Add an option to silence warnings about duplicate flags

src/main/java/com/google/devtools/build/lib/runtime/BlazeOptionHandler.java

@@ -490,7 +490,7 @@ DetailedExitCode parseOptions(List<String> args, ExtendedEventHandler eventHandl
       // to improve the user experience, but not required for safety or correctness.
       optionsPolicyEnforcer.enforce(optionsParser, commandAnnotation.name());
       // Print warnings for odd options usage
-      for (String warning : optionsParser.getWarnings()) {
+      for (String warning : getFilteredWarnings(optionsParser)) {
         eventHandler.handle(Event.warn(warning));
       }
       CommonCommandOptions commonOptions = optionsParser.getOptions(CommonCommandOptions.class);
@@ -704,4 +704,20 @@ private static void partitionCommandLineArgs(
       }
     }
   }
+
+  public static ImmutableList<String> getFilteredWarnings(OptionsParser parser) {
+    CommonCommandOptions commonOptions = parser.getOptions(CommonCommandOptions.class);
+    Preconditions.checkNotNull(commonOptions,
+        "getWarnings can only be called after options parsing");
+
+    ImmutableList.Builder<String> warnings = ImmutableList.<String>builder();
+    for (String warning : parser.getWarnings()) {
+      if (!commonOptions.reportDuplicateOptionsAndConfigs && warning.contains(
+          "was expanded to from both")) {
+        continue;
+      }
+      warnings.add(warning);
+    }
+    return warnings.build();
+  }
 }

src/main/java/com/google/devtools/build/lib/runtime/CommonCommandOptions.java

@@ -532,6 +532,14 @@ public String getTypeDescription() {
               + " them.")
   public boolean heuristicallyDropNodes;
 
+  @Option(
+      name = "snowflake_report_duplicate_options_and_configs",
+      defaultValue = "true",
+      documentationCategory = OptionDocumentationCategory.LOGGING,
+      effectTags = {OptionEffectTag.TERMINAL_OUTPUT},
+      help = "If enabled, reports flags and configs that were expanded multiple times as warnings.")
+  public boolean reportDuplicateOptionsAndConfigs;
+
   /** The option converter to check that the user can only specify legal profiler tasks. */
   public static class ProfilerTaskConverter extends EnumConverter<ProfilerTask> {
     public ProfilerTaskConverter() {

src/main/java/com/google/devtools/build/lib/runtime/ConfigExpander.java

@@ -150,7 +150,11 @@ static void expandConfigOptions(
 
     // At this point, we've expanded everything, identify duplicates, if any, to warn about
     // re-application.
-    List<String> configs = optionsParser.getOptions(CommonCommandOptions.class).configs;
+    CommonCommandOptions commonOptions = optionsParser.getOptions(CommonCommandOptions.class);
+    if (!commonOptions.reportDuplicateOptionsAndConfigs) {
+      return;
+    }
+    List<String> configs = commonOptions.configs;
     Set<String> configSet = new HashSet<>();
     LinkedHashSet<String> duplicateConfigs = new LinkedHashSet<>();
     for (String configValue : configs) {