c++/modules: Cleanup import handling [PR99682]HEADtrunkmaster

This patch fixes some issues with import handling.

The main functional change is to allow importing a module's interface
file into its implementation file indirectly.  [module.import] p9
forbids an explicit 'import M;' declaration, but there's no provision
against having 'import X;' where module X itself imports M, so this
patch splits up the detection of circular imports to handle this better.
I also updated the errors to be closer to the standard wording.

A second issue I found while testing this is that we don't properly
handle name visibility when a partition implementation unit imports its
primary module interface (g++.dg/modules/part-10).  This is resolved by
setting 'module_p' on the primary interface when it gets imported.

Solving this I incidentally removed the assertion that PR121808 was
failing on, which was never valid: we can enter import_module for a
module previously seen as a module-declaration if parsing bails before
declare_module is called.  I experimented with guaranteeing that
declare_module always gets called for a module_state generated during
preprocessing if at all possible, but the resulting errors didn't seem a
lot better so I've left it as-is for now.

I did make a small adjustment so that a direct import of a module
doesn't overwrite the location of a module-declaration from earlier in
the file; this is important because preprocessing (and thus the
assigning of these locations) seems to happen for the whole file before
parsing begins, which can otherwise cause confusing locations referring
to later in the file than parsing would otherwise indicate.

	PR c++/99682
	PR c++/121808

gcc/cp/ChangeLog:

	* module.cc (class module_state): Add comment to 'parent'.
	(module_state::check_not_purview): Rename to...
	(module_state::check_circular_import): ...this.  Only handle
	interface dependencies, adjust diagnostic message.
	(module_state::read_imports): Use new function.  Pass location
	of import as from_loc instead of the module location.
	(module_state::do_import): Set module_p when importing the
	primary interface for the current module.
	(import_module): Split out check for imports in own unit.
	Remove incorrect assertion.
	(preprocess_module): Don't overwrite module-decl location with
	later import.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/circ-1_c.C: Adjust diagnostic.
	* g++.dg/modules/mod-decl-1.C: Likewise.
	* g++.dg/modules/mod-decl-2_b.C: Likewise.
	* g++.dg/modules/pr99174.H: Likewise.
	* g++.dg/modules/import-3_a.C: New test.
	* g++.dg/modules/import-3_b.C: New test.
	* g++.dg/modules/import-3_c.C: New test.
	* g++.dg/modules/mod-decl-9.C: New test.
	* g++.dg/modules/part-10_a.C: New test.
	* g++.dg/modules/part-10_b.C: New test.
	* g++.dg/modules/part-10_c.C: New test.
	* g++.dg/modules/part-10_d.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
Reviewed-by: Jason Merrill <jason@redhat.com>

0 files changed, 0 insertions, 0 deletions