fix: sort discriminator entries by mapping order

src/services/models/Schema.ts

@@ -254,7 +254,7 @@ export class SchemaModel {
 
     const inversedMapping = { ...implicitInversedMapping, ...explicitInversedMapping };
 
-    const refs: Array<{ $ref; name }> = [];
+    let refs: Array<{ $ref; name }> = [];
 
     for (const $ref of Object.keys(inversedMapping)) {
       const names = inversedMapping[$ref];
@@ -267,6 +267,35 @@ export class SchemaModel {
       }
     }
 
+    // Make the listing respects the mapping 
+    // in case a mapping is defined, the user usually wants to have the order shown
+    // as it was defined in the yaml. This will sort the names given the provided
+    // mapping (if provided).
+    // The logic is:
+    // - If a name is among the mapping, promote it to first
+    // - Names among the mapping are sorted by their order in the mapping
+    // - Names outside the mapping are sorted alphabetically
+    const names = Object.keys(mapping);
+    if (names.length !== 0) {
+      refs = refs.sort((left, right) => {
+        const indexLeft = names.indexOf(left.name);
+        const indexRight = names.indexOf(right.name);
+
+        if (indexLeft < 0 && indexRight < 0) {
+          // out of mapping, order by name
+          return left.name.localCompare(right.name);
+        } else if (indexLeft < 0) {
+          // the right is found, so mapping wins
+          return 1;
+        } else if (indexRight < 0) {
+          // left wins as it's in mapping
+          return -1;
+        } else {
+          return indexLeft - indexRight;
+        }
+      });
+    }
+
     this.oneOf = refs.map(({ $ref, name }) => {
       const innerSchema = new SchemaModel(parser, parser.byRef($ref)!, $ref, this.options, true);
       innerSchema.title = name;