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anchors: Add new rule to detect undeclared or duplicated anchors
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According to the YAML specification [^1]:

- > It is an error for an alias node to use an anchor that does not
  > previously occur in the document.

  The `forbid-undeclared-aliases` option checks that aliases do have a
  matching anchor declared previously in the document. Since this is
  required by the YAML spec, this option is enabled by default.

- > The alias refers to the most recent preceding node having the same
  > anchor.

  This means that having a same anchor repeated in a document is
  allowed. However users could want to avoid this, so the new option
  `forbid-duplicated-anchors` allows that. It's disabled by default.

- > It is not an error to specify an anchor that is not used by any
  > alias node.

  This means that it's OK to declare anchors but don't have any alias
  referencing them. However users could want to avoid this, so a new
  option (e.g. `forbid-unused-anchors`) could be implemented in the
  future. See #537.

Fixes #395
Closes #420

[^1]: https://yaml.org/spec/1.2.2/#71-alias-nodes
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@adrienverge
adrienverge committed Mar 22, 2023
1 parent 8aaa226 commit ebd6b90
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5 changes: 5 additions & 0 deletions docs/rules.rst
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Expand Up @@ -14,6 +14,11 @@ This page describes the rules and their options.
:local:
:depth: 1

anchors
-------

.. automodule:: yamllint.rules.anchors

braces
------

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209 changes: 209 additions & 0 deletions tests/rules/test_anchors.py
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# Copyright (C) 2023 Adrien Vergé
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.

from tests.common import RuleTestCase


class AnchorsTestCase(RuleTestCase):
rule_id = 'anchors'

def test_disabled(self):
conf = 'anchors: disable'
self.check('---\n'
'- &b true\n'
'- &i 42\n'
'- &s hello\n'
'- &f_m {k: v}\n'
'- &f_s [1, 2]\n'
'- *b\n'
'- *i\n'
'- *s\n'
'- *f_m\n'
'- *f_s\n'
'---\n' # redeclare anchors in a new document
'- &b true\n'
'- &i 42\n'
'- &s hello\n'
'- *b\n'
'- *i\n'
'- *s\n'
'---\n'
'block mapping: &b_m\n'
' key: value\n'
'extended:\n'
' <<: *b_m\n'
' foo: bar\n'
'---\n'
'{a: 1, &x b: 2, c: &y 3, *x: 4, e: *y}\n'
'...\n', conf)
self.check('---\n'
'- &i 42\n'
'---\n'
'- &b true\n'
'- &b true\n'
'- &b true\n'
'- &s hello\n'
'- *b\n'
'- *i\n' # declared in a previous document
'- *f_m\n' # never declared
'- *f_m\n'
'- *f_m\n'
'- *f_s\n' # declared after
'- &f_s [1, 2]\n'
'---\n'
'block mapping: &b_m\n'
' key: value\n'
'---\n'
'block mapping 1: &b_m_bis\n'
' key: value\n'
'block mapping 2: &b_m_bis\n'
' key: value\n'
'extended:\n'
' <<: *b_m\n'
' foo: bar\n'
'---\n'
'{a: 1, &x b: 2, c: &x 3, *x: 4, e: *y}\n'
'...\n', conf)

def test_forbid_undeclared_aliases(self):
conf = ('anchors:\n'
' forbid-undeclared-aliases: true\n'
' forbid-duplicated-anchors: false\n')
self.check('---\n'
'- &b true\n'
'- &i 42\n'
'- &s hello\n'
'- &f_m {k: v}\n'
'- &f_s [1, 2]\n'
'- *b\n'
'- *i\n'
'- *s\n'
'- *f_m\n'
'- *f_s\n'
'---\n' # redeclare anchors in a new document
'- &b true\n'
'- &i 42\n'
'- &s hello\n'
'- *b\n'
'- *i\n'
'- *s\n'
'---\n'
'block mapping: &b_m\n'
' key: value\n'
'extended:\n'
' <<: *b_m\n'
' foo: bar\n'
'---\n'
'{a: 1, &x b: 2, c: &y 3, *x: 4, e: *y}\n'
'...\n', conf)
self.check('---\n'
'- &i 42\n'
'---\n'
'- &b true\n'
'- &b true\n'
'- &b true\n'
'- &s hello\n'
'- *b\n'
'- *i\n' # declared in a previous document
'- *f_m\n' # never declared
'- *f_m\n'
'- *f_m\n'
'- *f_s\n' # declared after
'- &f_s [1, 2]\n'
'---\n'
'block mapping: &b_m\n'
' key: value\n'
'---\n'
'block mapping 1: &b_m_bis\n'
' key: value\n'
'block mapping 2: &b_m_bis\n'
' key: value\n'
'extended:\n'
' <<: *b_m\n'
' foo: bar\n'
'---\n'
'{a: 1, &x b: 2, c: &x 3, *x: 4, e: *y}\n'
'...\n', conf,
problem1=(9, 3),
problem2=(10, 3),
problem3=(11, 3),
problem4=(12, 3),
problem5=(13, 3),
problem6=(24, 7),
problem7=(27, 36))

