Gain control of macro namespace visibility

This commit undefines all macros that are visible to XS code but
shouldn't be.  This stops macro namespace pollution by perl.

It works by changing embed.h to have two modes, controlled by a #ifdef
that is set by perl.h.  perl.h now #includes embed.h twice.  The first
time works as it always has.  The second sets the #ifdef, and causes
embed.h to #undef the macros that shouldn't be visible.  This call is
just before perl.h returns to its includer, so that these macros have
come and gone before the file that #included perl.h is affected by them.

The list of macros is determined by the visibility given by the apidoc
lines documenting them, and by painstaking experiments with our test
suite.  Those experiments, and some manual inspection, have produced
three long lists of items beyond what the apidoc lines currently give.

One list is for items that the re extension to Perl requires.

A second list is for items that other Perl extensions require.

The third list is for items that at least one module shipped with perl
requires (or that I know something on CPAN requires) even though the
items aren't marked as being visible.  There are over 700 items on this
list.  And smoking cpan with this will add others.

The experiments were done automatically, and I have not manually done
much manual inspection.

I have wanted this ability to happen for a long time; and now things
have come together to enable it.

This allows us to have a clear-cut boundary with CPAN.

It means you can add macros that have internal-only use without having
to worry about making them likely not to clash with user names.

It shows precisely what our names are that are visible to CPAN, and we
can change some of them to be less likely to clash.

