Add on_key_enter callback and close_on_enter

Closes https://gitlab.com/luk3yx/minetest-flow/-/issues/4

README.md

@@ -622,4 +622,42 @@ end)
 If multiple `on_quit` callbacks are specified in different elements, they will
 all get called.
 
+</details><details>
+<summary><b>Handling enter keypresses in fields</b></summary>
+
+`gui.Field` and `gui.Pwdfield` support an `on_key_enter` callback that gets
+called if enter is pressed:
+
+```lua
+local form = flow.make_gui(function(player, ctx)
+    return gui.VBox{
+        gui.Field{
+            label = "Press enter!",
+            name = "field",
+            on_key_enter = function(player, ctx)
+                core.chat_send_player(player:get_player_name(),
+                    "Field value: " .. dump(ctx.form.field))
+            end,
+
+            -- You can also specify close_on_enter to close the form when enter
+            -- is pressed.
+            close_on_enter = true,
+        },
+    }
+end)
+```
+
+Notes:
+
+ - If you're using this callback, please make sure there's some other way to
+   trigger the enter action (like a button) to support older flow versions and
+   in case I replace this API with a better one in the future.
+ - If you want recent mobile clients to call this callback when editing text,
+   add `enter_after_edit = true` to the field definition.
+ - The similarly named `on_event` gets called whenever the client submits the
+   field to the server, which could be at any time, and is not very useful, but
+   is still supported for compatibility (and there may be uses for it, such as
+   sanitising field values). Be careful not to accidentally use the wrong
+   callback.
+
 </details>

init.lua

@@ -200,11 +200,13 @@ local function insert_shorthand_elements(tree)
         if node.type == "container" or node.type == "scroll_container" then
             insert_shorthand_elements(node)
         elseif node.type == "field" then
-            table.insert(tree, i, {
-                type = 'field_close_on_enter',
-                name = node.name,
-                close_on_enter = false,
-            })
+            if not node.close_on_enter then
+                table.insert(tree, i, {
+                    type = 'field_close_on_enter',
+                    name = node.name,
+                    close_on_enter = false,
+                })
+            end
 
             if node.enter_after_edit then
                 table.insert(tree, i, {
@@ -250,9 +252,8 @@ function Form:_render(player, ctx, formspec_version, id1, embedded, lang_code)
     if not id1 or id1 > 1e6 then id1 = 0 end
 
     local tree = render_ast(box, embedded)
-    local callbacks, btn_callbacks, saved_fields, id2 = parse_callbacks(
-        tree, orig_form, id1, embedded, formspec_version
-    )
+    local callbacks, btn_callbacks, saved_fields, id2, on_key_enters =
+        parse_callbacks(tree, orig_form, id1, embedded, formspec_version)
 
     -- This should be after parse_callbacks so it can take advantage of
     -- automatic field naming
@@ -274,6 +275,7 @@ function Form:_render(player, ctx, formspec_version, id1, embedded, lang_code)
         callbacks = callbacks,
         btn_callbacks = btn_callbacks,
         saved_fields = saved_fields,
+        on_key_enters = on_key_enters,
         redraw_if_changed = redraw_if_changed,
         ctx = ctx,
         auto_name_id = id2,
@@ -496,6 +498,17 @@ function fs_process_events(player, form_info, fields)
         end
     end
 
+    -- Run on_key_enter callbacks
+    if fields.key_enter and form_info.on_key_enters then
+        local callback = form_info.on_key_enters[fields.key_enter_field]
+        if callback then
+            -- Enter callbacks and button fields can't be sent at the same
+            -- time (except from a hacked client), so make sure they aren't
+            -- both processed at once by returning now.
+            return callback(player, ctx) or redraw_fs
+        end
+    end
+
     -- Run button callbacks after all other callbacks as that seems to be the
     -- most intuitive thing to do
     -- Note: Try not to rely on the order of on_event callbacks, I may change

input.lua

@@ -155,7 +155,7 @@ local button_types = {
 -- Removes on_event from a formspec_ast tree and returns a callbacks table
 local function parse_callbacks(tree, ctx_form, auto_name_id,
         replace_backgrounds, formspec_version)
-    local callbacks
+    local callbacks, on_key_enters
     local btn_callbacks = {}
     local saved_fields = {}
     local tablecolumn_count = 1
@@ -297,13 +297,32 @@ local function parse_callbacks(tree, ctx_form, auto_name_id,
             node.on_event = nil
         end
 
+        local is_field = node.type == "field" or node.type == "pwdfield"
+        if node.on_key_enter and node_name then
+            if is_field then
+                on_key_enters = on_key_enters or {}
+                if on_key_enters[node_name] then
+                    error(("Multiple on_key_enter callbacks registered for " ..
+                        "elements with the same name (%q)"):format(node_name))
+                end
+                on_key_enters[node_name] = node.on_key_enter
+            else
+                core.log("warning",
+                    "[flow] on_key_enter only works with Field and Pwdfield")
+            end
+            node.on_key_enter = nil
+        elseif is_field and node.close_on_enter then
+            core.log("warning", ("[flow] Field %q has close_on_enter " ..
+                "enabled but no on_key_enter callback."):format(node_name))
+        end
+
         -- Call _after_positioned (used internally for ScrollableVBox)
         if node._after_positioned then
             node:_after_positioned()
             node._after_positioned = nil
         end
     end
-    return callbacks, btn_callbacks, saved_fields, auto_name_id
+    return callbacks, btn_callbacks, saved_fields, auto_name_id, on_key_enters
 end
 
 return parse_callbacks