scala: support multiple scala versions

src/python/pants/backend/java/compile/javac.py

@@ -149,7 +149,7 @@ async def compile_java_source(
     )
 
     usercp = "__cp"
-    user_classpath = Classpath(direct_dependency_classpath_entries)
+    user_classpath = Classpath(direct_dependency_classpath_entries, request.resolve)
     classpath_arg = ":".join(user_classpath.root_immutable_inputs_args(prefix=usercp))
     immutable_input_digests = dict(user_classpath.root_immutable_inputs(prefix=usercp))
 

src/python/pants/backend/scala/compile/scalac.py

@@ -81,12 +81,14 @@ async def compile_scala_source(
         for filename in dependency.filenames
     ]
 
+    scala_version = scala.version_for_resolve(request.resolve.name)
+
     # TODO(14171): Stop-gap for making sure that scala supplies all of its dependencies to
     # deploy targets.
     if not any(
         filename.startswith("org.scala-lang_scala-library_") for filename in all_dependency_jars
     ):
-        scala_library = await Get(ClasspathEntry, ScalaLibraryRequest(scala.version))
+        scala_library = await Get(ClasspathEntry, ScalaLibraryRequest(scala_version))
         direct_dependency_classpath_entries += (scala_library,)
 
     component_members_with_sources = tuple(
@@ -130,7 +132,8 @@ async def compile_scala_source(
     scalac_plugins_relpath = "__plugincp"
     usercp = "__cp"
 
-    user_classpath = Classpath(direct_dependency_classpath_entries)
+    user_classpath = Classpath(direct_dependency_classpath_entries, request.resolve)
+
     tool_classpath, sources_digest = await MultiGet(
         Get(
             ToolClasspath,
@@ -140,12 +143,12 @@ async def compile_scala_source(
                         Coordinate(
                             group="org.scala-lang",
                             artifact="scala-compiler",
-                            version=scala.version,
+                            version=scala_version,
                         ),
                         Coordinate(
                             group="org.scala-lang",
                             artifact="scala-library",
-                            version=scala.version,
+                            version=scala_version,
                         ),
                     ]
                 ),

src/python/pants/backend/scala/compile/scalac_test.py

@@ -3,6 +3,7 @@
 
 from __future__ import annotations
 
+import itertools
 from textwrap import dedent
 
 import pytest
@@ -20,7 +21,7 @@
 from pants.engine.fs import FileDigest
 from pants.engine.target import CoarsenedTargets
 from pants.jvm import jdk_rules, testutil
-from pants.jvm.compile import CompileResult, FallibleClasspathEntry
+from pants.jvm.compile import ClasspathEntry, CompileResult, FallibleClasspathEntry
 from pants.jvm.resolve.common import ArtifactRequirement, Coordinate, Coordinates
 from pants.jvm.resolve.coursier_fetch import CoursierLockfileEntry, CoursierResolvedLockfile
 from pants.jvm.resolve.coursier_fetch import rules as coursier_fetch_rules
@@ -52,6 +53,7 @@ def rule_runner() -> RuleRunner:
             QueryRule(CoarsenedTargets, (Addresses,)),
             QueryRule(FallibleClasspathEntry, (CompileScalaSourceRequest,)),
             QueryRule(RenderedClasspath, (CompileScalaSourceRequest,)),
+            QueryRule(ClasspathEntry, (CompileScalaSourceRequest,)),
         ],
         target_types=[JvmArtifactTarget, ScalaSourcesGeneratorTarget, ScalacPluginTarget],
     )
@@ -649,3 +651,64 @@ def example: Option[String] = {
         resolve=make_resolve(rule_runner),
     )
     rule_runner.request(RenderedClasspath, [request])
+
+
+@maybe_skip_jdk_test
+def test_compile_with_multiple_scala_versions(rule_runner: RuleRunner) -> None:
+    rule_runner.write_files(
+        {
+            "BUILD": dedent(
+                """\
+                scala_sources(
+                    name = 'main',
+                )
+                """
+            ),
+            "Example.scala": SCALA_LIB_SOURCE,
+            "3rdparty/jvm/scala2.12.lock": EMPTY_LOCKFILE,
+            "3rdparty/jvm/scala2.13.lock": EMPTY_LOCKFILE,
+        }
+    )
+    rule_runner.set_options(
+        ['--scala-version-for-resolve={"scala2.12":"2.12.15","scala2.13":"2.13.8"}'],
+        env_inherit=PYTHON_BOOTSTRAP_ENV,
+    )
+    classpath_2_12 = rule_runner.request(
+        ClasspathEntry,
+        [
+            CompileScalaSourceRequest(
+                component=expect_single_expanded_coarsened_target(
+                    rule_runner, Address(spec_path="", target_name="main")
+                ),
+                resolve=make_resolve(rule_runner, "scala2.12", "3rdparty/jvm/scala2.12.lock"),
+            )
+        ],
+    )
+    entries_2_12 = list(ClasspathEntry.closure([classpath_2_12]))
+    filenames_2_12 = sorted(
+        itertools.chain.from_iterable(entry.filenames for entry in entries_2_12)
+    )
+    assert filenames_2_12 == [
+        ".Example.scala.main.scalac.jar",
+        "org.scala-lang_scala-library_2.12.15.jar",
+    ]
+
+    classpath_2_13 = rule_runner.request(
+        ClasspathEntry,
+        [
+            CompileScalaSourceRequest(
+                component=expect_single_expanded_coarsened_target(
+                    rule_runner, Address(spec_path="", target_name="main")
+                ),
+                resolve=make_resolve(rule_runner, "scala2.13", "3rdparty/jvm/scala2.13.lock"),
+            )
+        ],
+    )
+    entries_2_13 = list(ClasspathEntry.closure([classpath_2_13]))
+    filenames_2_13 = sorted(
+        itertools.chain.from_iterable(entry.filenames for entry in entries_2_13)
+    )
+    assert filenames_2_13 == [
+        ".Example.scala.main.scalac.jar",
+        "org.scala-lang_scala-library_2.13.8.jar",
+    ]

