feat(java): add SchemaGenerator compile-time type-to-JSON-Schema utility (#1766)

* Initial plan

* feat(java): add SchemaGenerator compile-time type-to-JSON-Schema utility

Creates SchemaGenerator.java that maps javax.lang.model TypeMirror
instances to JSON Schema source code literals (Map.of(...) expressions).

Implements all 24 type mappings from the specification including:
- Primitives and boxed types (int/Integer, long/Long, etc.)
- String, UUID, OffsetDateTime
- Collections (List<T>, Collection<T>, Set<T>)
- Maps (Map<String, V> with typed values)
- Arrays (String[])
- Enums (with constant enumeration)
- Records and POJOs (with properties/required)
- Optional<T>, OptionalInt, OptionalDouble
- Sealed interfaces (oneOf)
- JsonNode and Object (any)

Also adds SchemaGeneratorTest using compilation-testing approach
with javax.tools.JavaCompiler to exercise the generator at compile time.

Closes #1759

* fix: address code review - remove unused param, handle all primitive types

* fix(java): correct SimpleJavaFileObject override - getCharContent not getContent

Co-authored-by: edburns <75821+edburns@users.noreply.github.com>

* spotless

* Remove .class files generated by test

* spotless

* fix: use Map.ofEntries for properties to avoid Map.of 10-entry limit

Address review comment r3461777483: Map.of() only supports up to 10
key-value pairs. Switch properties maps in SchemaGenerator to use
Map.ofEntries(Map.entry(...), ...) so records/POJOs/methods with >10
fields won't cause generated source compilation failures.

Update SchemaGeneratorTest expectations to match the new format.

* fix: add missing Byte/Short/Character boxed type mappings

Address review comment r3461777428: Byte and Short now map to
"integer", Character maps to "string", matching their primitive
equivalents. Add tests for all three.

* fix: add missing OptionalLong mapping in generateDeclaredTypeSchema

Address review comment r3461777459: OptionalLong was handled in
isOptionalType/unwrapOptional but missing from generateDeclaredTypeSchema,
causing it to fall through to POJO introspection when used as a direct
return type. Add the mapping and tests for OptionalInt, OptionalLong,
and OptionalDouble.

* fix: correct misleading @JsonSubTypes comment on sealed interface handling

Address review comment r3461777579: the implementation uses
getPermittedSubclasses() (Java sealed types), not Jackson annotations.

* test: add sealed interface test for oneOf schema generation

Address review comment r3461777685: the processor had special handling
for TestSealed* types but no test exercised generateSealedSchema().
Add a test with a sealed interface (TestSealedShape) and two record
permits (Circle, Rect) verifying the oneOf schema output.

* test: add >10-field record test proving Map.ofEntries compiles

Address review comment r3461777706: add a test with an 11-component
record that verifies the generated Map.ofEntries(...) expression
actually compiles, proving the Map.of 10-entry limit fix works
end-to-end.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: edburns <75821+edburns@users.noreply.github.com>
Co-authored-by: Ed Burns <edburns@microsoft.com>

