Contractually document BuildConfiguration.Fragment as immutable and strengthen

the immutability interfaces of existing implementations.

Eventually we want all implementations to comply, but right now CppConfiguration
is a glaring exception due to FDO/LIPO support.

We don't want more exceptions to arise.

This is prep work for pre-trimming ConfigurationFragment.key's BuildOptions input
to just the options needed by the fragment. That implies fragments can be shared across configurations, so that needs to be safe.

--
MOS_MIGRATED_REVID=113408041

1 files changed, 2 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/rules/python/PythonConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/python/PythonConfiguration.java
index 9ffcefa4e7..3898906374 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/python/PythonConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/python/PythonConfiguration.java
@@ -14,11 +14,13 @@
 package com.google.devtools.build.lib.rules.python;
 
 import com.google.devtools.build.lib.analysis.config.BuildConfiguration;
+import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
 
 /**
  * The configuration fragment containing information about the various pieces of infrastructure
  * needed to run Python compilations.
  */
+@Immutable
 public class PythonConfiguration extends BuildConfiguration.Fragment {
   private final boolean ignorePythonVersionAttribute;
   private final PythonVersion defaultPythonVersion;