Agent Skills: Makepad 2.0 Common Pitfalls & Troubleshooting Guide

Makepad 2.0 Common Pitfalls & Troubleshooting Guide

This skill covers common mistakes when building with Makepad 2.0 and the Splash scripting language. Each pitfall includes:

• What the user sees (symptom)
• Why it happens (root cause)
• How to fix it (correct code)

Reference documents: AGENTS.md, splash.md

Pitfall #1: Container height is 0px -- UI is invisible

Symptom: Your entire UI or a section of it does not appear. The container renders with zero height, making all children invisible.

Root Cause: All View-based containers (View, SolidView, RoundedView, etc.) default to height: Fill. When a Fill container is placed inside a Fit parent (or any context where the available height is determined by children), the height resolves to 0px due to circular dependency: the parent asks the child how tall it is, the child says "as tall as my parent", and the result is zero.

Fix: Always set height: Fit on containers that should shrink-wrap their content.

// WRONG -- height defaults to Fill, resolves to 0px in a Fit context
View{
    flow: Down
    Label{text: "Hello"}
}

// CORRECT -- height: Fit makes the container wrap its children
View{
    height: Fit
    flow: Down
    Label{text: "Hello"}
}

Rule of thumb: Write height: Fit immediately after the opening brace of every container unless you have a fixed-height parent or you explicitly want height: Fill inside a known fixed-size ancestor.

Exception: Inside a fixed-height parent, height: Fill is valid:

View{
    height: 300
    View{
        height: Fill
        Label{text: "I fill the 300px"}
    }
}

Pitfall #2: Text invisible on colored background -- missing new_batch

Symptom: You add a Label inside a RoundedView or SolidView with a background color, but the text is invisible. The container appears correctly colored but the text cannot be seen, even though draw_text.color is set to a contrasting color.

Root Cause: Makepad batches draw calls by shader type for GPU performance. All Label widgets using the same text shader get batched into one draw call, and all backgrounds into another. Without new_batch: true, the text draw call may execute before the background draw call, placing the text geometrically behind the opaque background.

Fix: Add new_batch: true to any View-based container that has a visible background (show_bg: true or pre-styled views like SolidView, RoundedView) and contains text children.

// WRONG -- text is drawn behind the background due to batching
RoundedView{
    height: Fit
    draw_bg.color: #333
    Label{text: "Can't see me"}
}

// CORRECT -- new_batch forces background to draw before children's text
RoundedView{
    height: Fit
    new_batch: true
    draw_bg.color: #333
    Label{text: "Now visible" draw_text.color: #fff}
}

When you MUST use new_batch: true:

• Any container with show_bg: true (or pre-styled like SolidView, RoundedView) that contains text
• Hoverable items with background animator -- text disappears on hover without it
• Parent containers of repeated items that each have their own background

Pitfall #3: Named child override does not work -- used : instead of :=

Symptom: You define a template with let and try to override a child property per-instance, but the override is silently ignored. The default text always shows.

Root Cause: In Splash, : creates a static property, while := creates a named/dynamic child that is addressable and overridable. If you declare label: Label{...} (with :), the child has no addressable name and the override path label.text: cannot find it.

Fix: Use := for any child you want to reference or override later.

// WRONG -- static child, override fails silently
let Card = View{
    height: Fit
    title: Label{text: "default"}
}
Card{title.text: "new text"}  // Fails! title is not addressable

// CORRECT -- named child with :=, override works
let Card = View{
    height: Fit
    title := Label{text: "default"}
}
Card{title.text: "new text"}  // Works! title is a named child

Additional rule: Named children inside anonymous containers are UNREACHABLE. Every container in the path from root to child must also be named:

// WRONG -- label is inside an anonymous View, unreachable
let Item = View{
    height: Fit
    View{
        flow: Down
        label := Label{text: "default"}
    }
}
Item{label.text: "new"}  // Fails! No path to label through anonymous View

// CORRECT -- full named path
let Item = View{
    height: Fit
    texts := View{
        flow: Down
        label := Label{text: "default"}
    }
}
Item{texts.label.text: "new"}  // Works! Full dot-path through named containers

Pitfall #4: Hex color with letter 'e' renders wrong or causes parse error

Symptom: A hex color like #2ecc71 causes a cryptic parse error such as expected at least one digit in exponent, or the color renders incorrectly.

Root Cause: The Rust tokenizer inside script_mod!{} interprets a digit followed by e as the start of a scientific notation number (e.g., 2e looks like 2 * 10^...). This breaks parsing of hex colors that contain the letter e adjacent to digits.

Fix: Use the #x prefix for any hex color containing the letter e or E.

// WRONG -- parser reads '2e' as scientific notation exponent
draw_bg.color: #2ecc71
draw_bg.color: #1e1e2e
draw_bg.color: #4466ee

// CORRECT -- #x prefix escapes the hex literal
draw_bg.color: #x2ecc71
draw_bg.color: #x1e1e2e
draw_bg.color: #x4466ee

When is #x NOT needed? Colors without the letter e work fine with plain #:

draw_bg.color: #ff4444    // OK -- no 'e'
draw_bg.color: #44cc44    // OK -- no 'e'
draw_bg.color: #333       // OK -- no 'e'

Pitfall #5: border_radius takes wrong type -- must be float, not Inset

Symptom: Attempting to set per-corner border radii with Inset causes a parse error or silently breaks the layout. The rounded corners do not appear.

Root Cause: Border radius is a single f32 uniform value applied uniformly to all corners. It is NOT an Inset-like struct with per-corner values. Passing an Inset or object silently breaks the entire layout.

CRITICAL: The property name differs by context:

• In Canvas Splash (POST /splash): Use draw_bg.radius with trailing-dot float
• In script_mod! macro: Use draw_bg.border_radius

Fix: Use a plain float value with the correct property name.

// WRONG -- border_radius is not an Inset
draw_bg.border_radius: Inset{top_left: 10 top_right: 10}

// WRONG -- not an object
draw_bg.border_radius: {top: 10 bottom: 0}

// CORRECT (Canvas Splash context) -- use draw_bg.radius with trailing dot
draw_bg.radius: 10.

// CORRECT (script_mod! context) -- use draw_bg.border_radius
draw_bg.border_radius: 10.0

// For per-corner radii, use RoundedAllView with a vec4
// (top-left, top-right, right-bottom, left-bottom)
RoundedAllView{
    height: Fit
    draw_bg.border_radius: vec4(10.0 10.0 0.0 0.0)
}

Pitfall #6: Widget not found from Rust -- registration order wrong

Symptom: At runtime, a widget type is not found or a script error occurs saying a widget is not registered. The app may panic or display nothing.