Author: Copilot

java/mvnw

@@ -0,0 +1,384 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *--------------------------------------------------------------------------------------------*/
+
+package com.github.copilot.tool;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import javax.lang.model.element.Element;
+import javax.lang.model.element.ElementKind;
+import javax.lang.model.element.RecordComponentElement;
+import javax.lang.model.element.TypeElement;
+import javax.lang.model.element.VariableElement;
+import javax.lang.model.type.ArrayType;
+import javax.lang.model.type.DeclaredType;
+import javax.lang.model.type.TypeKind;
+import javax.lang.model.type.TypeMirror;
+import javax.lang.model.util.Elements;
+import javax.lang.model.util.Types;
+
+/**
+ * Compile-time utility that maps {@code javax.lang.model} types to JSON Schema
+ * represented as Java source code literals ({@code Map.of(...)} expressions).
+ *
+ * <p>
+ * This class is invoked by the annotation processor and operates exclusively
+ * with the {@code javax.lang.model} API. It does NOT use
+ * {@code java.lang.reflect}.
+ *
+ * @since 1.0.2
+ */
+public class SchemaGenerator {
+
+    /**
+     * Given a {@link TypeMirror} from the annotation processing environment,
+     * returns a {@code String} containing Java source code for a {@code Map}
+     * literal representing the JSON Schema of that type.
+     *
+     * @param type
+     *            the type to generate schema for
+     * @param typeUtils
+     *            the {@link Types} utility from the processing environment
+     * @param elementUtils
+     *            the {@link Elements} utility from the processing environment
+     * @return a Java source code string representing the JSON Schema
+     */
+    public String generateSchemaSource(TypeMirror type, Types typeUtils, Elements elementUtils) {
+        return generateSchema(type, typeUtils, elementUtils);
+    }
+
+    /**
+     * Generates the full "parameters" schema source for a method's parameters.
+     * Produces a
+     * {@code Map.of("type", "object", "properties", Map.of(...), "required", List.of(...))}.
+     *
+     * @param parameters
+     *            the method parameters to generate schema for
+     * @param typeUtils
+     *            the {@link Types} utility from the processing environment
+     * @param elementUtils
+     *            the {@link Elements} utility from the processing environment
+     * @return a Java source code string representing the parameters JSON Schema
+     */
+    public String generateParametersSchemaSource(List<? extends VariableElement> parameters, Types typeUtils,
+            Elements elementUtils) {
+        if (parameters.isEmpty()) {
+            return "Map.of(\"type\", \"object\", \"properties\", Map.of(), \"required\", List.of())";
+        }
+
+        List<String> propertyEntries = new ArrayList<>();
+        List<String> requiredNames = new ArrayList<>();
+
+        for (VariableElement param : parameters) {
+            String paramName = param.getSimpleName().toString();
+            TypeMirror paramType = param.asType();
+
+            boolean isOptional = isOptionalType(paramType, typeUtils, elementUtils);
+            String schema;
+            if (isOptional) {
+                schema = generateSchema(unwrapOptional(paramType, typeUtils, elementUtils), typeUtils, elementUtils);
+            } else {
+                schema = generateSchema(paramType, typeUtils, elementUtils);
+            }
+
+            propertyEntries.add("Map.entry(\"" + paramName + "\", " + schema + ")");
+
+            if (!isOptional) {
+                Param paramAnnotation = param.getAnnotation(Param.class);
+                if (paramAnnotation == null || paramAnnotation.required()) {
+                    requiredNames.add("\"" + paramName + "\"");
+                }
+            }
+        }
+
+        String properties = "Map.ofEntries(" + String.join(", ", propertyEntries) + ")";
+        String required = "List.of(" + String.join(", ", requiredNames) + ")";
+
+        return "Map.of(\"type\", \"object\", \"properties\", " + properties + ", \"required\", " + required + ")";
+    }
+
+    private String generateSchema(TypeMirror type, Types typeUtils, Elements elementUtils) {
+        // Handle primitive types
+        if (type.getKind().isPrimitive()) {
+            return generatePrimitiveSchema(type.getKind());
+        }
+
+        // Handle array types
+        if (type.getKind() == TypeKind.ARRAY) {
+            ArrayType arrayType = (ArrayType) type;
+            TypeMirror componentType = arrayType.getComponentType();
+            String itemsSchema = generateSchema(componentType, typeUtils, elementUtils);
+            return "Map.of(\"type\", \"array\", \"items\", " + itemsSchema + ")";
+        }
+
+        // Handle declared types (classes, interfaces, enums, records)
+        if (type.getKind() == TypeKind.DECLARED) {
+            return generateDeclaredTypeSchema((DeclaredType) type, typeUtils, elementUtils);
+        }
+
+        // Fallback: any
+        return "Map.of()";
+    }
+
+    private String generatePrimitiveSchema(TypeKind kind) {
+        switch (kind) {
+            case INT :
+            case LONG :
+            case BYTE :
+            case SHORT :
+                return "Map.of(\"type\", \"integer\")";
+            case DOUBLE :
+            case FLOAT :
+                return "Map.of(\"type\", \"number\")";
+            case BOOLEAN :
