Cargo Build Timings graph hits browser’s max canvas size

[SimonSapin]

https://gistpreview.github.io/?eeb6459081cf75648d507eeaf1d414f3 is cargo build -Z timings for Servo. The canvas appears broken in Firefox and Chromium until the "Min unit time" slider is moved to a non-zero value. This appears to be because the canvas height exceeds i16::MAX:

• https://stackoverflow.com/questions/6081483/maximum-size-of-a-canvas-element
• https://developer.mozilla.org/en-US/docs/Web/HTML/Element/canvas#Maximum_canvas_size
• https://bugs.chromium.org/p/chromium/issues/detail?id=339725

Changing "Min unit time" to even 0.1 seconds filters out many units/crates, making a much smaller canvas.

I’m not sure what a proper solution would be, but maybe we could at least detect this situation and suggest that work-around?

[SimonSapin]

I’m not sure what a proper solution would be,

Maybe splitting the graph into multiple <canvas> elements? @ehuss, @alexcrichton, how involved would that be?

[nox]

Alternatively, maybe rustc should be producing something that can be fed to https://profiler.firefox.com/.

[SimonSapin]

@nox that could be good also, but an entirely different feature from Cargo’s -Z timings which IMO is about exploring dependencies in the crate graph.

[alexcrichton]

I believe this was fixed in #7397 which just hasn't made its way to nightly yet, but let us know if it's still not working after that update hits though!