fix(xdl): do not override google-services.json contents since SDK37 (#…

…1897)

# Why

Following [Using FCM doc](https://docs.expo.io/versions/latest/guides/using-fcm/) or [GoogleSignIn - Usage with Firebase part](https://docs.expo.io/versions/latest/sdk/google-sign-in/#usage-with-firebase) would not render the expected results — `googleSignIn` configuration was always being applied onto `google-services.json`, even if a custom one has been provided by the user. Most probably this is not how this should work or what the user expect.

When pushed to Turtle builders, should fix expo/expo#7727.

# How

Depending on the SDK version of the built project:
- if the SDK is >= 37:
  - only change `google-services.json` if none was provided (so we're operating on a placeholder one)
  - if both configuration settings are provided print a warning and not modify the custom `google-services.json`
- if the SDK is < 37:
  - if the user provides a custom `googleServicesFile`, print a warning that its contents are about to be modified,
  - always modify `google-services.json`, as it has been working before.

I have also moved the `replace "host.exp.exponent" with ${javaPackage}` to where the logic above is mentioned so that all `google-services.json` modifications are in one place.

# Test plan

- SDK37, only `googleServicesFile` — [job](https://staging.expo.io/dashboard/sjchmiela/builds/4dca157f-3ae5-4739-96a7-2a1fbcf2ec0e), no warning, used `google-services.json`
- SDK37, only `googleSignIn` — [job](https://staging.expo.io/dashboard/sjchmiela/builds/2c44d75e-9ce1-4098-ab64-04e76f01efda), no warning, uses placeholder project ID and `googleSignIn` key
- SDK37, both provided — [job](https://staging.expo.io/dashboard/sjchmiela/builds/23626002-acf2-4a30-a620-2062f134d671), warning present (google-services.json overrides others), used `google-services.json`
- SDK36, only `googleServicesFile` — ~[job](https://staging.expo.io/dashboard/sjchmiela/builds/8366c022-dcff-4047-bf0a-0264a52870a1), no warning, **removed key from google-services.json**~ force-pushed version where the warning should be printed and the key still removed
- SDK36, only `googleSignIn` — [job](https://staging.expo.io/dashboard/sjchmiela/builds/d59e4334-a815-4d6a-8ba2-108ab2f5d8bc), no warning, used `googleSignIn` and leaking project ID
- SDK36, both provided — [job](https://staging.expo.io/dashboard/sjchmiela/builds/d5a8ab8f-07f7-4aac-9c64-7012421d1b49), warning present (google-services.json overridden), google-services.json overridden

packages/xdl/src/detach/AndroidShellApp.js

@@ -546,13 +546,6 @@ export async function runShellAppModificationsAsync(context, sdkVersion, buildMo
     path.join(shellPath, 'app', 'build.gradle')
   );
 
-  // Push notifications
-  await regexFileAsync(
-    '"package_name": "host.exp.exponent"',
-    `"package_name": "${javaPackage}"`,
-    path.join(shellPath, 'app', 'google-services.json')
-  ); // TODO: actually use the correct file
-
   // TODO: probably don't need this in both places
   await regexFileAsync(
     /host\.exp\.exponent\.permission\.C2D_MESSAGE/g,
@@ -1074,6 +1067,89 @@ export async function runShellAppModificationsAsync(context, sdkVersion, buildMo
     );
   }
 
