ESQL: More code gen standardization (elastic#134935)

Makes a few changes to code gen that should be a noop but makes it
easier to make further code gen changes.
1. Extract the argument infrastructure from `EvaluatorImplementer` so we
   can share it more easily with aggs. Makes a whole package for it!
2. Read values into a local before calling the in `ExpressionEvaluator`.
   This mimics how aggregations work more closely and will make it
   easier to move aggregations to the same argument infrastructure.
   It's the bulk of this change but should be the same at runtime.
3. Moves parsing of aggregation parameters to the infrastructure we
   built for `ExpressionEvaluator`. In the future move aggs over to this
   infrastructure entirely but that's too much for this change.

Relates to elastic#108385

Author: nik9000

x-pack/plugin/esql/compute/gen/src/main/java/module-info.java

@@ -15,6 +15,7 @@
     requires java.compiler;
 
     exports org.elasticsearch.compute.gen;
+    exports org.elasticsearch.compute.gen.argument;
 
     provides javax.annotation.processing.Processor with AggregatorProcessor, ConsumeProcessor, EvaluatorProcessor;
 }

x-pack/plugin/esql/compute/gen/src/main/java/org/elasticsearch/compute/gen/AggregatorImplementer.java

@@ -18,6 +18,9 @@
 import org.elasticsearch.compute.ann.Aggregator;
 import org.elasticsearch.compute.ann.IntermediateState;
 import org.elasticsearch.compute.gen.Methods.TypeMatcher;
+import org.elasticsearch.compute.gen.argument.Argument;
+import org.elasticsearch.compute.gen.argument.ArrayArgument;
+import org.elasticsearch.compute.gen.argument.StandardArgument;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -30,8 +33,6 @@
 import javax.lang.model.element.ExecutableElement;
 import javax.lang.model.element.Modifier;
 import javax.lang.model.element.TypeElement;
-import javax.lang.model.element.VariableElement;
-import javax.lang.model.type.TypeKind;
 import javax.lang.model.type.TypeMirror;
 import javax.lang.model.util.Elements;
 
@@ -87,6 +88,7 @@ public class AggregatorImplementer {
 
     public AggregatorImplementer(
         Elements elements,
+        javax.lang.model.util.Types types,
         TypeElement declarationType,
         IntermediateState[] interStateAnno,
         List<TypeMirror> warnExceptions
@@ -108,7 +110,14 @@ public AggregatorImplementer(
             requireName("combine"),
             requireArgsStartsWith(requireType(aggState.declaredType()), requireAnyType("<aggregation input column type>"))
         );
-        this.aggParams = combine.getParameters().stream().skip(1).map(AggregationParameter::create).toList();
+        this.aggParams = combine.getParameters().stream().skip(1).map(v -> {
+            Argument a = Argument.fromParameter(types, v);
+            return switch (a) {
+                case StandardArgument sa -> new AggregationParameter(sa.name(), sa.type(), false);
+                case ArrayArgument aa -> new AggregationParameter(aa.name(), aa.componentType(), true);
+                default -> throw new IllegalArgumentException("unsupported argument [" + a + "]");
+            };
+        }).toList();
 
         this.createParameters = init.getParameters()
             .stream()
@@ -768,14 +777,6 @@ private static String primitiveStateStoreClassname(TypeName declaredType, boolea
     }
 
     public record AggregationParameter(String name, TypeName type, boolean isArray) {
-        public static AggregationParameter create(VariableElement v) {
-            return new AggregationParameter(
-                v.getSimpleName().toString(),
-                TypeName.get(v.asType()),
-                Objects.equals(v.asType().getKind(), TypeKind.ARRAY)
-            );
-        }
-
         public String blockName() {
             return name + "Block";
         }

x-pack/plugin/esql/compute/gen/src/main/java/org/elasticsearch/compute/gen/AggregatorProcessor.java

