rustlavel-chart

Charts for Rustlavel: a typed builder that produces a Chart.js configuration, and the vendored library to draw it — no CDN, no inline script.

This package vendors somebody else's library

That is unusual here, and deliberate. Chart.js is 69 KB gzipped and renders to a <canvas>; writing the same thing from scratch means an axis scaler, a tick formatter, a legend layout engine and a hit-tester, and the result still has no hover, no tooltips and no zoom. The copy lives in assets/, under its own MIT licence, with its copyright banner intact.

Using it

App::new()?.plugin(Charts::default())      // serves the two scripts

let revenue = Chart::line("Revenue")
    .labels(["Jan", "Feb", "Mar"])
    .series(Series::new("2026", [1200.0, 1800.0, 1500.0]).filled())
    .series(Series::sparse("2025", [Some(900.0), None, Some(1400.0)]))
    .y(Axis::new().prefix("Rp "));

req.view("dashboard", &ViewContext::new().with("revenue", revenue.to_json()))

<script src="/vendor/chart/chart.umd.js" defer></script>
<script src="/vendor/chart/rustlavel-chart.js" defer></script>

<canvas data-chart="{{ revenue }}" height="220"></canvas>

Chart::line, bar, horizontal_bar, doughnut, pie, scatter. A horizontal bar is a bar with the axes swapped, so the axis you set on y stays the category axis whichever way round it is drawn.

The configuration travels in an escaped attribute

{{ }} turns every " into " and every < into <; the browser reverses that when it reads dataset.chart, and the round trip is exact. A label reading a" onmouseover="alert(1) arrives in Chart.js as that string — measured, not assumed.

This is why there is no inline <script> anywhere in this package. A page that writes <script>new Chart(…)</script> needs script-src 'unsafe-inline', and a policy with unsafe-inline does not stop injected script — which is the one thing a Content-Security-Policy is for.

Under default-src 'self' your stylesheet must be external too. That policy blocks an inline <style> exactly as firmly as an inline <script>, and the theme hook below is CSS. The auth kit already ships its stylesheet as a file, so there is nothing to do there; a page with a <style> block will find its rules silently not applied.

Following the page's theme

Chart.js draws its own labels and grid lines, and its defaults are for a white page. The init script reads two CSS custom properties and hands them over, so a chart follows the theme the rest of the page is using:

:root { --chart-ink: #1f2937; --chart-grid: #e5e7eb; }
@media (prefers-color-scheme: dark) {
  :root { --chart-ink: #e5e7eb; --chart-grid: #374151; }
}

Set neither and Chart.js's own defaults apply.

Choices that are not Chart.js's

The value axis begins at zero. A bar chart whose axis starts at 95 turns a 1% difference into a doubling. Axis::zoomed() when the reading genuinely lives in a narrow band far from zero.
Lines are straight. Chart.js defaults tension to 0.4, drawing a curve through points nobody measured. Series::smooth() asks for it.
A gap is a gap. Series::sparse takes Option<f64>, and spanGaps is off — a month with no reading breaks the line rather than being drawn as zero.
Seven colours, separated by lightness as well as hue so they survive both themes and deuteranopia, wrapping rather than panicking on an eighth series.

`problems()`

Returns what is wrong with a chart rather than refusing to draw it: a series shorter than its labels, a doughnut given several series, a chart with nothing in it. Worth an assertion in a dashboard's tests — Chart.js silently draws the shorter of two mismatched lengths.

Licence

MIT. The vendored Chart.js is MIT too; see assets/LICENSE-chart.js.md.

rustlavel-chart 0.9.1