look for python2 symlinks before bootstrap python

Before this commit, if you're running x.py directly on a system where
`python` is symlinked to Python 3, then the `python` config option will
default to a Python 3 interpreter. This causes debuginfo tests to fail
with an opaque error message, since they have a hard requirement on
Python 2.

This commit modifies the Python probe behavior to look for python2.7 and
python2 *before* using the interpreter used to execute `x.py`.

1 files changed, 3 insertions, 0 deletions

diff --git a/config.toml.example b/config.toml.example
index f45db37c33b..b4ad15a8235 100644
--- a/config.toml.example
+++ b/config.toml.example
@@ -162,6 +162,9 @@
 # Python interpreter to use for various tasks throughout the build, notably
 # rustdoc tests, the lldb python interpreter, and some dist bits and pieces.
 # Note that Python 2 is currently required.
+#
+# Defaults to python2.7, then python2. If neither executable can be found, then
+# it defaults to the Python interpreter used to execute x.py.
 #python = "python2.7"
 
 # Force Cargo to check that Cargo.lock describes the precise dependency