This allows it to be set in nix.conf.

This is not used anywhere.

This allows distinguishing between an empty value and no value.

manual: nix-shell: Elaborate on using `-p` with expressions

Replace $TMPDIR with $TEST_ROOT in tests/fetchurl.sh

Fix extra semicolons warnings

Thanks @bhipple for catching!

This documents the outcome of the change in
https://github.com/NixOS/nix/issues/454:

> We can also automatically add parentheses in the generated
> `buildInputs`, so you can type `nix-shell -p "expr"`
> instead of `"(expr").

De-duplicate struct PrimOp forward declaration

$TMPDIR isn't necessarily set and would cause this test to fail.

gitignore /precompiled-headers.h.gch

libutil should not depend on libexpr.

https://hydra.nixos.org/build/105961653

It also OOMs.

https://hydra.nixos.org/build/105942679

This reverts commit 717e821b. It's
much more convenient to do 'make OPTIMIZE=0'.

This cuts 'make install -j6' on my laptop from 170s to 134s.

It constantly OOMs.

https://hydra.nixos.org/build/105784912

It's broken at the moment: https://hydra.nixos.org/build/105746055

Also it pulls in GHC which is a pretty big dependency.

Update man to show that nix-shell allows --arg

docs: fix upper bound on number of consumed cores

docs: xref doesn't render in title