iris/tests/scenario/mod.rs

//! The scenarios both fuzzers run, over the tree a [`Plan`] describes.
//!
//! One implementation rather than two. The oracle grew its trees from a seed
//! and the shrinker grew its own, with every scenario written out on each
//! side, so a failure the oracle found could not be handed to the shrinker:
//! there was no tree to pass it, only a seed, and a seed cannot be made
//! smaller. Both take a plan now, so whatever finds a counterexample can also
//! reduce it.
//!
//! Each target compiles this for itself, so what only one of them calls is
//! dead code in the other.
#![allow(dead_code)]

use iris::harness::Harness;
use iris::prelude::*;
use iris::random::{Aligns, Edits, Kind, Lens, Plan, Rng, SpanEdit, Tree, build};
use std::collections::HashMap;

/// A seed per thread but one, since a seed grows, lays out and drops its tree
/// alone. A failing seed still shrinks and panics on its own thread.
pub fn over_seeds(seeds: Vec<u64>, run: impl Fn(u64) + Sync) {
    let threads =
        std::thread::available_parallelism().map_or(1, |n| n.get().saturating_sub(1).max(1));
    let chunk = seeds.len().div_ceil(threads).max(1);
    std::thread::scope(|scope| {
        for part in seeds.chunks(chunk) {
            let run = &run;
            scope.spawn(move || part.iter().for_each(|&seed| run(seed)));
        }
    });
}

pub fn env<T: std::str::FromStr>(name: &str, fallback: T) -> T {
    std::env::var(name)
        .ok()
        .and_then(|v| v.parse().ok())
        .unwrap_or(fallback)
}

/// The window a tree is grown in, and the one a resize takes it to.
const OUTER: (f32, f32) = (1920.0, 1200.0);
const INNER: (f32, f32) = (640.0, 900.0);
const STILL: (f32, f32) = (900.0, 1200.0);

/// The same box, to two steps of the grid between the two ways of reaching
/// it. A move, a repaint, a row of shares and every length in pixels land on
/// the same number. What needs the slack is a position: a box centred in a
/// fraction of its parent against the same box centred in its own pixels,
/// and a box re-expressed as a fraction of a parent that changed length.
/// A step is a thousandth of a pixel, where this was a twentieth of one
/// before any of it was on a grid.
///
/// **One step is not enough**, tried 2026-09-17 once a length in pixels
/// stopped being composed: it passes the 100-seed oracle and fails the
/// 400-seed shrinker on `resize-size`, seeds 384 and 162, by 0.002 px. So
/// what is left here is the resize path's own rounding rather than a length
/// reached two ways.
const AGREE_STEPS: i32 = 2;

/// A way of changing what a span holds. Each is a shape worth its own case:
/// taking a child out of the middle is not the same as emptying a span, and
/// adding one is not the same as adding three.
#[derive(Clone, Copy, Debug, PartialEq)]
pub enum Shuffle {
    /// Every other child, so what is left is interleaved with what went.
    EveryOther,
    /// Everything but the first, which is the last step before empty.
    AllButFirst,
    /// Three more on the end at once.
    AddThree,
    /// The first out and three more on, so the count moves both ways.
    SwapForThree,
    /// One out of the middle and one on the end.
    TradeOne,
}

impl Shuffle {
    fn of(self, grown: usize) -> SpanEdit {
        let all = |step: usize, from: usize| (from..grown).step_by(step).collect();
        match self {
            Self::EveryOther => SpanEdit {
                detach: all(2, 0),
                attach: 0,
            },
            Self::AllButFirst => SpanEdit {
                detach: all(1, 1),
                attach: 0,
            },
            Self::AddThree => SpanEdit {
                detach: Vec::new(),
                attach: 3,
            },
            Self::SwapForThree => SpanEdit {
                detach: vec![0],
                attach: 3,
            },
            Self::TradeOne => SpanEdit {
                detach: vec![grown / 2],
                attach: 1,
            },
        }
    }
}

