Don't rely on SCALA_VERSION in phases

Use a new field of toolchain, `scala_version`, instead.

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

cross-compilation-doc.md

@@ -8,3 +8,21 @@ The support for cross-compilation is currently under development.
 File created there, `config.bzl`, consists of many variables. In particular:
 * `SCALA_VERSION` – representing the default Scala version, e.g. `"3.3.1"`;
 * `SCALA_VERSIONS` – representing all configured Scala versions (currently one), e.g. `["3.3.1"]`.
+
+
+## Version-dependent behaviour
+Don't rely on `SCALA_VERSION` as it represents the default Scala version, not necessarily the one that is currently requested.
+
+If you need to customize the behavior for specific Scala version, there are two scenarios.
+
+### From toolchain
+If you have an access to the Scala toolchain (`@io_bazel_rules_scala//scala:toolchain_type`), there is `scala_version` field provided in there:
+```starlark
+def _rule_impl(ctx):
+    ...
+    ctx.toolchains["@io_bazel_rules_scala//scala:toolchain_type"].scala_version
+    ...
+```
+
+### From config setting
+TODO

scala/private/phases/phase_compile.bzl

@@ -17,9 +17,6 @@ load(
     _compile_scala = "compile_scala",
 )
 load(":resources.bzl", _resource_paths = "paths")
-load("@io_bazel_rules_scala_config//:config.bzl", "SCALA_VERSION")
-
-buildijar_default_value = True if SCALA_VERSION.startswith("2.") else False
 
 def phase_compile_binary(ctx, p):
     args = struct(
@@ -105,6 +102,8 @@ def phase_compile_common(ctx, p):
     return _phase_compile_default(ctx, p)
 
 def _phase_compile_default(ctx, p, _args = struct()):
+    buildijar_default_value = True if ctx.toolchains["@io_bazel_rules_scala//scala:toolchain_type"].scala_version.startswith("2.") else False
+
     return _phase_compile(
         ctx,
         p,

scala/private/phases/phase_semanticdb.bzl

@@ -3,7 +3,6 @@ load(
     "find_deps_info_on",
 )
 load("@io_bazel_rules_scala//scala:semanticdb_provider.bzl", "SemanticdbInfo")
-load("@io_bazel_rules_scala_config//:config.bzl", "SCALA_MAJOR_VERSION")
 load("@bazel_skylib//lib:paths.bzl", "paths")
 
 def phase_semanticdb(ctx, p):
@@ -37,7 +36,7 @@ def phase_semanticdb(ctx, p):
                     outputfilename = "%s/%s/%s.semanticdb" % (semanticdb_intpath, semanticdb_outpath, currSrc.path)
                     output_files.append(ctx.actions.declare_file(outputfilename))
 
-        if SCALA_MAJOR_VERSION.startswith("2"):
+        if toolchain.scala_version.startswith("2"):
             semanticdb_deps = find_deps_info_on(ctx, toolchain_type_label, "semanticdb").deps
 
             if len(semanticdb_deps) == 0:

scala/scala_toolchain.bzl

@@ -6,6 +6,8 @@ load(
     "@io_bazel_rules_scala_config//:config.bzl",
     "ENABLE_COMPILER_DEPENDENCY_TRACKING",
     "SCALA_MAJOR_VERSION",
+    "SCALA_VERSION",
+    "SCALA_VERSIONS",
 )
 
 def _compute_strict_deps_mode(input_strict_deps_mode, dependency_mode):
@@ -101,6 +103,7 @@ def _scala_toolchain_impl(ctx):
         enable_semanticdb = ctx.attr.enable_semanticdb,
         semanticdb_bundle_in_jar = ctx.attr.semanticdb_bundle_in_jar,
         use_argument_file_in_runner = ctx.attr.use_argument_file_in_runner,
+        scala_version = ctx.attr.scala_version,
     )
     return [toolchain]
 
@@ -173,6 +176,12 @@ scala_toolchain = rule(
             default = False,
             doc = "Changes java binaries scripts (including tests) to use argument files and not classpath jars to improve performance, requires java > 8",
         ),
+        "scala_version": attr.string(
+            default = SCALA_VERSION,
+            values = SCALA_VERSIONS,
+            doc = "The Scala version used by the toolchain. Must be consistent with provided `dep_providers`." +
+                  "If default `dep_providers` are used, you need to use default value here as well.",
+        ),
     },
     fragments = ["java"],
 )