Add toggle for ijar in java_import

Problem: java_import has been unusably broken for years for JARs with Kotlin interfaces, since ijar strips out important information. This has caused multiple dependent projects (including official Bazel ones) to abandon java_import in favor of rolling their own versions, which themselves contain issues that are getting fixed in java_import. Fragmentation is bad, and fragmentation of bugs and fixes is worse.
For more, see
https://github.com/bazelbuild/rules_jvm_external/blob/master/private/rules/jvm_import.bzl
bazelbuild#4549
bazelbuild#14966
bazel-contrib/rules_jvm_external#672

Temporary solution: Until such time as ijar is fixed for Kotlin, this adds a toggle that optionally disables ijar on java_import. This should unblock use of java_import for libraries that might contain Kotlin and allow implementations to reunify.

src/main/java/com/google/devtools/build/lib/rules/java/JavaImport.java

@@ -32,6 +32,7 @@
 import com.google.devtools.build.lib.collect.nestedset.NestedSetBuilder;
 import com.google.devtools.build.lib.collect.nestedset.Order;
 import com.google.devtools.build.lib.rules.java.JavaRuleOutputJarsProvider.JavaOutput;
+import com.google.devtools.build.lib.packages.Type;
 import java.util.LinkedHashSet;
 import java.util.Set;
 
@@ -202,7 +203,8 @@ private ImmutableList<Artifact> processWithIjarIfNeeded(
  RuleContext ruleContext,
  ImmutableMap.Builder<Artifact, Artifact> compilationToRuntimeJarMap) {
  ImmutableList.Builder<Artifact> interfaceJarsBuilder = ImmutableList.builder();
- boolean useIjar = ruleContext.getFragment(JavaConfiguration.class).getUseIjars();
+ boolean useIjar = ruleContext.getFragment(JavaConfiguration.class).getUseIjars()
+ && !ruleContext.attributes().get("safe_for_kotlin_interfaces", Type.BOOLEAN);
  for (Artifact jar : jars) {
  Artifact interfaceJar =
  useIjar

src/main/java/com/google/devtools/build/lib/rules/java/JavaImportBaseRule.java

@@ -39,6 +39,14 @@ public RuleClass build(RuleClass.Builder builder, RuleDefinitionEnvironment envi
  The list of JAR files provided to Java targets that depend on this target.
  <!-- #END_BLAZE_RULE.ATTRIBUTE --> */
  .add(attr("jars", LABEL_LIST).mandatory().allowedFileTypes(JavaSemantics.JAR))
+ /* <!-- #BLAZE_RULE($java_import_base).ATTRIBUTE(safe_for_kotlin_interfaces) -->
+ If your JARs contain a Kotlin interface, you need to enable this or use
+ kt_jvm_import instead.
+ Otherwise, a caching, performance optimization (ijar) breaks compilation.
+ Temporarily available until ijar is updated to properly handle Kotlin.
+ For more, see https://github.com/bazelbuild/bazel/issues/4549.
+ <!-- #END_BLAZE_RULE.ATTRIBUTE --> */
+ .add(attr("safe_for_kotlin_interfaces", BOOLEAN).value(false))
  /* <!-- #BLAZE_RULE($java_import_base).ATTRIBUTE(srcjar) -->
  A JAR file that contains source code for the compiled JAR files.
  <!-- #END_BLAZE_RULE.ATTRIBUTE --> */