advice for debugging incremental compilation hashing failures etc

[nikomatsakis]

Over in rust-lang/rust#47935, @michaelwoerister wrote:

The [dependency tracking] readme is largely outdated. The "Testing the dependency graph" and "Debugging the dependency graph" sections are still correct, I think, but the rest is probably just confusing at this point.

I think we ought o move some of those sections over, and/or add some new material on how to debug incremental compilation failures. This is always something I have to kind of rediscover.

[nikomatsakis]

@michaelwoerister, think you'd be up for that? =)

[michaelwoerister]

It depends on how much of a priority it is :)

[mark-i-m]

Honestly, I was just going to create a new subchapter and copy/paste those two sections into it. But if you're interested in doing something more interesting with those sections, that would be great!

[nikomatsakis]

@mark-i-m starting with that seems ok =)

[mark-i-m]

Ok, created #92 which is pretty much a straight copy/paste.