Description
If the third expression of a for loop (loop-expression according to the spec Chapter 6.3) contains multiple statements... naga just takes the last one and forgets the the first. I haven't looked at more than two statements.

this leads to infinite loops and potential crashes. Likely root cause to finding gfx-rs/wgpu-native#416, maybe related to #4558

Repro steps
I have two semantically equivalent code snippets in glsl

for (int i = 0; i < 50; i+=1, b+=0.01) {
        a -= 0.01;
    }

for (int i = 0; i < 50; b+=0.01, i+=1) {
        a -= 0.01;
    }

the third expression contains the usual incrementor, as well as a completely unrelated statement.

translating them to wgls using naga gives me the following output for this loop

loop {
        let _e22 = i;
        if !((_e22 < 50i)) {
            break;
        }
        {
            let _e29 = a;
            a = (_e29 - 0.01f);
        }
        continuing {
            let _e26 = b;
            b = (_e26 + 0.01f);
        }
    }

loop {
        let _e22 = i;
        if !((_e22 < 50i)) {
            break;
        }
        {
            let _e29 = a;
            a = (_e29 - 0.01f);
        }
        continuing {
            let _e26 = i;
            i = (_e26 + 1i);
        }
    }

the difference is which statement is part of the continuing block. The other statement is completely lost. It is dependant on the order.

Expected vs observed behavior
A reference for this being valid in a shadertoy. Perhaps the continuing block could just include both statements?

Platform
naga 22.0.0