Use an outgoing transition to ensure Scala targets' dependencies are built once

Author: Jaden Peterson

rules/common/private/utils.bzl

@@ -65,7 +65,11 @@ def write_launcher(
     # runfiles_enabled = ctx.configuration.runfiles_enabled()
     runfiles_enabled = False
 
-    java_runtime_info = ctx.attr._target_jdk[java_common.JavaRuntimeInfo]
+    # See https://bazel.build/extending/config#accessing-attributes-with-transitions:
+    # "When attaching a transition to an outgoing edge (regardless of whether the transition is a
+    # 1:1 or 1:2+ transition), `ctx.attr` is forced to be a list if it isn't already. The order of
+    # elements in this list is unspecified."
+    java_runtime_info = ctx.attr._target_jdk[0][java_common.JavaRuntimeInfo]
     java_executable = java_runtime_info.java_executable_runfiles_path
     if not paths.is_absolute(java_executable):
         java_executable = workspace_name + "/" + java_executable

rules/private/phases/phase_binary_launcher.bzl

@@ -35,7 +35,12 @@ def phase_binary_launcher(ctx, g):
             files = inputs + files,
             transitive_files = depset(
                 order = "default",
-                transitive = [ctx.attr._target_jdk[java_common.JavaRuntimeInfo].files, g.javainfo.java_info.transitive_runtime_jars],
+
+                # See https://bazel.build/extending/config#accessing-attributes-with-transitions:
+                # "When attaching a transition to an outgoing edge (regardless of whether the
+                # transition is a 1:1 or 1:2+ transition), `ctx.attr` is forced to be a list if it
+                # isn't already. The order of elements in this list is unspecified."
+                transitive = [ctx.attr._target_jdk[0][java_common.JavaRuntimeInfo].files, g.javainfo.java_info.transitive_runtime_jars],
             ),
             collect_default = True,
         ),

rules/private/phases/phase_javainfo.bzl

@@ -1,3 +1,4 @@
+load("@rules_java//java/common:java_common.bzl", "java_common")
 load("@rules_java//toolchains:toolchain_utils.bzl", "find_java_toolchain")
 load(
     "@rules_scala_annex//rules:providers.bzl",
@@ -29,7 +30,12 @@ def phase_javainfo(ctx, g):
                 ctx.actions,
                 jar = ctx.outputs.jar,
                 target_label = ctx.label,
-                java_toolchain = find_java_toolchain(ctx, ctx.attr._java_toolchain),
+
+                # See https://bazel.build/extending/config#accessing-attributes-with-transitions:
+                # "When attaching a transition to an outgoing edge (regardless of whether the
+                # transition is a 1:1 or 1:2+ transition), `ctx.attr` is forced to be a list if it
+                # isn't already. The order of elements in this list is unspecified."
+                java_toolchain = find_java_toolchain(ctx, ctx.attr._java_toolchain[0]),
             )
 
         source_jar_name = ctx.outputs.jar.basename.replace(".jar", "-src.jar")
@@ -42,7 +48,7 @@ def phase_javainfo(ctx, g):
             ctx.actions,
             output_source_jar = output_source_jar,
             sources = ctx.files.srcs,
-            java_toolchain = find_java_toolchain(ctx, ctx.attr._java_toolchain),
+            java_toolchain = find_java_toolchain(ctx, ctx.attr._java_toolchain[0]),
         )
 
         java_info = JavaInfo(

rules/private/phases/phase_test_launcher.bzl

@@ -11,7 +11,11 @@ load("//rules/common:private/utils.bzl", _collect = "collect", _write_launcher =
 #
 
