Build doc error: No extension named gi for index page

Hi! i followed instruction from readme to generate doc but i hit an error when trying to build it:

$ meson compile -C build gst-doc
INFO: autodetecting backend as ninja
INFO: calculating backend command to run: /usr/bin/ninja -C /home/mathieu/Projets/gstreamer/build gst-doc
ninja: Entering directory `/home/mathieu/Projets/gstreamer/build'
[1/1] Generating subprojects/gst-docs/GStreamer-doc with a custom command
FAILED: subprojects/gst-docs/GStreamer-doc 
/home/mathieu/.local/bin/meson --internal hotdoc /home/mathieu/.local/bin/hotdoc run --conf-file GStreamer-doc.json --builddir /home/mathieu/Projets/gstreamer/build/subprojects/gst-docs
ERROR: [doc-tree]: (index-extension-not-found): /home/mathieu/Projets/gstreamer/build/subprojects/gst-docs/sitemap.txt:1:2: No extension named gi for index page
00001:gi-index
      ^
00002:        installing/index.md
00003:                installing/for-android-development.md
ninja: build stopped: subcommand failed.

any idea how to resolve that ?

Got hit by the same error. Hotdoc complaining about missing gi extension.
Solved for me after I installed packages:

llvm libclang-dev gobject-introspection clang

clang definitely made a difference, not sure about others listed at Installing

Try hotdoc --list-extensions, it should list c-extension and gi-extension among other things.