These PRs come about because of gfortran's single pass parsing. If the
function in the title is parsed after the associate construct, then its
type and rank are not known. The point at which this becomes a problem is
when expressions within the associate block are parsed. primary.cc
(gfc_match_varspec) could already deal with intrinsic types and so
component references were the trigger for the problem.

The two major parts of this patch are the fixup needed in gfc_match_varspec
and the resolution of  expressions with references in resolve.cc
(gfc_fixup_inferred_type_refs). The former relies on the two new functions
in symbol.cc to search for derived types with an appropriate component to
match the component reference and then set the associate name to have a
matching derived type. gfc_fixup_inferred_type_refs is called in resolution
and so the type of the selector function is known.
gfc_fixup_inferred_type_refs ensures that the component references use this
derived type and that array references occur in the right place in
expressions and match preceding array specs. Most of the work in preparing
the patch was sorting out cases where the selector was not a derived type
but, instead, a class function. If it were not for this, the patch would
have been submitted six months ago :-(

The patch is relatively safe because most of the chunks are guarded by
testing for the associate name being an inferred type, which is set in
gfc_match_varspec. For this reason, I do not think it likely that the patch
will cause regressions. However, it is more than possible that variants not
appearing in the submitted testcase will throw up new bugs.

Jerry has already given the patch a whirl and found that it applies
cleanly, regtests OK and works as advertised.

OK for trunk?

Paul

Fortran: Fix class/derived type function associate selectors [PR87477]

2024-01-06  Paul Thomas  <pault@gcc.gnu.org>

gcc/fortran
PR fortran/87477
PR fortran/89645
PR fortran/99065
* class.cc (gfc_change_class): New function needed for
associate names, when rank changes or a derived type is
produced by resolution
* dump-parse-tree.cc (show_code_node): Make output for SELECT
TYPE more comprehensible.
* gfortran.h : Add 'gfc_association_list' to structure
'gfc_association_list'. Add prototypes for
'gfc_find_derived_types', 'gfc_fixup_inferred_type_refs' and
'gfc_change_class'. Add macro IS_INFERRED_TYPE.
* match.cc (copy_ts_from_selector_to_associate): Add bolean arg
'select_type' with default false. If this is a select type name
and the selector is a inferred type, build the class type and
apply it to the associate name.
(build_associate_name): Pass true to 'select_type' in call to
previous.
* parse.cc (parse_associate): If the selector is a inferred type
the associate name is too. Make sure that function selector
class and rank, if known, are passed to the associate name. If
a function result exists, pass its typespec to the associate
name.
* primary.cc (gfc_match_varspec): If a scalar derived type
select type temporary has an array reference, match the array
reference, treating this in the same way as an equivalence
member. If this is a inferred type with a component reference,
call 'gfc_find_derived_types' to find a suitable derived type.
* resolve.cc (resolve_variable): Call new function below.
(gfc_fixup_inferred_type_refs): New function to ensure that the
expression references for a inferred type are consistent with
the now fixed up selector.
(resolve_assoc_var): Ensure that derived type or class function
selectors transmit the correct arrayspec to the associate name.
(resolve_select_type): If the selector is an associate name of
inferred type and has no component references, the associate
name should have its typespec.
* symbol.cc (gfc_set_default_type): If an associate name with
unknown type has a selector expression, try resolving the expr.
(find_derived_types, gfc_find_derived_types): New functions
that search for a derived type with a given name.
* trans-expr.cc (gfc_conv_variable): Some inferred type exprs
escape resolution so call 'gfc_fixup_inferred_type_refs'.
* trans-stmt.cc (trans_associate_var): Tidy up expression for
'class_target'. Correctly handle selectors that are class array
references, passed as derived types.

gcc/testsuite/
PR fortran/87477
PR fortran/89645
PR fortran/99065
* gfortran.dg/associate_64.f90 : New test