Root Cause: In Makepad 2.0, widget modules must be registered via script_mod(vm) calls in the correct order. Base widgets must be registered before custom widgets, and custom widgets before the UI that uses them. If the order is wrong, a module tries to use a widget type that has not been registered yet.

Fix: Follow the correct registration order in App::run().

impl App {
    fn run(vm: &mut ScriptVm) -> Self {
        // 1. Register base widget library (theme + all standard widgets)
        crate::makepad_widgets::script_mod(vm);

        // 2. Register your custom widget modules (if any)
        crate::my_custom_widgets::script_mod(vm);

        // 3. Register your app UI module (uses widgets from steps 1 and 2)
        crate::app_ui::script_mod(vm);

        // 4. Create the app from its own script_mod
        App::from_script_mod(vm, self::script_mod)
    }
}

Key rule: Widget modules must be registered BEFORE UI modules that use them. Always call lib.rs::script_mod before app_ui::script_mod.

Pitfall #7: Filler clips text -- used alongside width: Fill sibling

Symptom: Text in a horizontal layout is cut off halfway. The text label appears to have only half the available width.

Root Cause: Filler{} is defined as View{width: Fill height: Fill}. When placed next to a sibling that also has width: Fill, both compete for the remaining horizontal space and split it 50/50. The text label only gets half the width and text is clipped.

Fix: Remove Filler{} when a sibling already uses width: Fill. The Fill sibling naturally takes all remaining space, pushing Fit-sized siblings to the edge.

// WRONG -- Filler splits space with Fill sibling, text is clipped
View{
    flow: Right height: Fit
    Label{width: Fill text: "Long text that gets clipped"}
    Filler{}
    Button{text: "OK"}
}

// CORRECT -- width: Fill on label pushes button to the right edge
View{
    flow: Right height: Fit
    Label{width: Fill text: "Long text now has full space"}
    Button{text: "OK"}
}

// CORRECT use of Filler -- between Fit-sized siblings
View{
    flow: Right height: Fit
    Label{text: "left"}
    Filler{}
    Label{text: "right"}
}

Pitfall #8: Text disappears on hover -- animated View without new_batch

Symptom: A list item or button has hover effects. When you hover over it, the background color changes but the text vanishes completely. Moving the cursor away brings the text back.

Root Cause: The hover animator changes the View's background from transparent (#0000) to an opaque or semi-opaque color. Without new_batch: true, the background and text are in the same draw batch. When the background becomes opaque, it covers the text that was drawn in the same batch order.

Fix: Add new_batch: true to any View with show_bg: true that has a hover animator and contains text.

// WRONG -- text disappears when hover activates the background
View{
    width: Fill height: Fit
    show_bg: true
    draw_bg +: {
        color: uniform(#0000)
        color_hover: uniform(#fff2)
        hover: instance(0.0)
        pixel: fn(){
            return Pal.premul(self.color.mix(self.color_hover, self.hover))
        }
    }
    animator: Animator{
        hover: {
            default: @off
            off: AnimatorState{
                from: {all: Forward {duration: 0.15}}
                apply: {draw_bg: {hover: 0.0}}
            }
            on: AnimatorState{
                from: {all: Forward {duration: 0.15}}
                apply: {draw_bg: {hover: 1.0}}
            }
        }
    }
    Label{text: "Vanishes on hover!" draw_text.color: #fff}
}

// CORRECT -- add new_batch: true
View{
    width: Fill height: Fit
    new_batch: true
    show_bg: true
    draw_bg +: {
        color: uniform(#0000)
        color_hover: uniform(#fff2)
        hover: instance(0.0)
        pixel: fn(){
            return Pal.premul(self.color.mix(self.color_hover, self.hover))
        }
    }
    animator: Animator{
        hover: {
            default: @off
            off: AnimatorState{
                from: {all: Forward {duration: 0.15}}
                apply: {draw_bg: {hover: 0.0}}
            }
            on: AnimatorState{
                from: {all: Forward {duration: 0.15}}
                apply: {draw_bg: {hover: 1.0}}
            }
        }
    }
    Label{text: "Stays visible on hover!" draw_text.color: #fff}
}

Pitfall #9: Commas in Splash -- tolerated but not required

Symptom: Confusion about whether commas are allowed between properties in script_mod! blocks.

Root Cause: Splash is primarily whitespace-delimited. However, the Splash tokenizer treats commas as whitespace — they are silently consumed and do not cause parse errors. Many Makepad projects (including Robrix) use commas extensively in script_mod! blocks, inherited from Makepad 1.x live_design! syntax which required commas.

Guidance: Both styles are valid. Match the surrounding code style:

// Style A: with commas (common in codebases migrated from 1.x)
View{
    flow: Down,
    height: Fit,
    spacing: 10,
    padding: Inset{top: 5, bottom: 5, left: 10, right: 10}
}

// Style B: without commas (pure Splash style)
View{
    flow: Down
    height: Fit
    spacing: 10
    padding: Inset{top: 5 bottom: 5 left: 10 right: 10}
}

Note: Both compile and run identically. The tokenizer discards commas. Do NOT waste time removing commas from existing code — it creates noisy diffs with no functional change.

Pitfall #10: Using semicolons -- not valid in Splash

Symptom: Parse errors or unexpected behavior. The semicolons are treated as part of property values or cause tokenizer failures.

Root Cause: Splash does not use semicolons to terminate statements. This is a common mistake for developers coming from CSS, JavaScript, or Rust backgrounds.

Fix: Remove all semicolons.

// WRONG -- semicolons are not valid
View{
    flow: Down;
    height: Fit;
    Label{text: "Hello";};
}

// CORRECT -- no semicolons needed
View{
    flow: Down
    height: Fit
    Label{text: "Hello"}
}

Pitfall #11: Root container without width: Fill -- narrow or broken layout

Symptom: The UI appears as a narrow sliver on one side of the window, or the layout is entirely broken. Content does not fill the available window width.

Root Cause: Using a fixed pixel width (e.g., width: 400) on the outermost container means it does not adapt to the available window space. If the window is wider, the content is a small strip. If narrower, content is clipped.

Fix: Always use width: Fill on the root container. Fixed pixel widths are fine for inner elements.

