fix(php,csharp): order parameters with default values after required parameters

[davidkonigsberg]

Description

Refs #15998

PR #15998 (feat(openapi): Add better support for x-fern-base-path) introduced path parameters with clientDefault values (e.g. apiVersion = 'v1beta'). This caused two issues:

1. PHP SDK: Generated method signatures placed required parameters after parameters with default values, triggering PHPStan's PHP 8.0 deprecation: Required parameter $request follows optional parameter $apiVersion
2. C# SDK: Dynamic snippets passed positional arguments in the wrong order, causing type mismatch compilation errors
3. Both generators: Dynamic snippets emitted positional args in the old order even after the method signature was corrected

Changes Made

• generators/php/codegen/src/ast/Method.ts: Updated parameter ordering logic to also treat parameters with an initializer (default value) as optional, placing them after required parameters in the generated method signature
• generators/php/dynamic-snippets/src/EndpointSnippetGenerator.ts: Separated root-level path parameters (which may have defaults from x-fern-base-path) from endpoint-specific path parameters, placing root-level params after the body argument to match the corrected method signature ordering
• generators/csharp/dynamic-snippets/src/EndpointSnippetGenerator.ts: Applied the same root/endpoint path parameter separation for both getMethodArgsForBodyRequest and getMethodArgsForInlinedRequest, matching AbstractEndpointGenerator's ordering of [...requiredPathParams, requestParam, ...optionalPathParams]
• Updated seed snapshots for both php-sdk and csharp-sdk api-wide-base-path-with-default fixtures
• Added changelog entries for both PHP and C# SDK generators

Testing

• Seed test php-sdk --fixture api-wide-base-path-with-default passes
• Seed test csharp-sdk --fixture api-wide-base-path-with-default passes
• Verified generated PHP signature: create(Widget $request, string $apiVersion = 'v1beta', ?array $options = null)
• Verified generated C# snippet: CreateAsync(new Widget { Name = "name" }, "v1beta")
• Verified generated PHP snippet: create(new Widget([...]), 'v1beta')

Link to Devin session: https://app.devin.ai/sessions/8c891e927684448ea73ec4c26f9cd87a
Requested by: @davidkonigsberg

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SDK Generation Benchmark Results

Comparing PR branch against median of 5 nightly run(s) on main (latest: 2026-05-20T05:20:23Z).

Full benchmark table (click to expand)

Generator	Spec	main (generator)	main (E2E)	PR (generator)	Delta
csharp-sdk	square	67s (n=5)	105s (n=5)	68s	+1s (+1.5%)
php-sdk	square	54s (n=5)	81s (n=5)	56s	+2s (+3.7%)

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: 2026-05-20T05:20:23Z). Trigger benchmark-baseline to refresh.
Last updated: 2026-05-20 13:08 UTC