+  // Configure google-services.json
+  // It is either already in the shell app (placeholder or real one) or it has been added
+  // from `manifest.android.googleServicesFile`.
+  if (parseSdkMajorVersion(sdkVersion) >= 37) {
+    // New behavior - googleServicesFile overrides googleSignIn configuration
+    if (!manifest.android || !manifest.android.googleServicesFile) {
+      // No google-services.json file, let's use the placeholder one
+      // and insert keys manually ("the old way").
+
+      // This seems like something we can't really get away without:
+      //
+      // 1. A project with google-services plugin won't build without
+      //    a google-services.json file (the plugin makes sure to fail the build).
+      // 2. Adding the google-services plugin conditionally and properly (to be able
+      //    to build a project without that file) is too much hassle.
+      //
+      // So, let's use `host.exp.exponent` as a placeholder for the project's
+      // javaPackage. In custom shell apps there shouldn't ever be "host.exp.exponent"
+      // so this shouldn't cause any problems for advanced users.
+      await regexFileAsync(
+        '"package_name": "host.exp.exponent"',
+        `"package_name": "${javaPackage}"`,
+        path.join(shellPath, 'app', 'google-services.json')
+      );
+
+      // Let's not modify values of the original google-services.json file
+      // if they haven't been provided (in which case, googleAndroidApiKey
+      // and certificateHash will be an empty string). This will make sure
+      // we don't modify shell app's google-services needlessly.
+
+      // Google sign in
+      if (googleAndroidApiKey) {
+        await regexFileAsync(
+          /"current_key": "(.*?)"/,
+          `"current_key": "${googleAndroidApiKey}"`,
+          path.join(shellPath, 'app', 'google-services.json')
+        );
+      }
+      if (certificateHash) {
+        await regexFileAsync(
+          /"certificate_hash": "(.*?)"/,
+          `"certificate_hash": "${certificateHash}"`,
+          path.join(shellPath, 'app', 'google-services.json')
+        );
+      }
+    } else if (googleAndroidApiKey || certificateHash) {
+      // Both googleServicesFile and googleSignIn configuration have been provided.
+      // Let's print a helpful warning and not modify google-services.json.
+      fnLogger.warn(
+        'You have provided values for both `googleServicesFile` and `googleSignIn` in your `app.json`. Since SDK37 `googleServicesFile` overrides any other `google-services.json`-related configuration. Recommended way to fix this warning is to remove `googleSignIn` configuration from your `app.json` in favor of using only `googleServicesFile` to configure Google services.'
+      );
+    }
+  } else {
+    // Old behavior - googleSignIn overrides googleServicesFile
+
+    if (manifest.android && manifest.android.googleServicesFile) {
+      // googleServicesFile provided, let's warn the user that its contents
+      // are about to be modified.
+      fnLogger.warn(
+        'You have provided a custom `googleServicesFile` in your `app.json`. In projects below SDK37 `googleServicesFile` contents will be overridden with `googleSignIn` configuration. (Even if there is none, in which case the API key from `google-services.json` will be removed.) To mitigate this behavior upgrade to SDK37 or check out https://github.com/expo/expo/issues/7727#issuecomment-611544439 for a workaround.'
+      );
+    }
+
+    // Push notifications
+    await regexFileAsync(
+      '"package_name": "host.exp.exponent"',
+      `"package_name": "${javaPackage}"`,
+      path.join(shellPath, 'app', 'google-services.json')
+    );
+
+    // Google sign in
+    await regexFileAsync(
+      /"current_key": "(.*?)"/,
+      `"current_key": "${googleAndroidApiKey}"`,
+      path.join(shellPath, 'app', 'google-services.json')
+    );
+    await regexFileAsync(
+      /"certificate_hash": "(.*?)"/,
+      `"certificate_hash": "${certificateHash}"`,
+      path.join(shellPath, 'app', 'google-services.json')
+    );
+  }
+
   // Set manifest url for debug mode
   if (buildMode === 'debug') {
     await regexFileAsync(
@@ -1094,18 +1170,6 @@ export async function runShellAppModificationsAsync(context, sdkVersion, buildMo
     );
   }
 
-  // Google sign in
-  await regexFileAsync(
-    /"current_key": "(.*?)"/,
-    `"current_key": "${googleAndroidApiKey}"`,
-    path.join(shellPath, 'app', 'google-services.json')
-  );
-  await regexFileAsync(
-    /"certificate_hash": "(.*?)"/,
-    `"certificate_hash": "${certificateHash}"`,
-    path.join(shellPath, 'app', 'google-services.json')
-  );
-
   // Facebook configuration
 
   // There's no such pattern to replace in shell apps below SDK 36,