Add config.pre to override envvars used in library_builders.sh (#117)

* Add config.pre to override envvars used in `library_builders.sh`
Fixes part 2 of https://github.com/matthew-brett/multibuild/issues/116

* rename config_pre.sh to env_vars.sh as suggested

README.rst

@@ -49,8 +49,8 @@ functions and variables in earlier scripts:
 
 * multibuild/common_utils.sh
 * multibuild/osx_utils.sh
+* env_vars.sh
 * multibuild/library_builders.sh
-* multibuild/travis_osx_steps.sh
 * config.sh
 
 See ``travis_osx_steps.sh`` to review source order.
@@ -79,6 +79,7 @@ following bash scripts:
 
 * multibuild/common_utils.sh
 * multibuild/manylinux_utils.sh
+* env_vars.sh
 * multibuild/library_builders.sh
 * config.sh
 
@@ -319,6 +320,14 @@ To use these scripts
 
   Optionally you can specify a different location for ``config.sh`` file with
   the ``$CONFIG_PATH`` environment variable.
+
+* Optionally, create an ``env_vars.sh`` file to set defaults for any build
+  environment variables used in ``library_builders.sh``. In Linux, they cannot
+  be just set in the global environment because the build runs in Docker, so
+  only the variables explicitly passed to ``docker run`` are propagated.
+
+  Likewise, you can specify a different location for the file by setting the
+  the ``$ENV_VARS_PATH`` environment variable.
 
 * Make sure your project is set up to build on travis-ci, and you should now
   be ready (to begin the long slow debugging process, probably).
@@ -330,8 +339,9 @@ To use these scripts
   - https://github.com/MacPython/nipy-wheels/blob/master/appveyor.yml
   - https://github.com/MacPython/pytables-wheels/blob/master/appveyor.yml
 
-  Note the Windows test customisations etc are inside ``appveyor.yml``,
-  and that ``config.sh`` is only for the Linux/Mac builds on TravisCI.
+  Note the Windows test customizations etc are inside ``appveyor.yml``,
+  and that ``config.sh`` and ``env_vars.sh`` are only for the
+  Linux/Mac builds on TravisCI.
 
 * Make sure your project is set up to build on appveyor, and you should now
   be ready (for what could be another round of slow debugging).

docker_build_wrap.sh

@@ -17,10 +17,13 @@ WHEEL_SDIR=${WHEEL_SDIR:-wheelhouse}
 # Location of `config.sh` file, default "./config.sh"
 CONFIG_PATH=${CONFIG_PATH:-config.sh}
 
+ENV_VARS_PATH=${ENV_VARS_PATH:-env_vars.sh}
+
 # Always pull in common and library builder utils
 MULTIBUILD_DIR=$(dirname "${BASH_SOURCE[0]}")
 # These routines also source common_utils.sh
 source $MULTIBUILD_DIR/manylinux_utils.sh
+if [ -r "$ENV_VARS_PATH" ]; then source "$ENV_VARS_PATH"; fi
 source $MULTIBUILD_DIR/library_builders.sh
 
 if [ "$USE_CCACHE" == "1" ]; then

travis_linux_steps.sh

@@ -87,6 +87,7 @@ function build_multilinux {
         -e UNICODE_WIDTH="$UNICODE_WIDTH" \
         -e BUILD_COMMIT="$BUILD_COMMIT" \
         -e CONFIG_PATH="$CONFIG_PATH" \
+        -e ENV_VARS_PATH="$ENV_VARS_PATH" \
         -e WHEEL_SDIR="$WHEEL_SDIR" \
         -e MANYLINUX_URL="$MANYLINUX_URL" \
         -e BUILD_DEPENDS="$BUILD_DEPENDS" \

travis_osx_steps.sh

@@ -5,8 +5,12 @@ set -e
 # Get needed utilities
 MULTIBUILD_DIR=$(dirname "${BASH_SOURCE[0]}")
 MB_PYTHON_VERSION=${MB_PYTHON_VERSION:-$TRAVIS_PYTHON_VERSION}
+
+ENV_VARS_PATH=${ENV_VARS_PATH:-env_vars.sh}
+
 # These load common_utils.sh
 source $MULTIBUILD_DIR/osx_utils.sh
+if [ -r "$ENV_VARS_PATH" ]; then source "$ENV_VARS_PATH"; fi
 source $MULTIBUILD_DIR/library_builders.sh
 
 # NB - config.sh sourced at end of this function.