 def phase_test_launcher(ctx, g):
-    files = ctx.attr._target_jdk[java_common.JavaRuntimeInfo].files.to_list() + [g.compile.zinc_info.analysis_store]
+    # See https://bazel.build/extending/config#accessing-attributes-with-transitions:
+    # "When attaching a transition to an outgoing edge (regardless of whether the transition is a
+    # 1:1 or 1:2+ transition), `ctx.attr` is forced to be a list if it isn't already. The order of
+    # elements in this list is unspecified."
+    files = ctx.attr._target_jdk[0][java_common.JavaRuntimeInfo].files.to_list() + [g.compile.zinc_info.analysis_store]
 
     coverage_replacements = {}
     coverage_runner_jars = depset(direct = [])
@@ -26,7 +30,7 @@ def phase_test_launcher(ctx, g):
         coverage_replacements[jar] if jar in coverage_replacements else jar
         for jar in g.javainfo.java_info.transitive_runtime_jars.to_list()
     ])
-    runner_jars = depset(transitive = [ctx.attr.runner[JavaInfo].transitive_runtime_jars, coverage_runner_jars])
+    runner_jars = depset(transitive = [ctx.attr.runner[0][JavaInfo].transitive_runtime_jars, coverage_runner_jars])
     all_jars = [test_jars, runner_jars]
 
     args = ctx.actions.args()
@@ -38,7 +42,7 @@ def phase_test_launcher(ctx, g):
         args.add_all("--shared_classpath", shared_deps.transitive_runtime_jars, map_each = _test_launcher_short_path)
     elif ctx.attr.isolation == "process":
         subprocess_executable = ctx.actions.declare_file("{}/subprocess".format(ctx.label.name))
-        subprocess_runner_jars = ctx.attr.subprocess_runner[JavaInfo].transitive_runtime_jars
+        subprocess_runner_jars = ctx.attr.subprocess_runner[0][JavaInfo].transitive_runtime_jars
         all_jars.append(subprocess_runner_jars)
         files += _write_launcher(
             ctx,

rules/private/phases/phase_zinc_compile.bzl

@@ -27,7 +27,11 @@ def phase_zinc_compile(ctx, g):
     javacopts = [
         ctx.expand_location(option, ctx.attr.data)
         for option in ctx.attr.javacopts + java_common.default_javac_opts(
-            java_toolchain = find_java_toolchain(ctx, ctx.attr._java_toolchain),
+            # See https://bazel.build/extending/config#accessing-attributes-with-transitions:
+            # "When attaching a transition to an outgoing edge (regardless of whether the transition
+            # is a 1:1 or 1:2+ transition), `ctx.attr` is forced to be a list if it isn't already.
+            # The order of elements in this list is unspecified."
+            java_toolchain = find_java_toolchain(ctx, ctx.attr._java_toolchain[0]),
         )
     ]
 

rules/register_toolchain.bzl

@@ -1,3 +1,4 @@
+load("@rules_scala_annex_scala_toolchain//:default.bzl", "default_scala_toolchain_name")
 load(
     "//rules:providers.bzl",
     "CodeCoverageConfiguration",
@@ -206,21 +207,32 @@ def _make_register_toolchain(configuration_rule):
 register_bootstrap_toolchain = _make_register_toolchain(_bootstrap_configuration)
 register_zinc_toolchain = _make_register_toolchain(_zinc_configuration)
 
-def _scala_toolchain_transition_impl(_, attr):
+def _scala_toolchain_incoming_transition_impl(settings, attr):
     if attr.scala_toolchain_name == "":
         return {}
 
     return {
         "@rules_scala_annex_scala_toolchain//:scala-toolchain": attr.scala_toolchain_name,
     }
 
-scala_toolchain_transition = transition(
-    implementation = _scala_toolchain_transition_impl,
+scala_toolchain_incoming_transition = transition(
+    implementation = _scala_toolchain_incoming_transition_impl,
+    inputs = ["@rules_scala_annex_scala_toolchain//:scala-toolchain"],
+    outputs = ["@rules_scala_annex_scala_toolchain//:scala-toolchain"],
+)
+
+def _scala_toolchain_outgoing_transition_impl(_1, _2):
+    return {
+        "@rules_scala_annex_scala_toolchain//:scala-toolchain": default_scala_toolchain_name,
+    }
+
+scala_toolchain_outgoing_transition = transition(
+    implementation = _scala_toolchain_outgoing_transition_impl,
     inputs = [],
     outputs = ["@rules_scala_annex_scala_toolchain//:scala-toolchain"],
 )
 