// WRONG -- fixed width on root, does not adapt to window
RoundedView{
    width: 400
    height: Fit
    flow: Down
    Label{text: "Narrow!"}
}

// CORRECT -- root fills available width
RoundedView{
    width: Fill
    height: Fit
    flow: Down
    Label{text: "Full width!"}
}

Pitfall #12: Label does not support Animator -- silently ignored

Symptom: You add animator: Animator{...} and cursor: MouseCursor.Hand to a Label, but nothing happens on hover. No error, no effect.

Root Cause: Label (and H1-H4, P, TextBox, Image, Icon, Markdown, Html, Slider, DropDown, Splitter, Hr, Filler) do NOT have an animator field. Adding one is silently ignored.

Fix: Wrap the Label in a View that does support animator.

// WRONG -- animator on Label is silently ignored
Label{
    animator: Animator{
        hover: {
            default: @off
            off: AnimatorState{ from: {all: Forward{duration: 0.15}} apply: {draw_text: {hover: 0.0}} }
            on: AnimatorState{ from: {all: Forward{duration: 0.15}} apply: {draw_text: {hover: 1.0}} }
        }
    }
    text: "Hover me"
}

// CORRECT -- animate the wrapping View
View{
    width: Fill height: Fit
    new_batch: true
    cursor: MouseCursor.Hand
    show_bg: true
    draw_bg +: {
        color: uniform(#0000)
        color_hover: uniform(#fff2)
        hover: instance(0.0)
        pixel: fn(){ return Pal.premul(self.color.mix(self.color_hover, self.hover)) }
    }
    animator: Animator{
        hover: {
            default: @off
            off: AnimatorState{ from: {all: Forward{duration: 0.15}} apply: {draw_bg: {hover: 0.0}} }
            on: AnimatorState{ from: {all: Forward{duration: 0.15}} apply: {draw_bg: {hover: 1.0}} }
        }
    }
    Label{text: "Hover me" draw_text.color: #fff}
}

Widgets that SUPPORT animator: View, SolidView, RoundedView, ScrollXView, ScrollYView, ScrollXYView, Button, ButtonFlat, ButtonFlatter, CheckBox, Toggle, RadioButton, LinkLabel, TextInput

Pitfall #13: Default text color is white -- invisible on light backgrounds

Symptom: Text is present in the widget tree but invisible. On white or light-colored backgrounds, the text simply cannot be seen. It may appear if you select the text or change the background to a dark color.

Root Cause: All text widgets (Label, H1-H4, P, Button text, etc.) default to white (#fff) text color. On a light background, white text is invisible.

Fix: Explicitly set draw_text.color to a dark color for every text element on light backgrounds.

// WRONG -- white text on white background
View{
    height: Fit
    show_bg: true
    draw_bg.color: #fff
    Label{text: "Can't see this"}
}

// CORRECT -- explicit dark text color
View{
    height: Fit
    new_batch: true
    show_bg: true
    draw_bg.color: #fff
    Label{text: "Visible!" draw_text.color: #333}
}

Pitfall #14: Shader pixel function missing Pal.premul() -- colors render wrong

Symptom: Semi-transparent colors render as bright, fully opaque, or washed out. A subtle tint like #ffffff08 appears as bright white instead of nearly transparent.

Root Cause: Makepad uses premultiplied alpha for GPU rendering. When you return a color from a pixel: fn() without premultiplying the alpha, the alpha blending produces incorrect results.

Fix: Always wrap your final color return in Pal.premul() -- unless returning sdf.result, which is already premultiplied by sdf.fill() / sdf.stroke().

// WRONG -- alpha not premultiplied, renders incorrectly
draw_bg +: {
    pixel: fn() {
        return vec4(1.0 0.0 0.0 0.5)
    }
}

// CORRECT -- premultiply alpha
draw_bg +: {
    pixel: fn() {
        return Pal.premul(vec4(1.0 0.0 0.0 0.5))
    }
}

// ALSO CORRECT -- sdf.result is already premultiplied
draw_bg +: {
    pixel: fn() {
        let sdf = Sdf2d.viewport(self.pos * self.rect_size)
        sdf.box(0.0 0.0 self.rect_size.x self.rect_size.y 4.0)
        sdf.fill(#f00)
        return sdf.result
    }
}

// CORRECT -- color mixing with premultiply
draw_bg +: {
    pixel: fn() {
        return Pal.premul(self.color.mix(self.color_hover, self.hover))
    }
}

Pitfall #15: Using CSS property names -- not valid in Splash

Symptom: Properties are not recognized, causing parse errors or the property being silently ignored.

Root Cause: Splash is not CSS. Property names use Makepad's own naming convention with dot-path access to nested struct fields.

Fix: Use Makepad property names.

| CSS Name | Splash Name | |----------|-------------| | background-color | draw_bg.color | | color | draw_text.color | | font-size | draw_text.text_style.font_size | | border-radius | draw_bg.border_radius | | border-color | draw_bg.border_color | | border-width | draw_bg.border_size | | padding | padding (same) | | margin | margin (same) | | gap | spacing | | display: flex | flow: Right or flow: Down | | flex-direction: column | flow: Down | | flex-direction: row | flow: Right | | justify-content: center | align: Center | | width: 100% | width: Fill | | width: auto | width: Fit |

// WRONG -- CSS property names
View{
    background-color: #333
    font-size: 14
    border-radius: 8px
    gap: 10
}

// CORRECT -- Splash property names
RoundedView{
    height: Fit
    draw_bg.color: #333
    draw_bg.border_radius: 8.0
    spacing: 10
    Label{text: "Hello" draw_text.text_style.font_size: 14}
}

Pitfall #16: Inventing non-existent properties -- silent failures

Symptom: A property you wrote has no effect. No error is raised, but the widget does not behave as expected.

Root Cause: Splash silently ignores unknown properties. If you guess at a property name (e.g., background:, font_size:, text_color:, border:, opacity:), it is simply discarded.

Fix: Only use documented properties. If unsure, check splash.md or grep for usage in widgets/src/.

Common invented properties and their correct equivalents:

| Invented (WRONG) | Correct | |-------------------|---------| | background: | draw_bg.color: | | font_size: | draw_text.text_style.font_size: | | text_color: | draw_text.color: | | border: | draw_bg.border_size: + draw_bg.border_color: | | opacity: | Use alpha in color: #fff8 | | on_click: | Handle in Rust handle_actions() | | class: | Use let bindings for reusable styles | | id: | Use := for named instances |

Pitfall #17: Adding Root{} or Window{} in script output -- host-level wrappers

Symptom: When generating UI for streaming/splash context, the output does not display or causes errors. Duplicate Window wrappers may cause unexpected behavior.

