The lnt test suite defines custom result codes [1]. Support those via
an extension API instead of "by accident", which should offer the
advantage of properly handling them when we print test results.
[1] https://reviews.llvm.org/D77986
Reviewed By: Meinersbur
Differential Revision: https://reviews.llvm.org/D78164
The shtest-inject test relied on being executed in "single process" mode
and started to fail with a `PicklingError` after it was removed:
```
Can't pickle <class 'lit.TestingConfig.CustomFormat'>: attribute
lookup lit.TestingConfig.CustomFormat failed
```
This happened because the test config has to be serialized to the worker
process, but apparently the `CustomFormat` class defined inline is not
serializable.
This change allows passing the tested functionality (preamble_commands)
directly to `lit.formats.ShTest` so we can use it directly in the test.
This allows creating custom test formats on top of `executeShTest` that
inject commands at the beginning of the file being parsed, without
requiring these commands to physically appear in the test file itself.
For example, one could define a test format that prints out additional
debug information at the beginning of each test. More realistically,
this has been used to define custom test formats like one that supports
compilation failure tests (e.g. with the extension `compile.fail.cpp`)
by injecting a command that calls the compiler on the file itself and
expects it to fail.
Without this change, the only alternative is to create a temporary file
with the same content as the original test, then prepend the desired
`// RUN:` lines to that file, and call `executeShTest` on that file
instead. This is both slow and cumbersome to do.
Differential Revision: https://reviews.llvm.org/D76290
Julian Lettner