Introduce SignatureBuilder API

src/main/java/io/quarkus/gizmo/ClassSignatureBuilderImpl.java

@@ -0,0 +1,93 @@
+package io.quarkus.gizmo;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.jboss.jandex.DotName;
+
+import io.quarkus.gizmo.SignatureBuilder.ClassSignatureBuilder;
+import io.quarkus.gizmo.Type.ClassType;
+import io.quarkus.gizmo.Type.ParameterizedType;
+import io.quarkus.gizmo.Type.TypeVariable;
+
+class ClassSignatureBuilderImpl implements ClassSignatureBuilder {
+
+    private Type superClass = Type.classType(DotName.OBJECT_NAME);
+    private List<TypeVariable> typeParameters = new ArrayList<>();
+    private List<Type> superInterfaces = new ArrayList<>();
+
+    @Override
+    public String build() {
+        StringBuilder signature = new StringBuilder();
+
+        // type params
+        if (!typeParameters.isEmpty()) {
+            signature.append('<');
+            for (TypeVariable typeParameter : typeParameters) {
+                typeParameter.appendTypeParameterToSignature(signature);
+            }
+            signature.append('>');
+        }
+
+        // superclass
+        signature.append(superClass.toSignature());
+
+        // interfaces
+        if (!superInterfaces.isEmpty()) {
+            for (Type superInterface : superInterfaces) {
+                signature.append(superInterface.toSignature());
+            }
+        }
+        return signature.toString();
+    }
+
+    @Override
+    public ClassSignatureBuilder addTypeParameter(TypeVariable typeParameter) {
+        typeParameters.add(typeParameter);
+        return this;
+    }
+
+    @Override
+    public ClassSignatureBuilder setSuperClass(ClassType superClass) {
+        this.superClass = superClass;
+        return this;
+    }
+
+    @Override
+    public ClassSignatureBuilder setSuperClass(ParameterizedType superClass) {
+        if (containsWildcard(superClass)) {
+            throw new IllegalArgumentException("A super type may not specify a wilcard");
+        }
+        this.superClass = superClass;
+        return this;
+    }
+
+    @Override
+    public ClassSignatureBuilder addSuperInterface(ClassType interfaceType) {
+        superInterfaces.add(interfaceType);
+        return this;
+    }
+
+    @Override
+    public ClassSignatureBuilder addSuperInterface(ParameterizedType interfaceType) {
+        if (containsWildcard(interfaceType)) {
+            throw new IllegalArgumentException("A super type may not specify a wilcard");
+        }
+        superInterfaces.add(interfaceType);
+        return this;
+    }
+
+    private boolean containsWildcard(Type type) {
+        if (type.isWildcard()) {
+            return true;
+        } else if (type.isParameterizedType()) {
+            for (Type typeArgument : type.asParameterizedType().typeArguments) {
+                if (containsWildcard(typeArgument)) {
+                    return true;
+                }
+            }
+        }
+        return false;
+    }
+
+}

src/main/java/io/quarkus/gizmo/FieldSignatureBuilderImpl.java

@@ -0,0 +1,22 @@
+package io.quarkus.gizmo;
+
+import java.util.Objects;
+
+import io.quarkus.gizmo.SignatureBuilder.FieldSignatureBuilder;
+
+class FieldSignatureBuilderImpl implements FieldSignatureBuilder {
+
+    private Type type;
+
+    @Override
+    public String build() {
+        return type.toSignature();
+    }
+
+    @Override
+    public FieldSignatureBuilder setType(Type type) {
+        this.type = Objects.requireNonNull(type);
+        return this;
+    }
+
+}