/// What a warm tree is put through before it is compared with a cold one
/// grown the way it was left.
#[derive(Clone, Copy, Debug, PartialEq)]
pub enum Case {
    /// Nothing changes, so no box may either. What this exercises is the
    /// order a frame settles a dirty set in.
    Repaint,
    /// Every fifth widget rather than all of them: marking all of them
    /// redraws the whole tree, which is a cold start reached the long way,
    /// where the mixed case leaves a redrawn subtree beside a retained one.
    RepaintSome,
    Resize,
    ResizeRepaint,
    /// A resize and then a size change, so a retained answer is asked to
    /// survive two different kinds of invalidation in a row.
    ResizeSize,
    /// A few declared sizes.
    Size,
    /// Every declared size at once, so every reader of a size has a changed
    /// descendant in the same frame and the whole dirty set settles together.
    EverySize,
    Align,
    /// Giving a widget a movable region of its own, or taking it away, is a
    /// structural change: every primitive under it changes which chain
    /// resolves it.
    RegionNode,
    /// The same children in a different order, which moves every one of them
    /// without changing what any of them is.
    Reorder,
    Shuffle(Shuffle),
}

pub const ALL: [Case; 15] = [
    Case::Repaint,
    Case::RepaintSome,
    Case::Resize,
    Case::ResizeRepaint,
    Case::ResizeSize,
    Case::Size,
    Case::EverySize,
    Case::Align,
    Case::RegionNode,
    Case::Reorder,
    Case::Shuffle(Shuffle::EveryOther),
    Case::Shuffle(Shuffle::AllButFirst),
    Case::Shuffle(Shuffle::AddThree),
    Case::Shuffle(Shuffle::SwapForThree),
    Case::Shuffle(Shuffle::TradeOne),
];

impl Case {
    /// The name `CASE` selects it by, and the one a failure prints.
    pub fn name(self) -> &'static str {
        match self {
            Self::Repaint => "repaint",
            Self::RepaintSome => "repaint-some",
            Self::Resize => "resize",
            Self::ResizeRepaint => "resize-repaint",
            Self::ResizeSize => "resize-size",
            Self::Size => "size",
            Self::EverySize => "every-size",
            Self::Align => "align",
            Self::RegionNode => "region-node",
            Self::Reorder => "reorder",
            Self::Shuffle(Shuffle::EveryOther) => "shuffle-every-other",
            Self::Shuffle(Shuffle::AllButFirst) => "shuffle-all-but-first",
            Self::Shuffle(Shuffle::AddThree) => "shuffle-add-three",
            Self::Shuffle(Shuffle::SwapForThree) => "shuffle-swap-for-three",
            Self::Shuffle(Shuffle::TradeOne) => "shuffle-trade-one",
        }
    }

    pub fn named(name: &str) -> Option<Self> {
        ALL.into_iter().find(|case| case.name() == name)
    }

    /// Grown in the first, compared in the second.
    fn window(self) -> ((f32, f32), (f32, f32)) {
        match self {
            Self::Resize | Self::ResizeRepaint | Self::ResizeSize => (OUTER, INNER),
            _ => (STILL, STILL),
        }
    }
}

fn mark(warm: &mut Harness, tree: &Tree, step: usize) {
    for &id in tree.ids.iter().step_by(step) {
        warm.rsc.widgets_mut().get_dyn_mut(id);
    }
}

fn a_len(rng: &mut Rng) -> Option<LayoutLen> {
    Some(LayoutLen::px(20.0 + rng.below(180) as f32))
}

fn resize_one(warm: &mut Harness, tree: &Tree, idx: usize, rng: &mut Rng) -> Lens {
    let lens = [a_len(rng), a_len(rng)];
    warm.rsc
        .widgets_mut()
        .set_size_rules(tree.sized[idx], lens[0], lens[1]);
    lens
}

fn realign_one(warm: &mut Harness, tree: &Tree, idx: usize, rng: &mut Rng) -> Aligns {
    let side = |rng: &mut Rng| match rng.below(4) {
        0 => None,
        1 => Some(AxisAlign::NEG),
        2 => Some(AxisAlign::CENTER),
        _ => Some(AxisAlign::POS),
    };
    let align = [side(rng), side(rng)];
    let id = tree.aligned[idx];
    for (axis, align) in [Axis::X, Axis::Y].into_iter().zip(align) {
        warm.rsc
            .widgets_mut()
            .set_alignment(id, axis, align.unwrap_or_default());
    }
    align
}