-scala_toolchain_transition_attributes = {
+scala_toolchain_attributes = {
     "scala_toolchain_name": attr.string(
         doc = "The name of the Scala toolchain to use for this target (as provided to `register_*_toolchain`)",
     ),

rules/scala.bzl

@@ -43,12 +43,14 @@ load(":jvm.bzl", _labeled_jars = "labeled_jars")
 load(":providers.bzl", _ScalaRulePhase = "ScalaRulePhase")
 load(
     ":register_toolchain.bzl",
-    _scala_toolchain_transition = "scala_toolchain_transition",
-    _scala_toolchain_transition_attributes = "scala_toolchain_transition_attributes",
+    _scala_toolchain_attributes = "scala_toolchain_attributes",
+    _scala_toolchain_incoming_transition = "scala_toolchain_incoming_transition",
+    _scala_toolchain_outgoing_transition = "scala_toolchain_outgoing_transition",
 )
 
 _compile_private_attributes = {
     "_java_toolchain": attr.label(
+        cfg = _scala_toolchain_outgoing_transition,
         default = Label("@bazel_tools//tools/jdk:current_java_toolchain"),
     ),
     "_host_javabase": attr.label(
@@ -77,6 +79,7 @@ _compile_private_attributes = {
 
 _compile_attributes = {
     "srcs": attr.label_list(
+        cfg = _scala_toolchain_outgoing_transition,
         doc = "The source Scala and Java files (and `-sources.jar` `.srcjar` `-src.jar` files of those).",
         allow_files = [
             ".scala",
@@ -88,10 +91,12 @@ _compile_attributes = {
         flags = ["DIRECT_COMPILE_TIME_INPUT"],
     ),
     "data": attr.label_list(
+        cfg = _scala_toolchain_outgoing_transition,
         doc = "The additional runtime files needed by this library.",
         allow_files = True,
     ),
     "deps": attr.label_list(
+        cfg = _scala_toolchain_outgoing_transition,
         aspects = [
             _labeled_jars,
             _coverage_replacements_provider.aspect,
@@ -100,21 +105,25 @@ _compile_attributes = {
         providers = [JavaInfo],
     ),
     "deps_used_whitelist": attr.label_list(
+        cfg = _scala_toolchain_outgoing_transition,
         doc = "The JVM library dependencies to always consider used for `scala_deps_used` checks.",
         providers = [JavaInfo],
     ),
     "deps_unused_whitelist": attr.label_list(
+        cfg = _scala_toolchain_outgoing_transition,
         doc = "The JVM library dependencies to always consider unused for `scala_deps_direct` checks.",
         providers = [JavaInfo],
     ),
     "runtime_deps": attr.label_list(
+        cfg = _scala_toolchain_outgoing_transition,
         doc = "The JVM runtime-only library dependencies.",
         providers = [JavaInfo],
     ),
     "javacopts": attr.string_list(
         doc = "The Javac options.",
     ),
     "plugins": attr.label_list(
+        cfg = _scala_toolchain_outgoing_transition,
         doc = "The Scalac plugins.",
         providers = [JavaInfo],
     ),
@@ -123,10 +132,12 @@ _compile_attributes = {
     ),
     "resources": attr.label_list(
         allow_files = True,
+        cfg = _scala_toolchain_outgoing_transition,
         doc = "The files to include as classpath resources.",
     ),
     "resource_jars": attr.label_list(
         allow_files = [".jar"],
+        cfg = _scala_toolchain_outgoing_transition,
         doc = "The JARs to merge into the output JAR.",
     ),
     "scalacopts": attr.string_list(
@@ -139,6 +150,7 @@ _library_attributes = {
         aspects = [
             _coverage_replacements_provider.aspect,
         ],
+        cfg = _scala_toolchain_outgoing_transition,
         doc = "The JVM libraries to add as dependencies to any libraries dependent on this one.",
         providers = [JavaInfo],
     ),
@@ -157,17 +169,20 @@ _runtime_attributes = {
         doc = "The JVM runtime flags.",
     ),
     "runtime_deps": attr.label_list(
+        cfg = _scala_toolchain_outgoing_transition,
         doc = "The JVM runtime-only library dependencies.",
         providers = [JavaInfo],
     ),
 }
 
