fix(launchdoctor): make launch doctor to warn on Win7 (#4718)

Windows 7 was end-of-lifed on January 14, 2020. We don't support this
system, but we'd like to have a best-effort to work there.

It does look like Chromium is missing some libraries on Win 7, however
it still manages to work there. To support this usecase, this patch
starts printing console warning about missing libraries on Win 7 only
instead of refusing to launch.

Fixes #3496

src/server/validateDependencies.ts

@@ -31,7 +31,10 @@ export async function validateHostRequirements(browserPath: string, browser: Bro
   const ubuntuVersion = await getUbuntuVersion();
   if (browser.name === 'firefox' && ubuntuVersion === '16.04')
     throw new Error(`Cannot launch firefox on Ubuntu 16.04! Minimum required Ubuntu version for Firefox browser is 18.04`);
-  await validateDependencies(browserPath, browser);
+  if (os.platform() === 'linux')
+    return await validateDependenciesLinux(browserPath, browser);
+  if (os.platform() === 'win32' && os.arch() === 'x64')
+    return await validateDependenciesWindows(browserPath, browser);
 }
 
 const DL_OPEN_LIBRARIES = {
@@ -41,12 +44,14 @@ const DL_OPEN_LIBRARIES = {
   clank: [],
 };
 
-async function validateDependencies(browserPath: string, browser: BrowserDescriptor) {
-  // We currently only support Linux.
-  if (os.platform() === 'linux')
-    return await validateDependenciesLinux(browserPath, browser);
-  if (os.platform() === 'win32' && os.arch() === 'x64')
-    return await validateDependenciesWindows(browserPath, browser);
+function isSupportedWindowsVersion(): boolean {
+  if (os.platform() !== 'win32' || os.arch() !== 'x64')
+    return false;
+  const [major, minor] = os.release().split('.').map(token => parseInt(token, 10));
+  // This is based on: https://stackoverflow.com/questions/42524606/how-to-get-windows-version-using-node-js/44916050#44916050
+  // The table with versions is taken from: https://docs.microsoft.com/en-us/windows/win32/api/winnt/ns-winnt-osversioninfoexw#remarks
+  // Windows 7 is not supported and is encoded as `6.1`.
+  return major > 6 || (major === 6 && minor > 1);
 }
 
 async function validateDependenciesWindows(browserPath: string, browser: BrowserDescriptor) {
@@ -101,7 +106,13 @@ async function validateDependenciesWindows(browserPath: string, browser: Browser
       `    ${[...missingDeps].join('\n    ')}`,
       ``);
 
-  throw new Error(`Host system is missing dependencies!\n\n${details.join('\n')}`);
+  const message = `Host system is missing dependencies!\n\n${details.join('\n')}`;
+  if (isSupportedWindowsVersion()) {
+    throw new Error(message);
+  } else {
+    console.warn(`WARNING: running on unsupported windows version!`);
+    console.warn(message);
+  }
 }
 
 async function validateDependenciesLinux(browserPath: string, browser: BrowserDescriptor) {