feat(swift): generate Version.swift with sdkVersion constant

[Swimburger]

Description

Adds Version.swift generation to the Swift SDK generator, embedding the SDK version as a public source-level constant. This brings the Swift generator in line with other SDK generators and fixes auto-versioning for Swift SDKs (the magic placeholder version will now appear in git diffs, allowing the auto-versioning system to detect and bump versions).

Split from #14719 (git tag fallback for auto-versioning) so each concern can be reviewed independently.

Changes Made

• Added generateVersionFile() method to SdkGeneratorCli.ts that emits Version.swift with a top-level public let sdkVersion constant
• The file is only generated when minVersion is available (i.e., GitHub output mode with a version configured — not for local/download modes)
• Added versions.yml entry for Swift SDK generator 0.31.0

Updates since last revision

• Made sdkVersion constant public so SDK consumers can access it (Swift defaults to internal access)
• Ran seed tests (swift-sdk): 122/123 passed (1 expected failure in literal)
• Committed seed test snapshot updates — all fixtures now include Version.swift with public let sdkVersion = "0.0.1" (the seed default version)

Testing

• Seed tests run and passing (122/123, 1 expected failure)
• Seed snapshots committed (122 Version.swift files added across all swift-sdk fixtures)
• Manual testing not performed locally

Review Checklist

• Verify that addSourceAsIsFile with name "Version" won't collide with any IR-generated type names
• Confirm top-level public let sdkVersion = "..." is acceptable Swift style (vs. namespacing inside a struct or enum)
• Confirm the generated constant is intentionally not yet wired into User-Agent or other headers (this PR is purely for consistency and auto-versioning support)

Link to Devin session: https://app.devin.ai/sessions/eeaa831f68d14737a731b1c8cb4968b4
Requested by: @Swimburger

---

[devin-ai-integration]

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 2 additional findings.

[github-actions]

SDK Generation Benchmark Results

Comparing PR branch against latest nightly baseline on main (2026-04-07T04:47:12Z).

Full benchmark table (click to expand)

Generator	Spec	main (generator)	main (E2E)	PR (generator)	Delta
swift-sdk	square	142s	506s	140s	-2s (-1.4%)

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: 2026-04-07T04:47:12Z). Trigger benchmark-baseline to refresh.

[hex-security-app]

Unsanitized version string injected into generated Swift source code

The version string is interpolated directly into a Swift string literal without escaping " or \:

contents: `public let sdkVersion = "${version}"\n`

version is user-supplied (e.g. via --version CLI flag or generators.yml). A value containing " or a newline breaks out of the Swift string literal and injects arbitrary Swift statements into the generated Version.swift. For example, --version '1.0.0"\npublic func backdoor() {}' would produce valid, compilable Swift with an injected declaration that is committed to the SDK repo and distributed to every SDK consumer.

This was flagged in the previous review pass; the prior thread became "outdated" when the let → public let change landed without adding escaping.

Prompt To Fix With AI

In `generateVersionFile` in `generators/swift/sdk/src/SdkGeneratorCli.ts`, escape `\` and `"` before embedding the version in the Swift string literal.

```typescript
private generateVersionFile(context: SdkGeneratorContext): void {
    const spmDetails = context.getSPMDetails();
    const version = spmDetails.minVersion;
    if (version != null) {
        const escapedVersion = version.replace(/\\/g, "\\\\").replace(/"/g, '\\"');
        context.project.addSourceAsIsFile({
            nameCandidateWithoutExtension: "Version",
            directory: RelativeFilePath.of(""),
            contents: `public let sdkVersion = "${escapedVersion}"\n`
        });
    }
}
```

This is the only change needed — `\` must be escaped first (to avoid double-escaping), then `"`.

---

_{Severity: low | Confidence: 85%}

[github-actions]

SDK Generation Benchmark Results

Comparing PR branch against latest nightly baseline on main (2026-04-07T04:47:12Z).

Full benchmark table (click to expand)

Generator	Spec	main (generator)	main (E2E)	PR (generator)	Delta
swift-sdk	square	142s	506s	149s	+7s (+4.9%)

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: 2026-04-07T04:47:12Z). Trigger benchmark-baseline to refresh.

[kafkas]

All looks good