Add support for value provider

Improve the "hints" section of the metadata so that each hint can provide
the reference to a value provider.

A value provider defines how a tool can discover the potential values of
a property based on the context. The provider is identifed by a name and
may have an arbitrary number of parameters.

Closes gh-3303

spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/metadata/ItemHint.java

@@ -20,6 +20,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import java.util.Map;
 
 /**
  * Provide hints on an {@link ItemMetadata}. Defines the list of possible values for a
@@ -27,7 +28,7 @@ import java.util.List;
  * <p>
  * The {@code name} of the hint is the name of the related property with one major
  * exception for map types as both the keys and values of the map can have hints. In such
- * a case, the hint should be suffixed by ".key" or ".values" respectively. Creating a
+ * a case, the hint should be suffixed by ".keys" or ".values" respectively. Creating a
  * hint for a map using its property name is therefore invalid.
  *
  * @author Stephane Nicoll
@@ -39,9 +40,12 @@ public class ItemHint implements Comparable<ItemHint> {
 
 	private final List<ValueHint> values;
 
-	public ItemHint(String name, List<ValueHint> values) {
+	private final List<ProviderHint> providers;
+
+	public ItemHint(String name, List<ValueHint> values, List<ProviderHint> providers) {
 		this.name = toCanonicalName(name);
-		this.values = new ArrayList<ValueHint>(values);
+		this.values = (values != null ? new ArrayList<ValueHint>(values) : new ArrayList<ValueHint>());
+		this.providers = (providers != null ? new ArrayList<ProviderHint>(providers) : new ArrayList<ProviderHint>());
 	}
 
 	private String toCanonicalName(String name) {
@@ -62,19 +66,23 @@ public class ItemHint implements Comparable<ItemHint> {
 		return Collections.unmodifiableList(this.values);
 	}
 
+	public List<ProviderHint> getProviders() {
+		return Collections.unmodifiableList(this.providers);
+	}
+
 	@Override
 	public int compareTo(ItemHint other) {
 		return getName().compareTo(other.getName());
 	}
 
 	public static ItemHint newHint(String name, ValueHint... values) {
-		return new ItemHint(name, Arrays.asList(values));
+		return new ItemHint(name, Arrays.asList(values), Collections.<ProviderHint>emptyList());
 	}
 
 	@Override
 	public String toString() {
-		return "ItemHint{" + "name='" + this.name + '\'' + ", values=" + this.values
-				+ '}';
+		return "ItemHint{" + "name='" + this.name + ", values=" + this.values
+				+ "providers=" + this.providers + '}';
 	}
 
 	public static class ValueHint {
@@ -104,4 +112,28 @@ public class ItemHint implements Comparable<ItemHint> {
 
 	}
 
+	public static class ProviderHint {
+		private final String name;
+		private final Map<String,Object> parameters;
+
+		public ProviderHint(String name, Map<String, Object> parameters) {
+			this.name = name;
+			this.parameters = parameters;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public Map<String, Object> getParameters() {
+			return parameters;
+		}
+
+		@Override
+		public String toString() {
+			return "Provider{" + "name='" + this.name + ", parameters=" + this.parameters +
+					'}';
+		}
+	}
+
 }

spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/metadata/JsonMarshaller.java

@@ -24,8 +24,10 @@ import java.lang.reflect.Array;
 import java.nio.charset.Charset;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.HashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
+import java.util.Map;
 import java.util.Set;
 
 import org.json.JSONArray;
@@ -103,6 +105,22 @@ public class JsonMarshaller {
 			}
 			jsonObject.put("values", valuesArray);
 		}
+		if (!hint.getProviders().isEmpty()) {
+			JSONArray providersArray = new JSONArray();
+			for (ItemHint.ProviderHint providerHint : hint.getProviders()) {
+				JSONObject providerHintObject = new JSONOrderedObject();
+				providerHintObject.put("name", providerHint.getName());
+				if (providerHint.getParameters() != null && !providerHint.getParameters().isEmpty()) {
+					JSONObject parametersObject = new JSONOrderedObject();
+					for (Map.Entry<String, Object> entry : providerHint.getParameters().entrySet()) {
+						parametersObject.put(entry.getKey(), extractItemValue(entry.getValue()));
+					}
+					providerHintObject.put("parameters", parametersObject);
+				}
+				providersArray.put(providerHintObject);
+			}
+			jsonObject.put("providers", providersArray);
+		}
 		return jsonObject;
 	}
 
@@ -182,7 +200,14 @@ public class JsonMarshaller {
 				values.add(toValueHint((JSONObject) valuesArray.get(i)));
 			}
 		}
-		return new ItemHint(name, values);
+		List<ItemHint.ProviderHint> providers = new ArrayList<ItemHint.ProviderHint>();
+		if (object.has("providers")) {
+			JSONArray providersObject = object.getJSONArray("providers");
+			for (int i = 0; i < providersObject.length(); i++) {
+				providers.add(toProviderHint((JSONObject) providersObject.get(i)));
+			}
+		}
+		return new ItemHint(name, values, providers);
 	}
 
 	private ItemHint.ValueHint toValueHint(JSONObject object) {
@@ -191,6 +216,20 @@ public class JsonMarshaller {
 		return new ItemHint.ValueHint(value, description);
 	}
 
+	private ItemHint.ProviderHint toProviderHint(JSONObject object) {
+		String name = object.getString("name");
+		Map<String,Object> parameters = new HashMap<String,Object>();
+		if (object.has("parameters")) {
+			JSONObject parametersObject = object.getJSONObject("parameters");
+			for (Object k : parametersObject.keySet()) {
+				String key = (String) k;
+				Object value = readItemValue(parametersObject.get(key));
+				parameters.put(key, value);
+			}
+		}
+		return new ItemHint.ProviderHint(name, parameters);
+	}
+
 	private Object readItemValue(Object value) {
 		if (value instanceof JSONArray) {
 			JSONArray array = (JSONArray) value;