Support "size" and "spacing" list styles

These are only supported in inline styles so that flow can calculate the
size of the elements without having to look through the rest of the
tree.

doc/styling.md

@@ -45,8 +45,8 @@ See [the Luanti documentation](https://api.luanti.org/formspec/#styling-formspec
 for a list of valid property names and values. Flow accepts numbers and
 booleans as property values where applicable.
 
-**Warning:** Flow does not currently support styles that change the element
-size, like `font_size` for labels and `size` for lists.
+**Warning:** Styles that change the size of the element are currently only
+supported on `gui.List` (notably `font_size` on labels won't work properly)
 
 ## Separate style elements
 
@@ -70,3 +70,7 @@ gui.Button{
 ```
 
 The `Style` and `StyleType` elements are invisible and won't affect padding.
+
+**Warning:** `gui.Style` and `gui.StyleType` do not support *any* styles that
+change the element size, such as `font_size` for labels and `size` and `spacing`
+lists.

expand.lua

@@ -17,7 +17,8 @@
 -- along with this program.  If not, see <https://www.gnu.org/licenses/>.
 --
 
-local DEFAULT_SPACING, LABEL_OFFSET, invisible_elems = ...
+local DEFAULT_SPACING, LABEL_OFFSET, get_and_fill_in_sizes,
+    invisible_elems = ...
 local align_types = {}
 
 function align_types.fill(node, x, w, extra_space)
@@ -147,8 +148,7 @@ local function expand(box)
             if not invisible_elems[node.type] then
                 local width, height = node.w or 0, node.h or 0
                 if node.type == "list" then
-                    width = width * 1.25 - 0.25
-                    height = height * 1.25 - 0.25
+                    width, height = get_and_fill_in_sizes(node)
                 end
                 local padding_x2 = (node.padding or 0) * 2
                 align_types[node.align_h or "auto"](node, "x", "w", box.w -
@@ -191,8 +191,10 @@ local function expand(box)
             end
 
             if node.type == "list" then
-                width = width * 1.25 - 0.25
-                height = height * 1.25 - 0.25
+                width, height = get_and_fill_in_sizes(node)
+                if y == "x" then
+                    width, height = height, width
+                end
             end
             free_space = free_space - width - (node.padding or 0) * 2 -
                 (y == "x" and node._padding_top or 0)

init.lua

@@ -26,7 +26,7 @@ local apply_padding, get_and_fill_in_sizes, set_current_lang,
     dofile(modpath .. "/layout.lua")
 
 local expand = assert(loadfile(modpath .. "/expand.lua"))(
-    DEFAULT_SPACING, LABEL_OFFSET, invisible_elems
+    DEFAULT_SPACING, LABEL_OFFSET, get_and_fill_in_sizes, invisible_elems
 )
 
 local parse_callbacks = dofile(modpath .. "/input.lua")

layout.lua

@@ -105,9 +105,32 @@ end
 
 local size_getters = {}
 
+local function parse_v2f(str, default_x, default_y)
+    if str and type(str) == "string" then
+        local x, y = str:match("^%s-(%d+)%s-,%s-(%d+)%s-$")
+        return tonumber(x) or default_x, tonumber(y) or default_y
+    end
+
+    return default_x, default_y
+end
+
 local function get_and_fill_in_sizes(node)
     if node.type == "list" then
-        return node.w * 1.25 - 0.25, node.h * 1.25 - 0.25
+        if node._flow_w and node._flow_h then
+            return node._flow_w, node._flow_h
+        end
+
+        local style = node.style
+        local slot_w, slot_h = parse_v2f(style and style.size, 1, 1)
+        local spacing_w, spacing_h = parse_v2f(style and style.spacing, 0.25, 0.25)
+
+        local w = node.w * (slot_w + spacing_w) - spacing_w
+        local h = node.h * (slot_h + spacing_h) - spacing_h
+
+        -- Cache calculated size so we don't have to parse the list style again
+        node._flow_w, node._flow_h = w, h
+
+        return w, h
     end
 
     if node.w and node.h then