+                return "Map.of(\"type\", \"boolean\")";
+            case CHAR :
+                return "Map.of(\"type\", \"string\")";
+            default :
+                return "Map.of()";
+        }
+    }
+
+    private String generateDeclaredTypeSchema(DeclaredType type, Types typeUtils, Elements elementUtils) {
+        TypeElement typeElement = (TypeElement) type.asElement();
+        String qualifiedName = typeElement.getQualifiedName().toString();
+
+        // String
+        if ("java.lang.String".equals(qualifiedName)) {
+            return "Map.of(\"type\", \"string\")";
+        }
+
+        // Boxed primitives
+        if ("java.lang.Integer".equals(qualifiedName) || "java.lang.Long".equals(qualifiedName)
+                || "java.lang.Byte".equals(qualifiedName) || "java.lang.Short".equals(qualifiedName)) {
+            return "Map.of(\"type\", \"integer\")";
+        }
+        if ("java.lang.Double".equals(qualifiedName) || "java.lang.Float".equals(qualifiedName)) {
+            return "Map.of(\"type\", \"number\")";
+        }
+        if ("java.lang.Boolean".equals(qualifiedName)) {
+            return "Map.of(\"type\", \"boolean\")";
+        }
+        if ("java.lang.Character".equals(qualifiedName)) {
+            return "Map.of(\"type\", \"string\")";
+        }
+
+        // UUID
+        if ("java.util.UUID".equals(qualifiedName)) {
+            return "Map.of(\"type\", \"string\", \"format\", \"uuid\")";
+        }
+
+        // OffsetDateTime
+        if ("java.time.OffsetDateTime".equals(qualifiedName)) {
+            return "Map.of(\"type\", \"string\", \"format\", \"date-time\")";
+        }
+
+        // JsonNode (any)
+        if ("com.fasterxml.jackson.databind.JsonNode".equals(qualifiedName)) {
+            return "Map.of()";
+        }
+
+        // Object (any)
+        if ("java.lang.Object".equals(qualifiedName)) {
+            return "Map.of()";
+        }
+
+        // Optional types
+        if ("java.util.Optional".equals(qualifiedName)) {
+            List<? extends TypeMirror> typeArgs = type.getTypeArguments();
+            if (!typeArgs.isEmpty()) {
+                return generateSchema(typeArgs.get(0), typeUtils, elementUtils);
+            }
+            return "Map.of()";
+        }
+        if ("java.util.OptionalInt".equals(qualifiedName)) {
+            return "Map.of(\"type\", \"integer\")";
+        }
+        if ("java.util.OptionalDouble".equals(qualifiedName)) {
+            return "Map.of(\"type\", \"number\")";
+        }
+        if ("java.util.OptionalLong".equals(qualifiedName)) {
+            return "Map.of(\"type\", \"integer\")";
+        }
+
+        // List / Collection
+        if (isCollectionType(qualifiedName)) {
+            List<? extends TypeMirror> typeArgs = type.getTypeArguments();
+            if (!typeArgs.isEmpty()) {
+                String itemsSchema = generateSchema(typeArgs.get(0), typeUtils, elementUtils);
+                return "Map.of(\"type\", \"array\", \"items\", " + itemsSchema + ")";
+            }
+            return "Map.of(\"type\", \"array\")";
+        }
+
+        // Map<String, V>
+        if (isMapType(qualifiedName)) {
+            List<? extends TypeMirror> typeArgs = type.getTypeArguments();
+            if (typeArgs.size() == 2) {
+                TypeMirror valueType = typeArgs.get(1);
+                if (valueType.getKind() == TypeKind.DECLARED) {
+                    TypeElement valueElement = (TypeElement) ((DeclaredType) valueType).asElement();
+                    String valueQName = valueElement.getQualifiedName().toString();
+                    if ("java.lang.Object".equals(valueQName)) {
+                        return "Map.of(\"type\", \"object\")";
+                    }
+                }
+                String valueSchema = generateSchema(valueType, typeUtils, elementUtils);
+                return "Map.of(\"type\", \"object\", \"additionalProperties\", " + valueSchema + ")";
+            }
+            return "Map.of(\"type\", \"object\")";
+        }
+
+        // Enum types
+        if (typeElement.getKind() == ElementKind.ENUM) {
+            List<String> constants = typeElement.getEnclosedElements().stream()
+                    .filter(e -> e.getKind() == ElementKind.ENUM_CONSTANT)
+                    .map(e -> "\"" + e.getSimpleName().toString() + "\"").collect(Collectors.toList());
+            return "Map.of(\"type\", \"string\", \"enum\", List.of(" + String.join(", ", constants) + "))";
+        }
+
+        // Record types
+        if (typeElement.getKind() == ElementKind.RECORD) {
+            return generateRecordSchema(typeElement, typeUtils, elementUtils);
+        }
+
+        // POJO / class types — treat as object with fields
+        if (typeElement.getKind() == ElementKind.CLASS) {
+            return generateClassSchema(typeElement, typeUtils, elementUtils);
+        }
+
+        // Sealed interfaces — oneOf via permitted subclasses
+        if (typeElement.getKind() == ElementKind.INTERFACE) {
+            return generateSealedSchema(typeElement, typeUtils, elementUtils);
+        }
+
+        return "Map.of()";
+    }
+
+    private String generateRecordSchema(TypeElement typeElement, Types typeUtils, Elements elementUtils) {
+        List<String> propertyEntries = new ArrayList<>();
+        List<String> requiredNames = new ArrayList<>();
+
+        for (Element enclosed : typeElement.getEnclosedElements()) {
