add warning if cycle detected in extensions

Author: IanButterworth

base/loading.jl

@@ -1392,6 +1392,10 @@ function run_extension_callbacks(pkgid::PkgId)
     extids = pop!(EXT_DORMITORY, pkgid, nothing)
     extids === nothing && return
     for extid in extids
+        if in(extid.id.name, precompilation_stack) && !isprecompiled(extid.id)
+            @warn "Dependency cycle detected in extension precompilation: $(join(precompilation_stack, " > ")) > $(extid.id.name)"
+            continue
+        end
         if extid.ntriggers > 0
             # indicate pkgid is loaded
             extid.ntriggers -= 1