Avoid importing a non-vendored version of Tornado

Code depending on this conditional import could break if an old
version of Tornado is present in the environment, rendering pip
unusable.

1 files changed, 21 insertions, 0 deletions

diff --git a/tools/vendoring/patches/tenacity.patch b/tools/vendoring/patches/tenacity.patch
new file mode 100644
index 000000000..006588b36
--- /dev/null
+++ b/tools/vendoring/patches/tenacity.patch
@@ -0,0 +1,21 @@
+diff --git a/src/pip/_vendor/tenacity/__init__.py b/src/pip/_vendor/tenacity/__init__.py
+index 5f8cb5058..42e9d8940 100644
+--- a/src/pip/_vendor/tenacity/__init__.py
++++ b/src/pip/_vendor/tenacity/__init__.py
+@@ -22,10 +22,12 @@ try:
+ except ImportError:
+     iscoroutinefunction = None
+ 
+-try:
+-    import tornado
+-except ImportError:
+-    tornado = None
++# Replace a conditional import with a hard-coded None so that pip does
++# not attempt to use tornado even if it is present in the environment.
++# If tornado is non-None, tenacity will attempt to execute some code
++# that is sensitive to the version of tornado, which could break pip
++# if an old version is found.
++tornado = None
+ 
+ import sys
+ import threading