Re: Our build system may be broken: /bin vs /usr/bin

[Ian Jackson <ijackson@chiark.greenend.org.uk>]

Dirk Eddelbuettel writes ("Re: Our build system may be broken: /bin vs /usr/bin"):
> That was very much my gut feel but I am a little removed from the more core
> moving and shaking and I didn't know what changed recently.

This usrmerge change has been discussed here on -devel recently and
IIRC has been associated with other lossage too.

> FWIW GNU R is an rather obsessively clean user of to the autotools stack, so
> I would agree that it failing here is a good-enough proof for having to
> possibly revisiting things in our stack. I would expect much more breakage to
> follow.

I think the mechanism is probably as follows:

1. R's autoconfery is autodetecting the location of (say) `sed' at
   build time by searching the PATH.   R then bakes the discovered
   path into the built binaries.

2. With usrmerge, /bin is a symlink to /usr/bin or vice versa
   (I'm afraid I forget which.)

3. Consequently the R autoconfery always detects (say) `sed' in
   the first place out of /usr/bin and /bin it looks, and bakes
   /usr/bin/sed into its binaries.

4. On a system without usrmerge, /usr/bin/sed does not exist,
   because sed is in /bin.

I think this demonstrates that build environments must not have
usrmerge.  If they do, the information about where the file is on
non-usrmerge systems is not present.

I also think that the behaviour 1 above is poor practice; I think that
things in Debian should always search $PATH at runtime.  But I know
that this is not universally agreed and some important programs
disagree and require absolute paths.  Debian policy requires that
Debian-written scripts such as maintainer scripts honour $PATH, but I
think it does not make such a requirement for programs in general.

(Interestingly I think there is a cultural correlation between
communities in favour of usrmerge and communities in favour of baking
absolute paths into everything; this seems superficially a sensible
correlation but the analysis above reveals it to be troublesome.)

Hopefully someone will appear and remind us which package the usrmerge
change is in, so that you can file a bug report.  I think that bug
report should be RC.

Regards,
Ian.

-- 
Ian Jackson <ijackson@chiark.greenend.org.uk>   These opinions are my own.

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