comparison mercurial/debugcommands.py @ 42451:810f66b468cd

rust: module policy with importrust

We introduce two rust+c module policies and a new
`policy.importrust()` that makes use of them.

This simple approach provides runtime switching of
implementations, which is crucial for the performance
measurements such as those Octobus does with ASV.

It can also be useful for bug analysis.

It also has the advantage of making conditionals in
Rust callers more uniform, in particular
abstracting over specifics like `demandimport`

At this point, the build stays unchanged, with the rust-cpython based
`rustext` module being built if HGWITHRUSTEXT=cpython.

More transparency for the callers, i.e., just using
`policy.importmod` would be a much longer term and riskier
effort for the following reasons:

1. It would require to define common module boundaries
   for the three or four cases (pure, c, rust+ext, cffi) and that
   is premature with the Rust extension currently under heavy
   development in areas that are outside the scope of the C extensions.
2. It would imply internal API changes that are not currently wished,
   as the case of ancestors demonstrates.
3. The lack of data or property-like attributes (tp_member
   and tp_getset) in current `rust-cpython` makes it impossible to
   achieve direct transparent replacement of pure Python classes by
   Rust extension code, meaning that the caller sometimes has to be able
   to make adjustments or provide additional wrapping.

42450:9d31581cc44e

    fm.write('hgmodulepolicy', _("checking module policy (%s)\n"),
             policy.policy)
    fm.write('hgmodules', _("checking installed modules (%s)...\n"),
             os.path.dirname(pycompat.fsencode(__file__)))

    if policy.policy in ('c', 'allow'):
        err = None
        try:
            from .cext import (
                base85,
                bdiff,
                mpatch,
                osutil,
            )
            dir(bdiff), dir(mpatch), dir(base85), dir(osutil) # quiet pyflakes
        except Exception as inst:
            err = stringutil.forcebytestr(inst)
            problems += 1
        fm.condwrite(err, 'extensionserror', " %s\n", err)

42451:810f66b468cd

    fm.write('hgmodulepolicy', _("checking module policy (%s)\n"),
             policy.policy)
    fm.write('hgmodules', _("checking installed modules (%s)...\n"),
             os.path.dirname(pycompat.fsencode(__file__)))

    rustandc = policy.policy in ('rust+c', 'rust+c-allow')
    rustext = rustandc  # for now, that's the only case
    cext = policy.policy in ('c', 'allow') or rustandc
    nopure = cext or rustext
    if nopure:
        err = None
        try:
            if cext:
                from .cext import (
                    base85,
                    bdiff,
                    mpatch,
                    osutil,
                )
                # quiet pyflakes
                dir(bdiff), dir(mpatch), dir(base85), dir(osutil)
            if rustext:
                from .rustext import (
                    ancestor,
                    dirstate,
                )
                dir(ancestor), dir(dirstate) # quiet pyflakes
        except Exception as inst:
            err = stringutil.forcebytestr(inst)
            problems += 1
        fm.condwrite(err, 'extensionserror', " %s\n", err)