Add a tristate (off/warn/error) experimental_report_unused_deps

attribute to the toolchain.

Implement unused dependency checking in `JDepsMerger` tool.

Collect jdeps dependency artifacts if experimental_report_unused_deps
is enabled (warn/error) and pass to KotlinBuilder. Passing these inputs
triggers `JDepsMerge` action for each target causing the unused deps
checking logic to be executed. Currently these inputs are not used by
the `KotlinBuilder` but will be required for future work implementing
a reduced classpath feature.

Add tests for experimental_report_unused_deps off/warn/error

Enable experimental_report_unused_deps as "warn" for examples/android

examples/android/bzl/BUILD.bazel

@@ -13,6 +13,7 @@ define_kt_toolchain(
     name = "experimental_toolchain",
     api_version = "1.4",
     experimental_use_abi_jars = True,
+    experimental_report_unused_deps = "warn",
     javac_options = ":default_javac_options",
     kotlinc_options = ":default_kotlinc_options",
     language_version = "1.4",

kotlin/internal/jvm/compile.bzl

@@ -49,6 +49,15 @@ load(
 def _java_info(target):
     return target[JavaInfo] if JavaInfo in target else None
 
+def _deps_artifacts(toolchains, targets):
+    """Collect Jdeps artifacts if required."""
+    if not toolchains.kt.experimental_report_unused_deps == "off":
+        deps_artifacts = [t[JavaInfo].outputs.jdeps for t in targets if JavaInfo in t and t[JavaInfo].outputs.jdeps]
+    else:
+        deps_artifacts = []
+
+    return depset(deps_artifacts)
+
 def _partitioned_srcs(srcs):
     """Creates a struct of srcs sorted by extension. Fails if there are no sources."""
     kt_srcs = []
@@ -320,6 +329,7 @@ def _run_merge_jdeps_action(ctx, rule_kind, toolchains, jdeps, outputs):
         args.add("--" + f, path)
 
     args.add_all("--inputs", jdeps, omit_if_empty = True)
+    args.add("--report_unused_deps", toolchains.kt.experimental_report_unused_deps)
 
     mnemonic = "JdepsMerge"
     progress_message = "%s %s { jdeps: %d }" % (
@@ -356,6 +366,7 @@ def _run_kt_builder_action(
         generated_src_jars,
         friend,
         compile_deps,
+        deps_artifacts,
         annotation_processors,
         transitive_runtime_jars,
         plugins,
@@ -381,6 +392,7 @@ def _run_kt_builder_action(
     args.add_all("--classpath", compile_deps.compile_jars)
     args.add_all("--sources", srcs.all_srcs, omit_if_empty = True)
     args.add_all("--source_jars", srcs.src_jars + generated_src_jars, omit_if_empty = True)
+    args.add_all("--deps_artifacts", deps_artifacts, omit_if_empty = True)
 
     args.add_joined("--kotlin_friend_paths", friend.paths, join_with = "\n")
 
@@ -480,7 +492,7 @@ def _run_kt_builder_action(
         mnemonic = mnemonic,
         inputs = depset(
             srcs.all_srcs + srcs.src_jars + generated_src_jars,
-            transitive = [compile_deps.compile_jars, transitive_runtime_jars] + [p.classpath for p in compiler_plugins],
+            transitive = [compile_deps.compile_jars, transitive_runtime_jars, deps_artifacts] + [p.classpath for p in compiler_plugins],
         ),
         tools = tools,
         input_manifests = input_manifests,
@@ -519,6 +531,7 @@ def kt_jvm_produce_jar_actions(ctx, rule_kind):
     annotation_processors = _plugin_mappers.targets_to_annotation_processors(ctx.attr.plugins + ctx.attr.deps)
     transitive_runtime_jars = _plugin_mappers.targets_to_transitive_runtime_jars(ctx.attr.plugins + ctx.attr.deps)
     plugins = ctx.attr.plugins + _exported_plugins(deps = ctx.attr.deps)
+    deps_artifacts = _deps_artifacts(toolchains, ctx.attr.deps + friend.targets)
 
