Share generated interface member descriptors - #97

Summary

• Add the opt-in --shared-interface-members JavaScript codegen flag.
• Reuse canonical required-interface prototype descriptors on compatible concrete classes.
• Keep conflicts, overloads, ambiguous interface identities, and one-off interfaces class-local.
• Preserve the default generation path, raw interface APIs, deep imports, and mixed-flag incremental safety.

Compatibility

The implementation uses one canonical interface identity for source emission and descriptor copying. It falls back to class-local members for ambiguous flat filenames and rejects incompatible incremental overwrites.

When sharing replaces an inline raw-interface declaration, the class deep module preserves the same public JS/TypeScript import through an equivalent canonical re-export. Declaration APIs and import paths are preserved, but flag-on .d.ts files are not byte-identical. Flag-off/default output remains byte-compatible.

The option is JavaScript-only and disabled by default.

Corrected isolated Gallery A/B

Measured with the latest branch, the same 32 Gallery WinMDs and 99 references, and no bundle post-processing:

File sets and all 2,781 root exports are preserved. Deep modules lose no baseline exports; two modules gain canonical raw-interface re-exports. TypeScript root/deep import validation passes and unsafe copied sources are zero.

Validation

• Default JS/Python output matches the base branch.
• Uri deep IStringable JS/DTS imports are preserved, including Node 22 ESM named imports.
• Shared-to-unflagged incremental generation preserves existing source markers.
• Duplicate same-name TypeDefs retain distinct IIDs for ambiguity planning.
• Gallery Binding/Router smoke and E2E: 37/37 passed.
• Full cargo test -p dynwinrt-codegen passed.

Recommendation

Correctness and compatibility issues are resolved, but the final measured benefit is negligible and the first-screen dependency graph becomes larger and more cyclic. Based on the current data, this change does not provide enough value to justify merging in its present form.