* Change `InterfaceWitness` -> `ImplWitness`
* Include a `SpecificId` in the `ImplWitness`. This allows the
`InstBlock` it contains to have its own identity, allowing it to be
changed as the impl is processed. Evaluation only updates the specific.
* Create the `ImplWitness` at the start of the impl definition. In the
future, this will be populated with the values of non-function
associated constants. For now, it starts full of invalid instruction
ids.
* Implements the model suggested in #4672 .
Note that the non-SemIR testdata changes are to these file:
* `toolchain/check/testdata/impl/lookup/fail_todo_undefined_impl.carbon`
* `toolchain/check/testdata/struct/import.carbon`
* `toolchain/check/testdata/tuple/import.carbon`
The last two are due to an import of generics bug exposed by this PR,
which will be fixed in a follow-on.
---------
Co-authored-by: Josh L <josh11b@users.noreply.github.com>
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
Add `EXTRA-ARGS:` support to file_test, to add arguments without
overriding the default arguments. Use `EXTRA-ARGS: --no-dump-sem-ir` to
turn off SemIR dumping and thus SemIR testing in the int builtin tests,
which validate correct behavior through diagnostics instead.
This doesn't get us any closer to supporting more targeted SemIR dumping
/ testing, but this seems to be a generally useful feature anyway. Most
existing
tests using `ARGS` have been switched over to using `EXTRA-ARGS`.
Requested in review of #4716.
