add SLUGIFY_USES_TEXT_UNIDECODE support

CHANGELOG.md

 # Python Buildpack Changelog
 
-# 139
+# 140 (2018-10-09)
+
+Add support for detecting SLUGIFY_USES_TEXT_UNIDECODE, which is required to
+install Apache Airflow version 1.10 or higher.
+
+# 139 (2018-10-08)
 
 Improvements to Python install messaging
 

bin/steps/pip-install

@@ -8,10 +8,24 @@ if [ ! "$SKIP_PIP_INSTALL" ]; then
     # Install dependencies with Pip.
     puts-step "Installing requirements with pip"
 
-    # Set PIP_EXTRA_INDEX_URL
+    # Set Pip env vars
+    # This reads certain environment variables set on the Heroku app config
+    # and makes them accessible to the pip install process.
+    #
+    # PIP_EXTRA_INDEX_URL allows for an alternate pypi URL to be used.
     if [[ -r $ENV_DIR/PIP_EXTRA_INDEX_URL ]]; then
         PIP_EXTRA_INDEX_URL="$(cat "$ENV_DIR/PIP_EXTRA_INDEX_URL")"
         export PIP_EXTRA_INDEX_URL
+        mcount "buildvar.PIP_EXTRA_INDEX_URL"
+    fi
+
+    set +e
+
+    # Set SLUGIFY_USES_TEXT_UNIDECODE, required for Airflow versions >=1.10
+    if [[ -r $ENV_DIR/SLUGIFY_USES_TEXT_UNIDECODE ]]; then
+        SLUGIFY_USES_TEXT_UNIDECODE="$(cat "$ENV_DIR/SLUGIFY_USES_TEXT_UNIDECODE")"
+        export SLUGIFY_USES_TEXT_UNIDECODE
+        mcount "buildvar.SLUGIFY_USES_TEXT_UNIDECODE"
     fi
 
     set +e

bin/steps/pipenv

@@ -35,10 +35,22 @@ if [ ! "$SKIP_PIPENV_INSTALL" ]; then
         # Skip pip install, later.
         export SKIP_PIP_INSTALL=1
 
-        # Set PIP_EXTRA_INDEX_URL
+        # Set Pip env vars
+        # This reads certain environment variables set on the Heroku app config
+        # and makes them accessible to the pip install process.
+        #
+        # PIP_EXTRA_INDEX_URL allows for an alternate pypi URL to be used.
         if [[ -r $ENV_DIR/PIP_EXTRA_INDEX_URL ]]; then
             PIP_EXTRA_INDEX_URL="$(cat "$ENV_DIR/PIP_EXTRA_INDEX_URL")"
             export PIP_EXTRA_INDEX_URL
+            mcount "buildvar.PIP_EXTRA_INDEX_URL"
+        fi
+
+        # Set SLUGIFY_USES_TEXT_UNIDECODE, required for Airflow versions >=1.10
+        if [[ -r $ENV_DIR/SLUGIFY_USES_TEXT_UNIDECODE ]]; then
+            SLUGIFY_USES_TEXT_UNIDECODE="$(cat "$ENV_DIR/SLUGIFY_USES_TEXT_UNIDECODE")"
+            export SLUGIFY_USES_TEXT_UNIDECODE
+            mcount "buildvar.SLUGIFY_USES_TEXT_UNIDECODE"
         fi
 
         export PIPENV_VERSION="2018.5.18"

test/fixtures/airflow/.env

+SLUGIFY_USES_TEXT_UNIDECODE=yes

test/fixtures/airflow/requirements.txt

+apache-airflow==1.10