Initial bare-bones implementation of achievements

data/json/scores.json

@@ -36,14 +36,21 @@
     "id": "num_avatar_zombie_kills",
     "type": "event_statistic",
     "stat_type": "count",
-    "event_transformation": "avatar_zombie_kills"
+    "event_transformation": "avatar_zombie_kills",
+    "description": "Number of zombies killed"
   },
   {
     "id": "score_kills",
     "type": "score",
     "description": "Number of monsters killed: %s",
     "statistic": "num_avatar_kills"
   },
+  {
+    "id": "achievement_kill_zombie",
+    "type": "achievement",
+    "description": "One down, billions to go\u2026",
+    "requirements": [ { "event_statistic": "num_avatar_zombie_kills", "is": ">=", "target": 1 } ]
+  },
   {
     "id": "moves_not_mounted",
     "type": "event_transformation",

doc/JSON_INFO.md

@@ -1053,7 +1053,7 @@ request](https://github.com/CleverRaven/Cataclysm-DDA/pull/36657) and the
   }
 ```
 
-### Scores
+### Scores and achievements
 
 Scores are defined in two or three steps based on *events*.  To see what events
 exist and what data they contain, read [`event.h`](../src/event.h).
@@ -1178,6 +1178,11 @@ given field for that unique event:
 "field": "avatar_id"
 ```
 
+Regardless of `stat_type`, each `event_statistic` can also have:
+```C++
+"description": "Number of things" // Intended for use in describing achievement requirements.
+```
+
 #### `score`
 
 Scores simply associate a description to an event for formatting in tabulations
@@ -1194,6 +1199,28 @@ Note that even though most statistics yield an integer, you should still use
 "statistic": "avatar_num_headshots"
 ```
 
+#### `achievement`
+
+Achievements are goals for the player to aspire to, in the usual sense of the
+term as popularised in other games.
+
+An achievement is specified via requirements, each of which is a constraint on
+an `event_statistic`.  For example:
+
+```C++
+{
+  "id": "achievement_kill_zombie",
+  "type": "achievement",
+  // The achievement description is used for the UI.
+  "description": "One down, billions to go\u2026",
+  "requirements": [
+    // Each requirement must specify the statistic being constrained, and the
+    // constraint in terms of a comparison against some target value.
+    { "event_statistic": "num_avatar_zombie_kills", "is": ">=", "target": 1 }
+  ]
+},
+```
+
 ### Skills
 
 ```C++

lang/extract_json_strings.py

@@ -112,6 +112,7 @@ def warning_supressed(filename):
 #   "sound" member
 #   "messages" member containing an array of translatable strings
 automatically_convertible = {
+    "achievement",
     "activity_type",
     "AMMO",
     "ammunition_type",
@@ -125,6 +126,7 @@ def warning_supressed(filename):
     "CONTAINER",
     "dream",
     "ENGINE",
+    "event_statistic",
     "faction",
     "furniture",
     "GENERIC",