playwright-test: Add PLAYWRIGHT_BROWSERS_PATH to build environment

This allows writing self-contained node scripts (using a nix-shell
shebang), without requiring a separate shell.nix which sets
PLAYWRIGHT_BROWSERS_PATH to pkgs.playwright-driver.browsers.

pkgs/development/web/playwright/driver.nix

@@ -12,6 +12,7 @@
   makeFontsConf,
   makeWrapper,
   runCommand,
+  writeText,
   cacert,
 }:
 let
@@ -191,9 +192,25 @@ let
       runHook postInstall
     '';
 
+    setupHook = writeText "setupHook.sh" ''
+      addBrowsersPath () {
+        export PLAYWRIGHT_BROWSERS_PATH="${playwright-core.passthru.browsers}"
+      }
+
+      addEnvHooks "$targetOffset" addBrowsersPath
+    '';
+
     meta = playwright.meta // {
       mainProgram = "playwright";
     };
+
+    passthru.tests.env = runCommand "playwright-core-env-test" {
+      buildInputs = [
+        nodejs
+        playwright-core
+        playwright-test
+      ];
+    } "node ${./test.js}";
   });
 
   browsers-mac = stdenv.mkDerivation {

pkgs/development/web/playwright/test.js

@@ -0,0 +1,8 @@
+const playwright = require('playwright');
+const fs = require('fs');
+playwright.chromium.launch()
+    .then((browser) => {
+        console.log('OK');
+        fs.writeFileSync(process.env.out, '');
+        process.exit(0);
+    });