Don't hard remove --no_, give a warning first.

PiperOrigin-RevId: 153610163

2 files changed, 7 insertions, 9 deletions

diff --git a/src/main/java/com/google/devtools/common/options/IsolatedOptionsData.java b/src/main/java/com/google/devtools/common/options/IsolatedOptionsData.java
index 9c4c3a671a..1352a330a7 100644
--- a/src/main/java/com/google/devtools/common/options/IsolatedOptionsData.java
+++ b/src/main/java/com/google/devtools/common/options/IsolatedOptionsData.java
@@ -341,9 +341,11 @@ public class IsolatedOptionsData extends OpaqueOptionsData {
       Map<String, String> booleanAliasMap,
       String optionName) {
     // Check that the negating alias does not conflict with existing flags.
+    checkForCollisions(nameToFieldMap, "no_" + optionName, "boolean option alias");
     checkForCollisions(nameToFieldMap, "no" + optionName, "boolean option alias");
 
     // Record that the boolean option takes up additional namespace for its negating alias.
+    booleanAliasMap.put("no_" + optionName, optionName);
     booleanAliasMap.put("no" + optionName, optionName);
   }
 
diff --git a/src/main/java/com/google/devtools/common/options/OptionsParserImpl.java b/src/main/java/com/google/devtools/common/options/OptionsParserImpl.java
index c5f31c43e5..a4d905a547 100644
--- a/src/main/java/com/google/devtools/common/options/OptionsParserImpl.java
+++ b/src/main/java/com/google/devtools/common/options/OptionsParserImpl.java
@@ -620,18 +620,14 @@ class OptionsParserImpl {
       // Look for a "no"-prefixed option name: "no<optionName>".
       if (field == null && name.startsWith("no")) {
         // Give a nice error if someone is using the deprecated --no_ prefix.
-        // Note: With this check in place, is impossible to specify "--no_foo" for a flag named
-        // "--_foo", if a --foo flag also exists, since that'll be interpreted as the "no_"
-        // negating prefix for "--foo". Let that be a warning to anyone wanting to make flags that
-        // start with underscores.
         // TODO(Bazel-team): Remove the --no_ check when sufficient time has passed for users of
         // that feature to have stopped using it.
-        if (name.startsWith("no_") && optionsData.getFieldFromName(name.substring(3)) != null) {
-          throw new OptionsParsingException(
-              "'no_' prefixes are no longer accepted, --no<flag> is an accepted alternative.",
-              name.substring(3));
-        }
         name = name.substring(2);
+        if (name.startsWith("_") && optionsData.getFieldFromName(name.substring(1)) != null) {
+          name = name.substring(1);
+          warnings.add("Option '" + name + "' is specified using the deprecated --no_ prefix. "
+            + "Use --no without the underscore instead.");
+        }
         field = optionsData.getFieldFromName(name);
         booleanValue = false;
         if (field != null) {