/// Every span's children in a different order, said both to the warm tree and
/// to the plan the cold one is grown from.
fn reorder(warm: &mut Harness, tree: &Tree, plan: &Plan) -> Plan {
    for span in &tree.spans {
        let children = &mut warm.rsc[span.id].children;
        if !children.is_empty() {
            children.rotate_left(1);
        }
    }
    let mut out = plan.clone();
    out.walk_mut(&mut |node| {
        if let Kind::Span { order, .. } = &mut node.kind
            && !order.is_empty()
        {
            order.rotate_left(1);
        }
    });
    out
}

/// Applies `shuffle` to every third span. What it takes out is given back to
/// the span's spares: the last share of a widget must outlive the comparison,
/// or its id is handed to something else and the two trees stop lining up.
fn reshuffle(warm: &mut Harness, tree: &mut Tree, shuffle: Shuffle) -> HashMap<usize, SpanEdit> {
    let mut edits = HashMap::new();
    for (idx, span) in tree.spans.iter_mut().enumerate().step_by(3) {
        let edit = shuffle.of(span.grown);
        let mut take = edit.detach.clone();
        take.sort_unstable();
        let children = &mut warm.rsc[span.id].children;
        // Highest first, so an index means the same child however many of its
        // neighbours are going too.
        for j in take.into_iter().rev() {
            if j < children.len() {
                span.spares.push(children.remove(j));
            }
        }
        let attach = edit.attach.min(span.spares.len());
        let moved: Vec<_> = span.spares.drain(..attach).collect();
        warm.rsc[span.id].children.extend(moved);
        edits.insert(idx, edit);
    }
    edits
}

/// Changes the warm tree and answers with the plan a cold tree grown that way
/// comes from. Each arm settles its own frame, so a case that changes nothing
/// does not get a second one that could settle what the first left.
fn change(case: Case, warm: &mut Harness, tree: &mut Tree, plan: &Plan, rng: &mut Rng) -> Plan {
    let some_sizes = |warm: &mut Harness, tree: &Tree, rng: &mut Rng| {
        let mut sizes = HashMap::new();
        for _ in 0..4 {
            if tree.sized.is_empty() {
                break;
            }
            let idx = rng.below(tree.sized.len());
            sizes.insert(idx, resize_one(warm, tree, idx, rng));
        }
        sizes
    };
    let edits = match case {
        Case::Resize => return plan.clone(),
        Case::Repaint | Case::ResizeRepaint => {
            mark(warm, tree, 1);
            warm.frame();
            return plan.clone();
        }
        Case::RepaintSome => {
            mark(warm, tree, 5);
            warm.frame();
            return plan.clone();
        }
        Case::Reorder => {
            let out = reorder(warm, tree, plan);
            warm.frame();
            return out;
        }
        Case::Size | Case::ResizeSize => Edits {
            sizes: some_sizes(warm, tree, rng),
            ..Default::default()
        },
        Case::EverySize => Edits {
            sizes: (0..tree.sized.len())
                .map(|idx| (idx, resize_one(warm, tree, idx, rng)))
                .collect(),
            ..Default::default()
        },
        Case::Align => Edits {
            aligns: (0..tree.aligned.len())
                .step_by(3)
                .map(|idx| (idx, realign_one(warm, tree, idx, rng)))
                .collect(),
            ..Default::default()
        },
        Case::RegionNode => {
            let mut nodes = HashMap::new();
            for idx in (0..tree.nodes.len()).step_by(2) {
                let id = tree.nodes[idx];
                let take = !warm.rsc.widgets().is_region_node(id);
                warm.rsc.widgets_mut().set_region_node(id, take);
                nodes.insert(idx, take);
            }
            Edits {
                nodes,
                ..Default::default()
            }
        }
        Case::Shuffle(shuffle) => Edits {
            spans: reshuffle(warm, tree, shuffle),
            ..Default::default()
        },
    };
    warm.frame();
    plan.edited(&edits)
}

