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libcpp: Improve the diagnostic for poisoned identifiers [PR36887]

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The PR requests an enhancement to the diagnostic issued for the use of a
poisoned identifier. Currently, we show the location of the usage, but not
the location which requested the poisoning, which would be helpful for the
user if the decision to poison an identifier was made externally, such as
in a library header.

In order to output this information, we need to remember a location_t for
each identifier that has been poisoned, and that data needs to be preserved
as well in a PCH. One option would be to add a field to struct cpp_hashnode,
but there is no convenient place to add it without increasing the size of
the struct for all identifiers. Given this facility will be needed rarely,
it seemed better to add a second hash map, which is handled PCH-wise the
same as the current one in gcc/stringpool.cc. This hash map associates a new
struct cpp_hashnode_extra with each identifier that needs one. Currently
that struct only contains the new location_t, but it could be extended in
the future if there is other ancillary data that may be convenient to put
there for other purposes.

libcpp/ChangeLog:

	PR preprocessor/36887
	* directives.cc (do_pragma_poison): Store in the extra hash map the
	location from which an identifier has been poisoned.
	* lex.cc (identifier_diagnostics_on_lex): When issuing a diagnostic
	for the use of a poisoned identifier, also add a note indicating the
	location from which it was poisoned.
	* identifiers.cc (alloc_node): Convert to template function.
	(_cpp_init_hashtable): Handle the new extra hash map.
	(_cpp_destroy_hashtable): Likewise.
	* include/cpplib.h (struct cpp_hashnode_extra): New struct.
	(cpp_create_reader): Update prototype to...
	* init.cc (cpp_create_reader): ...accept an argument for the extra
	hash table and pass it to _cpp_init_hashtable.
	* include/symtab.h (ht_lookup): New overload for convenience.
	* internal.h (struct cpp_reader): Add EXTRA_HASH_TABLE member.
	(_cpp_init_hashtable): Adjust prototype.

gcc/c-family/ChangeLog:

	PR preprocessor/36887
	* c-opts.cc (c_common_init_options): Pass new extra hash map
	argument to cpp_create_reader().

gcc/ChangeLog:

	PR preprocessor/36887
	* toplev.h (ident_hash_extra): Declare...
	* stringpool.cc (ident_hash_extra): ...this new global variable.
	(init_stringpool): Handle ident_hash_extra as well as ident_hash.
	(ggc_mark_stringpool): Likewise.
	(ggc_purge_stringpool): Likewise.
	(struct string_pool_data_extra): New struct.
	(spd2): New GC root variable.
	(gt_pch_save_stringpool): Use spd2 to handle ident_hash_extra,
	analogous to how spd is used to handle ident_hash.
	(gt_pch_restore_stringpool): Likewise.

gcc/testsuite/ChangeLog:

	PR preprocessor/36887
	* c-c++-common/cpp/diagnostic-poison.c: New test.
	* g++.dg/pch/pr36887.C: New test.
	* g++.dg/pch/pr36887.Hs: New test.
This commit is contained in:
Lewis Hyatt 2023-09-07 17:02:47 -04:00
parent 02aa322c8c
commit cb05acdcea
13 changed files with 135 additions and 28 deletions
Download patch file Download diff file Expand all files Collapse all files

21
libcpp/include/cpplib.h
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@ -1009,6 +1009,14 @@ struct GTY(()) cpp_hashnode {
union _cpp_hashnode_value GTY ((desc ("%1.type"))) value;
};
/* Extra information we may need to store per identifier, which is needed rarely
enough that it's not worth adding directly into the main identifier hash. */
struct GTY(()) cpp_hashnode_extra
{
struct ht_identifier ident;
location_t poisoned_loc;
};
/* A class for iterating through the source locations within a
string token (before escapes are interpreted, and before
concatenation). */
@ -1055,12 +1063,15 @@ class cpp_substring_ranges
/* Call this first to get a handle to pass to other functions.
If you want cpplib to manage its own hashtable, pass in a NULL
pointer. Otherwise you should pass in an initialized hash table
that cpplib will share; this technique is used by the C front
ends. */
The first hash table argument is for associating a struct cpp_hashnode
with each identifier. The second hash table argument is for associating
a struct cpp_hashnode_extra with each identifier that needs one. For
either, pass in a NULL pointer if you want cpplib to create and manage
the hash table itself, or else pass a suitably initialized hash table to
be managed external to libcpp, as is done by the C-family frontends. */
extern cpp_reader *cpp_create_reader (enum c_lang, struct ht *,
class line_maps *);
class line_maps *,
struct ht * = nullptr);
/* Reset the cpp_reader's line_map. This is only used after reading a
PCH file. */