Run builds in a pseudo-terminal

[edolstra]

This allows many programs (e.g. gcc, clang, cmake) to print colorized log output (assuming $TERM is set to a value like xterm).

There are other ways to get colors, in particular setting CLICOLOR_FORCE, but they're less widely supported and can break programs that parse tool output.

Example output:

[dtzWill]

👍

After the --print-build-logs option I was really hoping for something like this, being somewhat disappointed my logs weren't already flush with color goodness. 😁

There are a few packages (if I dig up a good example I'll report back) that don't neatly handle not having a pty either at all or as stdin. This has caused strange behavior between sandbox/non-sandboxed builds in the past. Anyway this is all my way of saying "this is great and might improve some other pain points a bit too" 😁.

---

Setting TERM=xterm-256color raises questions/concerns about providing appropriate terminfo and such to builders, and is a hack since we're not xterm at all-- a common kludge but a kludge nevertheless :). TERM=nixbuild! 😁. We don't plan an actually parsing/responding to codes, which might be unexpected or problematic since a well-behaved program being told we're an xterm might expect responses. Shrug, solving this cleanly may take more work and cooperation elsewhere to be worth it. Shame, though :).

EDIT: shorter but also bits about TERM and such :)

[edolstra]

Yeah, it will be interesting to see how many packages fail to build because of this. The stdenv bootstrap worked fine BTW.

Regarding terminfo, anything in Nixpkgs that uses ncurses should work because it contains terminfo. There might be a better choice than xterm-256color though...

[nh2]

FYI this change made some Python

UnicodeEncodeError: 'ascii' codec can't encode character u'\xe0' in position 84: ordinal not in range(128)

errors go away in a way that I don't quite understand, see:

NixOS/nixpkgs#75676 (comment)

[nh2]

errors go away in a way that I don't quite understand

I understand it now, Python 2 detects the TTY to determine the default stdout encoding. Written up on NixOS/nixpkgs#75676 (comment).