Rename MessageStateValidation to OptionGenerator

Author: yevhenii-nadtochii

java/src/main/kotlin/io/spine/validation/java/JavaValidationRenderer.kt

@@ -42,7 +42,7 @@ import io.spine.validation.CompilationMessage
  */
 public class JavaValidationRenderer : JavaRenderer() {
 
-    private val valueConverter = JavaValueConverter(typeSystem)
+    private val valueConverter by lazy { JavaValueConverter(typeSystem) }
 
     override fun render(sources: SourceFileSet) {
         // We receive `grpc` and `kotlin` output sources roots here as well.

java/src/main/kotlin/io/spine/validation/java/MessageValidationCode.kt

@@ -79,7 +79,7 @@ private typealias BuilderPsiClass = PsiClass
 internal class MessageValidationCode(
     private val message: CompilationMessage,
     private val typeSystem: TypeSystem,
-    private val generators: List<MessageStateValidation>
+    private val generators: List<OptionGenerator>
 ) {
     private val messageType: TypeName = message.name
     private val messageClassName = messageType.javaClassName(typeSystem)
@@ -186,7 +186,8 @@ internal class MessageValidationCode(
      */
     private fun MessagePsiClass.declarePrivateValidateMethod() {
         val ruleConstraints = constraints
-        val generatedConstraints = generators.flatMap { it.constraints(messageType) }
+        // We are temporarily ignoring members for standalone generators.
+        val generatedConstraints = generators.flatMap { it.codeFor(messageType).constraints }
         val psiMethod = elementFactory.createMethodFromText(
             """
             |private java.util.Optional<io.spine.validate.ValidationError> validate(io.spine.base.FieldPath parent) {

java/src/main/kotlin/io/spine/validation/java/OptionGenerator.kt

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2025, TeamDev. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Redistribution and use in source and/or binary forms, with or without
+ * modification, must retain the above copyright notice and the following
+ * disclaimer.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package io.spine.validation.java
+
+import io.spine.protodata.ast.TypeName
+import io.spine.validation.java.protodata.CodeBlock
+import io.spine.validation.java.protodata.MemberDeclaration
+
+/**
+ * Generates Java code for a specific option.
+ */
+internal interface OptionGenerator {
+
+    /**
+     * Generates validation code for the option within the provided
+     * message [type].
+     *
+     * If multiple fields declare the option, the returned code handles them all.
+     */
+    fun codeFor(type: TypeName): OptionCode
+}
+
+/**
+ * Java code handling all applications of a specific option within a message.
+ */
+internal class OptionCode(
+
+    /**
+     * Code blocks to be added to the `validate()` method of the message.
+     */
+    val constraints: List<CodeBlock>,
+
+    /**
+     * Additional class-level declarations required by the validation logic.
+     *
+     * Some constraints may require defining extra fields or methods.
+     */
+    val declarations: List<MemberDeclaration> = emptyList()
+)

java/src/main/kotlin/io/spine/validation/java/RequiredOption.kt

@@ -59,18 +59,25 @@ import io.spine.validation.protodata.toBuilder
 internal class RequiredOption(
     private val querying: Querying,
     private val converter: JavaValueConverter
-) : MessageStateValidation {
+) : OptionGenerator {
 
-    private val allViews by lazy {
+    /**
+     * All required fields in the current compilation process.
+     */
+    private val allRequiredFields by lazy {
         querying.select<RequiredField>()
             .all()
     }
 
-    override fun constraints(type: TypeName): List<CodeBlock> =
-        allViews.filter { it.id.type == type }
-            .map { constraints(it) }
+    override fun codeFor(type: TypeName): OptionCode {
+        val requiredMessageFields = allRequiredFields.filter { it.id.type == type }
+        val constraints = requiredMessageFields.map { constraints((it)) }
+        return OptionCode(constraints)
+    }
 
-    // How do we know about variables `violations` and `parent`?
+    // TODO:2025-01-31:yevhenii.nadtochii: The OptionGenerater is already aware about `validate()`
+    //  method, it should pass expressions for `violations` and `parent` variables.  So, not to
+    //  hardcode them as text.
     private fun constraints(view: RequiredField): CodeBlock {
         val field = view.subject
         val getter = This<Message>()
@@ -88,12 +95,9 @@ internal class RequiredOption(
         )
     }
 
-    /**
-     * This approach with `equals()` is unified. Now we
-     */
-    // TODO:2025-01-31:yevhenii.nadtochii: Consider migration from the universal test
-    //  to type-specific tests. This approach with `equals()` was great for rules.
-    //  But now we can write, i.e., `list.size() == 0` instead of comparing it with empty
+    // TODO:2025-01-31:yevhenii.nadtochii: Consider migration from the general check
+    //  to type-specific checks. This approach with `equals()` was great for rules.
+    //  But now we can write, i.e., `list.size() == 0` instead of comparing it with an empty
     //  collection, which is always created just for that.
     private fun defaultValue(field: Field): Expression<*> {
         val unsetValue = UnsetValue.forField(field)!!
@@ -108,7 +112,7 @@ internal class RequiredOption(
 
     // TODO:2025-01-31:yevhenii.nadtochii: Set `field_value` when `TypeConverter` knows
     //  how to convert collections: Could not find a wrapper type for `java.util.Collections$EmptyList`.
-    //  I suppose the same story is with maps. An empty list is a default value for empty repeated.
+    //  I suppose the same story is with maps. An empty list is a default value for empty `repeated`.
     private fun violation(
         field: Field,
         path: Expression<FieldPath>,
@@ -125,6 +129,7 @@ internal class RequiredOption(
         return violation
     }
 
+    // TODO:2025-01-31:yevhenii.nadtochii: This method should be shared with `SetOnceConstraints`.
     private fun Field.templateString(
         template: String,
         placeholders: Map<ErrorPlaceholder, Expression<String>>

java/src/main/kotlin/io/spine/validation/java/MessageStateValidation.kt renamed to java/src/main/kotlin/io/spine/validation/java/protodata/MemberDeclaration.kt

@@ -24,12 +24,16 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-package io.spine.validation.java
+package io.spine.validation.java.protodata
 
-import io.spine.protodata.ast.TypeName
-import io.spine.validation.java.protodata.CodeBlock
+import io.spine.protodata.java.AnElement
 
-internal interface MessageStateValidation {
+/**
+ * Represents class level member declaration.
+ */
+public open class MemberDeclaration(code: String) : AnElement(code)
 
-    fun constraints(type: TypeName): List<CodeBlock>
-}
+// We already need the following children: FieldDeclaration, MethodDeclaration.
+// Also, we need the context. So, that instead of `Expression<Message>.call("getField")`
+// we could use `Context<Message>.call("getField"). We don't really need an explicit
+// `this` everywhere.