Expressions: Avoid creating a dynamic constant with BSM if MethodHandle descriptor can be used

Author: uschindler

lucene/expressions/src/java/org/apache/lucene/expressions/js/JavascriptCompiler.java

@@ -31,6 +31,7 @@
 import java.lang.classfile.instruction.BranchInstruction;
 import java.lang.classfile.instruction.OperatorInstruction;
 import java.lang.constant.ClassDesc;
+import java.lang.constant.ConstantDesc;
 import java.lang.constant.ConstantDescs;
 import java.lang.constant.DynamicConstantDesc;
 import java.lang.constant.MethodTypeDesc;
@@ -379,10 +380,10 @@ public Void visitNumeric(JavascriptParser.NumericContext ctx) {
 
       @Override
       public Void visitExternal(JavascriptParser.ExternalContext ctx) {
-        String text = ctx.VARIABLE().getText();
-        int arguments = ctx.expression().size();
-        boolean parens = ctx.LP() != null && ctx.RP() != null;
-        MethodHandle mh = parens ? functions.get(text) : null;
+        final String text = ctx.VARIABLE().getText();
+        final int arguments = ctx.expression().size();
+        final boolean parens = ctx.LP() != null && ctx.RP() != null;
+        final MethodHandle mh = parens ? functions.get(text) : null;
 
         if (mh != null) {
           final int arity = mh.type().parameterCount();
@@ -401,15 +402,19 @@ public Void visitExternal(JavascriptParser.ExternalContext ctx) {
                 ctx.start.getStartIndex());
           }
 
-          // place dynamic constant with MethodHandle on top of stack
-          final int index = constantsMap.computeIfAbsent(text, _ -> constantsMap.size());
-          final var constantDesc =
-              DynamicConstantDesc.ofNamed(
-                  ConstantDescs.BSM_CLASS_DATA_AT,
-                  ConstantDescs.DEFAULT_NAME,
-                  ConstantDescs.CD_MethodHandle,
-                  index);
-          gen.loadConstant(constantDesc);
+          // place reference to direct MethodHandle (usually if it is direct and reachable by system
+          // classloader) or a dynamic constant using BSM for classdata on stack:
+          final ConstantDesc constant =
+              mh.describeConstable()
+                  .map(ConstantDesc.class::cast)
+                  .orElseGet(
+                      () ->
+                          DynamicConstantDesc.ofNamed(
+                              ConstantDescs.BSM_CLASS_DATA_AT,
+                              ConstantDescs.DEFAULT_NAME,
+                              ConstantDescs.CD_MethodHandle,
+                              constantsMap.computeIfAbsent(text, _ -> constantsMap.size())));
+          gen.loadConstant(constant);
 
           // add arguments:
           typeStack.push(TypeKind.DOUBLE);
@@ -426,8 +431,8 @@ public Void visitExternal(JavascriptParser.ExternalContext ctx) {
 
           gen.conversion(TypeKind.DOUBLE, typeStack.peek());
         } else if (!parens || arguments == 0 && text.contains(".")) {
-          text = normalizeQuotes(ctx.getText());
-          final int index = externalsMap.computeIfAbsent(text, _ -> externalsMap.size());
+          final String var = normalizeQuotes(ctx.getText());
+          final int index = externalsMap.computeIfAbsent(var, _ -> externalsMap.size());
 
           gen.aload(gen.parameterSlot(0));
           gen.loadConstant(index);