src/python/pants/backend/scala/goals/repl.py

@@ -26,31 +26,31 @@ async def create_scala_repl_request(
     request: ScalaRepl, bash: BashBinary, jdk_setup: JdkSetup, scala_subsystem: ScalaSubsystem
 ) -> ReplRequest:
     jdk = jdk_setup.jdk
-    user_classpath, tool_classpath = await MultiGet(
-        Get(Classpath, Addresses, request.addresses),
-        Get(
-            ToolClasspath,
-            ToolClasspathRequest(
-                prefix="__toolcp",
-                artifact_requirements=ArtifactRequirements.from_coordinates(
-                    [
-                        Coordinate(
-                            group="org.scala-lang",
-                            artifact="scala-compiler",
-                            version=scala_subsystem.version,
-                        ),
-                        Coordinate(
-                            group="org.scala-lang",
-                            artifact="scala-library",
-                            version=scala_subsystem.version,
-                        ),
-                        Coordinate(
-                            group="org.scala-lang",
-                            artifact="scala-reflect",
-                            version=scala_subsystem.version,
-                        ),
-                    ]
-                ),
+
+    user_classpath = await Get(Classpath, Addresses, request.addresses)
+    scala_version = scala_subsystem.version_for_resolve(user_classpath.resolve.name)
+    tool_classpath = await Get(
+        ToolClasspath,
+        ToolClasspathRequest(
+            prefix="__toolcp",
+            artifact_requirements=ArtifactRequirements.from_coordinates(
+                [
+                    Coordinate(
+                        group="org.scala-lang",
+                        artifact="scala-compiler",
+                        version=scala_version,
+                    ),
+                    Coordinate(
+                        group="org.scala-lang",
+                        artifact="scala-library",
+                        version=scala_version,
+                    ),
+                    Coordinate(
+                        group="org.scala-lang",
+                        artifact="scala-reflect",
+                        version=scala_version,
+                    ),
+                ]
             ),
         ),
     )

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

@@ -3,16 +3,56 @@
 
 from __future__ import annotations
 
+import logging
+from typing import cast
+
 from pants.option.option_types import StrOption
 from pants.option.subsystem import Subsystem
 
 DEFAULT_SCALA_VERSION = "2.13.6"
 
+_logger = logging.getLogger(__name__)
+
 
 class ScalaSubsystem(Subsystem):
     options_scope = "scala"
     help = "Scala programming language"
 
     version = StrOption(
-        "--version", default=DEFAULT_SCALA_VERSION, help="The version of Scala to use"
-    )
+        "--version",
+        default=DEFAULT_SCALA_VERSION,
+        help=(
+            "The version of Scala to use.\n\n"
+            "This option is deprecated in favor of the `[scala].version_for_resolve` option. If "
+            "`[scala].version_for_resolve` does not have an entry for a resolve, then the value of "
+            "this option will be used as the Scala version for that resolve."
+        ),
+    ).deprecated(removal_version="2.11.0.dev0", hint="Use `[scala].version_for_resolve` instead.")
+
+    @classmethod
+    def register_options(cls, register):
+        super().register_options(register)
+
+        register(
+            "--version-for-resolve",
+            type=dict,
+            help=(
+                "A dictionary mapping the name of a resolve to the Scala version to use for all Scala "
+                "targets consuming that resolve.\n\n"
+                'All Scala-compiled jars on a resolve\'s classpath must be "compatible" with one another and '
+                "with all Scala-compiled first-party sources from `scala_sources` (and other Scala target types) "
+                "using that resolve. The option sets the Scala version that will be used to compile all "
+                "first-party sources using the resolve. This ensures that the compatibility property is "
+                "maintained for a resolve. To support multiple Scala versions, use multiple resolves."
+            ),
+        )
+
+    @property
+    def _version_for_resolve(self) -> dict[str, str]:
+        return cast("dict[str, str]", self.options.version_for_resolve)
+
+    def version_for_resolve(self, resolve: str) -> str:
+        version = self._version_for_resolve.get(resolve)
+        if version:
+            return version
+        return self.version

