These exception types are intended as a hook for a programming
environment to recommend packages that can provide a module that isn't
found (through an uncaught-exception handler). The new exceptions are
generated by the default module name resolver and defaultload
handler. In addition to the exceptions, there's a new
`prop:exn:missing-module' property and `exn:missing-module?', which is
what an environment should use to detect relevant exceptions.
There's also a new `current-module-path-for-load' parameter, which
just provides a commuincation path from the module name resolver to
the the load handler. The parameter is a relatively ugly piece of the
puzzle, but it's the best I could find to squash the new functionality
into the existing stack of handlers.
When a module is loaded from bytecode and then the value of
`use-compiled-file-paths' changes, an attempt to load a submodule
would fail, because source isn't used if the main module is
already declared, and the bytecode code is not used according to
`use-compiled-file-paths'. Make the bytecode path stick when it
is used once, so that submodule loads succeed, and make it work
even with `namespace-module-attach'.
The module-attach part of this protocol requires a change to the
API of a module name resolver: the notification mode gets two
arguments, instead of one, where the second argument is an
environment.
The preserved path is exposed by a new `module-path-index-submodule'
function, and `module-path-index-join' now accepts an optional
submodule path.
Also, fixed a problem with `collapse-module-path-index' when
a module path indx is built on a resolved module path that
is a submodule path.
In addition to the main repair, `collapse-module-path[-index]' is
correctly documented to allow '(quote <sym>) rel-to paths.
Finally, `collapse-module-path-index' changed to use a symbolic
resolved module path that appears as the base of a module path
index, rather than falling back to the given rel-to path. It's
possble that the old beavior was intentional, but it wasn't tested,
and it seems more likely to have been a bug.
Closes PR 12724
Although th eoriginal idea was to distinguish "text" paths
from derived filesystem paths, practically everythign that accepts
a module path also accepts a path. Building the generalization into
`module-path?' makes it easier to support `submod' wrappers on paths,
and it seems to fix things rather than break them.