Root Cause: Root{} and Window{} are host-level wrappers that are defined in the app's script_mod! block. Script content that renders inside a body +: {} block should NOT include these wrappers -- the content goes inside the body.

Fix: Your script output should start directly with the UI content, without Root{} or Window{} wrappers.

// WRONG -- do not add host-level wrappers in script output
Root{
    Window{
        body +: {
            View{ height: Fit Label{text: "Hello"} }
        }
    }
}

// CORRECT -- just the content
View{
    height: Fit
    Label{text: "Hello"}
}

In app code (where Root and Window ARE correct):

script_mod!{
    use mod.prelude.widgets.*
    load_all_resources() do #(App::script_component(vm)){
        ui: Root{
            main_window := Window{
                window.inner_size: vec2(800 600)
                body +: {
                    // UI content goes HERE
                    View{ height: Fit Label{text: "Hello"} }
                }
            }
        }
    }
}

Pitfall #18: on_render not called -- must call render() explicitly

Symptom: You implement on_render on a widget but it is never called. The widget's render logic does not execute.

Root Cause: Makepad does not automatically call on_render in all situations. You must explicitly trigger rendering by calling ui.widget.render() or ensuring the widget is part of the active draw tree.

Fix: Ensure render() is called on the widget, typically from the parent's draw pass. Check that the widget is properly included in the widget hierarchy and that handle_event and draw_walk are correctly implemented.

// Make sure your widget is in the draw tree and draw_walk is implemented
impl Widget for MyWidget {
    fn draw_walk(&mut self, cx: &mut Cx2d, scope: &mut Scope, walk: Walk) -> DrawStep {
        cx.begin_turtle(walk, self.layout);
        // ... drawing code ...
        cx.end_turtle_with_area(&mut self.area);
        DrawStep::done()
    }

    fn handle_event(&mut self, cx: &mut Cx, event: &Event, scope: &mut Scope) {
        // ... event handling ...
    }
}

Pitfall #19: MapView with height: Fill or Fit -- must use fixed pixel height

Symptom: A MapView renders with zero height or behaves erratically. The map area is invisible.

Root Cause: MapView has no intrinsic content height. Using height: Fit gives 0px (no content to fit). Using height: Fill may also resolve to 0px in certain contexts (same circular dependency as Pitfall #1).

Fix: Always give MapView a fixed pixel height.

// WRONG -- no intrinsic height, resolves to 0px
MapView{
    width: Fill
    height: Fit
}

// WRONG -- may resolve to 0px in a Fit parent
MapView{
    width: Fill
    height: Fill
}

// CORRECT -- fixed pixel height
MapView{
    width: Fill
    height: 500
}

Pitfall #20: Modal not showing -- must call .open(cx) from Rust

Symptom: A Modal is defined in the script but never appears. There is no visible dialog or overlay.

Root Cause: Modals are hidden by default. They must be opened programmatically from Rust code by calling .open(cx) on the modal widget reference.

Fix: Call .open(cx) from your Rust event handler when you want to show the modal.

// In script_mod! -- define the modal
my_modal := Modal{
    content +: {
        width: 300 height: Fit
        RoundedView{
            height: Fit
            new_batch: true
            padding: 20 flow: Down spacing: 10
            draw_bg.color: #333
            draw_bg.border_radius: 8.0
            Label{text: "Are you sure?" draw_text.color: #fff}
            confirm_btn := Button{text: "Confirm"}
            cancel_btn := ButtonFlat{text: "Cancel"}
        }
    }
}

// In Rust -- open the modal when a button is clicked
impl MatchEvent for App {
    fn handle_actions(&mut self, cx: &mut Cx, actions: &Actions) {
        if self.ui.button(ids!(open_modal_btn)).clicked(actions) {
            self.ui.modal(ids!(my_modal)).open(cx);
        }
        if self.ui.button(ids!(cancel_btn)).clicked(actions) {
            self.ui.modal(ids!(my_modal)).close(cx);
        }
    }
}

Pitfall #21: apply_over vs script_eval -- use script_apply_eval! in 2.0

Symptom: apply_over(cx, live!{...}) does not compile or does not work. The old 1.x runtime property update mechanism is gone.

Root Cause: Makepad 2.0 replaced the live! macro and apply_over with the script_apply_eval! macro. The old macros from the live_design! system no longer exist.

Fix: Use script_apply_eval! for runtime property updates. Use #(expr) for Rust expression interpolation inside the macro.

// OLD 1.x way (WRONG in 2.0)
item.apply_over(cx, live!{
    height: (height)
    draw_bg: {is_even: (if is_even {1.0} else {0.0})}
});

// NEW 2.0 way (CORRECT)
script_apply_eval!(cx, item, {
    height: #(height)
    draw_bg: {is_even: #(if is_even {1.0} else {0.0})}
});

// For colors
let color = self.color_focus;
script_apply_eval!(cx, item, {
    draw_bg: {
        color: #(color)
    }
});

Pitfall #22: Old derive macros -- Live -> Script, LiveHook -> ScriptHook

Symptom: Compilation errors about unknown derive macros Live, LiveHook, or unresolved traits.

Root Cause: Makepad 2.0 renamed the derive macros: Live became Script, LiveHook became ScriptHook. The old names no longer exist.

Fix: Update all derive macros to the new names.

// OLD 1.x (WRONG in 2.0)
#[derive(Live, LiveHook)]
pub struct App {
    #[live] ui: WidgetRef,
}

// NEW 2.0 (CORRECT)
#[derive(Script, ScriptHook)]
pub struct App {
    #[live] ui: WidgetRef,
}

// For widgets:
// OLD
#[derive(Live, LiveHook, Widget)]
// NEW
#[derive(Script, ScriptHook, Widget)]

// For animated widgets:
// OLD
#[derive(Live, LiveHook, Widget, Animator)]
// NEW
#[derive(Script, ScriptHook, Widget, Animator)]

Also renamed: DefaultNone derive is gone -- use standard #[derive(Default)] with #[default] attribute on the None variant:

// OLD (WRONG)
#[derive(DefaultNone)]
pub enum MyAction {
    Clicked,
    None,
}

// NEW (CORRECT)
#[derive(Clone, Default)]
pub enum MyAction {
    Clicked,
    #[default]
    None,
}

Pitfall #23: THEME_COLOR vs theme.color -- old syntax replaced

Symptom: (THEME_COLOR_X) causes a parse error or is not recognized. Theme values are not applied.