     generated_src_jars = []
     if toolchains.kt.experimental_use_abi_jars:
@@ -531,6 +544,7 @@ def kt_jvm_produce_jar_actions(ctx, rule_kind):
             generated_src_jars = [],
             friend = friend,
             compile_deps = compile_deps,
+            deps_artifacts = deps_artifacts,
             annotation_processors = annotation_processors,
             transitive_runtime_jars = transitive_runtime_jars,
             plugins = plugins,
@@ -548,6 +562,7 @@ def kt_jvm_produce_jar_actions(ctx, rule_kind):
             generated_src_jars = [],
             friend = friend,
             compile_deps = compile_deps,
+            deps_artifacts = deps_artifacts,
             annotation_processors = annotation_processors,
             transitive_runtime_jars = transitive_runtime_jars,
             plugins = plugins,
@@ -620,7 +635,7 @@ def kt_jvm_produce_jar_actions(ctx, rule_kind):
 """Runs the necessary KotlinBuilder and JavaBuilder actions to compile a jar
 """
 
-def _run_kt_java_builder_actions(ctx, rule_kind, toolchains, srcs, generated_src_jars, friend, compile_deps, annotation_processors, transitive_runtime_jars, plugins, compile_jar):
+def _run_kt_java_builder_actions(ctx, rule_kind, toolchains, srcs, generated_src_jars, friend, compile_deps, deps_artifacts, annotation_processors, transitive_runtime_jars, plugins, compile_jar):
     compile_jars = []
     output_jars = []
     kt_stubs_for_java = []
@@ -638,6 +653,7 @@ def _run_kt_java_builder_actions(ctx, rule_kind, toolchains, srcs, generated_src
             generated_src_jars = [],
             friend = friend,
             compile_deps = compile_deps,
+            deps_artifacts = deps_artifacts,
             annotation_processors = annotation_processors,
             transitive_runtime_jars = transitive_runtime_jars,
             plugins = plugins,
@@ -682,6 +698,7 @@ def _run_kt_java_builder_actions(ctx, rule_kind, toolchains, srcs, generated_src
             generated_src_jars = generated_src_jars,
             friend = friend,
             compile_deps = compile_deps,
+            deps_artifacts = deps_artifacts,
             annotation_processors = [],
             transitive_runtime_jars = transitive_runtime_jars,
             plugins = plugins,

kotlin/internal/toolchains.bzl

@@ -78,6 +78,7 @@ def _kotlin_toolchain_impl(ctx):
         jvm_stdlibs = java_common.merge(compile_time_providers + runtime_providers),
         js_stdlibs = ctx.attr.js_stdlibs,
         experimental_use_abi_jars = ctx.attr.experimental_use_abi_jars,
+        experimental_report_unused_deps = ctx.attr.experimental_report_unused_deps,
         javac_options = ctx.attr.javac_options[JavacOptions] if ctx.attr.javac_options else None,
         kotlinc_options = ctx.attr.kotlinc_options[KotlincOptions] if ctx.attr.kotlinc_options else None,
         empty_jar = ctx.file._empty_jar,
@@ -187,6 +188,15 @@ _kt_toolchain = rule(
             `kt_abi_plugin_incompatible`""",
             default = False,
         ),
+        "experimental_report_unused_deps": attr.string(
+            doc = "Report unused dependencies",
+            default = "off",
+            values = [
+                "off",
+                "warn",
+                "error",
+            ],
+        ),
         "javac_options": attr.label(
             doc = "Compiler options for javac",
             providers = [JavacOptions],
@@ -224,6 +234,7 @@ def define_kt_toolchain(
         api_version = None,
         jvm_target = None,
         experimental_use_abi_jars = False,
+        experimental_report_unused_deps = None,
         javac_options = None,
         kotlinc_options = None):
     """Define the Kotlin toolchain."""
@@ -248,6 +259,7 @@ def define_kt_toolchain(
             absolute_target("//kotlin/internal:noexperimental_use_abi_jars"): False,
             "//conditions:default": experimental_use_abi_jars,
         }),
+        experimental_report_unused_deps = experimental_report_unused_deps,
         javac_options = javac_options,
         kotlinc_options = kotlinc_options,
         visibility = ["//visibility:public"],

