regen/embed.pl: Handle m with p flags

Prior to this commit these were illegal.

This causes embed.fnc to generate macro 'Perl_foo' #defined to be  macro
'foo'.  If the macro name is all upper case, we instead get macro
'PERL_FOO' for 'FOO'.  This could be used to easily convert existing
macros into having long names should some become a name space pollution
problem.

This also documents in embed.fnc, under the 'm' flag discussion, how to
use this instead of placing things in mathoms.c, or creating stub
functions.

autodoc.pl

@@ -1878,7 +1878,11 @@ ($fh, $section_name, $element_name, $docref)
                     || $needs_Perl_entry
                     || $cant_use_short_name)
                 {
-                    $name = "Perl_$name";
+                    # An all uppercase macro name gets an uppercase prefix.
+                    my $perl = ($flags =~ /m/ && $name !~ /[[:lower:]]/)
+                               ? "PERL_"
+                               : "Perl_";
+                    $name = "$perl$name";
 
                     # We can't hide the existence of any thread context
                     # parameter when using the "Perl_" long form.  So it must

embed.fnc

@@ -14,7 +14,8 @@
 : real (full) name, with any appropriate thread context paramaters, thus hiding
 : that detail from the typical code.
 :
-: Most macros (as opposed to functions) listed here are the complete full name.
+: Many macros (as opposed to functions) listed here are the complete full name,
+: though we may want to start converting those to have full names.
 :
 : All non-static functions defined by perl need to be listed in this file.
 : embed.pl uses the entries here to construct:
@@ -157,8 +158,9 @@
 : and you know at a glance that the macro actually has documentation.  It
 : doesn't by itself create any documentation; instead the other apidoc lines
 : pull in information specified by these lines.  Many of the lines in this
-: file for macros could be pulled out of here and replaced by these lines
-: throughout the source.  It is a goal to do that as convenience dictates.
+: file for macros that don't also have the 'p' flag (described below) could be
+: pulled out of here and replaced by these lines throughout the source.  It is
+: a goal to do that as convenience dictates.
 :
 : The other apidoc lines either have the usage data as part of the line, or
 : pull in the data from this file or apidoc_defn lines.
@@ -210,10 +212,10 @@
 : line that begins with an '='.  In particular, an '=cut' line ends that
 : documentation without introducing something new.
 :
-: Various macros and other elements aren't listed here in embed.fnc.  They are
-: documented in the same manner, but since they don't have this file to get
-: information from, the defining lines have the syntax and meaning they do in
-: this file, so it can be specified:
+: Various macros and other elements aren't listed here in embed.fnc (though
+: they could be).  They are documented in the same manner, but since they don't
+: have this file to get information from, the defining lines have the syntax
+: and meaning they do in this file, so it can be specified:
 :
 :   =for apidoc flags|return_type|name|arg1|arg2|...|argN
 :   =for apidoc_item flags|return_type|name|arg1|arg2|...|argN
@@ -301,14 +303,13 @@
 :        functions flagged with this, the installation can run Configure with
 :        the -Accflags='-DNO_MATHOMS' parameter to not even compile them.
 :
-:        Sometimes the function has been subsumed by a more general one (say,
-:        by adding a flags parameter), and a macro exists with the original
-:        short name API, and it calls the new function, bypassing this one, and
-:        the original 'Perl_' form is being deprecated. In this case also
-:        specify the 'M' flag.
+:        If the function can be implemented as a macro (that evaluates its
+:        arguments exactly once), use the 'm' and 'p' flags together to implement
+:        this.  (See the discussion under 'm'.)  Another option for this is to
+:        use the 'M' flag.
 :
-:        Without the M flag, these functions should be deprecated, and it is an
-:        error to not also specify the 'D' flag.
+:        Without the m or M flags, these functions should be deprecated, and it
+:        is an error to not also specify the 'D' flag.
 :
 :        The 'b' functions are normally moved to mathoms.c, but if
 :        circumstances dictate otherwise, they can be anywhere, provided the
@@ -439,24 +440,50 @@
 :                  __attribute__always_inline__ is added
 :
 :   'm'  Implemented as a macro; there is no function associated with this
-:        name, and hence no long Perl_ or S_ name. However, if the macro name
-:        itself begins with 'Perl_', autodoc.pl will show a thread context
-:        parameter unless the 'T' flag is specified.
+:        name.  There is no long S_ name.
+:
+:        However, you may #define the macro with a long name like 'Perl_foo',
+:        and specify the 'p' flag.  This will cause an embed.h entry to be
+:        created that #defines 'foo' as 'Perl_foo'.  This can be used to make
+:        any macro have a long name, perhaps to avoid name collisions.  If
+:        instead you define the macro as 'PERL_FOO' (all uppercase), the
+:        embed.h entry will use all uppercase.
+:
+:	 It is particularly useful tp preserve backward compatibility when a
+:	 function is converted to be a macro (remembering to not create a macro
+:	 which evaluates its parameters more than once).  Most of mathoms.c
+:	 could be converted to use this facility.  When there is no thread
+:	 context involved, you just do something like
+:
+:           #define Perl_foo(a, b, c)  Perl_bar(a, b, 0, c)
+:
+:        Otherwise consider this general case where there is a series of macros
+:        that build on the previous ones by calling something with a different
+:        name or with an extra parameter beyond what the previous one did:
+:
+:           #define Perl_foo(mTHX, a)         Perl_bar1(aTHX, a)
+:           #define Perl_bar1(mTHX, a)        Perl_bar2(aTHX, a, 0)
+:           #define Perl_bar2(mTHX, a, b)     Perl_bar3(aTHX, a, b, 0)
+:           #define Perl_bar3(mTHX, a, b, c)  Perl_func(aTHX_ a, b, c, 0)
+:
+:        Use the formal parameter name 'mTHX,' (which stands for "macro thread
+:        context") as the first in each macro definition, and call the next
+:        macro in the sequence with 'aTHX,' (Note the commas).  Eventually, the
+:        sequence will end with a function call (or else there would be no need
+:        for thread context).  For that instead call it with 'aTHX_' (with an
+:        underscore instead of a comma).
 :
 :         suppress proto.h entry (actually, not suppressed, but commented out)
 :         suppress entry in the list of exported symbols available on all
 :             platforms
-:         suppress embed.h entry, as the implementation should furnish the macro
+:         suppress embed.h entry (when no 'p' flag), as the implementation
+:             should furnish the macro
 :
 :   'M'  The implementation is furnishing its own macro instead of relying on
 :        the automatically generated short name macro (which simply expands to
 :        call the real name function). One reason to do this is if the
-:        parameters need to be cast from what the caller has, or if there is a
-:        macro that bypasses this function (whose long name is being retained
-:        for backward compatibility for those who call it with that name). An
-:        example is when a new function is created with an extra parameter and
-:        a wrapper macro is added that has the old API, but calls the new one
-:        with the exta parameter set to a default.
+:        parameters need to be cast from what the caller has.  There is less
+:        need to do this now that 'm' and 'p' together is supported.
 :
 :        This flag requires the 'p' flag to be specified, as there would be no
 :        need to do this if the function weren't publicly accessible before.
@@ -492,8 +519,8 @@
 :
 :        This is used for whatever reason to force the function to be called
 :        with the long name.  Perhaps there is a varargs issue.  Use the 'M'
-:        flag instead for wrapper macros, and legacy-only functions should
-:        also use 'b'.
+:        or 'm' flags instead for wrapper macros, and legacy-only functions
+:        should also use 'b'.
 :
 :          embed.h: suppress "#define foo Perl_foo"
 :
@@ -518,9 +545,10 @@
 :
 :          proto.h: add __attribute__pure__
 :
-:   'p'  Function in source code has a Perl_ prefix:
+:   'p'  Function or macro in source code has a Perl_ prefix:
 :
-:          proto.h: function is declared as Perl_foo rather than foo
+:          proto.h: function or macro is declared as Perl_foo rather than foo
+:                   (though the entries for macros will be commented out)
 :          embed.h: "#define foo Perl_foo" entries added
 :
 :   'R'  Return value must not be ignored (also implied by 'a' and 'P' flags):