Root Cause: Makepad 2.0 replaced the parenthesized constant syntax (THEME_COLOR_X) with dot-path access via theme.color_x. Similarly, <THEME_FONT> became theme.font_regular, and all theme access now uses the theme. prefix.

Fix: Replace all old theme references with theme. prefix syntax.

// OLD 1.x (WRONG in 2.0)
draw_bg.color: (THEME_COLOR_BG_APP)
draw_text.text_style: <THEME_FONT_REGULAR>
padding: (THEME_SPACE_2)

// NEW 2.0 (CORRECT)
draw_bg.color: theme.color_bg_app
draw_text.text_style: theme.font_regular
padding: theme.space_2

| Old Syntax | New Syntax | |------------|------------| | (THEME_COLOR_X) | theme.color_x | | <THEME_FONT_X> | theme.font_x | | (THEME_SPACE_X) | theme.space_x | | (THEME_FONT_SIZE_X) | theme.font_size_x |

Pitfall #24: Forgot to call self.match_event(cx, event) -- MatchEvent does not fire

Symptom: handle_actions() in your MatchEvent implementation is never called. Button clicks and other widget actions are not handled.

Root Cause: The MatchEvent trait's handle_actions method is called internally by match_event(). If you do not call self.match_event(cx, event) in your AppMain::handle_event, the trait dispatch never happens.

Fix: Always call self.match_event(cx, event) in handle_event.

// WRONG -- match_event not called, handle_actions never fires
impl AppMain for App {
    fn handle_event(&mut self, cx: &mut Cx, event: &Event) {
        self.ui.handle_event(cx, event, &mut Scope::empty());
    }
}

// CORRECT -- call match_event before or after ui.handle_event
impl AppMain for App {
    fn handle_event(&mut self, cx: &mut Cx, event: &Event) {
        self.match_event(cx, event);  // THIS IS REQUIRED
        self.ui.handle_event(cx, event, &mut Scope::empty());
    }
}

impl MatchEvent for App {
    fn handle_actions(&mut self, cx: &mut Cx, actions: &Actions) {
        // Now this actually gets called!
        if self.ui.button(ids!(my_button)).clicked(actions) {
            log!("Button clicked!");
        }
    }
}

Pitfall #25: State not persisting between renders -- use proper state management

Symptom: Variables you set during one render pass are reset on the next frame. Counter values reset to zero, list state is lost, toggled states revert.

Root Cause: Local variables inside draw_walk or event handlers are re-initialized each call. Splash let bindings are template definitions, not mutable runtime state. For persistent state, you need to use #[rust] fields on your widget struct or manage state in the app struct.

Fix: Use #[rust] fields on your widget/app struct for persistent state.

// WRONG -- local variable resets every frame
impl Widget for Counter {
    fn draw_walk(&mut self, cx: &mut Cx2d, scope: &mut Scope, walk: Walk) -> DrawStep {
        let count = 0;  // Resets to 0 every frame!
        // ...
        DrawStep::done()
    }
}

// CORRECT -- persistent state in the struct
#[derive(Script, ScriptHook, Widget)]
pub struct Counter {
    #[source] source: ScriptObjectRef,
    #[walk] walk: Walk,
    #[layout] layout: Layout,
    #[rust] count: i32,  // Persists between frames
    #[deref] view: View,
}

impl MatchEvent for App {
    fn handle_actions(&mut self, cx: &mut Cx, actions: &Actions) {
        if self.ui.button(ids!(increment)).clicked(actions) {
            // State persists because it lives on the App struct
            self.count += 1;
            let label = self.ui.label(ids!(count_label));
            label.set_text(cx, &format!("{}", self.count));
        }
    }
}

Quick Reference: Diagnostic Decision Tree

Problem: UI is invisible / blank screen
  |
  +-- Are containers missing height: Fit?              --> Pitfall #1
  +-- Is text on a colored background?                 --> Pitfall #2 (new_batch)
  +-- Is text white on white?                          --> Pitfall #13
  +-- Is root container using width: Fill?             --> Pitfall #11
  +-- Did you add Root{} or Window{} in script output? --> Pitfall #17

Problem: Text disappears
  |
  +-- On hover?                                        --> Pitfall #8 (new_batch)
  +-- On colored background?                           --> Pitfall #2 (new_batch)
  +-- On light background?                             --> Pitfall #13 (text color)

Problem: Override does not work
  |
  +-- Used : instead of :=?                            --> Pitfall #3
  +-- Named child inside anonymous container?          --> Pitfall #3 (path issue)

Problem: Parse error
  |
  +-- Hex color with letter 'e'?                       --> Pitfall #4 (use #x)
  +-- Using commas?                                    --> Pitfall #9
  +-- Using semicolons?                                --> Pitfall #10
  +-- border_radius with Inset?                        --> Pitfall #5

Problem: Widget behavior not working
  |
  +-- Animator on Label?                               --> Pitfall #12
  +-- Modal not showing?                               --> Pitfall #20
  +-- MatchEvent not firing?                           --> Pitfall #24
  +-- State resetting between frames?                  --> Pitfall #25

Problem: Compilation error
  |
  +-- Derive macro not found?                          --> Pitfall #22 (Script/ScriptHook)
  +-- apply_over / live! not found?                    --> Pitfall #21 (script_apply_eval!)
  +-- Theme constant not found?                        --> Pitfall #23 (theme.xxx)
  +-- Widget type not found at runtime?                --> Pitfall #6 (registration order)

Additional Notes

Splash Syntax Quick Rules

1. Commas are optional between properties (tokenizer treats them as whitespace)
2. No semicolons anywhere
3. := for named/addressable children, : for static properties
4. +: to merge with parent instead of replacing
5. #x prefix for hex colors containing the letter e
6. height: Fit on every container (unless inside fixed-height parent)
7. width: Fill on root container
8. new_batch: true on any background container with text children

Registration Order in App::run()

1. crate::makepad_widgets::script_mod(vm) -- base widgets
2. Your custom widget modules
3. Your app UI modules
4. App::from_script_mod(vm, self::script_mod)

Widgets That Support Animator

View, SolidView, RoundedView, ScrollXView, ScrollYView, ScrollXYView, Button, ButtonFlat, ButtonFlatter, CheckBox, Toggle, RadioButton, LinkLabel, TextInput

Widgets That Do NOT Support Animator

Label, H1-H4, P, TextBox, Image, Icon, Markdown, Html, Slider, DropDown, Splitter, Hr, Filler

Pitfall #26: Hot reload not working -- missing --hot flag or file watcher issues

Symptom: You edit script_mod! code in a Rust source file but the running app does not update. No hot reload occurs.

