Exceptions: implement C API. (#12861)

* Exceptions: implement C API.

This PR implements C (and C++) API support for Wasm exceptions, one
final remaining hurdle (aside from fuzz-testing) for making

Exceptions: implement C API. (#12861)

* Exceptions: implement C API.

This PR implements C (and C++) API support for Wasm exceptions, one
final remaining hurdle (aside from fuzz-testing) for making exceptions
tier-1 and on-by-default.

* Review feedback, and add exnref case to `wasmtime_val_t`.

* Review feedback: GC feature guard.

* clang-format

* add docs to exn.hh.

* Remove tag size asserts: broken on 32-bit platforms, but not needed for correctness wrt C struct.

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Merge wasm_tag type into wasm_functype / clean up C API tag headers (#12803)

* Merge wasm_tag type into wasm_functype / clean up C API tag headers

- Move tag type info into wasm.h alongside other c

Merge wasm_tag type into wasm_functype / clean up C API tag headers (#12803)

* Merge wasm_tag type into wasm_functype / clean up C API tag headers

- Move tag type info into wasm.h alongside other core types instead of
a separate wasmtime/tag.h header
- Remove wasmtime/tag.h (contents merged into wasm.h / wasm.hh)
- Update extern.hh and tag.hh to reflect new layout
- Add tag param accessors in func.rs
- Refactor tag.rs to match updated C API surface
- Update tag_type.cc tests accordingly

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

* doc-wasm.h: add wasm_tagtype_t documentation and fix wasm_name typo

Add Doxygen documentation for the `wasm_tagtype_t` type and its
associated functions (`wasm_tagtype_new`, `wasm_tagtype_functype`,
vec helpers, and externtype conversion functions). Also document
`WASM_EXTERN_TAG` and the `wasm_tagtype_as_externtype*` /
`wasm_externtype_as_tagtype*` conversion functions.

Fix pre-existing typo: `wasm_name_new_new_uninitialized` ->
`wasm_name_new_uninitialized`.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

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Co-authored-by: Claude Sonnet 4.6 <[email protected]>

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c-api: implement wasm_tagtype_t for exception tag types (#10252) (#12763)

* c-api: implement wasm_tagtype_t for exception tag types (#10252)

Implement the C embedder API for WebAssembly exception t

c-api: implement wasm_tagtype_t for exception tag types (#10252) (#12763)

* c-api: implement wasm_tagtype_t for exception tag types (#10252)

Implement the C embedder API for WebAssembly exception tags, resolving
the long-standing todo!() in CExternType::new() that caused a Rust panic
whenever a module with tag exports had its exports enumerated via the
C API (e.g. wasm_module_exports / wasmtime_module_exports).

Changes:
- Add wasm_tagtype_t type with wasm_tagtype_new/params/delete/copy and
the standard as_externtype / externtype_as_tagtype cast functions
- Add WASM_EXTERN_TAG = 4 constant to wasm_externkind_enum in wasm.h
- Add CExternType::Tag(CTagType) variant; wire into CExternType::new()
and wasm_externtype_kind()
- Add wasmtime/types/tag.hh C++ wrapper (TagType / TagType::Ref)
- Extend ExternType::Ref variant and ref_from_c() switch in extern.hh
- Add TagType tests: construction, module export enumeration (regression
for #10252), and wasm_externtype_kind / cast function correctness

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

* c-api: move tag type declarations to wasmtime/tag.h

- Revert wasm.h to its vendored upstream state (it must not be modified
locally; tag support is not yet in the upstream wasm-c-api spec header)
- Add crates/c-api/include/wasmtime/tag.h with wasm_tagtype_t forward
declaration, WASM_EXTERN_TAG constant, and all wasm_tagtype_* /
wasm_externtype_as_tagtype* function declarations
- Include wasmtime/tag.h from wasmtime.h

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

* Apply rustfmt and clang-format to tag type implementation

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

* Fix Clippy warnings: remove unused imports and dead code

Drop unused `wasm_tagtype_t` import from extern.rs, and remove the
`force`/`ty`/`wasm_tagtype_t::new` dead-code paths from tag.rs that
were written for future engine-resolution support but are not yet called.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

* Redesign tag type API with wasmtime_* prefix per reviewer feedback

- Rename wasm_tagtype_t → wasmtime_tagtype_t and all wasm_tagtype_*
functions → wasmtime_tagtype_* to avoid clashing with future wasm.h
additions (as requested by alexcrichton)
- Constructor now takes wasm_engine_t* + wasm_valkind_t array + count
instead of wasm_valtype_vec_t, eliminating the lazy-init complexity
- Replace wasm_tagtype_params() (returning a vec) with
wasmtime_tagtype_param_count() + wasmtime_tagtype_param(nth),
matching the component type accessor iterator pattern
- Rename WASM_EXTERN_TAG → WASMTIME_EXTERN_TAG
- Simplify CTagType: stores TagType directly, no Arc<Mutex<LazyTagType>>
- Update C++ TagType wrapper: constructor takes Engine&, Ref exposes
param_count() / param(nth) instead of params() returning ListRef
- Add ValType::c_to_kind() static helper used by TagType::Ref::param()
- Fix null-pointer panic for zero-length param arrays in Rust

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

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Co-authored-by: Claude Sonnet 4.6 <[email protected]>

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