Make the BUILD_WITH_GEO_LIBRARIES warning fatal (#1115)

The `BUILD_WITH_GEO_LIBRARIES` feature was removed in the previous PR,
and replaced with a warning that the feature is no longer supported.

After further thought I believe it would be best to make this warning
fatal, to prevent unexpected failures at runtime, if consumers of the
library either aren't invoked during the build, or were previously
installed/cached and were dynamically linked against the library.

Continuation of #1113 / @W-7654424@.

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- Error if the unsupported `BUILD_WITH_GEO_LIBRARIES` env var is set (#1115).
 - Remove deprecated GDAL/GEOS/PROJ support (#1113).
 - Remove vendored `jq` binary (#1112).
 - Remove redundant Mercurial install step (#1111).

bin/compile

@@ -35,15 +35,6 @@ ENV_DIR=$3
 # Export Path variables, for use in sub-scripts.
 export BUILD_DIR CACHE_DIR ENV_DIR
 
-if [[ "${STACK}" == "cedar-14" ]]; then
-  puts-warn "The Cedar-14 stack is no longer supported by the latest release of this buildpack."
-  puts-warn "Please switch to the Cedar-14 support branch by using this buildpack URL:"
-  puts-warn "https://github.com/heroku/heroku-buildpack-python#cedar-14"
-  puts-warn "For instructions on how to change the buildpacks used by an app, see:"
-  puts-warn "https://devcenter.heroku.com/articles/buildpacks#setting-a-buildpack-on-an-application"
-  exit 1
-fi
-
 # Set the base URL for downloading buildpack assets like Python runtimes.
 # The user can provide BUILDPACK_S3_BASE_URL to specify a custom target.
 # Note: this is designed for non-Heroku use, as it does not use the user-provided
@@ -105,6 +96,31 @@ source "$BIN_DIR/utils"
 # shellcheck source=bin/warnings
 source "$BIN_DIR/warnings"
 
+if [[ "${STACK}" == "cedar-14" ]]; then
+  mcount "failure.unsupported.cedar-14"
+  puts-warn "The Cedar-14 stack is no longer supported by the latest release of this buildpack."
+  puts-warn
+  puts-warn "Please switch to the Cedar-14 support branch by using this buildpack URL:"
+  puts-warn "https://github.com/heroku/heroku-buildpack-python#cedar-14"
+  puts-warn
+  puts-warn "For instructions on how to change the buildpacks used by an app, see:"
+  puts-warn "https://devcenter.heroku.com/articles/buildpacks#setting-a-buildpack-on-an-application"
+  exit 1
+fi
+
+if [[ -f "${ENV_DIR}/BUILD_WITH_GEO_LIBRARIES" ]]; then
+  mcount "failure.unsupported.BUILD_WITH_GEO_LIBRARIES"
+  puts-warn "The Python buildpack's BUILD_WITH_GEO_LIBRARIES functonality is no longer supported:"
+  puts-warn "https://help.heroku.com/D5INLB1A/python-s-build_with_geo_libraries-legacy-feature-is-now-deprecated"
+  puts-warn
+  puts-warn "For GDAL, GEOS and PROJ support, use the Geo buildpack alongside the Python buildpack:"
+  puts-warn "https://github.com/heroku/heroku-geo-buildpack"
+  puts-warn
+  puts-warn "To remove this error message, unset the BUILD_WITH_GEO_LIBRARIES variable using:"
+  puts-warn "heroku config:unset BUILD_WITH_GEO_LIBRARIES"
+  exit 1
+fi
+
 # Make the directory in which we will create symlinks from the temporary build directory
 # to `/app`.
 # Symlinks are required, since Python is not a portable installation.

bin/warnings

@@ -46,21 +46,7 @@ six-included() {
   fi
 }
 
-geo-gdal-support() {
-  if [[ -f "${ENV_DIR}/BUILD_WITH_GEO_LIBRARIES" ]]; then
-    mcount "warnings.BUILD_WITH_GEO_LIBRARIES"
-    echo
-    puts-warn "The Python buildpack's BUILD_WITH_GEO_LIBRARIES functonality is no longer supported:"
-    puts-warn "https://help.heroku.com/D5INLB1A/python-s-build_with_geo_libraries-legacy-feature-is-now-deprecated"
-    puts-warn
-    puts-warn "For GDAL, GEOS and PROJ support, use the Geo buildpack alongside the Python buildpack:"
-    puts-warn "https://github.com/heroku/heroku-geo-buildpack"
-    puts-warn
-    puts-warn "To hide this message, unset the BUILD_WITH_GEO_LIBRARIES variable using:"
-    puts-warn "heroku config:unset BUILD_WITH_GEO_LIBRARIES"
-    echo
-    return
-  fi
+gdal-missing() {
   if grep -qi 'Could not find gdal-config' "$WARNINGS_LOG"; then
     mcount 'warnings.gdal'
     echo
@@ -76,6 +62,6 @@ show-warnings() {
   scipy-included
   distribute-included
   six-included
-  geo-gdal-support
+  gdal-missing
 }