Allow transitioning scala version with scala_version attribute of rules (#1569)

Co-authored-by: mkuta <mkuta@virtuslab.com>

Author: aszady

cross-compilation-doc.md

@@ -117,6 +117,45 @@ scala_library(
 ```
 
 
+## Requesting specific version
+To use other than default version of Scala, you need to change the current `@io_bazel_rules_scala_config//:scala_version` build setting.
+
+Simple transition, setting the Scala version to one found in `scala_version` attribute:
+```starlark
+def _scala_version_transition_impl(settings, attr):
+    if attr.scala_version:
+        return {"@io_bazel_rules_scala_config//:scala_version": attr.scala_version}
+    else:
+        return {}
+
+scala_version_transition = transition(
+    implementation = _scala_version_transition_impl,
+    inputs = [],
+    outputs = ["@io_bazel_rules_scala_config//:scala_version"],
+)
+```
+
+To use it in a rule, use the `scala_version_transition` as `cfg` and use `toolchain_transition_attr` in `attrs`:
+```starlark
+load("@io_bazel_rules_scala//scala:scala_cross_version.bzl", "scala_version_transition", "toolchain_transition_attr")
+
+_scala_library_attrs.update(toolchain_transition_attr)
+
+def make_scala_library(*extras):
+    return rule(
+        attrs = _dicts.add(
+            ...
+            toolchain_transition_attr,
+            ...
+        ),
+        ...
+        cfg = scala_version_transition,
+        incompatible_use_toolchain_transition = True,
+        ...
+    )
+```
+
+
 ## Toolchains
 Standard [toolchain resolution](https://bazel.build/extending/toolchains#toolchain-resolution) procedure determines which toolchain to use for Scala targets.
 

scala/private/rules/scala_binary.bzl

@@ -9,6 +9,7 @@ load(
     "resolve_deps",
 )
 load("@io_bazel_rules_scala//scala/private:common_outputs.bzl", "common_outputs")
+load("@io_bazel_rules_scala//scala:scala_cross_version.bzl", "scala_version_transition", "toolchain_transition_attr")
 load(
     "@io_bazel_rules_scala//scala/private:phases/phases.bzl",
     "extras_phases",
@@ -70,6 +71,8 @@ _scala_binary_attrs.update(common_attrs)
 
 _scala_binary_attrs.update(resolve_deps)
 
+_scala_binary_attrs.update(toolchain_transition_attr)
+
 def make_scala_binary(*extras):
     return rule(
         attrs = _dicts.add(
@@ -87,6 +90,7 @@ def make_scala_binary(*extras):
             "@io_bazel_rules_scala//scala:toolchain_type",
             "@bazel_tools//tools/jdk:toolchain_type",
         ],
+        cfg = scala_version_transition,
         incompatible_use_toolchain_transition = True,
         implementation = _scala_binary_impl,
     )

scala/private/rules/scala_junit_test.bzl

@@ -8,6 +8,7 @@ load(
     "launcher_template",
 )
 load("@io_bazel_rules_scala//scala/private:common_outputs.bzl", "common_outputs")
+load("@io_bazel_rules_scala//scala:scala_cross_version.bzl", "scala_version_transition", "toolchain_transition_attr")
 load(
     "@io_bazel_rules_scala//scala/private:phases/phases.bzl",
     "extras_phases",
@@ -123,6 +124,8 @@ _scala_junit_test_attrs.update({
     "tests_from": attr.label_list(providers = [[JavaInfo]]),
 })
 
+_scala_junit_test_attrs.update(toolchain_transition_attr)
+
 def make_scala_junit_test(*extras):
     return rule(
         attrs = _dicts.add(
@@ -140,6 +143,7 @@ def make_scala_junit_test(*extras):
             "@io_bazel_rules_scala//scala:toolchain_type",
             "@bazel_tools//tools/jdk:toolchain_type",
         ],
+        cfg = scala_version_transition,
         incompatible_use_toolchain_transition = True,
         implementation = _scala_junit_test_impl,
     )

scala/private/rules/scala_library.bzl

@@ -15,6 +15,7 @@ load(
     "@io_bazel_rules_scala//scala/private:coverage_replacements_provider.bzl",
     _coverage_replacements_provider = "coverage_replacements_provider",
 )
+load("@io_bazel_rules_scala//scala:scala_cross_version.bzl", "scala_version_transition", "toolchain_transition_attr")
 load(
     "@io_bazel_rules_scala//scala/private:phases/phases.bzl",
     "extras_phases",
@@ -87,6 +88,8 @@ _scala_library_attrs.update(_library_attrs)
 
 _scala_library_attrs.update(resolve_deps)
 
+_scala_library_attrs.update(toolchain_transition_attr)
+
 def make_scala_library(*extras):
     return rule(
         attrs = _dicts.add(
@@ -103,6 +106,7 @@ def make_scala_library(*extras):
             "@io_bazel_rules_scala//scala:toolchain_type",