Root Cause: Hot reload requires the --hot flag to start the file watcher. Without it, the app runs normally without watching for file changes. Also, the watcher normalizes paths and deduplicates content -- if your change produces identical extracted script_mod content, no reload triggers.

Fix:

# Run with hot reload enabled
cargo run -p my-app -- --hot

Additional checks:

• Ensure the script_mod! block is well-formed (syntax errors prevent extraction)
• Check that raw strings, byte strings, and comments within script_mod! are properly closed
• The watcher tracks #(...) Rust placeholder counts -- adding/removing placeholders requires a full rebuild
• File paths are normalized across platforms (handles Windows backslashes, symlinks)

Pitfall #27: WASM server port conflict -- stale lock file

Symptom: cargo makepad wasm run fails with a port-in-use error or hangs during startup. Multiple WASM servers may conflict.

Root Cause: The WASM server manager uses per-workspace lock files tracking PID and port. A stale lock from a crashed process can block new server startup.

Fix:

• The server manager automatically detects and cleans stale locks (checks PID alive AND port ownership)
• If auto-detection fails, manually remove the lock file in your workspace
• The startup mutex prevents concurrent wasm run startups with configurable timeouts

Diagnostics: The server manager reports detailed port occupant info using lsof (Unix) or netstat (Windows).

Pitfall #28: IME popup appears without TextInput focus

Symptom: The IME (Input Method Editor) popup window appears when no TextInput has focus, or appears at the wrong position.

Root Cause: On Linux X11, IME events could be dispatched without proper focus tracking. This was fixed to only show IME popups when a TextInput widget has keyboard focus.

Fix: Ensure your TextInput calls cx.set_key_focus(area) on FingerDown. The platform layer now correctly gates IME popup visibility on focus state.

Pitfall #29: Wayland context menu crash -- repeated open/close

Symptom: On Wayland, rapidly opening and closing context menus (popup windows) causes a crash or protocol error.

Root Cause: The xdg_popup protocol requires proper grab semantics. Repeated popup open/close without waiting for compositor acknowledgment triggered protocol violations.

Fix: This is fixed in the platform layer. Popup windows now use xdg_popup with compositor-driven grab and emit PopupDismissed events. Apps must handle PopupDismissed for explicit-close semantics (don't re-open immediately in the dismiss handler).

Updated Quick Reference: Diagnostic Decision Tree

Problem: Hot reload not working
  |
  +-- Missing --hot flag?                               --> Pitfall #26
  +-- script_mod! has syntax errors?                    --> Pitfall #26
  +-- Content unchanged (same extracted script)?        --> Pitfall #26

Problem: WASM build/server issues
  |
  +-- Port conflict?                                    --> Pitfall #27
  +-- Server hangs on startup?                          --> Pitfall #27
  +-- Binary too large?                                 --> Use --wasm-opt, --split-functions

Problem: Platform-specific issues
  |
  +-- IME popup at wrong time?                          --> Pitfall #28
  +-- Wayland popup crash?                              --> Pitfall #29
  +-- Selection handles not showing (mobile)?           --> Check iOS 16+ / Android JNI bridge

Problem: Splash eval issues (POST /splash, set_text)
  |
  +-- ScrollYView renders blank in eval?                --> Pitfall #30
  +-- Code block has no syntax highlighting?            --> Pitfall #31
  +-- CJK characters overlap in CodeView?              --> Pitfall #32
  +-- Type default properties not inherited?            --> Pitfall #33
  +-- on_after_apply not called for eval widgets?      --> Pitfall #33

Pitfall #30: ScrollYView renders blank in Splash eval

Symptom: Sending ScrollYView{...} via POST /splash renders a blank/empty panel. The same code works fine in compiled script_mod!.

Root Cause: ScrollYView requires internal initialization that doesn't complete properly during Splash runtime eval. The scroll view creates but its viewport dimensions are not set up correctly in the eval context.

Fix: Use plain View with height: Fit instead. Canvas wraps the splash panel in its own scroll container.

// WRONG -- blank in Splash eval
ScrollYView{ width: Fill height: Fill flow: Down
    Label{ text: "content" }
}

// CORRECT -- works in eval
View{ width: Fill height: Fit flow: Down
    Label{ text: "content" }
}

Pitfall #31: Markdown code blocks have no syntax highlighting in Splash eval

Symptom: Markdown{body: "...```rust\n...\n```..."} sent via POST /splash shows code blocks as plain monospace text without syntax coloring. The same Markdown in compiled script_mod! has full syntax highlighting via CodeView.

Root Cause: Canvas overrides mod.widgets.Markdown with set_type_default() adding code_block := View{CodeView{...}} and use_code_block_widget: true. But instances created via Splash eval don't inherit these because: (1) on_after_apply is not called in eval path, (2) the type default vec entries (named children) are not fully copied to instances.

Fix (applied 2026-03-23): widgets/src/markdown.rs now lazily looks up the type default in draw_walk via vm.bx.heap.type_default_for_object() and registers missing templates. Also auto-enables use_code_block_widget when a code_block template is found.

Pitfall #32: CJK characters overlap in CodeView / CodeEditor

Symptom: Chinese, Japanese, or Korean characters in code blocks overlap with adjacent characters. The monospace grid doesn't account for double-width CJK glyphs.

Root Cause: code_editor/src/char.rs had column_count() returning 1 for ALL characters. CJK characters need 2 columns in a monospace grid.

Fix (applied 2026-03-23): char.rs now returns 2 for CJK Unified Ideographs, Hiragana, Katakana, Hangul, fullwidth Latin, and related Unicode ranges. Also added LXGWWenKaiRegular.ttf as Chinese fallback in font_code across all three theme files.

Pitfall #33: Type default overrides not inherited in Splash eval

Symptom: When a widget type is overridden via set_type_default() (e.g., Canvas overriding Markdown with extra templates), instances created through Splash eval (POST /splash) don't pick up the override's properties or named children.

Root Cause: The Splash eval path creates widgets by applying only the eval value (e.g., {body: "..."}) without triggering ScriptHook::on_after_apply. The #[live] field defaults are used instead of the type default values. Vec entries (named children like templates) from the type default may also be lost during the proto copy chain.

