tests/test-config-parselist.py

update: add a Rust fast-path when updating from null (and clean)

This case is easy to detect and we have all we need to generate a valid
working copy and dirstate entirely in Rust, which speeds things up
considerably:

On my machine updating a repo of ~300k files goes from 10.00s down to 4.2s,
all while consuming 50% less system time, with all caches hot.
Something to note is that further improvements will probably happen
with the upcoming `InnerRevlog` series that does smarter
mmap hanlding, especially for filelogs.

Here are benchmark numbers on a machine with only 4 cores (and no SMT enabled)

```
### data-env-vars.name               = heptapod-public-2024-03-25-ds2-pnm
  # benchmark.name                   = hg.command.update
  # bin-env-vars.hg.py-re2-module    = default
  # bin-env-vars.hg.changeset.node   = <this change>
  # benchmark.variants.atomic-update = no
  # benchmark.variants.scenario      = null-to-tip
  # benchmark.variants.worker        = default
default: 5.328762  ~~~~~
rust: 1.308654  (-75.44%, -4.02)
### data-env-vars.name               = mercurial-devel-2024-03-22-ds2-pnm
  # benchmark.name                   = hg.command.update
  # bin-env-vars.hg.py-re2-module    = default
  # bin-env-vars.hg.changeset.node   = <this change>
  # benchmark.variants.atomic-update = no
  # benchmark.variants.scenario      = null-to-tip
  # benchmark.variants.worker        = default
default: 1.693271  ~~~~~
rust: 1.151053  (-32.02%, -0.54)
### data-env-vars.name               = mozilla-unified-2024-03-22-ds2-pnm
  # benchmark.name                   = hg.command.update
  # bin-env-vars.hg.py-re2-module    = default
  # bin-env-vars.hg.changeset.node   = <this change>
  # benchmark.variants.atomic-update = no
  # benchmark.variants.scenario      = null-to-tip
  # benchmark.variants.worker        = default
default: 38.901613  ~~~~~
rust: 11.637880 (-70.08%, -27.26)
### data-env-vars.name               = netbsd-xsrc-public-2024-09-19-ds2-pnm
  # benchmark.name                   = hg.command.update
  # bin-env-vars.hg.py-re2-module    = default
  # bin-env-vars.hg.changeset.node   = <this change>
  # benchmark.variants.atomic-update = no
  # benchmark.variants.scenario      = null-to-tip
  # benchmark.variants.worker        = default
default: 4.793727  ~~~~~
rust: 1.505905  (-68.59%, -3.29)
```

"""
List-valued configuration keys have an ad-hoc microsyntax. From `hg help config`:

> List values are separated by whitespace or comma, except when values are
> placed in double quotation marks:
>
>     allow_read = "John Doe, PhD", brian, betty
>
> Quotation marks can be escaped by prefixing them with a backslash. Only
> quotation marks at the beginning of a word is counted as a quotation
> (e.g., ``foo"bar baz`` is the list of ``foo"bar`` and ``baz``).

That help documentation is fairly light on details, the actual parser has many
other edge cases. This test tries to cover them.
"""

from mercurial.utils import stringutil


def assert_parselist(input, expected):
    result = stringutil.parselist(input)
    if result != expected:
        raise AssertionError(
            "parse_input(%r)\n     got %r\nexpected %r"
            % (input, result, expected)
        )


# Keep these Python tests in sync with the Rust ones in `rust/hg-core/src/config/values.rs`

assert_parselist(b'', [])
assert_parselist(b',', [])
assert_parselist(b'A', [b'A'])
assert_parselist(b'B,B', [b'B', b'B'])
assert_parselist(b', C, ,C,', [b'C', b'C'])
assert_parselist(b'"', [b'"'])
assert_parselist(b'""', [b'', b''])
assert_parselist(b'D,"', [b'D', b'"'])
assert_parselist(b'E,""', [b'E', b'', b''])
assert_parselist(b'"F,F"', [b'F,F'])
assert_parselist(b'"G,G', [b'"G', b'G'])
assert_parselist(b'"H \\",\\"H', [b'"H', b',', b'H'])
assert_parselist(b'I,I"', [b'I', b'I"'])
assert_parselist(b'J,"J', [b'J', b'"J'])
assert_parselist(b'K K', [b'K', b'K'])
assert_parselist(b'"K" K', [b'K', b'K'])
assert_parselist(b'L\tL', [b'L', b'L'])
assert_parselist(b'"L"\tL', [b'L', b'', b'L'])
assert_parselist(b'M\x0bM', [b'M', b'M'])
assert_parselist(b'"M"\x0bM', [b'M', b'', b'M'])
assert_parselist(b'"N"  , ,"', [b'N"'])
assert_parselist(b'" ,O,  ', [b'"', b'O'])