Added simple path/filename validation field type

Allows specifying what it accepts (folder, filename, filename extensions)
Supports having the path/filename relative to the current mod folder

src/ui/forms/fields/path.lua

@@ -0,0 +1,69 @@
+local utils = require("utils")
+local mods = require("mods")
+local loadedState = require("loaded_state")
+local stringField = require("ui.forms.fields.string")
+
+local pathField = {}
+
+pathField.fieldType = "path"
+
+function pathField.getElement(name, value, options)
+    -- Add extra options and pass it onto string field
+
+    local allowEmpty = options.allowEmpty
+    local allowMissingPath = options.allowMissingPath
+    local allowFolders = options.allowFolders
+    local allowFiles = options.allowFiles
+    local allowedExtensions = options.allowedExtensions
+    local relativeToMod = options.relativeToMod
+
+    options.validator = function(filename)
+        local fieldEmpty = filename == nil or #filename == 0
+
+        if fieldEmpty then
+            return allowEmpty ~= false
+        end
+
+        if relativeToMod ~= false then
+            local modPath = mods.getFilenameModPath(loadedState.filename)
+
+            if not modPath then
+                return false
+            end
+
+            filename = utils.joinpath(modPath, filename)
+        end
+
+        local attributes = utils.pathAttributes(filename)
+
+        if not attributes and allowMissingPath ~= false then
+            return false
+        end
+
+        local attributeMode = attributes.mode or "missing"
+
+        if attributeMode == "directory" and not allowFolders then
+            return false
+        end
+
+        if attributeMode == "file" then
+            local fileExtension = utils.fileExtension(filename)
+
+            if allowFiles == false then
+                return false
+            end
+
+            if allowedExtensions and not utils.contains(fileExtension, allowedExtensions) then
+                return false
+            end
+        end
+
+        -- TODO - Custom validator at this point?
+
+        return true
+    end
+
+    return stringField.getElement(name, value, options)
+end
+
+return pathField