Loop variable does not propagate to (implicit) rule body

[cspiel]

Consider the following OMakefile:

extensions[] =
        .a
        .b
        .c

foreach(ext => ..., $(extensions))
        x = $(ext)
        %.q: %$(ext)
                echo $"ext = $(ext), x = $x" # Comment out this line and the error disappears.
                cp $< $@
        export .RULE

It defines a set of implicit rules for %.q targets. Call it for example with

touch foo.b;  rm -f foo.q;  omake foo.q

omake raises the error

unbound variable: public.ext

A simple workaround is shown in the example. If we capture the loop
variable ext inside the foreach-loop, but outside of the (implicit) rule
in variable x, we can use x inside the rule body without an error.