Workaround: Implement lazy initialization in draw_walk that checks for missing state and looks up the type default via vm.bx.heap.type_default_for_object(self.source.as_object()). This is the pattern used by Markdown for code_block templates.

Pitfall #34: instance in draw_bg +: crashes — "cannot push to frozen vec"

Symptom: Runtime crash: "cannot push to frozen vec" when adding instance my_var: 0.5 inside draw_bg +: { }.

Root Cause: Splash +: blocks can override pixel: fn() and set existing variables, but CANNOT add new instance/uniform fields. GPU layout is compile-time.

Fix: Use built-in variables (self.draw_pass.time, self.pos, self.rect_size) or create a custom Rust DrawQuad type.

Pitfall #35: Transparent window still shows opaque background

Symptom: Setting window.transparent: true but the window still has a gray/dark background.

Root Cause: window.transparent only tells the OS the window is transparent. The render pass still clears to an opaque color by default.

Fix: Must set BOTH:

window.transparent: true
pass.clear_color: #x00000000    // CRITICAL: fully transparent clear color

And do NOT set draw_bg.color on body +: {} — it overrides the transparency.

Reference: tools/canvas/src/app.rs in Makepad source.

Pitfall #36: sdf.box() with large border_radius produces diamond/spiky shape

Symptom: Using border_radius: 28.0 on a 56px-tall RoundedView with width: Fit produces pointy diamond-shaped ends instead of rounded capsule ends.

Root Cause: sdf.box() formula size.xy - vec2(2*r, 2*r) goes negative when r >= min(w,h)/2, breaking the SDF.

Fix: Use a custom capsule SDF: let cx = clamp(px, r, max(r, w-r)) — see makepad-2.0-shaders skill "SDF Capsule Pattern".

Pitfall #37: Child widget bleeds through parent SDF mask

Symptom: A LoadingSpinner or other child widget renders outside the parent View's custom SDF capsule shape, causing visible artifacts at the edges.

Root Cause: Each widget has its own draw call. Child widgets are not clipped by the parent's SDF shader — they draw independently in their own rect.

Fix: Embed animation directly in the parent's pixel: fn() shader instead of using child widgets. Or use clip_x: true + clip_y: true (may not fully solve it for rounded shapes).

Pitfall #38: show_in_dock(false) hides NSStatusBar items

Symptom: Calling cx.show_in_dock(false) makes the app invisible in Dock, but also hides any NSStatusBar items (menu bar icons).

Root Cause: show_in_dock(false) sets NSApplicationActivationPolicyAccessory, which prevents the app from owning status bar items.

Fix: Don't call show_in_dock(false) at runtime. Use LSUIElement=true in Info.plist for .app bundles instead. During cargo run, accept the Dock icon.

Pitfall #39: Emoji renders as garbage/box character

Symptom: Some emoji (✨ ⏳) display as boxes or garbled characters in Label text.

Root Cause: Makepad's font atlas doesn't include all emoji glyphs. Only a subset of basic emoji is supported.

Fix: Test each emoji. Known working: 🎙 🔍 🔄. Known broken: ✨ ⏳. Use ASCII alternatives as fallback.

Pitfall #40: script_apply_eval! has no effect on dynamically-created widgets

Symptom: You create a widget via widget_ref_from_live_ptr(cx, Some(ptr)) (or cx.with_vm(|vm| WidgetRef::script_from_value(vm, value))), then use script_apply_eval!(cx, item, { draw_bg.color: #(color) }) to change its properties at runtime. The call executes without error, but the widget's appearance doesn't change.

Root Cause: script_apply_eval! internally calls self.script_source() to get the widget's ScriptObject, then evaluates the script code against it. For widgets created dynamically from LivePtr/ScriptValue templates, script_source() returns ScriptObject::ZERO (the default). This means the eval scope is empty — property assignments silently fail because there is no valid target object.

This affects ALL of these approaches:

• script_apply_eval!(cx, item, { draw_bg.color: #(color) }) — no effect
• script_apply_eval!(cx, item, { draw_bg +: { color: #(color) } }) — no effect
• script_apply_eval!(cx, item, { show_bg: true }) — no effect
• ViewRef.set_uniform(cx, live_id!(color), &[r,g,b,a]) — also no effect

Fix: Use Animator states with shader instance variables instead:

1. Define an instance variable and pixel shader in the DSL template:

mod.widgets.MyItem = View {
    show_bg: true
    draw_bg +: {
        color: (COLOR_PRIMARY)
        selected: instance(0.0)

        pixel: fn() {
            let sdf = Sdf2d.viewport(self.pos * self.rect_size)
            sdf.box(0. 0. self.rect_size.x self.rect_size.y self.border_radius)
            let highlight = #x1E90FF30
            sdf.fill(Pal.premul(self.color.mix(highlight self.selected)))
            return sdf.result
        }
    }

    animator: Animator {
        highlight: {
            default: @off
            off: AnimatorState {
                from: { all: Forward { duration: 0.12 } }
                apply: { draw_bg: { selected: 0.0 } }
            }
            on: AnimatorState {
                from: { all: Forward { duration: 0.08 } }
                apply: { draw_bg: { selected: 1.0 } }
            }
        }
    }
}

2. Toggle the state from Rust:

let view = item.as_view();
if is_highlighted {
    view.animator_cut(cx, ids!(highlight.on));
} else {
    view.animator_cut(cx, ids!(highlight.off));
}

Key insight: Animator states work because they operate through Makepad's animation system which directly modifies shader instance variables in the GPU buffer — this bypasses the ScriptObject/eval mechanism entirely.

Pitfall #41: script_apply_eval! cannot use DSL constants at runtime

Symptom: Runtime errors like variable Right not found in scope, variable Fit not found in scope, variable Align not found in scope, variable MouseCursor not found in scope when using script_apply_eval!.

Root Cause: script_apply_eval! evaluates code in a restricted runtime scope that does NOT include DSL constants like Right, Down, Fit, Fill, Align, Inset, MouseCursor, etc. These constants are only available during script_mod! evaluation (compile/init time), not at runtime.

