extension-js/Makefile.am is pretty heavily broken.  Taking just a few lines as an example:



%.plugin: extension-js.plugin
        $(AM_V_GEN) cp $< $@ && \
        $(SED) -i -e 's/JS_LOADER/$(@:extension-%.plugin=%)/g' $@


This rule is broken in two ways.  First, you cannot use "/" as a separator for sed expressions with pathnames because the pathnames will have "/" in them, causing the expression to be mis-parsed.

Second is that implicit rule is quite dangerous.  It will produce any *.plugin file.

The trouble is that at the start of the file there is:

include $(top_srcdir)/tests/Makefile.plugin

And this dangerous rule gets matched and regenerates that Makefile.plugin as a keyfile.

The result of these two problems is that the first time you run the build, you get a sed error (from using '/' as a separator).  The second time you run the build, the Makefile has been replaced with a keyfile so you get an error for that.