[TypeScript-Fetch] Generate oneOf schemas as type unions (#2617)

* Generate oneOf schemas as type unions for typescript-fetch

* Adjust oneOf imports to only include refs of oneOf

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

@@ -165,6 +165,16 @@ public class TypeScriptFetchClientCodegen extends AbstractTypeScriptClientCodege
                     }
                 }
             }
+            if (cm.oneOf.size() > 0) {
+                // For oneOfs only import $refs within the oneOf
+                TreeSet<String> oneOfRefs = new TreeSet<String>();
+                for (String im : cm.imports) {
+                    if (cm.oneOf.contains(im)) {
+                        oneOfRefs.add(im);
+                    }
+                }
+                cm.imports = oneOfRefs;
+            }
         }
 
         return objs;

modules/openapi-generator/src/main/resources/typescript-fetch/modelOneOf.mustache

@@ -0,0 +1,14 @@
+{{#hasImports}}
+import {
+    {{#imports}}
+    {{{.}}},
+    {{/imports}}
+} from './';
+
+{{/hasImports}}
+/**
+ * @type {{classname}}{{#description}}
+ * {{{description}}}{{/description}}
+ * @export
+ */
+export type {{classname}} = {{#oneOf}}{{{.}}}{{^-last}} | {{/-last}}{{/oneOf}};

modules/openapi-generator/src/main/resources/typescript-fetch/models.mustache

@@ -6,7 +6,14 @@
 {{>modelEnum}}
 {{/isEnum}}
 {{^isEnum}}
+{{#oneOf}}
+{{#-first}}
+{{>modelOneOf}}
+{{/-first}}
+{{/oneOf}}
+{{^oneOf}}
 {{>modelGeneric}}
+{{/oneOf}}
 {{/isEnum}}
 {{/model}}
 {{/models}}