ifdescribe(process.platform === 'darwin')('window.webContents initial paint', () => {
+  describe('window.webContents initial paint', () => {
     afterEach(closeAllWindows);
-    it('paints when a window is initially hidden', async () => {
-      const w = new BrowserWindow({ show: false });
+    it('paints when a window is initially hidden with paintWhenInitiallyHidden', async () => {
+      const w = new BrowserWindow({
+        show: false,
+        paintWhenInitiallyHidden: true
+      });
       await w.loadFile(path.join(fixtures, 'pages', 'a.html'));
 
       const entries = await w.webContents.executeJavaScript(`
         new Promise((resolve) => {
-          const observer = new PerformanceObserver((performance) => {
-            observer.disconnect();
-            resolve(performance.getEntries());
+          const observer = new PerformanceObserver((list) => {
+            const paintEntries = list.getEntries().filter(
+              e => e.name === 'first-paint' || e.name === 'first-contentful-paint'
+            );
+            if (paintEntries.length > 0) {
+              observer.disconnect();
+              resolve(paintEntries.map(e => e.name));
+            }
           });
           observer.observe({ entryTypes: ['paint'] });
-        });
 
-        const header = document.createElement('h1');
-        header.innerText = 'Paint me!!';
-        document.getElementById('div').appendChild(header);
+          const header = document.createElement('h1');
+          header.innerText = 'Paint me!!';
+          document.getElementById('div').appendChild(header);
+        });
       `);
 
-      expect(JSON.stringify(entries)).to.eq('{}');
+      expect(entries).to.be.an('array').that.includes('first-contentful-paint');
     });
   });