Compile with -warnings-as-errors in CI (incl. StrictSendability)

[simonjbeaumont]

Motivation

We were not compiling with -warnings-as-errors in CI because some of the reference source code contained deprecation annotations. This meant that we are not getting CI failures for other warnings that we'd like to be clean of; specifically strict concurrency. However, in addition to the file-based reference tests, we now have in-memory snippet-based reference tests, which contain tests for deprecated OpenAPI schemas and operations.

Modifications

• Remove deprecated tests from file-based reference test.
• Clean up warnings under StrictConcurrency.
• Compile with -warnings-as-errors in CI.
• Opt into StrictConcurrency and -warnings-as-errors locally with environment variable.

Result

• CI will catch sendability warning regressions.
• Developing locally with SWIFT_OPENAPI_STRICT_CONCURRENCY will enable the same behaviour.

Test Plan

• Added a canary commit to the end of this PR with a sendability issue, which will be reverted before merging.

[simonjbeaumont]

Canary commit shows that the CI will help us catch the warnings¹:

[737/761] Compiling OpenAPIGeneratorReferenceTests CompatabilityTest.swift
/code/Tests/OpenAPIGeneratorReferenceTests/CompatabilityTest.swift:213:42: error: capture of 'diagnosticsCollector' with non-sendable type 'RecordingDiagnosticCollector' in a `@Sendable` closure
                            diagnostics: diagnosticsCollector
                                         ^
/code/Tests/OpenAPIGeneratorReferenceTests/CompatabilityTest.swift:335:21: note: class 'RecordingDiagnosticCollector' does not conform to the 'Sendable' protocol
private final class RecordingDiagnosticCollector: DiagnosticCollector {
                    ^
...
error: fatalError
1

I'll now revert the canary commit for review.

Footnotes

1. https://ci.swiftserver.group/job/swift-openapi-generator-swift59-prb/500/console ↩

[czechboy0]