Add support for Scalafix (pantsbuild#20394)

Implemented for `fix` and `lint` goals.

.scalafix.conf

@@ -0,0 +1,10 @@
+rules = [
+  NoAutoTupling,
+  DisableSyntax,
+  NoValInForComprehension,
+  RedundantSyntax,
+  RemoveUnused,
+  ProcedureSyntax
+]
+
+DisableSyntax.noThrows = true

3rdparty/jvm/org/scalameta/BUILD

@@ -1,11 +1,22 @@
 # Copyright 2021 Pants project contributors (see CONTRIBUTORS.md).
 # Licensed under the Apache License, Version 2.0 (see LICENSE).
 
+scala_artifact(
+    name="semanticdb-jar",
+    group="org.scalameta",
+    artifact="semanticdb-scalac",
+    version="4.8.4",
+    resolve="jvm_testprojects",
+    crossversion="full",
+)
+
+scalac_plugin(name="semanticdb", artifact=":semanticdb-jar")
+
 # Note: This target must be kept in sync with the requirements in `generate_scala_parser_lockfile_request`.
-jvm_artifact(
+scala_artifact(
     name="scalameta",
     group="org.scalameta",
-    artifact="scalameta_2.13",
+    artifact="scalameta",
     version="4.8.7",
     packages=["scala.meta.**"],
     resolve="scala_parser_dev",

3rdparty/jvm/testprojects.lockfile

@@ -1,12 +1,13 @@
 # This lockfile was autogenerated by Pants. To regenerate, run:
 #
-#    ./pants generate-lockfiles
+#    pants generate-lockfiles
 #
 # --- BEGIN PANTS LOCKFILE METADATA: DO NOT EDIT OR REMOVE ---
 # {
 #   "version": 1,
 #   "generated_with_requirements": [
-#     "org.scala-lang:scala-library:2.13.6,url=not_provided,jar=not_provided"
+#     "org.scala-lang:scala-library:2.13.6,url=not_provided,jar=not_provided",
+#     "org.scalameta:semanticdb-scalac_2.13.6:4.8.4,url=not_provided,jar=not_provided"
 #   ]
 # }
 # --- END PANTS LOCKFILE METADATA ---
@@ -24,3 +25,26 @@ packaging = "jar"
 [entries.file_digest]
 fingerprint = "f19ed732e150d3537794fd3fe42ee18470a3f707efd499ecd05a99e727ff6c8a"
 serialized_bytes_length = 5955737
+[[entries]]
+file_name = "org.scalameta_semanticdb-scalac_2.13.6_4.8.4.jar"
+[[entries.directDependencies]]
+group = "org.scala-lang"
+artifact = "scala-library"
+version = "2.13.6"
+packaging = "jar"
+
+[[entries.dependencies]]
+group = "org.scala-lang"
+artifact = "scala-library"
+version = "2.13.6"
+packaging = "jar"
+
+
+[entries.coord]
+group = "org.scalameta"
+artifact = "semanticdb-scalac_2.13.6"
+version = "4.8.4"
+packaging = "jar"
+[entries.file_digest]
+fingerprint = "acc1f667d4e98b42ba851309feb391cf301afeeeeddb8c172874a2184b18b057"
+serialized_bytes_length = 17073222

