25357472185

Committed 05 May 2026 04:13AM UTC coverage: 92.941% (-0.02%) from 92.956%

Build # 25357472185

Build Type

push

github

Committed by

web-flow

Commit Message

Better change detection on deleted files (#23311)

There are several longstanding issues on this:

https://github.com/pantsbuild/pants/issues/13232
https://github.com/pantsbuild/pants/issues/14975
https://github.com/pantsbuild/pants/issues/17512
https://github.com/pantsbuild/pants/issues/23240

This has historically been intractable because the
design of dep inference and of change detection
are at odds with each other.

A fully robust solution is still somewhat out of reach,
but this change provides a general-purpose mechanism
that backends can opt in to, and uses that mechanism
in the python backend.

The result is a substantial yet incremental improvement
in the most prominent use case.

The limitation of this mechanism is that it can only
be used if a backend can infer a likely dependency on
a file simply from its path. In Python this is possible because
dotted module paths must recapitulate the filesystem path
from the source root. But this is not true in general for
all languages.

Coverage Stats

56 of 78 new or added lines in 8 files covered. (71.79%)

4 existing lines in 3 files now uncovered.

91907 of 98887 relevant lines covered (92.94%)

4.04 hits per line

Source File
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96.15

/src/python/pants/backend/tools/preamble/subsystem.py

# Copyright 2022 Pants project contributors (see CONTRIBUTORS.md).
# Licensed under the Apache License, Version 2.0 (see LICENSE).
from __future__ import annotations

from collections.abc import Sequence

from pants.option.option_types import DictOption, SkipOption
from pants.option.subsystem import Subsystem
from pants.source.filespec import FilespecMatcher
from pants.util.strutil import help_text, softwrap


class PreambleSubsystem(Subsystem):
    options_scope = "preamble"
    name = "preamble"
    help = help_text(
        """
        Formats files with a preamble, with the preamble looked up based on path.

        This is useful for things such as copyright headers or shebang lines.

        Pants substitutes the following identifiers (following Python's `string.Template` substitutions):
        - $year: The current year (only used when actually writing the year to the file).
        """
    )

    skip = SkipOption("fmt")

    _template_by_globs = DictOption[str](
        help=softwrap(
            """
            Which preamble template to use based on the path globs (relative to the build root).

            Example:

                {
                    '*.rs': '// Copyright (c) $year\\n// Line 2\\n'
                    '*.py:!__init__.py': '# Copyright (c) $year\\n# Line 2\\n',
                }

            It might be helpful to load this config from a JSON or YAML file. To do that, set
            `[preamble].config = '@path/to/config.yaml'`, for example.
            """
        ),
        fromfile=True,
    )

    @property
    def template_by_globs(self) -> dict[tuple[str, ...], str]:
        return {tuple(key.split(":")): value for key, value in self._template_by_globs.items()}

    def get_template_by_path(self, filepaths: Sequence[str]) -> dict[str, str]:
        """Returns a mapping from path to (most-relevant) template."""
        filepaths_to_test = set(filepaths)
        template_by_path = {}
        for globs, template in self.template_by_globs.items():
            if not filepaths_to_test:
                break

            matched_filepaths = FilespecMatcher(
                includes=[
                    (glob[2:] if glob.startswith(r"\\!") else glob)
                    for glob in globs
                    if not glob.startswith("!")
                ],
                excludes=[glob[1:] for glob in globs if glob.startswith("!")],
            ).matches(tuple(filepaths_to_test))
            filepaths_to_test -= set(matched_filepaths)
            for filepath in matched_filepaths:
                template_by_path[filepath] = template

        return template_by_path

1	# Copyright 2022 Pants project contributors (see CONTRIBUTORS.md).
2	# Licensed under the Apache License, Version 2.0 (see LICENSE).
3	from __future__ import annotations	1✔
4
5	from collections.abc import Sequence	1✔
6
7	from pants.option.option_types import DictOption, SkipOption	1✔
8	from pants.option.subsystem import Subsystem	1✔
9	from pants.source.filespec import FilespecMatcher	1✔
10	from pants.util.strutil import help_text, softwrap	1✔
11
12
13	class PreambleSubsystem(Subsystem):	1✔
14	options_scope = "preamble"	1✔
15	name = "preamble"	1✔
16	help = help_text(	1✔
17	"""
18	Formats files with a preamble, with the preamble looked up based on path.
19
20	This is useful for things such as copyright headers or shebang lines.
21
22	Pants substitutes the following identifiers (following Python's `string.Template` substitutions):
23	- $year: The current year (only used when actually writing the year to the file).
24	"""
25	)
26
27	skip = SkipOption("fmt")	1✔
28
29	_template_by_globs = DictOption[str](	1✔
30	help=softwrap(
31	"""
32	Which preamble template to use based on the path globs (relative to the build root).
33
34	Example:
35
36	{
37	'*.rs': '// Copyright (c) $year\\n// Line 2\\n'
38	'*.py:!__init__.py': '# Copyright (c) $year\\n# Line 2\\n',
39	}
40
41	It might be helpful to load this config from a JSON or YAML file. To do that, set
42	`[preamble].config = '@path/to/config.yaml'`, for example.
43	"""
44	),
45	fromfile=True,
46	)
47
48	@property	1✔
49	def template_by_globs(self) -> dict[tuple[str, ...], str]:	1✔
50	return {tuple(key.split(":")): value for key, value in self._template_by_globs.items()}	1✔
51
52	def get_template_by_path(self, filepaths: Sequence[str]) -> dict[str, str]:	1✔
53	"""Returns a mapping from path to (most-relevant) template."""
54	filepaths_to_test = set(filepaths)	1✔
55	template_by_path = {}	1✔
56	for globs, template in self.template_by_globs.items():	1✔
57	if not filepaths_to_test:	1✔
UNCOV 58	break	×
59
60	matched_filepaths = FilespecMatcher(	1✔
61	includes=[
62	(glob[2:] if glob.startswith(r"\\!") else glob)
63	for glob in globs
64	if not glob.startswith("!")
65	],
66	excludes=[glob[1:] for glob in globs if glob.startswith("!")],
67	).matches(tuple(filepaths_to_test))
68	filepaths_to_test -= set(matched_filepaths)	1✔
69	for filepath in matched_filepaths:	1✔
70	template_by_path[filepath] = template	1✔
71
72	return template_by_path	1✔

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