Author: khwilliamson

embed.h

@@ -707,9 +707,6 @@
 #   undef ckWARNexperimental_with_arg
 #   undef ckWARNreg
 #   undef ckWARNregdep
-#   undef CLANG_DIAG_IGNORE_DECL
-#   undef CLANG_DIAG_PRAGMA
-#   undef CLANG_DIAG_RESTORE_DECL
 #   undef classnum_to_namedclass
 #   undef CLEAR_ARGARRAY
 #   undef CLEAR_OPTSTART
@@ -795,8 +792,6 @@
 #   undef cSVOP
 #   undef cSVOP_sv
 #   undef cSVOPx_svp
-#   undef CTIME_LOCK
-#   undef CTIME_UNLOCK
 #   undef Ctl
 #   undef cUNOP
 #   undef cUNOP_AUX
@@ -1573,83 +1568,53 @@
 #   undef get_extended_os_errno
 #   undef GET_REGCLASS_AUX_DATA
 #   undef GETATARGET
-#   undef GETENV_LOCK
-#   undef GETENV_UNLOCK
 #   undef GETGRENT_R_HAS_BUFFER
 #   undef GETGRENT_R_HAS_FPTR
 #   undef GETGRENT_R_HAS_PTR
 #   undef GETGRGID_R_HAS_BUFFER
 #   undef GETGRGID_R_HAS_PTR
 #   undef GETGRNAM_R_HAS_BUFFER
 #   undef GETGRNAM_R_HAS_PTR
-#   undef GETHOSTBYADDR_LOCK
 #   undef GETHOSTBYADDR_R_HAS_BUFFER
 #   undef GETHOSTBYADDR_R_HAS_ERRNO
 #   undef GETHOSTBYADDR_R_HAS_PTR
-#   undef GETHOSTBYADDR_UNLOCK
-#   undef GETHOSTBYNAME_LOCK
 #   undef GETHOSTBYNAME_R_HAS_BUFFER
 #   undef GETHOSTBYNAME_R_HAS_ERRNO
 #   undef GETHOSTBYNAME_R_HAS_PTR
-#   undef GETHOSTBYNAME_UNLOCK
 #   undef GETHOSTENT_R_HAS_BUFFER
 #   undef GETHOSTENT_R_HAS_ERRNO
 #   undef GETHOSTENT_R_HAS_PTR
-#   undef GETNETBYADDR_LOCK
 #   undef GETNETBYADDR_R_HAS_BUFFER
 #   undef GETNETBYADDR_R_HAS_ERRNO
 #   undef GETNETBYADDR_R_HAS_PTR
-#   undef GETNETBYADDR_UNLOCK
-#   undef GETNETBYNAME_LOCK
 #   undef GETNETBYNAME_R_HAS_BUFFER
 #   undef GETNETBYNAME_R_HAS_ERRNO
 #   undef GETNETBYNAME_R_HAS_PTR
-#   undef GETNETBYNAME_UNLOCK
 #   undef GETNETENT_R_HAS_BUFFER
 #   undef GETNETENT_R_HAS_ERRNO
 #   undef GETNETENT_R_HAS_PTR
-#   undef GETPROTOBYNAME_LOCK
 #   undef GETPROTOBYNAME_R_HAS_BUFFER
 #   undef GETPROTOBYNAME_R_HAS_PTR
-#   undef GETPROTOBYNAME_UNLOCK
-#   undef GETPROTOBYNUMBER_LOCK
 #   undef GETPROTOBYNUMBER_R_HAS_BUFFER
 #   undef GETPROTOBYNUMBER_R_HAS_PTR
-#   undef GETPROTOBYNUMBER_UNLOCK
-#   undef GETPROTOENT_LOCK
 #   undef GETPROTOENT_R_HAS_BUFFER
 #   undef GETPROTOENT_R_HAS_PTR
-#   undef GETPROTOENT_UNLOCK
 #   undef GETPWENT_R_HAS_BUFFER
 #   undef GETPWENT_R_HAS_FPTR
 #   undef GETPWENT_R_HAS_PTR
-#   undef GETPWNAM_LOCK
 #   undef GETPWNAM_R_HAS_BUFFER
 #   undef GETPWNAM_R_HAS_PTR
-#   undef GETPWNAM_UNLOCK
-#   undef GETPWUID_LOCK
 #   undef GETPWUID_R_HAS_PTR
-#   undef GETPWUID_UNLOCK
-#   undef GETSERVBYNAME_LOCK
 #   undef GETSERVBYNAME_R_HAS_BUFFER
 #   undef GETSERVBYNAME_R_HAS_PTR
-#   undef GETSERVBYNAME_UNLOCK
-#   undef GETSERVBYPORT_LOCK
 #   undef GETSERVBYPORT_R_HAS_BUFFER
 #   undef GETSERVBYPORT_R_HAS_PTR
-#   undef GETSERVBYPORT_UNLOCK
-#   undef GETSERVENT_LOCK
 #   undef GETSERVENT_R_HAS_BUFFER
 #   undef GETSERVENT_R_HAS_PTR
-#   undef GETSERVENT_UNLOCK
-#   undef GETSPNAM_LOCK
 #   undef GETSPNAM_R_HAS_BUFFER
 #   undef GETSPNAM_R_HAS_PTR
-#   undef GETSPNAM_UNLOCK
 #   undef GETTARGET
 #   undef GETTARGETSTACKED
-#   undef GMTIME_LOCK
-#   undef GMTIME_UNLOCK
 #   undef GOSUB
 #   undef GOSUB_t8
 #   undef GOSUB_t8_p8
@@ -1727,10 +1692,6 @@
 #   undef GvONCE_FATAL_off
 #   undef GvONCE_FATAL_on
 #   undef GvREFCNT
-#   undef gwLOCALE_LOCK
-#   undef gwLOCALE_UNLOCK
-#   undef gwLOCALEr_LOCK
-#   undef gwLOCALEr_UNLOCK
 #   undef HADNV
 #   undef HAS_BUILTIN_UNREACHABLE
 #   undef HAS_C99
@@ -1791,9 +1752,7 @@
 #   undef HINT_UTF8
 #   undef HINTS_DEFAULT
 #   undef HINTS_REFCNT_INIT
-#   undef HINTS_REFCNT_LOCK
 #   undef HINTS_REFCNT_TERM
-#   undef HINTS_REFCNT_UNLOCK