src/main/java/io/quarkus/gizmo/MethodSignatureBuilderImpl.java

@@ -0,0 +1,80 @@
+package io.quarkus.gizmo;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+
+import io.quarkus.gizmo.SignatureBuilder.MethodSignatureBuilder;
+import io.quarkus.gizmo.Type.ClassType;
+import io.quarkus.gizmo.Type.TypeVariable;
+
+class MethodSignatureBuilderImpl implements MethodSignatureBuilder {
+
+    private Type returnType = Type.voidType();
+    private List<Type> parameterTypes = new ArrayList<>();
+    private List<TypeVariable> typeParameters = new ArrayList<>();
+    private List<Type> exceptions = new ArrayList<>();
+
+    @Override
+    public String build() {
+        StringBuilder signature = new StringBuilder();
+
+        // type params
+        if (!typeParameters.isEmpty()) {
+            signature.append('<');
+            for (TypeVariable typeParameter : typeParameters) {
+                typeParameter.appendTypeParameterToSignature(signature);
+            }
+            signature.append('>');
+        }
+
+        // params
+        signature.append('(');
+        for (Type parameterType : parameterTypes) {
+            signature.append(parameterType.toSignature());
+        }
+        signature.append(')');
+
+        // return type
+        signature.append(returnType.toSignature());
+
+        // exceptions
+        if (!exceptions.isEmpty()) {
+            for (Type exceptionType : exceptions) {
+                signature.append('^').append(exceptionType.toSignature());
+            }
+        }
+        return signature.toString();
+    }
+
+    @Override
+    public MethodSignatureBuilder addTypeParameter(TypeVariable typeParameter) {
+        typeParameters.add(Objects.requireNonNull(typeParameter));
+        return this;
+    }
+
+    @Override
+    public MethodSignatureBuilder setReturnType(Type returnType) {
+        this.returnType = Objects.requireNonNull(returnType);
+        return this;
+    }
+
+    @Override
+    public MethodSignatureBuilder addParameter(Type parameterType) {
+        this.parameterTypes.add(Objects.requireNonNull(parameterType));
+        return this;
+    }
+
+    @Override
+    public MethodSignatureBuilder addException(ClassType exceptionType) {
+        this.exceptions.add(Objects.requireNonNull(exceptionType));
+        return this;
+    }
+
+    @Override
+    public MethodSignatureBuilder addException(TypeVariable exceptionType) {
+        this.exceptions.add(Objects.requireNonNull(exceptionType));
+        return this;
+    }
+
+}

src/main/java/io/quarkus/gizmo/SignatureBuilder.java

@@ -0,0 +1,62 @@
+package io.quarkus.gizmo;
+
+import io.quarkus.gizmo.Type.ClassType;
+import io.quarkus.gizmo.Type.ParameterizedType;
+import io.quarkus.gizmo.Type.TypeVariable;
+
+/**
+ * Builds a signature as defined in JVMS 17, chapter "4.7.9.1. Signatures".
+ * 
+ * @see SignatureElement#setSignature(String)
+ */
+public interface SignatureBuilder {
+
+    static ClassSignatureBuilder forClass() {
+        return new ClassSignatureBuilderImpl();
+    }
+
+    static MethodSignatureBuilder forMethod() {
+        return new MethodSignatureBuilderImpl();
+    }
+
+    static FieldSignatureBuilder forField() {
+        return new FieldSignatureBuilderImpl();
+    }
+
+    /**
+     * @return the signature
+     */
+    String build();
+
+    interface ClassSignatureBuilder extends SignatureBuilder {
+
+        ClassSignatureBuilder addTypeParameter(TypeVariable typeParameter);
+
+        ClassSignatureBuilder setSuperClass(ClassType superClass);
+
+        ClassSignatureBuilder setSuperClass(ParameterizedType superClass);
+
+        ClassSignatureBuilder addSuperInterface(ClassType interfaceType);
+
+        ClassSignatureBuilder addSuperInterface(ParameterizedType interfaceType);
+    }
+
+    interface MethodSignatureBuilder extends SignatureBuilder {
+
+        MethodSignatureBuilder addTypeParameter(TypeVariable typeParameter);
+
+        MethodSignatureBuilder setReturnType(Type returnType);
+
+        MethodSignatureBuilder addParameter(Type parameter);
+
+        MethodSignatureBuilder addException(ClassType exceptionType);
+
+        MethodSignatureBuilder addException(TypeVariable exceptionType);
+    }
+
+    interface FieldSignatureBuilder extends SignatureBuilder {
+
+        FieldSignatureBuilder setType(Type type);
+    }
+
+}

src/main/java/io/quarkus/gizmo/SignatureElement.java

@@ -1,11 +1,18 @@
 package io.quarkus.gizmo;
 
 /**
- * An element that has a signature attribute
+ * An element that has a signature attribute.
  */
 public interface SignatureElement<S> {
 
     String getSignature();
 
+    /**
+     * Use the convenient {@link SignatureBuilder} to build signatures for classes, methods and fields.
+     * 
+     * @param signature The signature as defined in JVMS 17, chapter "4.7.9.1. Signatures"
+     * @return the element
+     * @see SignatureBuilder
+     */
     S setSignature(String signature);
 }