Graham Dennis

Enable Boehm memory garbage collection

16

Nix uses the conservative memory garbage collector Boehm, however this was previously explicitly [disabled in nix-eval-jobs][disabled-gc]: ``` /* We are doing the garbage collection by killing forks */ setenv("GC_DONT_GC", "1",...

fix: Improve error message returned by Subsume

4

Previously when Subsume determined that a field did not subsume a previous field, the error returned was: ``` field x not present in ``` which is simply not true. Now...

Previously if a task was run as a dependency of another task, the error message simply reported something like: ``` exit status 1 ``` It is desirable instead to name...

## Motivation Under high build load, we were seeing the nix daemon segfault around [here](https://github.com/NixOS/nix/blob/2.33.0/src/libstore/unix/build/derivation-builder.cc#L750). Further investigation suggested that this was a heap-use-after-free issue where the [initialOutputs](https://github.com/NixOS/nix/blob/2.33.0/src/libstore/include/nix/store/build/derivation-builder.hh#L82) field referenced data...