fix Python.h discovery on Ubuntu 18.04 in CI

The Autotools build system looks for the C header Python.h to determine the
include path for the local Python installation. However, on Ubuntu 18.04 it was
not finding it. The reason is that the libpython3-dev package on Ubuntu 18.04
installs Python 3.6 under a “python3.6m” prefix that it does not add to C/C++
include paths. This seems to be a deliberate choice in the structure of this
package for Ubuntu 18.04, to avoid conflicts with default Python 2.

A reasonable question to ask is then why Python 3 detection succeeds on the CI
Ubuntu 18.04 jobs. The answer is that libpython2-dev is installed. That is, the
Python 3 detection finds the Python.h from the libpython2-dev installation and
incorrectly assumes it has found the Python 3 header. This confusion may play a
role in #227 and #1042.

This coincidental alignment of headers is exposed when libpython2-dev is removed
and Python 3 detection starts failing. This commit pre-empts this failure in
upcoming changes that remove Python 2 support by explicitly making the Python 3
Python.h findable. Related to #1992.

diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index a688fc783fe0a0bdac83fd20d75ca30759493f83..32b56f580dd4eacc4075d3f964bee7a0607c1463 100644 (file)
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -15,6 +15,10 @@ portable-source:
     tags:
         - linux
     image: "$CI_REGISTRY_IMAGE/ubuntu-18.04:$CI_COMMIT_SHA"
+    before_script:
+        # Make Python.h findable
+        - export C_INCLUDE_PATH="/usr/include/python3.6m"
+        - export CPLUS_INCLUDE_PATH="/usr/include/python3.6m"
     script:
         - ./autogen.sh
         - ./configure --enable-man-pdfs
@@ -285,6 +289,10 @@ ubuntu18-04-build:
           artifacts: false
         - job: portable-source
           artifacts: true
+    before_script:
+        # Make Python.h findable
+        - export C_INCLUDE_PATH="/usr/include/python3.6m"
+        - export CPLUS_INCLUDE_PATH="/usr/include/python3.6m"
     tags:
         - linux
     variables: