fix: fallback to open rules when Storage emulator rules are missing

[christhompsongoogle]

Description

Prevent missing configurations for the Storage emulator from crashing emulators:start and blocking the rest of the emulator suite:

• Fall back to default open rules with a warning for Storage emulator when rules are unconfigured on non-demo projects.
• Fall back to default open rules with a warning when storage target in firebase.json is not configured in .firebaserc.
• Refactor duplicated warning logging logic into a helper function.

Fixes b/546204399

Scenarios Tested

• Unit tests in storage/rules/config.spec.ts for missing storage config, missing rules, and demo/non-demo projects.

Sample Commands

• firebase init emulators (select all emulators)
• firebase emulators:start

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[gemini-code-assist]

Code Review

This pull request updates the Storage emulator to fall back to default open rules with a warning when rules or targets are unconfigured, rather than throwing an error. The review feedback correctly identifies that returning default rules immediately within the target loop will discard successfully parsed rules for other targets. The reviewer suggests using continue to skip unconfigured targets, returning default rules only if no targets were successfully configured, and adding a test case to verify this multi-target behavior.

[gemini-code-assist]

Returning defaultStorageRules() immediately here will discard any successfully parsed rules for other targets that were already processed and added to results. Instead, we should continue the loop to skip this unconfigured target, and only fall back to the default rules at the end of the function if no targets were successfully configured.

Suggested change

	return defaultStorageRules();
	continue;

References

1. The style guide recommends using continue statements in loops to handle edge cases early and keep main logic flat. ^(link)

[gemini-code-assist]

If all targets were skipped because they were unconfigured (meaning results is empty), we should fall back to the default open rules. Otherwise, we should return the successfully parsed rules in results.

Suggested change

	return results;
	if (results.length === 0) {
	return defaultStorageRules();
	}
	return results;

[gemini-code-assist]

Let's add a test case to verify that when multiple targets are configured, but only some are missing in .firebaserc, the emulator successfully parses the configured targets and skips the missing ones instead of discarding all rules.

  it("should use default config when target is missing in .firebaserc", () => {
    const config = getOptions({
      data: {
        storage: [{ target: "missing-target", rules: "main.rules" }],
      },
      path: resolvePath,
    });
    const result = getStorageRulesConfig(PROJECT_ID, config) as SourceFile;

    expect(result.name).to.contain("templates/emulators/default_storage.rules");
    expect(result.content).to.contain("allow read, write;");
  });

  it("should parse configured targets and skip missing targets in .firebaserc", () => {
    const mainRulesContent = Buffer.from(StorageRulesFiles.readWriteIfTrue.content);
    const mainRulesPath = persistence.appendBytes("storage_main.rules", mainRulesContent);

    const config = getOptions({
      data: {
        storage: [
          { target: "main", rules: mainRulesPath },
          { target: "missing-target", rules: "missing.rules" },
        ],
      },
      path: resolvePath,
    });
    config.rc.applyTarget(PROJECT_ID, "storage", "main", ["bucket_0"]);
    const result = getStorageRulesConfig(PROJECT_ID, config) as RulesConfig[];

    expect(result.length).to.equal(1);
    expect(result[0].resource).to.eql("bucket_0");
    expect(result[0].rules.name).to.equal(mainRulesPath);
  });