 _runtime_private_attributes = {
     "_target_jdk": attr.label(
+        cfg = _scala_toolchain_outgoing_transition,
         default = Label("@bazel_tools//tools/jdk:current_java_runtime"),
         providers = [java_common.JavaRuntimeInfo],
     ),
     "_java_stub_template": attr.label(
+        cfg = _scala_toolchain_outgoing_transition,
         default = Label("@anx_java_stub_template//file"),
         allow_single_file = True,
     ),
@@ -243,11 +258,11 @@ def make_scala_library(*extras):
             _compile_attributes,
             _compile_private_attributes,
             _library_attributes,
-            _scala_toolchain_transition_attributes,
+            _scala_toolchain_attributes,
             _extras_attributes(extras),
             *[extra["attrs"] for extra in extras]
         ),
-        cfg = _scala_toolchain_transition,
+        cfg = _scala_toolchain_incoming_transition,
         doc = "Compiles a Scala JVM library.",
         implementation = _scala_library_implementation,
         outputs = _dicts.add(
@@ -271,7 +286,7 @@ def make_scala_binary(*extras):
             _compile_private_attributes,
             _runtime_attributes,
             _runtime_private_attributes,
-            _scala_toolchain_transition_attributes,
+            _scala_toolchain_attributes,
             {
                 "main_class": attr.string(
                     doc = "The main class. If not provided, it will be inferred by its type signature.",
@@ -280,7 +295,7 @@ def make_scala_binary(*extras):
             _extras_attributes(extras),
             *[extra["attrs"] for extra in extras]
         ),
-        cfg = _scala_toolchain_transition,
+        cfg = _scala_toolchain_incoming_transition,
         doc = """
 Compiles and links a Scala JVM executable.
 
@@ -317,7 +332,7 @@ def make_scala_test(*extras):
             _compile_private_attributes,
             _runtime_attributes,
             _runtime_private_attributes,
-            _scala_toolchain_transition_attributes,
+            _scala_toolchain_attributes,
             _testing_private_attributes,
             {
                 "isolation": attr.string(
@@ -331,6 +346,7 @@ def make_scala_test(*extras):
                 ),
                 "scalacopts": attr.string_list(doc = "Options to pass to scalac."),
                 "shared_deps": attr.label_list(
+                    cfg = _scala_toolchain_outgoing_transition,
                     doc = "If isolation is \"classloader\", the list of deps to keep loaded between tests",
                     providers = [JavaInfo],
                 ),
@@ -345,13 +361,19 @@ def make_scala_test(*extras):
                     ],
                     doc = "The list of test frameworks to check for. These should conform to the sbt test interface (https://github.com/sbt/test-interface).",
                 ),
-                "runner": attr.label(default = "@rules_scala_annex//src/main/scala/higherkindness/rules_scala/workers/zinc/test"),
-                "subprocess_runner": attr.label(default = "@rules_scala_annex//src/main/scala/higherkindness/rules_scala/common/sbt-testing:subprocess"),
+                "runner": attr.label(
+                    cfg = _scala_toolchain_outgoing_transition,
+                    default = "@rules_scala_annex//src/main/scala/higherkindness/rules_scala/workers/zinc/test",
+                ),
+                "subprocess_runner": attr.label(
+                    cfg = _scala_toolchain_outgoing_transition,
+                    default = "@rules_scala_annex//src/main/scala/higherkindness/rules_scala/common/sbt-testing:subprocess",
+                ),
             },
             _extras_attributes(extras),
             *[extra["attrs"] for extra in extras]
         ),
-        cfg = _scala_toolchain_transition,
+        cfg = _scala_toolchain_incoming_transition,
         doc = """
 Compiles and links a collection of Scala tests.
 
