1 files changed, 27 insertions, 4 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/config/ConfigRuleClasses.java b/src/main/java/com/google/devtools/build/lib/analysis/config/ConfigRuleClasses.java
index 3703fed081..8ad856f795 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/config/ConfigRuleClasses.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/config/ConfigRuleClasses.java
@@ -171,14 +171,37 @@ public class ConfigRuleClasses {
           ImmutableList.builder();
       AttributeMap attributes = NonconfigurableAttributeMapper.of(rule);
       for (String optionName : attributes.get(SETTINGS_ATTRIBUTE, Type.STRING_DICT).keySet()) {
-        Class<? extends BuildConfiguration.Fragment> value = optionsToFragmentMap.get(optionName);
-        // Null values come directly from BuildConfiguration.Options, which is implicitly included.
-        if (value != null) {
-          builder.add(value);
+        if (optionName.equals("cpu")) {
+          // The "cpu" flag is special: it's defined in BuildConfiguration.Options but its value
+          // is set in CppConfiguration (which reads a CROSSTOOL to determine that value).
+          // So this requires a special mapping.
+          builder.add(getCppConfiguration(optionsToFragmentMap.values()));
+        } else {
+          Class<? extends BuildConfiguration.Fragment> value = optionsToFragmentMap.get(optionName);
+          // Null values come from BuildConfiguration.Options, which is implicitly included.
+          if (value != null) {
+            builder.add(value);
+          }
         }
       }
       return builder.build();
     }
+
+    /**
+     * We can't directly reference CppConfiguration.class because it's in a different Bazel library.
+     * While we could add that library as a dep, that would bring in a bunch of unnecessary C++ and
+     * crosstool code to what's otherwise a language-agnostic library. So we use a bit of
+     * introspection instead.
+     */
+    private static Class<? extends BuildConfiguration.Fragment> getCppConfiguration(
+        Iterable<Class<? extends BuildConfiguration.Fragment>> configs) {
+      for (Class<? extends BuildConfiguration.Fragment> clazz : configs) {
+        if (clazz.getSimpleName().equals("CppConfiguration")) {
+          return clazz;
+        }
+      }
+      throw new IllegalStateException("Couldn't find the C++ fragment");
+    }
   }
 
 /*<!-- #BLAZE_RULE (NAME = config_setting, TYPE = OTHER, FAMILY = General)[GENERIC_RULE] -->