+            if (enclosed.getKind() == ElementKind.RECORD_COMPONENT) {
+                RecordComponentElement component = (RecordComponentElement) enclosed;
+                String name = component.getSimpleName().toString();
+                TypeMirror componentType = component.asType();
+
+                boolean isOptional = isOptionalType(componentType, typeUtils, elementUtils);
+                String schema;
+                if (isOptional) {
+                    schema = generateSchema(unwrapOptional(componentType, typeUtils, elementUtils), typeUtils,
+                            elementUtils);
+                } else {
+                    schema = generateSchema(componentType, typeUtils, elementUtils);
+                    requiredNames.add("\"" + name + "\"");
+                }
+
+                propertyEntries.add("Map.entry(\"" + name + "\", " + schema + ")");
+            }
+        }
+
+        String properties = "Map.ofEntries(" + String.join(", ", propertyEntries) + ")";
+        String required = "List.of(" + String.join(", ", requiredNames) + ")";
+
+        return "Map.of(\"type\", \"object\", \"properties\", " + properties + ", \"required\", " + required + ")";
+    }
+
+    private String generateClassSchema(TypeElement typeElement, Types typeUtils, Elements elementUtils) {
+        List<String> propertyEntries = new ArrayList<>();
+        List<String> requiredNames = new ArrayList<>();
+
+        for (Element enclosed : typeElement.getEnclosedElements()) {
+            if (enclosed.getKind() == ElementKind.FIELD) {
+                VariableElement field = (VariableElement) enclosed;
+                // Skip static fields
+                if (field.getModifiers().contains(javax.lang.model.element.Modifier.STATIC)) {
+                    continue;
+                }
+                String name = field.getSimpleName().toString();
+                TypeMirror fieldType = field.asType();
+
+                boolean isOptional = isOptionalType(fieldType, typeUtils, elementUtils);
+                String schema;
+                if (isOptional) {
+                    schema = generateSchema(unwrapOptional(fieldType, typeUtils, elementUtils), typeUtils,
+                            elementUtils);
+                } else {
+                    schema = generateSchema(fieldType, typeUtils, elementUtils);
+                    requiredNames.add("\"" + name + "\"");
+                }
+
+                propertyEntries.add("Map.entry(\"" + name + "\", " + schema + ")");
+            }
+        }
+
+        if (propertyEntries.isEmpty()) {
+            return "Map.of(\"type\", \"object\")";
+        }
+
+        String properties = "Map.ofEntries(" + String.join(", ", propertyEntries) + ")";
+        String required = "List.of(" + String.join(", ", requiredNames) + ")";
+
+        return "Map.of(\"type\", \"object\", \"properties\", " + properties + ", \"required\", " + required + ")";
+    }
+
+    private String generateSealedSchema(TypeElement typeElement, Types typeUtils, Elements elementUtils) {
+        List<? extends TypeMirror> permittedSubclasses = typeElement.getPermittedSubclasses();
+        if (permittedSubclasses != null && !permittedSubclasses.isEmpty()) {
+            List<String> schemas = permittedSubclasses.stream().map(sub -> generateSchema(sub, typeUtils, elementUtils))
+                    .collect(Collectors.toList());
+            return "Map.of(\"oneOf\", List.of(" + String.join(", ", schemas) + "))";
+        }
+        return "Map.of(\"type\", \"object\")";
+    }
+
+    private boolean isOptionalType(TypeMirror type, Types typeUtils, Elements elementUtils) {
+        if (type.getKind() != TypeKind.DECLARED) {
+            return false;
+        }
+        DeclaredType declaredType = (DeclaredType) type;
+        TypeElement element = (TypeElement) declaredType.asElement();
+        String name = element.getQualifiedName().toString();
+        return "java.util.Optional".equals(name) || "java.util.OptionalInt".equals(name)
+                || "java.util.OptionalDouble".equals(name) || "java.util.OptionalLong".equals(name);
+    }
+
+    private TypeMirror unwrapOptional(TypeMirror type, Types typeUtils, Elements elementUtils) {
+        if (type.getKind() != TypeKind.DECLARED) {
+            return type;
+        }
+        DeclaredType declaredType = (DeclaredType) type;
+        TypeElement element = (TypeElement) declaredType.asElement();
+        String name = element.getQualifiedName().toString();
+
+        if ("java.util.Optional".equals(name)) {
+            List<? extends TypeMirror> typeArgs = declaredType.getTypeArguments();
+            if (!typeArgs.isEmpty()) {
+                return typeArgs.get(0);
+            }
+        }
+        if ("java.util.OptionalInt".equals(name)) {
+            return typeUtils.getPrimitiveType(TypeKind.INT);
+        }
+        if ("java.util.OptionalDouble".equals(name)) {
+            return typeUtils.getPrimitiveType(TypeKind.DOUBLE);
+        }
+        if ("java.util.OptionalLong".equals(name)) {
+            return typeUtils.getPrimitiveType(TypeKind.LONG);
+        }
+        return type;
+    }
+
+    private boolean isCollectionType(String qualifiedName) {
+        return "java.util.List".equals(qualifiedName) || "java.util.Collection".equals(qualifiedName)
+                || "java.util.Set".equals(qualifiedName);
+    }
+
+    private boolean isMapType(String qualifiedName) {
+        return "java.util.Map".equals(qualifiedName);
+    }
+}