Plugin upgrade guide

How to adjust for changes made to the Plugin API.

2.8

See https://github.com/pantsbuild/pants/blob/main/src/python/pants/notes/2.8.x.md for the changelog.

Target modeling changes

Pants 2.8 cleaned up the modeling of targets. Now, there are targets that describe the atom of each language, like python_test and python_source which correspond to a single file. There are also target generators which exist solely for less boilerplate, like python_tests and python_sources.

We recommend re-reading Targets and BUILD files.

SourcesField

The Sources class was replaced with SourcesField, SingleSourceField, and MultipleSourcesField.

When defining new target types with the Target API, you should choose between subclassing SingleSourceField and MultipleSourcesField, depending on if you want the field to be source: str or sources: list[str].

Wherever you were using Sources in your @rules, simply replace with SourcesField.

Renames of some Sources subclasses

You should update all references to these classes in your @rules.

  • FilesSources -> FileSourceField
  • ResourcesSources -> ResourceSourceField
  • PythonSources -> PythonSourceField

OutputPathField.value_or_default()

The method OutputPathField.value_or_default() no longer takes Address as an argument.

2.7

See https://github.com/pantsbuild/pants/blob/main/src/python/pants/notes/2.7.x.md for the changelog.

Type hints work properly

Pants was not using PEP 561 properly, which means that MyPy would not enforce type hints when using Pants APIs. Oops! This is now fixed.

Options scopes should not have _

For example, use my-subsystem instead of my_subsystem. This is to avoid ambiguity with target types.

2.6

See https://github.com/pantsbuild/pants/blob/main/src/python/pants/notes/2.6.x.md for the changelog.

ProcessCacheScope

ProcessCacheScope.NEVER was renamed to ProcessCacheScope.PER_SESSION to better reflect that a rule never runs more than once in a session (i.e. a single Pants run) given the same inputs.

ProcessCacheScope.PER_RESTART was replaced with ProcessCacheScope.PER_RESTART_ALWAYS and ProcessCacheScope.PER_RESTART_SUCCESSFUL.

PexInterpreterConstraints

Now called InterpreterConstraints and defined in pants.backend.python.util_rules.interpreter_constraints.

2.5

See https://github.com/pantsbuild/pants/blob/main/src/python/pants/notes/2.5.x.md for the changelog.

TriBoolField

BoolField.value is no longer bool | None, but simply bool. This means that you must either set required = True or set the default.

Use TriBoolField if you still want to be able to represent a trinary state: False, True, and None.

Added RuleRunner.write_files()

This is a more declarative way to set up files than the older API of RuleRunner.create_file(), .create_files(), and .add_to_build_files(). See Testing plugins.

2.4

See https://github.com/pantsbuild/pants/blob/main/src/python/pants/notes/2.4.x.md for the changelog.

PexRequest changes how entry point is set

See https://github.com/pantsbuild/pants/pull/11620. Instead of setting entry_point="pytest" in the PexRequest constructor, now you set main=ConsoleScript("black") or main=EntryPoint("pytest").

Must use EnvironmentRequest for accessing environment variables

See https://github.com/pantsbuild/pants/pull/11641. Pants now eagerly purges environment variables from the run, so using os.environ in plugins won't work anymore.

Instead, use await Get(Environment, EnvironmentRequest(["MY_ENV_VAR"]).

For RuleRunner tests, you must now either set env or the new env_inherit arguments for environment variables to be set. Tests are now hermetic.

2.3

There were no substantial changes to the Plugin API in 2.3. See https://github.com/pantsbuild/pants/blob/main/src/python/pants/notes/2.3.x.md for the changelog.

2.2

See https://github.com/pantsbuild/pants/blob/main/src/python/pants/notes/2.2.x.md for the changelog.

PrimitiveField and AsyncField are removed (2.2.0.dev0)

Rather than subclassing PrimitiveField, subclass Field directly. Field now behaves like PrimitiveField used to, and PrimitiveField was removed for simplicity.

