snap pack returned non-zero exit status 20

[Nathan Teodosio]

Problem
-------

See [3][4].

Command '['snap', 'pack', '--filename', 'llvm-chromium_llvmorg-19-init-14561-gecea8371+_amd64.snap', '--compression', 'xz', PosixPath('/build/llvm-chromium/prime'), PosixPath('/build/llvm-chromium')]' returned non-zero exit status 20.

or

Command '['snap', 'pack', '--filename', 'llvm-chromium_llvmorg-19-init-14561-gecea8371e_amd64.snap', '--compression', 'xz', PosixPath('/build/llvm-chromium/prime'), PosixPath('/build/llvm-chromium')]' returned non-zero exit status 20.

Background
----------

I've been trying to do one simple thing, namely programatically setting the version of this snap[0]. But Snapcraft really wants me to surrender. :P

Block [1]: Version string is "llvmorg-19-init-14561-gecea8371-3000" but must be <= 32 bytes.
Fix 1: Filter it through 'head -c32'.

Block [2]: Version string is "llvmorg-19-init-14561-gecea8371-" but must end with an ASCII alphanumeric or one of '+' or '~' (and not '-').
Fix 2: Filter it through 'head -c31' and add a + to it.

Block [3]: Command '['snap', 'pack', '--filename', 'llvm-chromium_llvmorg-19-init-14561-gecea8371+_amd64.snap', '--compression', 'xz', PosixPath('/build/llvm-chromium/prime'), PosixPath('/build/llvm-chromium')]' returned non-zero exit status 20.
Fix 3: So for some reason I thought this might be the + and substituted it with an e.

Block [4]: Command '['snap', 'pack', '--filename', 'llvm-chromium_llvmorg-19-init-14561-gecea8371e_amd64.snap', '--compression', 'xz', PosixPath('/build/llvm-chromium/prime'), PosixPath('/build/llvm-chromium')]' returned non-zero exit status 20.

[0] https://launchpad.net/~chromium-team/+snap/llvm-chromium
[1] https://launchpadlibrarian.net/741481652/buildlog_snap_ubuntu_noble_amd64_llvm-chromium_BUILDING.txt.gz
[2] https://launchpadlibrarian.net/741581930/buildlog_snap_ubuntu_noble_amd64_llvm-chromium_BUILDING.txt.gz
[3] https://launchpadlibrarian.net/741697371/buildlog_snap_ubuntu_noble_amd64_llvm-chromium_BUILDING.txt.gz
[4] https://launchpadlibrarian.net/741729763/buildlog_snap_ubuntu_noble_amd64_llvm-chromium_BUILDING.txt.gz

[Nathan Teodosio (nteodosio)]

Added Snapd component because I think it's https://github.com/canonical/snapd/blob/master/snap/pack/pack.go#L245.