Macro build_path 

build_path!() { /* proc-macro */ }

Turn SVG path data into a PathBuilder chain, at compile time.

let heart = build_path!("M 12,21 C 2,14 2,7 7,5 c 3,-1 5,1 5,3 …").build();
d.fill(heart, CORAL);

The whole SVG 1.1 path grammar is accepted: absolute and relative commands, H/V, the smooth forms S/T, elliptical arcs, implicit command repetition, and SVG’s number syntax (1e2, .5.5, 10-5). Malformed data is a compile error naming the offending character, not a path that silently draws nothing.

The result is a PathBuilder, so the fill rule and any further segments still chain on:

build_path!("M0,0 h10 v10 h-10 Z").rule(FillRule::EvenOdd).build()

Arcs are converted to cubics here, once, rather than by each of the nine backends at draw time, because an arc is the one command with no counterpart in the 2-D APIs Day draws through.

Everything is evaluated at compile time, so a path costs the same at runtime as writing the method chain by hand: there is no string left in the binary and no parsing on the draw path.