[Python-checkins] Fix AppVeyor doc short-circuit (GH-5633)

[Zachary Ware]

https://github.com/python/cpython/commit/09df4b761f6365e315be26c89d2af70a4fda6985
commit: 09df4b761f6365e315be26c89d2af70a4fda6985
branch: 3.7
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: Zachary Ware <zachary.ware at gmail.com>
date: 2018-02-11T16:14:45-06:00
summary:

Fix AppVeyor doc short-circuit (GH-5633)

(cherry picked from commit 6ea20fc719dcaf102d2cefa1786f0421514f7a58)

files:
M .github/appveyor.yml

diff --git a/.github/appveyor.yml b/.github/appveyor.yml
index a4c11df2795e..9d47c9975e5a 100644
--- a/.github/appveyor.yml
+++ b/.github/appveyor.yml
@@ -14,12 +14,15 @@ before_build:
       } elseif (!$env:APPVEYOR_PULL_REQUEST_HEAD_COMMIT) {
         echo 'Not a PR, doing full build.'
       } else {
-        $mergebase = git merge-base $env:APPVEYOR_PULL_REQUEST_HEAD_COMMIT $env:APPVEYOR_REPO_BRANCH
+        git fetch -q origin +refs/heads/$env:APPVEYOR_REPO_BRANCH
+        $mergebase = git merge-base HEAD FETCH_HEAD
         $changes = git diff --name-only HEAD $mergebase | grep -vE '(\.rst$)|(^Doc)|(^Misc)'
         If (!$changes) {
           echo 'Only docs were updated, stopping build process.'
           Exit-AppveyorBuild
         }
+        echo 'Doing full build due to non-doc changes in these files:'
+        echo $changes
       }