fix(swift): support multi-URL environments in client initialization

[devin-ai-integration]

Description

The Swift SDK generator did not handle APIs whose environments expose multiple base URLs per server group (IR environment type multipleBaseUrls). For those APIs the generator emitted a single baseURL: String client initializer and routed every request through clientConfig.baseURL, so there was no way to target the correct server per endpoint. This is why the multi-url-environment-reference fixture was listed under allowedFailures in seed/swift-sdk/seed.yml.

This PR adds general multi-URL environment support so the fixture compiles and passes seed tests, and removes it from allowedFailures.

Changes Made

• Added MultiUrlEnvironmentGenerator which emits an environment struct holding one URL field per server group and a static let for each declared environment, e.g.:

  public struct ApiEnvironment: Sendable {
      public let base: String
      public let auth: String
      public let upload: String
      public static let production: ApiEnvironment = ApiEnvironment(
          base: "https://api.example.com/2.0",
          auth: "https://auth.example.com/oauth2",
          upload: "https://upload.example.com/2.0"
      )
      // ...
  }

• SdkGeneratorCli.generateSourceEnvironmentFile now switches on the environment IR type, using the existing single-URL enum generator for singleBaseUrl and the new struct generator for multipleBaseUrls.
• RootClientGenerator now generates an environment: parameter (instead of baseURL:) for multi-URL APIs and flattens it into the client config as a baseURLs dictionary keyed by server id.
• EndpointMethodGenerator threads the endpoint's baseUrl id into performRequest(..., baseUrlId:) so each call resolves the right server.
• Client templates (ClientConfig, HTTPClient) gained a backwards-compatible optional baseURLs map and baseUrlId parameter; HTTPClient.resolveBaseURL(baseUrlId:) returns the per-server URL when present and otherwise falls back to baseURL. The new parameters default to nil, so single-URL SDKs are unaffected.
• Regenerated seed/swift-sdk snapshots (the template additions touch every fixture's ClientConfig/HTTPClient; multi-URL fixtures also get an environment struct).
• Removed multi-url-environment-reference from allowedFailures in seed/swift-sdk/seed.yml.
• Added a changelog entry under generators/swift/sdk/changes/unreleased/.

Testing

• seed test --generator swift-sdk --fixture multi-url-environment-reference → 1/1 passed (compiles + wire tests).
• Verified no regression on a multi-URL fixture not in allowedFailures (websocket-multi-url) and a single-URL fixture (imdb) — both build and pass.
• pnpm run check (biome) clean; @fern-api/swift-sdk typechecks.

Link to Devin session: https://app.devin.ai/sessions/89ba0b887e2a43e4ba37cf802d84981f
Requested by: @iamnamananand996

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[devin-ai-integration]

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[devin-ai-integration]

Devin Review found 1 potential issue.

[devin-ai-integration]

🚩 multi-url-environment and multi-url-environment-no-default remain in allowedFailures

This PR removes multi-url-environment-reference from allowedFailures but leaves multi-url-environment and multi-url-environment-no-default in the list, even though the PR generates proper multi-URL environment structs and client code for those fixtures as well (visible in the seed output diffs). This might be intentional if those fixtures fail for reasons unrelated to environment generation (e.g., other unsupported features), but it's worth confirming whether they can now also be removed from allowedFailures.

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[devin-ai-integration]

Good catch — I verified both locally with the full seed test (compile + wire tests):

• multi-url-environment-no-default → still fails to build. With no default environment there's no value to seed the convenience initializer's environment: default with, so it doesn't yet compile. It legitimately needs more work and stays in allowedFailures.
• multi-url-environment → now passes with this change (it just emits the non-fatal ⚠ test cases succeeded unexpectedly warning while it remains in the list).

This PR is intentionally scoped to only multi-url-environment-reference per the task; multi-url-environment / multi-url-environment-no-default are owned by separate PRs, so I left both entries intact here rather than removing multi-url-environment out of scope.

[github-actions]

SDK Generation Benchmark Results

Comparing PR branch against median of 5 nightly run(s) on main (latest: 2026-06-22T05:47:30Z).

Full benchmark table (click to expand)

Generator	Spec	main (generator)	main (E2E)	PR (generator)	Delta
swift-sdk	square	58s (n=5)	435s (n=5)	49s	-9s (-15.5%)

main (generator): generator-only time via --skip-scripts (includes Docker image build, container startup, IR parsing, and code generation — this is the same Docker-based flow customers use via fern generate). main (E2E): full customer-observable time including build/test scripts (nightly baseline, informational). Delta is computed against generator-only baseline.
⚠️ = generation exited with a non-zero exit code (timing may not reflect a successful run).
Baseline from nightly runs on main (latest: 2026-06-22T05:47:30Z). Trigger benchmark-baseline to refresh.
Last updated: 2026-06-23 05:34 UTC