schema-type-name-sanitization

name	schema-type-name-sanitization
description	Handle malformed OpenAPI schema names that collapse to empty generated C# type names, especially trailing-dot definition keys.
domain	generator
confidence	high
source	observed

Context

Use this when Refitter emits a blank contract declaration (partial class with no name) or an empty generic like Task<> for a response type even though the OpenAPI schema exists.

Patterns

• Refitter inherits schema type names from NSwag/NJsonSchema unless it explicitly injects a custom TypeNameGenerator.
• NJsonSchema DefaultTypeNameGenerator treats . as a segment separator via GetLastSegment().
• A trailing-dot schema key such as LookUpErnResponse. yields an empty final segment, and the anonymous-name fallback can also return an empty string.
• Once that empty name is registered in the resolver, the failure propagates everywhere that schema type is used: DTO declarations, method return types, and file names.
• The safest Refitter-side mitigation is a narrow custom type-name generator in CSharpClientGeneratorFactory that only repairs empty-tail/blank-name cases while preserving default naming for normal schemas.
• If a malformed schema key normalizes to the same hint as an existing clean schema key (for example LookUpErnResponse. vs LookUpErnResponse), prefer the clean key's base name and force the malformed key onto the counted collision variant (LookUpErnResponse2, etc.).
• The tester-side regression shape is a minimal inline Swagger/OpenAPI fixture plus four proofs: no blank partial class, no Task<>, one concrete sanitized DTO name reused in both contract and interface signature assertions, and a compile gate.

Examples

• Swagger/OpenAPI definition key LookUpErnResponse. -> generated internal partial class with no identifier.
• Response $ref: "#/definitions/LookUpErnResponse." -> generated Task<> instead of Task<LookUpErnResponse>.
• Safe normalization target: LookUpErnResponse. -> LookUpErnResponse.
• Safe collision target: clean LookUpErnResponse stays LookUpErnResponse, malformed LookUpErnResponse. becomes LookUpErnResponse2.

Anti-Patterns

• Do not patch RefitInterfaceGenerator to special-case empty return types; that only masks the upstream DTO naming failure.
• Do not rewrite component/definition keys and all refs unless absolutely necessary; that is broader and riskier than fixing emitted type naming.
• Do not replace every dot blindly; preserve the current "last non-empty segment" behavior for normal dotted hints and only repair malformed empty-tail cases.