rustbuild should not grab the latest beta unless instructed to (or on first run)

[nrc]

There is a principle - one should opt-in to a build tool accessing the internet, but also a practical effect - I was in the middle of debugging and my 5 min edit-compile-debug cycle is now an hour because there a new beta got released and now I'm re-compiling llvm :-(

[est31]

related #37305

[alexcrichton]

I somewhat disagree with this in the sense that we're doing exactly the same thing as the previous build system, and no one complained about the makefiles...

[nrc]

@alexcrichton I thought I had to git pull in order to get a new snapshot? Or maybe configure? I don't remember the snapshot changing on a plain make.

[alexcrichton]

Hm there could perhaps be a bug, but I don't think that "rustbuild downloading stage0 compilers when it thinks it needs to" is a bug. If it thinks it should and it shouldn't then that's a bug.

[nrc]

Nominating for discussion at tools meeting, we can probably talk this through much quicker than in comments

[ranma42]

What was the outcome of the discussion?

[alexcrichton]

This was discussed during the recent tools triage meeting and the conclusion was that the current behavior should be working as intended (pinned betas, not the most recent beta), but if this reproduces again we can investigate!