 #   undef HS_GETAPIVERLEN
 #   undef HS_GETINTERPSIZE
 #   undef HS_GETXSVERLEN
@@ -2022,9 +1981,7 @@
 #   undef KEY_y
 #   undef KEYWORD_PLUGIN_DECLINE
 #   undef KEYWORD_PLUGIN_MUTEX_INIT
-#   undef KEYWORD_PLUGIN_MUTEX_LOCK
 #   undef KEYWORD_PLUGIN_MUTEX_TERM
-#   undef KEYWORD_PLUGIN_MUTEX_UNLOCK
 #   undef kGVOP_gv
 #   undef kLISTOP
 #   undef kLOGOP
@@ -2095,8 +2052,6 @@
 #   undef LOCALE_TERM
 #   undef LOCALE_TERM_POSIX_2008_
 #   undef LOCALE_UNLOCK_
-#   undef LOCALTIME_LOCK
-#   undef LOCALTIME_UNLOCK
 #   undef LOCK_LC_NUMERIC_STANDARD
 #   undef LOGICAL
 #   undef LOGICAL_t8
@@ -2531,8 +2486,6 @@
 #   undef PoisonPADLIST
 #   undef POPpconstx
 #   undef POSIX_CC_COUNT
-#   undef POSIX_SETLOCALE_LOCK
-#   undef POSIX_SETLOCALE_UNLOCK
 #   undef POSIXA
 #   undef POSIXA_t8
 #   undef POSIXA_t8_p8
@@ -3074,8 +3027,6 @@
 #   undef S_iv_add_may_overflow
 #   undef S_iv_mul_may_overflow
 #   undef S_iv_sub_may_overflow
-#   undef S_IWOTH
-#   undef S_IXOTH
 #   undef S_PAT_MODS
 #   undef S_uv_add_overflow
 #   undef S_uv_mul_overflow
@@ -3329,8 +3280,6 @@
 #   undef STAR_tb_p8
 #   undef STAR_tb_pb
 #   undef StashHANDLER
-#   undef STATIC_ASSERT_STRUCT_BODY_
-#   undef STATIC_ASSERT_STRUCT_NAME_
 #   undef STATUS_ALL_FAILURE
 #   undef STATUS_ALL_SUCCESS
 #   undef STATUS_EXIT_SET
@@ -3344,10 +3293,6 @@
 #   undef STR_LENl
 #   undef STR_LENs
 #   undef STR_SZ
-#   undef STRFMON_LOCK
-#   undef STRFMON_UNLOCK
-#   undef STRFTIME_LOCK
-#   undef STRFTIME_UNLOCK
 #   undef STRING
 #   undef STRINGl
 #   undef STRINGs
@@ -3651,7 +3596,6 @@
 #   undef UNLESSM_tb_pb
 #   undef UNLINK
 #   undef UNLOCK_LC_NUMERIC_STANDARD
-#   undef UNOP_AUX_item_sv
 #   undef UPDATE_WARNINGS_LOC
 #   undef UPG_VERSION
 #   undef uproot_SV
@@ -3852,8 +3796,6 @@
 #   undef WIN32SCK_IS_STDSCK
 #   undef with_t_UTF8ness
 #   undef with_tp_UTF8ness
-#   undef WSETLOCALE_LOCK
-#   undef WSETLOCALE_UNLOCK
 #   undef xI
 #   undef xI_offset
 #   undef xio_any
@@ -3885,6 +3827,8 @@
 #     undef AMGf_unary
 #     undef ASCTIME_LOCK
 #     undef ASCTIME_UNLOCK
+#     undef av_tindex_skip_len_mg
+#     undef av_top_index_skip_len_mg
 #     undef BhkENTRY
 #     undef BHKf_bhk_eval
 #     undef BHKf_bhk_post_end
@@ -3914,10 +3858,6 @@
 #     undef CHANGE_MULTICALL_FLAGS
 #     undef CHECK_AND_WARN_PROBLEMATIC_LOCALE_
 #     undef ckDEAD
-#     undef CLANG_DIAG_IGNORE
-#     undef CLANG_DIAG_IGNORE_STMT
-#     undef CLANG_DIAG_RESTORE
-#     undef CLANG_DIAG_RESTORE_STMT
 #     undef cLISTOPo
 #     undef cLISTOPx
 #     undef cLOGOPo
@@ -4017,7 +3957,6 @@
 #     undef ENV_UNLOCK
 #     undef ENVr_LOCALEr_LOCK
 #     undef ENVr_LOCALEr_UNLOCK
-#     undef ESC_NATIVE
 #     undef EVAL_INEVAL
 #     undef EVAL_INREQUIRE
 #     undef EVAL_KEEPERR
@@ -4137,8 +4076,6 @@
 #     undef LvTARGOFF
 #     undef LvTYPE
 #     undef MAX_UNICODE_UTF8_BYTES
-#     undef MBRLEN_LOCK_
-#     undef MBRLEN_UNLOCK_
 #     undef MDEREF_ACTION_MASK
 #     undef MDEREF_AV_gvav_aelem
 #     undef MDEREF_AV_gvsv_vivify_rv2av_aelem
@@ -4530,8 +4467,6 @@
 #     undef UTF_START_MASK
 #     undef want_vtbl_bm
 #     undef want_vtbl_fm
-#     undef WCRTOMB_LOCK_
-#     undef WCRTOMB_UNLOCK_
 #     undef xlv_targoff
 #     undef XOPf_xop_dump
 #     undef XOPf_xop_peep

perl.h

@@ -9349,6 +9349,16 @@ END_EXTERN_C
 
 */
 
+START_EXTERN_C
+
+/* #including a second time causes it to #undef any unwanted symbols to avoid
+ * polluting the user name space */
+#  define PERL_DO_UNDEFS
+#  include "embed.h"
+#  undef PERL_DO_UNDEFS
+
+END_EXTERN_C
+
 #endif /* Include guard */
 
 /*