Vendor File not found during node-gyp build - node.js

Question

I am willing to install a custom build of libvips with sharp on heroku. I use buildpacks that run without errors, but when it comes to node-gyp compilation, it fails here saying it cannot access /app/vendor/vips/lib/libvips-cpp.so. When I run the build without installing sharp and then connect with heroku run bash, I can see that the file is at this location.
Why node-gyp cannot find it then ?
My buildpacks
=== my-site Buildpack URLs
1. heroku-community/apt
2. https://github.com/lechinoix/heroku-buildpack-vips
3. heroku/nodejs
The error
remote: -----> vips (heroku-20 stack) app detected
remote: -----> Vendoring binaries
remote: Fetching /tmp/codon/tmp/buildpacks/2ef659928923e1b5ae4bf85b886e53d084c6a3d4/build/heroku-20.tar.gz
remote: Changing permissions on libvips folder
remote: -----> Configuring build environment
remote: -----> Building runtime environment
remote: -----> Node.js app detected
remote:
remote: -----> Creating runtime environment
remote:
remote: NPM_CONFIG_LOGLEVEL=error
remote: NODE_VERBOSE=false
remote: NODE_ENV=production
remote: NODE_MODULES_CACHE=false
remote:
remote: -----> Installing binaries
remote: engines.node (package.json): unspecified
remote: engines.npm (package.json): unspecified (use default)
remote:
remote: Resolving node version 14.x...
remote: Downloading and installing node 14.18.1...
remote: Using default npm version: 6.14.15
remote:
remote: -----> Restoring cache
remote: Caching has been disabled because NODE_MODULES_CACHE=false
remote:
remote: -----> Installing dependencies
remote: Installing node modules (package.json)
remote:
remote: > sharp#0.28.1 install /tmp/build_1f4c5c03/node_modules/sharp
remote: > (node install/libvips && node install/dll-copy && prebuild-install) || (node-gyp rebuild && node install/dll-copy)
remote:
remote: sharp: Detected globally-installed libvips v8.10.6
remote: sharp: Building from source via node-gyp
remote: readelf: Error: '/app/vendor/vips/lib/libvips-cpp.so': No such file
remote: gyp: Call to 'if readelf -Ws "$(PKG_CONFIG_PATH="/tmp/build_1f4c5c03/.apt/usr/lib/x86_64-linux-gnu/pkgconfig:/tmp/build_1f4c5c03/.apt/usr/lib/i386-linux-gnu/pkgconfig:/tmp/build_1f4c5c03/.apt/usr/lib/pkgconfig::/tmp/build_1f4c5c03/vendor/vips/lib/pkgconfig:/tmp/build_1f4c5c03/.apt/usr/lib/x86_64-linux-gnu/pkgconfig:/tmp/build_1f4c5c03/.apt/usr/lib/i386-linux-gnu/pkgconfig:/tmp/build_1f4c5c03/.apt/usr/lib/pkgconfig::/usr/local/lib/pkgconfig:/usr/lib/pkgconfig" pkg-config --variable libdir vips-cpp)/libvips-cpp.so" | c++filt | grep -qF __cxx11;then echo "1";else echo "0";fi' returned exit status 0 while in binding.gyp. while trying to load binding.gyp
Thank you so much for your help !

Answer 1

Finally found that heroku is creating the whole /app folder in a directory /tmp/build_1f4c5c03 that also contains the freshly installed vendors. In my .pc files, the package is located in /app so it cannot be found. I used a heroku-prebuild npm script to sed inplace the paths :
TMP_DIR=$(pwd)
for file in $(grep -rl /app/vendor ${TMP_DIR}/vendor/vips/lib/pkgconfig)
do
sed -i "s+/app/vendor+${TMP_DIR}/vendor+g" $file
done
Not perfectly sure it is the best way to do...