depfixer: install_rpath gets split into multiple with each having one character(!)

[pbrzez]

I'm building a library and setting an install_rpath on it, like so: install_rpath : '/usr/lib/swift'.

Expected behaviour
Before 1.4.1, this would result in the rpath getting correctly added on install, as follows (otool -l library.dylib):

Load command 54
          cmd LC_RPATH
      cmdsize 32
         path /usr/lib/swift (offset 12)

Current behaviour
However, with 1.4.1 onwards (testing on master), this happens:

Load command 69
          cmd LC_RPATH
      cmdsize 16
         path / (offset 12)
Load command 70
          cmd LC_RPATH
      cmdsize 16
         path u (offset 12)
Load command 71
          cmd LC_RPATH
      cmdsize 16
         path s (offset 12)
Load command 72
          cmd LC_RPATH
      cmdsize 16
         path r (offset 12)
Load command 73
          cmd LC_RPATH
      cmdsize 16
         path l (offset 12)
Load command 74
          cmd LC_RPATH
      cmdsize 16
         path i (offset 12)
Load command 75
          cmd LC_RPATH
      cmdsize 16
         path b (offset 12)
Load command 76
          cmd LC_RPATH
      cmdsize 16
         path w (offset 12)
Load command 77
          cmd LC_RPATH
      cmdsize 16
         path f (offset 12)
Load command 78
          cmd LC_RPATH
      cmdsize 16
         path t (offset 12)

Which is, obviously, quite not right :)
Not sure if that makes a difference, but I also manually add that rpath via -Wl,-rpath at link time. No matter what though, this shouldn't happen.

The faulty code was added here: https://github.com/mesonbuild/meson/pull/13012/files#diff-d708bb4ba1cd44eef4be4fa7a95a66e78e29816178905b4a95b5276eaa046431R409

meson/mesonbuild/scripts/depfixer.py

Lines 407 to 409 in d2e7250

	new_rpaths: OrderedSet[str] = OrderedSet()
	if new_rpath:
	new_rpaths.update(new_rpath)

new_rpath is a str, so this splits it into separate entries per character I think...

system parameters
macOS 14.5, Meson 1.4.1 onwards

This is quite breaking, and would be nice to get this fixed for 1.5.0 if possible.

As a side note, the linked PR is also causing another set of differences in my builds (a lot of RPATHs being left over after installing, compared to earlier on, and I'm sure they are supposed to be removed even after that PR) but I'll make a separate issue once I make sure it's definitely not correct.