Add countryCodes and notCountryCodes properties for fields (close #7085)

Add documentation note about `prerequisiteTag` property getting ignored if a value is present

data/presets/README.md

@@ -410,6 +410,18 @@ For example, this is how we show the Internet Access Fee field only if the featu
 }
 ```
 
+If a feature has a value for this field's `key` or `keys`, it will display regardless of the `prerequisiteTag` property.
+
+##### `countryCodes`
+
+An array of two-letter, lowercase [ISO 3166-1 alpha-2](https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2) country codes. The field will only be available for features in the specified, whitelisted countries.
+
+By default, fields are available everywhere.
+
+##### `notCountryCodes`
+
+An array of two-letter, lowercase [ISO 3166-1 alpha-2](https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2) country codes. Similar to `countryCodes` except a blacklist instead of a whitelist.
+
 
 ## Building
 

data/presets/schema/field.json

@@ -183,6 +183,24 @@
             "items": {
                 "type": "string"
             }
+        },
+        "countryCodes":  {
+            "description": "Countries where to allow the field, as lowercase ISO 3166-1 alpha-2 codes (https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2)",
+            "type": "array",
+            "uniqueItems": true,
+            "items": {
+                "type": "string",
+                "pattern": "^[a-z]{2}$"
+            }
+        },
+        "notCountryCodes":  {
+            "description": "Countries where NOT to allow the field, as lowercase ISO 3166-1 alpha-2 codes (https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2)",
+            "type": "array",
+            "uniqueItems": true,
+            "items": {
+                "type": "string",
+                "pattern": "^[a-z]{2}$"
+            }
         }
     },
     "additionalProperties": false

modules/ui/field.js

@@ -1,3 +1,4 @@
+import * as countryCoder from '@ideditor/country-coder';
 import { dispatch as d3_dispatch } from 'd3-dispatch';
 import { event as d3_event, select as d3_select } from 'd3-selection';
 
@@ -295,13 +296,30 @@ export function uiField(context, presetField, entity, options) {
     // An allowed field can appear in the UI or in the 'Add field' dropdown.
     // A non-allowed field is hidden from the user altogether
     field.isAllowed = function() {
-        if (!entity || tagsContainFieldKey()) return true;   // a field with a value should always display
 
-        var latest = context.hasEntity(entity.id);   // check the most current copy of the entity
+        var latest = entity && context.hasEntity(entity.id);   // check the most current copy of the entity
         if (!latest) return true;
 
+        if (field.countryCodes || field.notCountryCodes) {
+            var center = latest.extent(context.graph()).center();
+            var countryCode = countryCoder.iso1A2Code(center);
+
+            if (!countryCode) return false;
+
+            countryCode = countryCode.toLowerCase();
+
+            if (field.countryCodes && field.countryCodes.indexOf(countryCode) === -1) {
+                return false;
+            }
+            if (field.notCountryCodes && field.notCountryCodes.indexOf(countryCode) !== -1) {
+                return false;
+            }
+        }
+
         var prerequisiteTag = field.prerequisiteTag;
-        if (prerequisiteTag) {
+
+        if (!tagsContainFieldKey() && // ignore tagging prerequisites if a value is already present
+            prerequisiteTag) {
             if (prerequisiteTag.key) {
                 var value = latest.tags[prerequisiteTag.key];
                 if (!value) return false;
@@ -316,6 +334,7 @@ export function uiField(context, presetField, entity, options) {
                 if (latest.tags[prerequisiteTag.keyNot]) return false;
             }
         }
+
         return true;
     };