Implement a flag to forbid the `+` operator for dicts

Usage: --incompatible_dict_plus=true (the default value is false).
PiperOrigin-RevId: 155094639

2 files changed, 15 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/syntax/BinaryOperatorExpression.java b/src/main/java/com/google/devtools/build/lib/syntax/BinaryOperatorExpression.java
index ec81e07219..ef8b7f1c55 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/BinaryOperatorExpression.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/BinaryOperatorExpression.java
@@ -219,6 +219,13 @@ public final class BinaryOperatorExpression extends Expression {
     }
 
     if (lval instanceof SkylarkDict && rval instanceof SkylarkDict) {
+      if (env.getSemantics().incompatibleDictPlus) {
+        throw new EvalException(
+            location,
+            "The `+` operator for dicts is deprecated and no longer supported. Please use the "
+                + "`update` method instead. You can temporarily enable the `+` operator by passing "
+                + "the flag --incompatible_dict_plus=false");
+      }
       return SkylarkDict.plus((SkylarkDict<?, ?>) lval, (SkylarkDict<?, ?>) rval, env);
     }
 
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemanticsOptions.java b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemanticsOptions.java
index 5909ea7155..abd5611704 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemanticsOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemanticsOptions.java
@@ -68,4 +68,12 @@ public class SkylarkSemanticsOptions extends OptionsBase implements Serializable
             + "list. Otherwise it copies the original list without mutating it."
   )
   public boolean incompatibleListPlusEquals;
+
+  @Option(
+    name = "incompatible_dict_plus",
+    defaultValue = "false",
+    category = "incompatible changes",
+    help = "If set to true, the `+` becomes disabled for dicts."
+  )
+  public boolean incompatibleDictPlus;
 }