"""Utilities for reading values from pyproject.toml."""

load("@toml.bzl", "toml")

load(":version.bzl", "version")

def read_pyproject(module_ctx, pyproject):

"""Read a pyproject.toml file and return the relevant fields.

The file is parsed with a pure-Starlark TOML decoder; no Python

interpreter is required. The raw `requires-python` value is returned

as-is so that callers can decide how to interpret it.

Args:

module_ctx: the module extension context (needs `path` and `read`).

pyproject: {type}`Label` pointing at the pyproject.toml file.

Returns:

{type}`struct` with the attributes:

* `requires_python`: {type}`str | None` the raw `requires-python`

value (e.g. `"==3.13.9"`), or `None` if it is not set.

"""

data = toml.decode(module_ctx.read(module_ctx.path(pyproject), watch = "yes"))

return struct(

requires_python = data.get("project", {}).get("requires-python"),

)

def version_from_requires_python(requires_python):

"""Derive a concrete Python version from a `requires-python` value.

Currently only an exact `==X.Y.Z` specifier is supported. The value is

validated and normalized via {obj}`//python/private:version.bzl` so that

malformed input fails in a consistent way. Broader specifier support

(e.g. `>=`, `X.Y`) can be layered on here in the future.

Args:

requires_python: {type}`str` the raw `requires-python` value.

Returns:

{type}`str` the normalized version string (e.g. `"3.13.9"`).

"""

if not requires_python:

fail("`requires-python` must be specified")

if not requires_python.startswith("=="):

fail("`requires-python` must pin an exact version with `==`, got: {}".format(requires_python))

bare_version = requires_python[len("=="):].strip()

# Parse strictly so malformed versions fail cleanly, then normalize.

version.parse(bare_version, strict = True)

return version.normalize(bare_version)