@@ -396,13 +418,15 @@ _scala_repl_private_attributes = _dicts.add(
 scala_repl = rule(
     attrs = _dicts.add(
         _scala_repl_private_attributes,
-        _scala_toolchain_transition_attributes,
+        _scala_toolchain_attributes,
         {
             "data": attr.label_list(
+                cfg = _scala_toolchain_outgoing_transition,
                 doc = "The additional runtime files needed by this REPL.",
                 allow_files = True,
             ),
             "deps": attr.label_list(
+                cfg = _scala_toolchain_outgoing_transition,
                 doc = "Dependencies that should be made available to the REPL.",
                 providers = [JavaInfo],
             ),
@@ -412,7 +436,7 @@ scala_repl = rule(
             "scalacopts": attr.string_list(doc = "Options to pass to scalac."),
         },
     ),
-    cfg = _scala_toolchain_transition,
+    cfg = _scala_toolchain_incoming_transition,
     doc = """
 Launches a REPL with all given dependencies available.
 
@@ -469,14 +493,16 @@ Use this only for libraries with macros. Otherwise, use `java_import`.""",
 
 scaladoc = rule(
     attrs = _dicts.add(
-        _scala_toolchain_transition_attributes,
+        _scala_toolchain_attributes,
         _scaladoc_private_attributes,
         {
             "compiler_deps": attr.label_list(
+                cfg = _scala_toolchain_outgoing_transition,
                 doc = "JVM targets that should be included on the compile classpath.",
                 providers = [JavaInfo],
             ),
             "deps": attr.label_list(
+                cfg = _scala_toolchain_outgoing_transition,
                 doc = "Dependencies that should be made available to the Scaladoc tool. These may include libraries referenced in Scaladoc or public signatures.",
                 providers = [JavaInfo],
             ),
@@ -488,13 +514,14 @@ scaladoc = rule(
                     "-sources.jar",
                     "-src.jar",
                 ],
+                cfg = _scala_toolchain_outgoing_transition,
                 doc = "Sources from which to generate Scaladoc. These may include `*.java` files, `*.scala` files, and source JARs.",
             ),
             "scalacopts": attr.string_list(doc = "Options to pass to scalac."),
             "title": attr.string(doc = "The name of the project. If none is provided, the target label will be used."),
         },
     ),
-    cfg = _scala_toolchain_transition,
+    cfg = _scala_toolchain_incoming_transition,
     doc = "Generates Scaladoc.",
     implementation = _scaladoc_implementation,
     toolchains = [

rules/scala/private/repl.bzl

@@ -49,7 +49,12 @@ def scala_repl_implementation(ctx):
             runfiles = ctx.runfiles(
                 collect_default = True,
                 collect_data = True,
-                files = ctx.attr._target_jdk[java_common.JavaRuntimeInfo].files.to_list(),
+
+                # See https://bazel.build/extending/config#accessing-attributes-with-transitions:
+                # "When attaching a transition to an outgoing edge (regardless of whether the
+                # transition is a 1:1 or 1:2+ transition), `ctx.attr` is forced to be a list if it
+                # isn't already. The order of elements in this list is unspecified."
+                files = ctx.attr._target_jdk[0][java_common.JavaRuntimeInfo].files.to_list(),
                 transitive_files = files,
             ),
         ),