Mark implicit _{n} so they do not show up as variables in metaprogramming

Author: enebo

src/main/java/org/jruby/prism/builder/IRBuilderPrism.java

@@ -467,11 +467,23 @@ private Operand buildBegin(BeginNode node) {
 
     private Operand buildBlock(BlockNode node) {
         StaticScope staticScope = createStaticScopeFrom(node.locals, StaticScope.Type.BLOCK);
+        markImplicitVariables(staticScope, node.locals, node.parameters);
         Signature signature = calculateSignature(node.parameters);
         staticScope.setSignature(signature);
         return buildIter(node.parameters, node.body, staticScope, signature, getLine(node), getEndLine(node));
     }
 
+    private void markImplicitVariables(StaticScope staticScope, RubySymbol[] locals, Node parameters) {
+        if (parameters instanceof NumberedParametersNode num) markImplcitNums(staticScope, num.maximum);
+    }
+
+    private void markImplcitNums(StaticScope staticScope, int maximum) {
+        for (int i = 0; i < maximum; i++) {
+            int slot = staticScope.existsOrImplicit("_" + (i + 1));
+            staticScope.markImplicitVariable(slot & 0xffff);
+        }
+    }
+
     protected Variable receiveBlockArg(Variable v, Operand argsArray, int argIndex, boolean isSplat) {
         if (argsArray != null) {
             // We are in a nested receive situation -- when we are not at the root of a masgn tree
@@ -1480,6 +1492,7 @@ private Operand buildKeywordHash(KeywordHashNode node, int[] flags) {
 
     private Operand buildLambda(LambdaNode node) {
         StaticScope staticScope = createStaticScopeFrom(node.locals, StaticScope.Type.BLOCK);
+        markImplicitVariables(staticScope, node.locals, node.parameters);
         Signature signature = calculateSignature(node.parameters);
         staticScope.setSignature(signature);
         return buildLambda(node.parameters, node.body, staticScope, signature, getLine(node));