             "@bazel_tools//tools/jdk:toolchain_type",
         ],
+        cfg = scala_version_transition,
         incompatible_use_toolchain_transition = True,
         implementation = _scala_library_impl,
     )
@@ -185,6 +189,8 @@ _scala_library_for_plugin_bootstrapping_attrs.update(
     common_attrs_for_plugin_bootstrapping,
 )
 
+_scala_library_for_plugin_bootstrapping_attrs.update(toolchain_transition_attr)
+
 def make_scala_library_for_plugin_bootstrapping(*extras):
     return rule(
         attrs = _dicts.add(
@@ -201,6 +207,7 @@ def make_scala_library_for_plugin_bootstrapping(*extras):
             "@io_bazel_rules_scala//scala:toolchain_type",
             "@bazel_tools//tools/jdk:toolchain_type",
         ],
+        cfg = scala_version_transition,
         incompatible_use_toolchain_transition = True,
         implementation = _scala_library_for_plugin_bootstrapping_impl,
     )
@@ -245,6 +252,8 @@ _scala_macro_library_attrs.update(_library_attrs)
 
 _scala_macro_library_attrs.update(resolve_deps)
 
+_scala_macro_library_attrs.update(toolchain_transition_attr)
+
 # Set unused_dependency_checker_mode default to off for scala_macro_library
 _scala_macro_library_attrs["unused_dependency_checker_mode"] = attr.string(
     default = "off",
@@ -273,6 +282,7 @@ def make_scala_macro_library(*extras):
             "@io_bazel_rules_scala//scala:toolchain_type",
             "@bazel_tools//tools/jdk:toolchain_type",
         ],
+        cfg = scala_version_transition,
         incompatible_use_toolchain_transition = True,
         implementation = _scala_macro_library_impl,
     )

scala/private/rules/scala_repl.bzl

@@ -9,6 +9,7 @@ load(
     "resolve_deps",
 )
 load("@io_bazel_rules_scala//scala/private:common_outputs.bzl", "common_outputs")
+load("@io_bazel_rules_scala//scala:scala_cross_version.bzl", "scala_version_transition", "toolchain_transition_attr")
 load(
     "@io_bazel_rules_scala//scala/private:phases/phases.bzl",
     "extras_phases",
@@ -65,6 +66,8 @@ _scala_repl_attrs.update(common_attrs)
 
 _scala_repl_attrs.update(resolve_deps)
 
+_scala_repl_attrs.update(toolchain_transition_attr)
+
 def make_scala_repl(*extras):
     return rule(
         attrs = _dicts.add(
@@ -79,6 +82,7 @@ def make_scala_repl(*extras):
             *[extra["outputs"] for extra in extras if "outputs" in extra]
         ),
         toolchains = ["@io_bazel_rules_scala//scala:toolchain_type"],
+        cfg = scala_version_transition,
         incompatible_use_toolchain_transition = True,
         implementation = _scala_repl_impl,
     )

scala/private/rules/scala_test.bzl

@@ -9,6 +9,7 @@ load(
 )
 load("@io_bazel_rules_scala//scala/private:common.bzl", "sanitize_string_for_usage")
 load("@io_bazel_rules_scala//scala/private:common_outputs.bzl", "common_outputs")
+load("@io_bazel_rules_scala//scala:scala_cross_version.bzl", "scala_version_transition", "toolchain_transition_attr")
 load(
     "@io_bazel_rules_scala//scala/private:phases/phases.bzl",
     "extras_phases",
@@ -108,6 +109,8 @@ _scala_test_attrs.update(common_attrs)
 
 _scala_test_attrs.update(_test_resolve_deps)
 
+_scala_test_attrs.update(toolchain_transition_attr)
+
 def make_scala_test(*extras):
     return rule(
         attrs = _dicts.add(
@@ -126,6 +129,7 @@ def make_scala_test(*extras):
             "@io_bazel_rules_scala//scala:toolchain_type",
             "@bazel_tools//tools/jdk:toolchain_type",
         ],
+        cfg = scala_version_transition,
         incompatible_use_toolchain_transition = True,
         implementation = _scala_test_impl,
     )

scala/scala_cross_version.bzl

@@ -51,3 +51,22 @@ def sanitize_version(scala_version):
 
 def version_suffix(scala_version):
     return "_" + sanitize_version(scala_version)
+
+def _scala_version_transition_impl(settings, attr):
+    if attr.scala_version:
+        return {"@io_bazel_rules_scala_config//:scala_version": attr.scala_version}
+    else:
+        return {}
+
+scala_version_transition = transition(
+    implementation = _scala_version_transition_impl,
+    inputs = [],
+    outputs = ["@io_bazel_rules_scala_config//:scala_version"],
+)
+
+toolchain_transition_attr = {
+    "scala_version": attr.string(),
+    "_allowlist_function_transition": attr.label(
+        default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
+    ),
+}