File not found building port with --use-port=sdl2_image:formats=webp or formats=tif

[lv-99-slime]

When trying to build a project with --use-port=sdl2_image:formats=webp or formats=tif, building the port fails because the header files aren't found. Neither command line arguments nor environment variables seem to be used here, so I don't know if there's anything I could do to make it work.

If I add flags += [f'-I{src_dir}/VisualC/external/include'] to create in tools/ports/sdl2_image.py, it compiles, but I don't know if that's an appropriate fix. A simple webp test works this way; I didn't check tiff beyond verifying that the same error doesn't occur.

Version of emscripten/emsdk:

emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 4.0.10 (b7dc6e5747465580df5984e723b9d1f10d8e804b)
clang version 21.0.0git (https:/github.com/llvm/llvm-project 8f7e57485ee73205e108d74abb5565d5c63beaca)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /home/user/Projects/emsdk/upstream/bin

Failing command line in full:

$ emcc main.c --use-port=sdl2 --use-port=sdl2_image:formats=webp --preload-file=image.webp -Llibwebp-1.5.0/webp_js -lwebpdecoder
cache:INFO: generating port: sysroot/lib/wasm32-emscripten/libSDL2_image-webp.a... (this will be cached in "/home/user/Projects/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/libSDL2_image-webp.a" for subsequent builds)
/home/user/Projects/emsdk/upstream/emscripten/cache/ports/sdl2_image/SDL_image-release-2.6.0/IMG_webp.c:42:10: fatal error: 'webp/decode.h' file not found
   42 | #include <webp/decode.h>
      |          ^~~~~~~~~~~~~~~
1 error generated.
emcc: error: subprocess 14/19 failed (returned 1)! (cmdline: /home/user/Projects/emsdk/upstream/emscripten/emcc -c /home/user/Projects/emsdk/upstream/emscripten/cache/ports/sdl2_image/SDL_image-release-2.6.0/IMG_webp.c -o /home/user/Projects/emsdk/upstream/emscripten/cache/build/sdl2_image/wasm32_libSDL2_image-webp/IMG_webp.c.o -g -sSTRICT -Werror -ffile-prefix-map=/home/user/Projects/emsdk/upstream/emscripten=/emsdk/emscripten -ffile-prefix-map=../../../..=/emsdk/emscripten -fdebug-compilation-dir=/emsdk/emscripten -O2 -I/home/user/Projects/emsdk/upstream/emscripten/cache/ports/sdl2_image/SDL_image-release-2.6.0 -sUSE_SDL=2 -Wno-format-security -DLOAD_WEBP)

$ emcc main.c --use-port=sdl2 --use-port=sdl2_image:formats=tif
cache:INFO: generating port: sysroot/lib/wasm32-emscripten/libSDL2_image-tif.a... (this will be cached in "/home/user/Projects/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/libSDL2_image-tif.a" for subsequent builds)
/home/user/Projects/emsdk/upstream/emscripten/cache/ports/sdl2_image/SDL_image-release-2.6.0/IMG_tif.c:30:10: fatal error: 'tiffio.h' file not found
   30 | #include <tiffio.h>
      |          ^~~~~~~~~~
1 error generated.
emcc: error: subprocess 10/19 failed (returned 1)! (cmdline: /home/user/Projects/emsdk/upstream/emscripten/emcc -c /home/user/Projects/emsdk/upstream/emscripten/cache/ports/sdl2_image/SDL_image-release-2.6.0/IMG_tif.c -o /home/user/Projects/emsdk/upstream/emscripten/cache/build/sdl2_image/wasm32_libSDL2_image-tif/IMG_tif.c.o -g -sSTRICT -Werror -ffile-prefix-map=/home/user/Projects/emsdk/upstream/emscripten=/emsdk/emscripten -ffile-prefix-map=../../../..=/emsdk/emscripten -fdebug-compilation-dir=/emsdk/emscripten -O2 -I/home/user/Projects/emsdk/upstream/emscripten/cache/ports/sdl2_image/SDL_image-release-2.6.0 -sUSE_SDL=2 -Wno-format-security -DLOAD_TIF)