@@ -87,7 +87,13 @@ public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnv
             );
             if (aggClass.getAnnotation(Aggregator.class) != null) {
                 IntermediateState[] intermediateState = aggClass.getAnnotation(Aggregator.class).value();
-                implementer = new AggregatorImplementer(env.getElementUtils(), aggClass, intermediateState, warnExceptionsTypes);
+                implementer = new AggregatorImplementer(
+                    env.getElementUtils(),
+                    env.getTypeUtils(),
+                    aggClass,
+                    intermediateState,
+                    warnExceptionsTypes
+                );
                 write(aggClass, "aggregator", implementer.sourceFile(), env);
             }
             GroupingAggregatorImplementer groupingAggregatorImplementer = null;
@@ -98,6 +104,7 @@ public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnv
                 }
                 groupingAggregatorImplementer = new GroupingAggregatorImplementer(
                     env.getElementUtils(),
+                    env.getTypeUtils(),
                     aggClass,
                     intermediateState,
                     warnExceptionsTypes

x-pack/plugin/esql/compute/gen/src/main/java/org/elasticsearch/compute/gen/ConvertEvaluatorImplementer.java

@@ -13,6 +13,10 @@
 import com.squareup.javapoet.TypeName;
 import com.squareup.javapoet.TypeSpec;
 
+import org.elasticsearch.compute.gen.argument.Argument;
+import org.elasticsearch.compute.gen.argument.FixedArgument;
+import org.elasticsearch.compute.gen.argument.StandardArgument;
+
 import java.util.ArrayList;
 import java.util.List;
 import java.util.stream.Collectors;
@@ -61,14 +65,14 @@ public ConvertEvaluatorImplementer(
         this.processFunction = new EvaluatorImplementer.ProcessFunction(types, processFunction, warnExceptions);
         this.canProcessOrdinals = warnExceptions.isEmpty()
             && this.processFunction.returnType().equals(BYTES_REF)
-            && this.processFunction.args.getFirst() instanceof EvaluatorImplementer.StandardProcessFunctionArg s
+            && this.processFunction.args.getFirst() instanceof StandardArgument s
             && s.type().equals(BYTES_REF);
 
-        if (this.processFunction.args.getFirst() instanceof EvaluatorImplementer.StandardProcessFunctionArg == false) {
+        if (this.processFunction.args.getFirst() instanceof StandardArgument == false) {
             throw new IllegalArgumentException("first argument must be the field to process");
         }
         for (int a = 1; a < this.processFunction.args.size(); a++) {
-            if (this.processFunction.args.get(a) instanceof EvaluatorImplementer.FixedProcessFunctionArg == false) {
+            if (this.processFunction.args.get(a) instanceof FixedArgument == false) {
                 throw new IllegalArgumentException("fixed function args supported after the first");
                 // TODO support more function types when we need them
             }
@@ -101,7 +105,7 @@ private TypeSpec type() {
         builder.superclass(ABSTRACT_CONVERT_FUNCTION_EVALUATOR);
         builder.addField(baseRamBytesUsed(implementation));
 
-        for (EvaluatorImplementer.ProcessFunctionArg a : processFunction.args) {
+        for (Argument a : processFunction.args) {
             a.declareField(builder);
         }
         builder.addMethod(ctor());
@@ -124,7 +128,7 @@ private MethodSpec ctor() {
         MethodSpec.Builder builder = MethodSpec.constructorBuilder().addModifiers(Modifier.PUBLIC);
         builder.addParameter(SOURCE, "source");
         builder.addStatement("super(driverContext, source)");
-        for (EvaluatorImplementer.ProcessFunctionArg a : processFunction.args) {
+        for (Argument a : processFunction.args) {
             a.implementCtor(builder);
         }
         builder.addParameter(DRIVER_CONTEXT, "driverContext");
@@ -134,7 +138,7 @@ private MethodSpec ctor() {
     private MethodSpec next() {
         MethodSpec.Builder builder = MethodSpec.methodBuilder("next").addAnnotation(Override.class).addModifiers(Modifier.PUBLIC);
         builder.returns(EXPRESSION_EVALUATOR);
-        builder.addStatement("return $N", ((EvaluatorImplementer.StandardProcessFunctionArg) processFunction.args.getFirst()).name());
+        builder.addStatement("return $N", ((StandardArgument) processFunction.args.getFirst()).name());
         return builder.build();
     }