Wrong build directory number shown in environment-variables file

> I was doing guix build with "--keep-missing" and looking around

> in a few

> of the output directories. I was peeking in:

>

> /tmp/guix-build-u-boot-mnt-reform2-2021.06.drv-4

>

> But wait... the "environment-variables" file says:

>

> #+BEGIN_SRC sh

> export TEMP=\

> "/tmp/guix-build-u-boot-mnt-reform2-2021.06.drv-0"

> I was doing guix build with "--keep-missing" and looking around in a few

> of the output directories. I was peeking in:

>

> /tmp/guix-build-u-boot-mnt-reform2-2021.06.drv-4

>

> But wait... the "environment-variables" file says:

>

> #+BEGIN_SRC sh

> export TEMP=\

> "/tmp/guix-build-u-boot-mnt-reform2-2021.06.drv-0"

> export TEMPDIR=\

> "/tmp/guix-build-u-boot-mnt-reform2-2021.06.drv-0"

> export TMP=\

> "/tmp/guix-build-u-boot-mnt-reform2-2021.06.drv-0"

> export TMPDIR=\

> "/tmp/guix-build-u-boot-mnt-reform2-2021.06.drv-0"

> #+END_SRC

>

> Now wait a minute. Look at that last number. What the hell is going on

> here? Is this a bug in Guix? Why is it pointing at -0 in the -4 build

> directory?

>

> Does this point at a more serious issue? What's going on?

> Part of the build environment isolation/reproducibility is that

> processes inside it always see a build directory ending in ‘-0’,

> regardless of the file name on the host system.

> Hello Christine,

>

> Christine Lemmer-Webber <cwebber@dustycloud.org> writes:

>

>> I was doing guix build with "--keep-missing" and looking around in a few

>> of the output directories. I was peeking in:

>>

>> /tmp/guix-build-u-boot-mnt-reform2-2021.06.drv-4

>>

>> But wait... the "environment-variables" file says:

>>

>> #+BEGIN_SRC sh

>> export TEMP=\

>> "/tmp/guix-build-u-boot-mnt-reform2-2021.06.drv-0"

>> export TEMPDIR=\

>> "/tmp/guix-build-u-boot-mnt-reform2-2021.06.drv-0"

>> export TMP=\

>> "/tmp/guix-build-u-boot-mnt-reform2-2021.06.drv-0"

>> export TMPDIR=\

>> "/tmp/guix-build-u-boot-mnt-reform2-2021.06.drv-0"

>> #+END_SRC

>>

>> Now wait a minute. Look at that last number. What the hell is going on

>> here? Is this a bug in Guix? Why is it pointing at -0 in the -4 build

>> directory?

>>

>> Does this point at a more serious issue? What's going on?

>

> I've definitely noticed this before as well, and had to work around it

> (I needed to inspect temp caches). Thanks for actually sending a bug

> report :)

>

> I'm not at all familiar with the nix code, but it looks like this might

> be related:

>

> nix/libstore/build.cc:1654

>

> /* In a sandbox, for determinism, always use the same temporary

> directory. */

> tmpDirInSandbox = useChroot ? canonPath("/tmp", true) + "/guix-build-" + drvName + "-0" : tmpDir;

>

> /* For convenience, set an environment pointing to the top build

> directory. */

> env["NIX_BUILD_TOP"] = tmpDirInSandbox;

>

> /* Also set TMPDIR and variants to point to this directory. */

> env["TMPDIR"] = env["TEMPDIR"] = env["TMP"] = env["TEMP"] = tmpDirInSandbox;

>

> /* Explicitly set PWD to prevent problems with chroot builds. In

> particular, dietlibc cannot figure out the cwd because the

> inode of the current directory doesn't appear in .. (because

> getdents returns the inode of the mount point). */

> env["PWD"] = tmpDirInSandbox;

>

> I'm not entirely sure what's going on. I think we build in chroot by

> default, which would explain why the temp vars get set to "-0" even

> though everything else seems to work okay.

> [[PGP Signed Part:Undecided]]

> Christine,

>

> Christine Lemmer-Webber ???

>> I was doing guix build with "--keep-missing" and looking around in a

>> few

>> of the output directories. I was peeking in:

>>

>> /tmp/guix-build-u-boot-mnt-reform2-2021.06.drv-4

>>

>> But wait... the "environment-variables" file says:

>>

>> #+BEGIN_SRC sh

>> export TEMP=\

>> "/tmp/guix-build-u-boot-mnt-reform2-2021.06.drv-0"

>

> Part of the build environment isolation/reproducibility is that

> processes inside it always see a build directory ending in ‘-0’,

> regardless of the file name on the host system.

>

> Kind regards,

>

> T G-R

>

> [[End of PGP Signed Part]]

> Tobias Geerinckx-Rice <me@tobias.gr> writes:

>>> #+BEGIN_SRC sh

>>> export TEMP=\

>>> "/tmp/guix-build-u-boot-mnt-reform2-2021.06.drv-0"

>>

>> Part of the build environment isolation/reproducibility is that

>> processes inside it always see a build directory ending in ‘-0’,

>> regardless of the file name on the host system.

>>

>> Kind regards,

>>

>> T G-R

>>

>> [[End of PGP Signed Part]]

>

> This makes sense in general, though I wonder if when using --keep-failed

> if environment-variables should dump out something different, since

> that file is around for debugging, and sourcing it might set up the

> wrong paths I guess? What do you think?