src/python/pants/jvm/classpath.py

@@ -4,9 +4,9 @@
 from __future__ import annotations
 
 import logging
+from dataclasses import dataclass
 from typing import Iterator
 
-from pants.engine.collection import Collection
 from pants.engine.fs import Digest
 from pants.engine.rules import Get, MultiGet, collect_rules, rule
 from pants.engine.target import CoarsenedTargets
@@ -17,7 +17,8 @@
 logger = logging.getLogger(__name__)
 
 
-class Classpath(Collection[ClasspathEntry]):
+@dataclass(frozen=True)
+class Classpath:
     """A transitive classpath which is sufficient to launch the target(s) it was generated for.
 
     There are two primary ways to consume a Classpath:
@@ -31,33 +32,38 @@ class Classpath(Collection[ClasspathEntry]):
     This classpath is guaranteed to contain only JAR files.
     """
 
+    entries: tuple[ClasspathEntry, ...]
+    resolve: CoursierResolveKey
+
     def args(self, *, prefix: str = "") -> Iterator[str]:
         """All transitive filenames for this Classpath."""
-        return ClasspathEntry.args(ClasspathEntry.closure(self), prefix=prefix)
+        return ClasspathEntry.args(ClasspathEntry.closure(self.entries), prefix=prefix)
 
     def root_args(self, *, prefix: str = "") -> Iterator[str]:
         """The root filenames for this Classpath."""
-        return ClasspathEntry.args(self, prefix=prefix)
+        return ClasspathEntry.args(self.entries, prefix=prefix)
 
     def digests(self) -> Iterator[Digest]:
         """All transitive Digests for this Classpath."""
-        return (entry.digest for entry in ClasspathEntry.closure(self))
+        return (entry.digest for entry in ClasspathEntry.closure(self.entries))
 
     def immutable_inputs(self, *, prefix: str = "") -> Iterator[tuple[str, Digest]]:
         """Returns (relpath, Digest) tuples for use with `Process.immutable_input_digests`."""
-        return ClasspathEntry.immutable_inputs(ClasspathEntry.closure(self), prefix=prefix)
+        return ClasspathEntry.immutable_inputs(ClasspathEntry.closure(self.entries), prefix=prefix)
 
     def immutable_inputs_args(self, *, prefix: str = "") -> Iterator[str]:
         """Returns relative filenames for the given entries to be used as immutable_inputs."""
-        return ClasspathEntry.immutable_inputs_args(ClasspathEntry.closure(self), prefix=prefix)
+        return ClasspathEntry.immutable_inputs_args(
+            ClasspathEntry.closure(self.entries), prefix=prefix
+        )
 
     def root_immutable_inputs(self, *, prefix: str = "") -> Iterator[tuple[str, Digest]]:
         """Returns root (relpath, Digest) tuples for use with `Process.immutable_input_digests`."""
-        return ClasspathEntry.immutable_inputs(self, prefix=prefix)
+        return ClasspathEntry.immutable_inputs(self.entries, prefix=prefix)
 
     def root_immutable_inputs_args(self, *, prefix: str = "") -> Iterator[str]:
         """Returns root relative filenames for the given entries to be used as immutable_inputs."""
-        return ClasspathEntry.immutable_inputs_args(self, prefix=prefix)
+        return ClasspathEntry.immutable_inputs_args(self.entries, prefix=prefix)
 
 
 @rule
@@ -81,7 +87,7 @@ async def classpath(
         for t in coarsened_targets
     )
 
-    return Classpath(classpath_entries)
+    return Classpath(classpath_entries, resolve)
 
 
 def rules():

src/python/pants/jvm/testutil.py

@@ -93,7 +93,8 @@ async def render_classpath_entry(
 @rule
 async def render_classpath(classpath: Classpath) -> RenderedClasspath:
     rendered_classpaths = await MultiGet(
-        Get(RenderedClasspath, ClasspathEntry, cpe) for cpe in ClasspathEntry.closure(classpath)
+        Get(RenderedClasspath, ClasspathEntry, cpe)
+        for cpe in ClasspathEntry.closure(classpath.entries)
     )
     return RenderedClasspath({k: v for rc in rendered_classpaths for k, v in rc.content.items()})