Fix: For layout changes, set properties in the DSL template at definition time. If you must change layout at runtime, use the Rust API directly:

// WRONG — DSL constants not available at runtime
script_apply_eval!(cx, item, {
    flow: Right
    height: Fit
    align: Align{y: 0.5}
});

// CORRECT — Use Rust values with #(expr) interpolation
let height = 36.0_f64;
script_apply_eval!(cx, item, {
    height: #(height)
});

// CORRECT — For colors (hex literals work)
let color = vec4(0.1, 0.2, 0.3, 1.0);
script_apply_eval!(cx, item, {
    draw_bg +: { color: #(color) }
});

// CORRECT — Bake layout into DSL template instead
mod.widgets.MyItem = View {
    flow: Right
    height: 36
    align: Align{y: 0.5}
}

What DOES work in script_apply_eval!: Numeric values, hex colors (#fff), #(rust_expr) interpolation, and property paths (draw_bg +: { ... }).

What does NOT work: Type constructors (Align{}, Inset{}), enum variants (Right, Down, Fit, Fill), and widget type references (MouseCursor.Hand).

Pitfall #42: Dock.load_state() corrupts DrawList references — blank rendering

Symptom: After restoring a dock layout from persisted state (e.g., on app restart), the entire dock area renders blank/grey. Console shows massive Drawlist id generation wrong index: N current gen:1 in pointer:0 errors.

Root Cause: Dock.load_state() calls self.tab_bars.clear() during event handling, which drops TabBarWrap instances containing DrawList2d. This frees the DrawList pool entries (incrementing their generation). However, Makepad's rendering pipeline still holds cached DrawListId references from the previous draw frame with generation 0. On the next frame, accessing these stale references causes generation mismatches.

Fix: Don't call dock.load_state() to restore persisted state. Instead, recreate tabs programmatically:

// WRONG — corrupts DrawList references
dock.borrow_mut().load_state(cx, saved_dock_items.clone());

// CORRECT — use normal Dock API
self.close_all_tabs(cx);
for room in &saved_room_order {
    self.focus_or_create_tab(cx, room.clone());
}

Trade-off: This approach doesn't restore custom splitter positions or multi-pane layouts. Those require a fix in Makepad's Dock widget upstream.

Pitfall #43: Named children use = in 1.0 but := in 2.0 DSL templates

Symptom: When migrating live_design! to script_mod!, named children defined with name = Widget { } cause runtime errors like variable name not found in scope. The children exist in the widget tree but are not addressable from Rust via ids!(name).

Root Cause: In Makepad 1.0 live_design!, both = and := create named children. In Makepad 2.0 script_mod!, only := creates named, addressable children. Using = in 2.0 creates a local variable assignment, not a named child widget.

Fix:

// 1.0 (live_design!) — both work
avatar = <Avatar> { width: 24, height: 24 }
avatar := <Avatar> { width: 24, height: 24 }

// 2.0 (script_mod!) — ONLY := works for named children
avatar := Avatar { width: 24 height: 24 }  // CORRECT
avatar = Avatar { width: 24 height: 24 }   // WRONG — local variable, not child

Pitfall #44: draw_bg: replaces, draw_bg +: merges in DSL and script_apply_eval!

Symptom: Setting draw_bg: { color: #f00 } in a DSL template or script_apply_eval! causes all other draw_bg properties (border_radius, border_color, hover states, shader code) to be lost.

Root Cause: The : operator REPLACES the entire property value. The +: operator MERGES with the existing value, only overriding specified sub-properties.

Fix: Always use +: when you want to modify a sub-property of draw_bg, draw_text, or any nested struct:

// WRONG — replaces ALL of draw_bg, losing border_radius, shader, etc.
draw_bg: { color: #f00 }

// CORRECT — only changes color, keeps everything else
draw_bg +: { color: #f00 }

// In script_apply_eval!, same rule applies:
// WRONG
script_apply_eval!(cx, item, { draw_bg: { color: #(color) } });

// CORRECT
script_apply_eval!(cx, item, { draw_bg +: { color: #(color) } });

// Dot-path shorthand also works (equivalent to +: merge):
draw_bg.color: #f00
draw_bg.border_radius: 8.0

Pitfall #45: Popup/menu opens in the wrong place -- treating layout spacing as overlay positioning

Symptom: A popup menu or language selector should appear above a button, but it keeps appearing below it, pinned to the wrong corner, or behaving as if your Y-position math is being ignored.

Root Cause: You built the popup as an ordinary child in a local layout tree and tried to position it with margin.top / margin.left or other layout offsets. In Makepad, that is still layout negotiation, not a true overlay anchor. For real popup behavior, the popup should usually live in a top-level overlay owner (Modal, tooltip layer, popup owner) and be positioned with walk.abs_pos.

Fix: Move popup ownership to a common ancestor or overlay owner. Read the trigger button position with button.area().clipped_rect(cx), compute the popup's absolute position in the overlay's coordinate space, and write it to popup.walk.abs_pos.

// WRONG -- local child + layout spacing fights the turtle
script_apply_eval!(cx, popup, {
    margin.left: #(x)
    margin.top: #(y)
});

// CORRECT -- top-level overlay popup with explicit absolute anchor
let button_rect = button.area().clipped_rect(cx);
let popup_pos = dvec2(button_rect.pos.x, button_rect.pos.y - 294.0);

if let Some(mut popup) = self.view(cx, ids!(popup)).borrow_mut() {
    popup.walk.abs_pos = Some(popup_pos);
}

Important distinction:

• clip_x: false / clip_y: false only let a local child paint outside its parent.
• They do NOT make that child behave like a true overlay.

Rule of thumb: If the popup must escape the component that triggered it, lift the popup state to a common ancestor and let that ancestor own the overlay.

Updated Diagnostic Decision Tree (additions)

Problem: script_apply_eval! has no effect on widget
  |
  +-- Widget created via widget_ref_from_live_ptr()?    --> Pitfall #40 (use Animator)
  +-- Using DSL constants (Right, Fit, Align)?          --> Pitfall #41 (use Rust values)
  +-- Using draw_bg: instead of draw_bg +: ?            --> Pitfall #44 (use merge operator)

Problem: Dock renders blank after state restore
  |
  +-- Called Dock.load_state() in event handler?         --> Pitfall #42 (use tab recreation)

Problem: Named child not addressable from Rust
  |
  +-- Used = instead of := in script_mod!?               --> Pitfall #43 (use :=)

Problem: Popup/menu anchored to button but renders in wrong place
  |
  +-- Built as normal child and moved with margin?       --> Pitfall #45 (use top-level overlay + walk.abs_pos)
  +-- Only disabled clip_x/clip_y on local parent?       --> Pitfall #45 (overflow is not a true overlay)