/// What a widget was configured with, so a tree a fuzzer found can be written
/// out by hand. A failure is a lead; the fast test that replaces it has to be
/// buildable from what the failure printed.
fn describe(id: WidgetId, h: &Harness) -> String {
    let rules = h.rsc.widgets().size_rules(id);
    let rule = |r: SizeRule| match r.exact() {
        Some(len) => format!("{len}"),
        None => "-".into(),
    };
    let align = h.rsc.widgets().alignment(id);
    let side = |a: AxisAlign| {
        if a == AxisAlign::NEG {
            "neg".into()
        } else if a == AxisAlign::CENTER {
            "mid".into()
        } else if a == AxisAlign::POS {
            "pos".into()
        } else {
            format!("{:.2}", a.rel())
        }
    };
    // A rule and an alignment are properties of whatever carries them, so
    // they print with that widget rather than as widgets of their own.
    let mut out = describe_widget(id, h);
    if (rules.x, rules.y) != (SizeRule::Free, SizeRule::Free) {
        out += &format!("[x:{},y:{}]", rule(rules.x), rule(rules.y));
    }
    if align != RegionAlign::default() {
        out += &format!("@{},{}", side(align.x), side(align.y));
    }
    out
}

fn describe_widget(id: WidgetId, h: &Harness) -> String {
    let label = h.rsc.widgets().label(id).to_string();
    let Some(widget) = h.rsc.widgets().get_dyn(id) else {
        return label;
    };
    let any: &dyn std::any::Any = widget;
    if let Some(w) = any.downcast_ref::<Span>() {
        let sign = if w.dir.sign == Sign::Neg { "-" } else { "+" };
        return format!(
            "Span{{dir:{:?}{sign},gap:{},n:{}}}",
            w.dir.axis,
            w.gap,
            w.children.len()
        );
    }
    if let Some(w) = any.downcast_ref::<Pad>() {
        let p = &w.padding;
        return format!(
            "Pad{{l:{},r:{},t:{},b:{}}}",
            p.left, p.right, p.top, p.bottom
        );
    }
    if let Some(w) = any.downcast_ref::<Stack>() {
        return format!("Stack{{n:{}}}", w.children.len());
    }
    label
}

fn same_region(got: Option<PixelRegion>, want: Option<PixelRegion>) -> bool {
    match (got, want) {
        (Some(got), Some(want)) => {
            let same = |a: Px, b: Px| (a - b).abs() <= Px::STEP.mul_int(AGREE_STEPS);
            same(got.top_left.x, want.top_left.x)
                && same(got.top_left.y, want.top_left.y)
                && same(got.bot_right.x, want.bot_right.x)
                && same(got.bot_right.y, want.bot_right.y)
        }
        (None, None) => true,
        _ => false,
    }
}

/// Runs `case` on the tree `plan` describes, warm and cold, and says where
/// the two disagree. `seed` chooses only the values a case picks at random,
/// so one plan under one case is one comparison however it was reached.
pub fn diverges(plan: &Plan, case: Case, seed: u64) -> Option<String> {
    let (start, end) = case.window();
    let mut warm = Harness::new(start);
    let (root, mut tree) = build(&mut warm.rsc, plan);
    warm.state.root = Some(root);
    // The frame that makes it warm: without it nothing is retained and the
    // comparison is two cold starts agreeing with each other.
    warm.frame();
    if start != end {
        warm.resize(end);
        warm.frame();
    }
    let cold_plan = change(case, &mut warm, &mut tree, plan, &mut Rng::new(seed));

    let mut cold = Harness::new(end);
    let (root, cold_tree) = build(&mut cold.rsc, &cold_plan);
    cold.state.root = Some(root);
    cold.frame();

    let mut drawn = 0;
    for (i, (&w, &c)) in tree.ids.iter().zip(&cold_tree.ids).enumerate() {
        let (got, want) = (warm.region(&w), cold.region(&c));
        drawn += got.is_some() as usize;
        if same_region(got, want) {
            continue;
        }
        // Where two trees disagree is rarely where the cause is, so the
        // ancestry comes with it, marking the widgets that own a region.
        let mut chain = Vec::new();
        let mut at = Some(w);
        while let Some(id) = at {
            let active = &warm.render.active[&id];
            let node = match active.move_idx == active.parent_move {
                true => "",
                false => "*",
            };
            chain.push(format!("{}{node}", describe(id, &warm)));
            at = active.parent;
        }
        return Some(format!(
            "widget {i}\n  warm {got:?}\n  cold {want:?}\n  {}",
            chain.join(" < ")
        ));
    }
    match drawn {
        0 => Some("nothing was drawn".into()),
        _ => None,
    }
}