bug#23780: guix import pypi jedi: weird backtrace, no proper error message

[Danny Milosavljevic <dannym@scratchpost.org>]

$ guix import pypi jedi

Starting download of /tmp/guix-file.n01KoB
From https://pypi.python.org/packages/3a/37/629080b92b87bc65e3b1b4f5d539e22aa5dc45637eab0dd4b0cd8cf236c2/jedi-0.9.0.tar.gz...
 ….0.tar.gz  326KiB                 402KiB/s 00:01 [####################] 100.0%

Starting download of /tmp/guix-file.CbhRLk
From https://pypi.python.org/packages/c4/59/e48a369168a84c8aef9127c227fc3b9f53bc9c528b24c2cda20487bc2deb/jedi-0.9.0-py2.py3-none-any.whl...
 …py3-none-any.whl  154KiB          291KiB/s 00:01 [####################] 100.0%
Backtrace:
In ice-9/boot-9.scm:
 157: 19 [catch srfi-34 #<procedure 57736c0 at ice-9/eval.scm:416:20 ()> ...]
In ice-9/r4rs.scm:
  90: 18 [dynamic-wind #<procedure 5773570 at ice-9/eval.scm:416:20 ()> ...]
In ice-9/eval.scm:
 387: 17 [eval # #]
 387: 16 [eval # #]
 387: 15 [eval # #]
 387: 14 [eval # #]
 387: 13 [eval # #]
 387: 12 [eval # #]
 387: 11 [eval # #]
 387: 10 [eval # #]
 387: 9 [eval # #]
 387: 8 [eval # #]
 387: 7 [eval # #]
 411: 6 [eval # #]
In ice-9/r4rs.scm:
  90: 5 [dynamic-wind #<procedure 57d3900 at ice-9/eval.scm:416:20 ()> ...]
  90: 4 [dynamic-wind #<procedure 5c332a0 at ice-9/boot-9.scm:1133:2 _> ...]
In ice-9/boot-9.scm:
 867: 3 [call-with-input-file "jedi-0.9.0.dist-info/metadata.json" ...]
In ice-9/eval.scm:
 411: 2 [eval # #]
 387: 1 [eval # #]
In unknown file:
   ?: 0 [list-ref #f 0]

This stacktrace is ... unhelpful. I think there was a post somewhere where it detailed how to debug that but I can't find it again :(

$ cat metadata.json 
{"classifiers": ["Development Status :: 4 - Beta", "Environment :: Plugins", "Intended Audience :: Developers", "License :: OSI Approved :: MIT License", "Operating System :: OS Independent", "Programming Language :: Python :: 2", "Programming Language :: Python :: 2.6", "Programming Language :: Python :: 2.7", "Programming Language :: Python :: 3", "Programming Language :: Python :: 3.2", "Programming Language :: Python :: 3.3", "Programming Language :: Python :: 3.4", "Topic :: Software Development :: Libraries :: Python Modules", "Topic :: Text Editors :: Integrated Development Environments (IDE)", "Topic :: Utilities"], "summary": "An autocompletion tool for Python that can be used for text editors.", "platform": "any", "generator": "bdist_wheel (0.24.0)", "metadata_version": "2.0", "version": "0.9.0", "extensions": {"python.details": {"contacts": [{"role": "author", "email": "davidhalter88@gmail.com", "name": "David Halter"}], "project_urls": {"Home": "https://github.com/davidhalter/jedi"}, "document_names": {"description": "DESCRIPTION.rst"}}}, "license": "MIT", "keywords": ["python", "completion", "refactoring", "vim"], "name": "jedi"}