bug#23723: patch-shebang phase breaks symlinks

[ludo@gnu.org (Ludovic Courtès)]

Hello!

Jelle Licht <jlicht@fsfe.org> skribis:

> It seems that the patch-shebang functionality does not deal gracefully
> with symlinks: it just overwrites them!
>
> After struggling somewhat with getting the recently packaged node 6.0.0
> to behave, I found out that `patch-shebang' in (guix build
> gnu-build-system) does not work properly on symlinks.

There’s ‘patch-shebangs’ (plural) in this file, but it explicitly
touches only regular files (see ‘list-of-files’).

However, ‘patch-source-shebangs’ indeed overwrites symlinks.  Is it the
one that’s causing problems?

> To illustrate, in this specific case, there was an executable
> script included with the node tarball, namely
> `lib/node-modules/npm/bin/npm-cli.js' with an env-based shebang:
> `/usr/bin/env node'.
>
> As the `node' executable will only be available after the `install'
> phase of the build system, it is not patched before hand. During the
> `install' phase, a symlink is created from `bin/npm' to
> `lib/node-modules/npm/bin/npm-cli.js' (in the store output directory
> this time, of course). Then the `patch-shebangs' phase finds this
> symlink and proceeds to patch it. Instead of transparently following the
> symlink and patching the `npm-cli.js' script, the `npm' symlink is
> overwritten with a shebang-patched copy of `npm-cli.js'.

I don’t think ‘patch-shebangs’ is to blame; could it be
‘patch-source-shebangs’?

Thanks!

Ludo’.