Add [scala-infer].force_add_siblings_as_dependencies and deprecate …

…it defaulting to true (#15841)

Fixes #14382

src/python/pants/backend/scala/subsystems/scala_infer.py

@@ -3,6 +3,7 @@
 
 from pants.option.option_types import BoolOption
 from pants.option.subsystem import Subsystem
+from pants.util.strutil import softwrap
 
 
 class ScalaInferSubsystem(Subsystem):
@@ -19,3 +20,18 @@ class ScalaInferSubsystem(Subsystem):
         default=True,
         help="Infer a target's dependencies by parsing consumed types from sources.",
     )
+    force_add_siblings_as_dependencies = BoolOption(
+        "--force-add-siblings-as-dependencies",
+        default=True,
+        help=softwrap(
+            """
+            If true, add a dependency on all scala_source targets generated by the same scala_sources target generator.
+            If false, the dependencies will only be added if [scala-infer].imports is also set to false.
+
+            Setting this option to true reduces the precision of dependency information.
+            That means that you may end up compiling more than is necessary for a particular task,
+            and that compilation will be invalidated more frequently than actually necessary.
+            However, setting to true may be helpful if compilation fails due to missing dependencies.
+            """
+        ),
+    )

src/python/pants/backend/scala/target_types.py

@@ -5,6 +5,8 @@
 
 from dataclasses import dataclass
 
+from pants.backend.scala.subsystems.scala_infer import ScalaInferSubsystem
+from pants.base.deprecated import warn_or_error
 from pants.engine.rules import collect_rules, rule
 from pants.engine.target import (
     COMMON_TARGET_FIELDS,
@@ -36,9 +38,35 @@ class ScalaSettingsRequest(TargetFilesGeneratorSettingsRequest):
 
 
 @rule
-def scala_settings_request(_: ScalaSettingsRequest) -> TargetFilesGeneratorSettings:
-    # TODO: See https://github.com/pantsbuild/pants/issues/14382.
-    return TargetFilesGeneratorSettings(add_dependencies_on_all_siblings=True)
+def scala_settings_request(
+    scala_infer_subsystem: ScalaInferSubsystem, _: ScalaSettingsRequest
+) -> TargetFilesGeneratorSettings:
+    if scala_infer_subsystem.options.is_default("force_add_siblings_as_dependencies"):
+        warn_or_error(
+            removal_version="2.14.0.dev0",
+            entity="`force_add_siblings_as_dependencies` defaulting to True",
+            hint=softwrap(
+                """
+                Setting this option to true reduces the precision of dependency information.
+                That means that you may end up compiling more than is necessary for a particular task,
+                and that compilation will be invalidated more frequently than actually necessary.
+                However, setting to true may be helpful if compilation fails due to missing dependencies.
+
+                We have made several improvements to Pants's Scala dependency inference,
+                where we no longer think it's necessary to adding dependencies on sibling targets.
+                If you have compilation failures after disabling this option, please consider opening an issue at
+                https://github.com/pantsbuild/pants/issues/new so that we can continue to improve Pants's dependency inference.
+
+                To opt into the new default early, set `force_add_siblings_as_dependencies = false` in the `[scala_infer]`
+                section in `pants.toml`. Otherwise, set to `true` to silence this warning.
+                """
+            ),
+        )
+
+    return TargetFilesGeneratorSettings(
+        add_dependencies_on_all_siblings=scala_infer_subsystem.force_add_siblings_as_dependencies
+        or not scala_infer_subsystem.imports
+    )
 
 
 class ScalaSourceField(SingleSourceField):