src/main/kotlin/io/bazel/kotlin/builder/tasks/jvm/JdepsMerger.kt

@@ -5,14 +5,15 @@ import io.bazel.kotlin.builder.tasks.CommandLineProgram
 import io.bazel.kotlin.builder.utils.ArgMap
 import io.bazel.kotlin.builder.utils.ArgMaps
 import io.bazel.kotlin.builder.utils.Flag
-import java.io.BufferedInputStream
-import java.io.BufferedOutputStream
-import java.io.File
+import io.bazel.kotlin.builder.utils.jars.JarHelper.Companion.INJECTING_RULE_KIND
+import io.bazel.kotlin.builder.utils.jars.JarHelper.Companion.TARGET_LABEL
+import java.io.*
 import java.nio.charset.StandardCharsets
 import java.nio.file.FileSystems
 import java.nio.file.Files
 import java.nio.file.Path
 import java.nio.file.Paths
+import java.util.jar.JarFile
 
 /**
  * Persistent worker capable command line program for merging multiple Jdeps files into a single
@@ -31,12 +32,30 @@ class JdepsMerger: CommandLineProgram {
       INPUTS("--inputs"),
       OUTPUT("--output"),
       TARGET_LABEL("--target_label"),
+      REPORT_UNUSED_DEPS("--report_unused_deps"),
+    }
+
+    private fun readJarOwnerFromManifest(jarPath: Path): JarOwner {
+      try {
+        JarFile(jarPath.toFile()).use { jarFile ->
+          val manifest = jarFile.manifest ?: return JarOwner(jarPath)
+          val attributes = manifest.mainAttributes
+          val label = attributes[TARGET_LABEL] as String?
+            ?: return JarOwner(jarPath)
+          val injectingRuleKind = attributes[INJECTING_RULE_KIND] as String?
+          return JarOwner(jarPath, label, injectingRuleKind)
+        }
+      } catch (e: IOException) {
+        // This jar file pretty much has to exist.
+        throw UncheckedIOException(e)
+      }
     }
 
     fun merge(
       label: String,
       inputs: List<String>,
-      output: String) {
+      output: String,
+      reportUnusedDeps: String): Int {
 
       val rootBuilder = Deps.Dependencies.newBuilder()
       rootBuilder.success = false
@@ -64,9 +83,33 @@ class JdepsMerger: CommandLineProgram {
       BufferedOutputStream(File(output).outputStream()).use {
         it.write(rootBuilder.build().toByteArray())
       }
+
+      if (reportUnusedDeps != "off") {
+        val unusedLabels = dependencyMap.values
+          .filter { it.kind == Deps.Dependency.Kind.UNUSED }
+          .mapNotNull { readJarOwnerFromManifest(Paths.get(it.path)).label }
+          .filter {it != label}
+
+        if (unusedLabels.isNotEmpty()) {
+          val open = "\u001b[35m\u001b[1m"
+          val close = "\u001b[0m"
+          val command =
+            """
+            |$open ** Please remove the following dependencies:$close ${unusedLabels.joinToString(" ")} from $label 
+            |$open ** You can use the following buildozer command:$close buildozer 'remove deps ${unusedLabels.joinToString(" ")}' $label
+          """.trimMargin()
+
+          println(command)
+          return if(reportUnusedDeps == "error") 1 else 0
+        }
+      }
+
+      return 0
     }
   }
 
+  private data class JarOwner(val jar: Path, val label: String? = null, val aspect: String? = null)
+
   private fun getArgs(args: List<String>): ArgMap {
     check(args.isNotEmpty()) { "expected at least a single arg got: ${args.joinToString(" ")}" }
     val lines = FLAGFILE_RE.matchEntire(args[0])?.groups?.get(1)?.let {
@@ -77,12 +120,12 @@ class JdepsMerger: CommandLineProgram {
   }
 
   override fun apply(workingDir: Path, args: List<String>): Int {
-    var status = 0
     val argMap = getArgs(args)
     val inputs = argMap.mandatory(JdepsMergerFlags.INPUTS)
     val output = argMap.mandatorySingle(JdepsMergerFlags.OUTPUT)
     val label = argMap.mandatorySingle(JdepsMergerFlags.TARGET_LABEL)
-    merge(label, inputs, output)
-    return status
+    val reportUnusedDeps = argMap.mandatorySingle(JdepsMergerFlags.REPORT_UNUSED_DEPS)
+
+    return merge(label, inputs, output, reportUnusedDeps)
   }
 }