def test_forbid_duplicated_anchors(self):
conf = ('anchors:\n'
' forbid-undeclared-aliases: false\n'
' forbid-duplicated-anchors: true\n')
self.check('---\n'
'- &b true\n'
'- &i 42\n'
'- &s hello\n'
'- &f_m {k: v}\n'
'- &f_s [1, 2]\n'
'- *b\n'
'- *i\n'
'- *s\n'
'- *f_m\n'
'- *f_s\n'
'---\n' # redeclare anchors in a new document
'- &b true\n'
'- &i 42\n'
'- &s hello\n'
'- *b\n'
'- *i\n'
'- *s\n'
'---\n'
'block mapping: &b_m\n'
' key: value\n'
'extended:\n'
' <<: *b_m\n'
' foo: bar\n'
'---\n'
'{a: 1, &x b: 2, c: &y 3, *x: 4, e: *y}\n'
'...\n', conf)
self.check('---\n'
'- &i 42\n'
'---\n'
'- &b true\n'
'- &b true\n'
'- &b true\n'
'- &s hello\n'
'- *b\n'
'- *i\n' # declared in a previous document
'- *f_m\n' # never declared
'- *f_m\n'
'- *f_m\n'
'- *f_s\n' # declared after
'- &f_s [1, 2]\n'
'---\n'
'block mapping: &b_m\n'
' key: value\n'
'---\n'
'block mapping 1: &b_m_bis\n'
' key: value\n'
'block mapping 2: &b_m_bis\n'
' key: value\n'
'extended:\n'
' <<: *b_m\n'
' foo: bar\n'
'---\n'
'{a: 1, &x b: 2, c: &x 3, *x: 4, e: *y}\n'
'...\n', conf,
problem1=(5, 3),
problem2=(6, 3),
problem3=(21, 18),
problem4=(27, 20))
1 change: 1 addition & 0 deletions yamllint/conf/default.yaml
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Expand Up @@ -6,6 +6,7 @@ yaml-files:
- '.yamllint'

rules:
anchors: enable
braces: enable
brackets: enable
colons: enable
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2 changes: 2 additions & 0 deletions yamllint/rules/__init__.py
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Expand Up @@ -14,6 +14,7 @@
# along with this program. If not, see <http://www.gnu.org/licenses/>.

from yamllint.rules import (
anchors,
braces,
brackets,
colons,
Expand All @@ -39,6 +40,7 @@
)

_RULES = {
anchors.ID: anchors,
braces.ID: braces,
brackets.ID: brackets,
colons.ID: colons,
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118 changes: 118 additions & 0 deletions yamllint/rules/anchors.py
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# Copyright (C) 2023 Adrien Vergé
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.

"""
Use this rule to report duplicated anchors and aliases referencing undeclared
anchors.
.. rubric:: Options
* Set ``forbid-undeclared-aliases`` to ``true`` to avoid aliases that reference
an anchor that hasn't been declared (either not declared at all, or declared
later in the document).
* Set ``forbid-duplicated-anchors`` to ``true`` to avoid duplications of a same
anchor.
.. rubric:: Default values (when enabled)
.. code-block:: yaml
rules:
anchors:
forbid-undeclared-aliases: true
forbid-duplicated-anchors: false
.. rubric:: Examples
#. With ``anchors: {forbid-undeclared-aliases: true}``
the following code snippet would **PASS**:
::
---
- &anchor
foo: bar
- *anchor
the following code snippet would **FAIL**:
::
---
- &anchor
foo: bar
- *unknown
the following code snippet would **FAIL**:
::
---
- &anchor
foo: bar
- <<: *unknown
extra: value
#. With ``anchors: {forbid-duplicated-anchors: true}``
the following code snippet would **PASS**:
::
---
- &anchor1 Foo Bar
- &anchor2 [item 1, item 2]
the following code snippet would **FAIL**:
::
---
- &anchor Foo Bar
- &anchor [item 1, item 2]
"""


import yaml

from yamllint.linter import LintProblem


ID = 'anchors'
TYPE = 'token'
CONF = {'forbid-undeclared-aliases': bool,
'forbid-duplicated-anchors': bool}
DEFAULT = {'forbid-undeclared-aliases': True,
'forbid-duplicated-anchors': False}


def check(conf, token, prev, next, nextnext, context):
if conf['forbid-undeclared-aliases'] or conf['forbid-duplicated-anchors']:
if isinstance(token, (yaml.StreamStartToken, yaml.DocumentStartToken)):
context['anchors'] = set()

if (conf['forbid-undeclared-aliases'] and
isinstance(token, yaml.AliasToken) and
token.value not in context['anchors']):
yield LintProblem(
token.start_mark.line + 1, token.start_mark.column + 1,
f'found undeclared alias "{token.value}"')

if (conf['forbid-duplicated-anchors'] and
isinstance(token, yaml.AnchorToken) and
token.value in context['anchors']):
yield LintProblem(
token.start_mark.line + 1, token.start_mark.column + 1,
f'found duplicated anchor "{token.value}"')

if conf['forbid-undeclared-aliases'] or conf['forbid-duplicated-anchors']:
if isinstance(token, yaml.AnchorToken):
context['anchors'].add(token.value)

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