Install support for checking for 'one version' correctness of java_binary

rules: If the collection of jars for a java_binary contain more than one
instance of the same class, one of them will be arbitrarily loaded at runtime.

This is problematic if the instances of the class are not identical, as methods
or fields from one class version might be missing in the other, leading to
runtime failures when methods are missing.

This change adds an experimental flag to enable one version enforcement. The
actual enforcement tool will come later.

--
PiperOrigin-RevId: 147166361
MOS_MIGRATED_REVID=147166361

1 files changed, 12 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/rules/java/JavaOptions.java b/src/main/java/com/google/devtools/build/lib/rules/java/JavaOptions.java
index c345ff5826..a7b7086ee8 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/java/JavaOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/java/JavaOptions.java
@@ -340,6 +340,16 @@ public class JavaOptions extends FragmentOptions {
   )
   public boolean headerCompilationDirectClasspathFallbackError;
 
+  @Option(
+    name = "experimental_one_version_enforcement",
+    defaultValue = "false",
+    category = "undocumented",
+    help =
+        "When enabled, enforce that a java_binary rule can't contain more than one version "
+            + "of the same class file on the classpath"
+  )
+  public boolean enforceOneVersion;
+
   @Override
   public FragmentOptions getHost(boolean fallback) {
     JavaOptions host = (JavaOptions) getDefault();
@@ -365,6 +375,8 @@ public class JavaOptions extends FragmentOptions {
 
     host.strictJavaDeps = strictJavaDeps;
 
+    host.enforceOneVersion = enforceOneVersion;
+
     return host;
   }