Allow to delete freeform keys again, partial fix of #2008

src/Models/ThemeConfig/Json/QuestionableTagRenderingConfigJson.ts

@@ -133,7 +133,16 @@ export interface MappingConfigJson {
      * question: What extra tags should be added to the object if this object is chosen?
      * type: simple_tag
      *
-     * If chosen as answer, these tags will be applied onto the object, together with the tags from the `if`
+     * If chosen as answer, these tags will be applied onto the object, together with the tags from the `if`.
+     * Note that if the contributor picks this mapping, saves and then changes their mind and uses a different mapping,
+     * the extraTags will reside.
+     * E.g. when picking `memorial:type=bench`, then `amenity=bench` will also be applied.
+     * If someone later on changes the type to `memorial:statue`, `amenity=bench` will stay onto the object
+     * (which is the desired behaviour, see e.g. for https://www.openstreetmap.org/node/5620038478)
+     * Use 'ifNot' to explicitly remove an tag if this is important
+     *
+     * If someone marks the question as 'unknown', the extra tags will not be erased
+     *
      * Not compatible with multiAnswer.
      *
      * This can be used e.g. to erase other keys which indicate the 'not' value:

src/Models/ThemeConfig/TagRenderingConfig.ts

@@ -911,6 +911,24 @@ export default class TagRenderingConfig {
 
         return Utils.NoNull(tags)
     }
+
+    /**
+     * The keys that should be erased if one has to revert to 'unknown'.
+     * Might give undefined
+     */
+    public settableKeys(): string[] | undefined {
+        const toDelete = new Set<string>()
+        if(this.freeform){
+            toDelete.add(this.freeform.key)
+        }
+        for (const mapping of this.mappings) {
+            for (const usedKey of mapping.if.usedKeys()) {
+                toDelete.add(usedKey)
+            }
+        }
+
+        return Array.from(toDelete)
+    }
 }
 
 export class TagRenderingConfigUtils {