Merge pull request #5027 from minrk/pin-less

pin lessc to 1.4

IPython/html/fabfile.py

@@ -3,11 +3,15 b''
 from fabric.api import local,lcd
 from fabric.utils import abort
 import os
+from distutils.version import LooseVersion as V
+from subprocess import check_output
 
 pjoin = os.path.join
 static_dir = 'static'
 components_dir = os.path.join(static_dir, 'components')
 
+min_less_version = '1.4.0'
+max_less_version = '1.5.0' # exclusive
 
 def css(minify=True, verbose=False):
     """generate the css from less files"""
@@ -27,6 +31,16 b' def _compile_less(source, target, minify=True, verbose=False):'
     verbose = _to_bool(verbose)
     min_flag = '-x' if minify is True else ''
     ver_flag = '--verbose' if verbose is True else ''
+    
+    # pin less to 1.4
+    out = check_output(['lessc', '--version'])
+    out = out.decode('utf8', 'replace')
+    less_version = out.split()[1]
+    if V(less_version) < V(min_less_version):
+        raise ValueError("lessc too old: %s < %s" % (less_version, min_less_version))
+    if V(less_version) > V(max_less_version):
+        raise ValueError("lessc too new: %s > %s" % (less_version, max_less_version))
+    
     with lcd(static_dir):
         local('lessc {min_flag} {ver_flag} {source} {target}'.format(**locals()))