Rather than subclassing AsyncField or AsyncStringSequenceField, subclass Field or a template like StringField and also subclass AsyncFieldMixin:

from pants.engine.target import AsyncFieldMixin, StringField)

class MyField(StringField, AsyncFieldMixin):
    alias = "my_field"
    help = "Description."

Async fields now access the raw value with the property .value, rather than .sanitized_raw_value. To override the eager validation, override compute_value(), rather than sanitize_raw_value(). Both these changes bring async fields into alignment with non-async fields.

Set the property help with Subsystems, Targets, and Fields (2.2.0.dev3)

Previously, you were supposed to set the class's docstring for the ./pants help message. Instead, now set a class property help, like this:

class MyField(StringField):
    alias = "my_field"
    help = "A summary.\n\nOptional extra information."

Pants will now properly wrap strings and preserve newlines. You may want to run ./pants help ${target/subsystem} to verify things render properly.

2.1

See https://github.com/pantsbuild/pants/blob/master/src/python/pants/notes/2.1.x.rst for the changelog.

SourcesSnapshot is now SpecsSnapshot (2.1.0rc0)

The type was renamed for clarity. Still import it from pants.engine.fs.

2.0

See https://github.com/pantsbuild/pants/blob/master/src/python/pants/notes/2.0.x.rst for the changelog.

Use TransitiveTargetsRequest as input for resolving TransitiveTargets (2.0.0rc0)

Rather than await Get(TransitiveTargets, Addresses([addr1])), use await Get(TransitiveTargets, TransitiveTargetsRequest([addr1])), from pants.engine.target.

It's no longer possible to include TransitiveTargets in your @rule signature in order to get the transitive closure of what the user specified on the command. Instead, put Addresses in your rule's signature, and use await Get(TransitiveTargets, TransitiveTargetsRequest(addresses)).

Codegen implementations: use DependenciesRequestLite and TransitiveTargetsLite (2.0.0rc0)

Due to a new cycle in the rule graph, for any codegen implementations, you must use DependenciesRequestLite instead of DependenciesRequest, and TransitiveTargetsLite instead of TransitiveTargetsRequest. Both imports are still from pants.engine.target.

These behave identically, except that they do not include dependency inference in the results. Unless you are generating for input = PythonSources, this should be fine, as dependency inference is currently only used with Python.

This is tracked by https://github.com/pantsbuild/pants/issues/10917.

Dependencies-like fields have more robust support (2.0.0rc0)

If you have any custom fields that act like the dependencies field, but do not subclass Dependencies, there are two new mechanisms for better support.

  1. Instead of subclassing StringSequenceField, subclass SpecialCasedDependencies from pants.engine.target. This will ensure that the dependencies show up with ./pants dependencies and ./pants dependees.
  2. You can use UnparsedAddressInputs from pants.engine.addresses to resolve the addresses:
from pants.engine.addresses import Address, Addresses, UnparsedAddressedInputs
from pants.engine.target import Targets

...

addresses = await Get(Addresses, UnparsedAddressedInputs(["//:addr1", "project/addr2"], owning_address=None)

# Or, use this.
targets = await Get(
    Targets,
    UnparsedAddressedInputs(["//:addr1", "project/addr2"], owning_address=Address("project", target_name="original")
)

If you defined a subclass of SpecialCasedDependencies, you can use await Get(Addresses | Targets, UnparsedAddressInputs, my_tgt[MyField].to_unparsed_address_inputs()).

(Why would you ever do this? If you have dependencies that you don't treat like normal—e.g. that you will call the equivalent of ./pants package on those deps—it's often helpful to call out this magic through a dedicated field. For example, Pants's archive target type has the fields files and packages, rather than dependencies.)

package implementations may want to add the field output_path (2.0.0rc0)

All of Pants's target types that can be built via ./pants package now have an output_path field, which allows the user to override the path used for the created asset.

You optionally may want to add this output_path field to your custom target type for consistency:

  1. Include OutputPathField from pants.core.goals.package in your target's core_fields class property.
  2. In your PackageFieldSet subclass, include output_path: OutputPathField.
  3. When computing the filename in your rule, use my_package_field_set.output_path.value_or_default(field_set.address, file_ending="my_ext").

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