docs/docs/jvm/java-and-scala.mdx

@@ -312,6 +312,43 @@ Once enabled, `lint` and `fmt` will check and automatically reformat your code:
 ❯ pants --changed-since=HEAD fmt
 ```
 
+### Fix Scala code
+
+Additionally to the previously mentioned tools, `scalafix` can also be enabled by adding the `pants.backend.experimental.scala.lint.scalafix` backend to `backend_packages` in the `[GLOBAL]` section of `pants.toml`. However to take full advantage of it additional settings are required.
+
+If we want to use Scalafix's semantic rules, Scalafix needs to be able to find `.semanticdb` compiled files in our classpath. In versions prior to Scala 3 this is achieved by adding the `semanticdb` scalac plugin to our build. Find which is the right version of it for the Scala version you are using and add the following targets:
+
+```python
+scala_artifact(
+    name="semanticdb-jar",
+    group="org.scalameta",
+    artifact="semanticdb-scalac",
+    version="<SEMANTICDB_VERSION>",
+    crossversion="full",
+)
+
+scalac_plugin(name="semanticdb", artifact=":semanticdb-jar")
+```
+
+Now you will need to add the `scalac_plugins` field to your scala targets like in the following:
+
+```python
+scala_sources(scalac_plugins=["semanticdb"])
+```
+
+Alternatively, you could add `semanticdb` to the `[scalac].plugins_for_resolve` setting:
+
+```toml pants.toml
+[scalac.plugins_for_resolve]
+jvm-default = "semanticdb"
+```
+
+:::note Scalafix and Scala 3
+At the moment the support for Scalac 3 in Scalafix is limited, most of the syntactic rules work but not that many in the semantic front.
+
+Despite those raugh edges, Scalafix is a great linting tool for Scala 3, just note that the setup is different than from prior versions: Instead of adding a scalac plugin to our build, we only need to add the `-Xsemanticdb` flag to our `[scalac].args` settings to enable the generation of `.semanticdb` compiled files.
+:::
+
 ## Working in an IDE
 
 Pants supports loading Java and Scala projects in IntelliJ via the [BSP protocol](https://build-server-protocol.github.io/) (which should ease VSCode support [via Metals](https://scalameta.org/metals/docs/editors/vscode), although it is not yet supported).

pants.toml

@@ -32,6 +32,7 @@ backend_packages.add = [
   "pants.backend.experimental.python.packaging.pyoxidizer",
   "pants.backend.experimental.scala",
   "pants.backend.experimental.scala.lint.scalafmt",
+  "pants.backend.experimental.scala.lint.scalafix",
   "pants.backend.experimental.scala.debug_goals",
   "pants.backend.experimental.tools.workunit_logger",
   "pants.backend.experimental.visibility",
@@ -234,5 +235,8 @@ jar_tool_dev = "src/python/pants/jvm/jar_tool/jar_tool.lock"
 [scala]
 version_for_resolve = { "scala_parser_dev" = "2.13.8" }
 
+[scalac]
+args = ["-Yrangepos", "-Xlint:unused"]
+
 [scala-infer]
 force_add_siblings_as_dependencies = false

src/python/pants/backend/experimental/scala/lint/BUILD

@@ -0,0 +1,4 @@
+# Copyright 2024 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+python_sources()

src/python/pants/backend/experimental/scala/lint/scalafix/BUILD

@@ -0,0 +1,4 @@
+# Copyright 2023 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+python_sources()

src/python/pants/backend/experimental/scala/lint/scalafix/register.py

@@ -0,0 +1,14 @@
+# Copyright 2024 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+from pants.backend.experimental.scala.register import rules as all_scala_rules
+from pants.backend.scala.lint.scalafix import extra_fields
+from pants.backend.scala.lint.scalafix import rules as scalafix_rules
+
+
+def rules():
+    return [
+        *all_scala_rules(),
+        *scalafix_rules.rules(),
+        *extra_fields.rules(),
+    ]

src/python/pants/backend/scala/dependency_inference/BUILD

@@ -10,8 +10,9 @@ python_tests(name="tests", timeout=240)
 scala_sources(
     name="scala_parser",
     resolve="scala_parser_dev",
-    # TODO: Allow the parser files to be formatted.
+    # TODO: Allow the parser files to be formatted and linted.
     skip_scalafmt=True,
+    skip_scalafix=True,
 )
 
 jvm_artifact(

src/python/pants/backend/scala/lint/scalafix/BUILD

@@ -0,0 +1,10 @@
+# Copyright 2023 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+python_sources(dependencies=[":lockfile"])
+
+python_tests(name="tests", dependencies=[":test-lockfiles"])
+
+resource(name="lockfile", source="scalafix.default.lockfile.txt")
+
+resources(name="test-lockfiles", sources=["*.test.lock"])

src/python/pants/backend/scala/lint/scalafix/extra_fields.py

@@ -0,0 +1,15 @@
+# Copyright 2023 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+from pants.backend.scala.target_types import SCALA_SOURCES_TARGET_TYPES
+from pants.engine.target import BoolField
+
+
+class SkipScalafixField(BoolField):
+    alias = "skip_scalafix"
+    default = False
+    help = "If true, don't run `scalafix` on this target's code."
+
+
+def rules():
+    return [tgt.register_plugin_field(SkipScalafixField) for tgt in SCALA_SOURCES_TARGET_TYPES]