add default to empty container option

Author: wing328

bin/configs/java-okhttp-gson.yaml

@@ -10,6 +10,7 @@ parameterNameMappings:
   _type: underscoreType
   type_: typeWithUnderscore
 additionalProperties:
+  defaultToEmptyContainer: "array?"
   artifactId: petstore-okhttp-gson
   hideGenerationTimestamp: true
   useOneOfDiscriminatorLookup: true

modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java

@@ -333,6 +333,11 @@ apiTemplateFiles are for API outputs only (controllers/handlers).
     // Whether to automatically hardcode params that are considered Constants by OpenAPI Spec
     @Setter protected boolean autosetConstants = false;
 
+    @Setter @Getter boolean arrayDefaultToEmpty, arrayNullableDefaultToEmpty, arrayOptionalNullableDefaultToEmpty, arrayOptionalDefaultToEmpty;
+    @Setter @Getter boolean mapDefaultToEmpty, mapNullableDefaultToEmpty, mapOptionalNullableDefaultToEmpty, mapOptionalDefaultToEmpty;
+    final String DEFAULT_TO_EMPTY_CONTAINER = "defaultToEmptyContainer";
+    final List EMPTY_LIST = new ArrayList();
+
     @Override
     public boolean getAddSuffixToDuplicateOperationNicknames() {
         return addSuffixToDuplicateOperationNicknames;
@@ -392,8 +397,11 @@ public void processOpts() {
         convertPropertyToBooleanAndWriteBack(CodegenConstants.DISALLOW_ADDITIONAL_PROPERTIES_IF_NOT_PRESENT, this::setDisallowAdditionalPropertiesIfNotPresent);
         convertPropertyToBooleanAndWriteBack(CodegenConstants.ENUM_UNKNOWN_DEFAULT_CASE, this::setEnumUnknownDefaultCase);
         convertPropertyToBooleanAndWriteBack(CodegenConstants.AUTOSET_CONSTANTS, this::setAutosetConstants);
-        }
 
+        if (additionalProperties.containsKey(DEFAULT_TO_EMPTY_CONTAINER) && additionalProperties.get(DEFAULT_TO_EMPTY_CONTAINER) instanceof String) {
+            parseDefaultToEmptyContainer((String) additionalProperties.get(DEFAULT_TO_EMPTY_CONTAINER));
+        }
+    }
 
     /***
      * Preset map builder with commonly used Mustache lambdas.
@@ -4172,6 +4180,11 @@ public CodegenProperty fromProperty(String name, Schema p, boolean required, boo
             }
         }
 
+        // override defaultValue if it's not set and defaultToEmptyContainer is set
+        if (p.getDefault() == null && additionalProperties.containsKey("defaultToEmptyContainer")) {
+            updateDefaultToEmptyContainer(property, p);
+        }
+
         // set the default value
         property.defaultValue = toDefaultValue(property, p);
         property.defaultValueWithParam = toDefaultValueWithParam(name, p);
@@ -4181,6 +4194,90 @@ public CodegenProperty fromProperty(String name, Schema p, boolean required, boo
         return property;
     }
 
+    /**
+     * update container's default to empty container according rules provided by the user.
+     *
+     * @param cp codegen property
+     * @param p schema
+     */
+    void updateDefaultToEmptyContainer(CodegenProperty cp, Schema p) {
+        if (cp.isArray) {
+            if (!cp.required) { // optional
+                if (cp.isNullable && arrayOptionalNullableDefaultToEmpty) { // nullable
+                    p.setDefault(EMPTY_LIST);
+                } else if (!cp.isNullable && arrayOptionalDefaultToEmpty) { // non-nullable
+                    p.setDefault(EMPTY_LIST);
+                }
+            } else { // required
+                if (cp.isNullable && arrayNullableDefaultToEmpty) { // nullable
+                    p.setDefault(EMPTY_LIST);
+                } else if (!cp.isNullable && arrayDefaultToEmpty) { // non-nullable
+                    p.setDefault(EMPTY_LIST);
+                }
+            }
+        } else if (cp.isMap) {
+            if (!cp.required) { // optional
+                if (cp.isNullable && mapOptionalNullableDefaultToEmpty) { // nullable
+                    p.setDefault(EMPTY_LIST);
+                } else if (!cp.isNullable && mapOptionalDefaultToEmpty) { // non-nullable
+                    p.setDefault(EMPTY_LIST);
+                }
+            } else { // required
+                if (cp.isNullable && mapNullableDefaultToEmpty) { // nullable
+                    p.setDefault(EMPTY_LIST);
+                } else if (!cp.isNullable && mapOptionalDefaultToEmpty) { // non-nullable
+                    p.setDefault(EMPTY_LIST);
+                }
+            }
+        }
+    }
+
+    /**
+     * Parse the rules for defaulting to the empty container.
+     *
+     * @param input a set of rules separated by `|`
+     */
+    void parseDefaultToEmptyContainer(String input) {
+        String[] inputs = ((String) input).split("[|]");
+        String containerType;
+        for (String rule: inputs) {
+            if (StringUtils.isEmpty(rule)) {
+                LOGGER.error("updateDefaultToEmptyContainer: Skipped empty input in `{}`.", input);
+                continue;
+            }
+
+            if (rule.startsWith("?") && rule.endsWith("?")) { // nullable optional
+                containerType = rule.substring(1, rule.length() - 1);
+                if ("array".equalsIgnoreCase(containerType)) {
+                    arrayOptionalNullableDefaultToEmpty = true;
+                } else if ("map".equalsIgnoreCase(containerType)) {
+                    mapOptionalNullableDefaultToEmpty = true;
+                } else {
+                    LOGGER.error("Skipped invalid container type `{}` in `{}`.", containerType, input);
+                }
+            } else if (rule.startsWith("?")) { // nullable (required)
+                containerType = rule.substring(1, rule.length());
+                if ("array".equalsIgnoreCase(containerType)) {
+                    arrayNullableDefaultToEmpty = true;
+                } else if ("map".equalsIgnoreCase(containerType)) {
+                    mapNullableDefaultToEmpty = true;
+                } else {
+                    LOGGER.error("Skipped invalid container type `{}` in `{}`.", containerType, input);
+                }
+            } else if (rule.endsWith("?")) { // optional
+                containerType = rule.substring(0, rule.length()-1);
+                if ("array".equalsIgnoreCase(containerType)) {
+                    arrayOptionalDefaultToEmpty = true;
+                } else if ("map".equalsIgnoreCase(containerType)) {
+                    mapOptionalDefaultToEmpty = true;
+                } else {
+                    LOGGER.error("Skipped invalid container type `{}` in the rule `{}`.", containerType, input);
+                }
+            }
+        }
+
+    }
+
     /**
      * Update property for array(list) container
      *