GHC boot script can't handle Git remote not named origin

Problem

I ran the following to get the sources for GHC to build them:

git clone -o ghc --recursive http://git.haskell.org/ghc.git

Note especially the -o ghc part, which uses the Git remote name ghc instead of the default origin. When a custom remote name is used, ./boot fails:

$ ./boot
Traceback (most recent call last):
  File "./boot", line 193, in <module>
    check_for_url_rewrites()
  File "./boot", line 29, in check_for_url_rewrites
    subprocess.check_output('git config remote.origin.url'.split()).find(b'github.com') != -1 and \
  File "/usr/lib/python3.5/subprocess.py", line 626, in check_output
    **kwargs).stdout
  File "/usr/lib/python3.5/subprocess.py", line 708, in run
    output=stdout, stderr=stderr)
subprocess.CalledProcessError: Command '['git', 'config', 'remote.origin.url']' returned non-zero exit status 1

$ git config remote.origin.url

$ echo $?
1

Solution

git config remote.origin.url can be used first. Whenever git config remote.origin.url fails, a git rev-parse command (thanks to freenode/#git/ikke for it) can be used to get the remote name and branch that would be pushed to:

$ git rev-parse --symbolic-full-name --abbrev-ref @{upstream}
ghc/coercible

$ git rev-parse --symbolic-full-name --abbrev-ref @{upstream} | sed 's/\/.*$//'
ghc

$ git config "remote.$( git rev-parse --symbolic-full-name --abbrev-ref @{upstream} | sed 's/\/.*$//' ).url"
http://git.haskell.org/ghc.git

Workaround

Rename the remote to origin:

$ git remote rename "$( git config branch.master.remote )" origin
$ ./boot
Creating libraries/mtl/ghc.mk
Creating libraries/unix/ghc.mk
Creating libraries/text/ghc.mk
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