[PATCH v3] py3: handle meta-path finders that only use pre-python3.4 API

[Ludovic Chabant]

# HG changeset patch
# User Ludovic Chabant <ludovic at chabant.com>
# Date 1555683918 0
#      Fri Apr 19 14:25:18 2019 +0000
# Branch stable
# Node ID 3611368a1af3037427eb59635c7dad8dab67c606
# Parent  4a8d9ed864754837a185a642170cde24392f9abf
py3: handle meta-path finders that only use pre-python3.4 API

diff --git a/mercurial/__init__.py b/mercurial/__init__.py
--- a/mercurial/__init__.py
+++ b/mercurial/__init__.py
@@ -54,7 +54,16 @@
                 if finder == self:
                     continue
 
-                spec = finder.find_spec(fullname, path, target=target)
+                # Originally the API was a `find_module` method, but it was
+                # renamed to `find_spec` in python 3.4, with a new `target`
+                # argument.
+                find_spec_method = getattr(finder, 'find_spec', None)
+                if find_spec_method:
+                    spec = find_spec_method(fullname, path, target=target)
+                else:
+                    spec = finder.find_module(fullname)
+                    if spec is not None:
+                        spec = importlib.util.spec_from_loader(fullname, spec)
                 if spec:
                     break