mathoms.c

@@ -22,15 +22,15 @@
 /*
  * This file contains mathoms, various binary artifacts from previous
  * versions of Perl which we cannot completely remove from the core
- * code. There are two reasons functions should be here:
+ * code. There is only one reason these days for functions should be here:
  *
  * 1) A function has been replaced by a macro within a minor release,
  *    so XS modules compiled against an older release will expect to
  *    still be able to link against the function
- * 2) A function Perl_foo(...) with #define foo Perl_foo(aTHX_ ...)
- *    has been replaced by a macro, e.g. #define foo(...) foo_flags(...,0)
- *    but XS code may still explicitly use the long form, i.e.
- *    Perl_foo(aTHX_ ...)
+ *
+ * It used to be that this was the way to handle the case were a function
+ * Perl_foo(...) had been replaced by a macro.  But see the 'm' flag discussion
+ * in embed.fnc for a better way to handle this.
  *
  * This file can't just be cleaned out periodically, because that would break
  * builds with -DPERL_NO_SHORT_NAMES

regen/embed.pl

@@ -49,7 +49,14 @@ ($$)
                      # prefixes 'S_' or 'Perl_'
     my ($func, $flags) = @_;
 
-    return "Perl_$func" if $flags =~ /[ps]/;
+    if ($flags =~ /[ps]/) {
+
+	# An all uppercase macro name gets an uppercase prefix.
+	return ($flags =~ /m/ && $flags =~ /p/ && $func !~ /[[:lower:]]/)
+	       ? "PERL_$func"
+	       : "Perl_$func";
+    }
+
     return "S_$func" if $flags =~ /[SIi]/;
     return $func;
 }
@@ -141,10 +148,6 @@ sub generate_proto_h {
 	    if ($flags =~ /S/) {
 		die_at_end "$plain_func: m and S flags are mutually exclusive";
 	    }
-	    elsif ($flags =~ /p/ && $has_context) {
-		die_at_end "$plain_func: m flag with p flag currently requires"
-		         . " T flag";
-	    }
 	}
 	else {
 	    die_at_end "$plain_func: u flag only usable with m" if $flags =~ /u/;
@@ -509,7 +512,7 @@ sub embed_h {
         my $inner_ind= $ind ? "  " : " ";
         if ($flags !~ /[omM]/ or ($flags =~ /m/ && $flags =~ /p/)) {
             my $argc = scalar @$args;
-            if ($flags =~ /[Tm]/) {
+            if ($flags =~ /[T]/) {
                 my $full_name = full_name($func, $flags);
                 next if $full_name eq $func;    # Don't output a no-op.
                 $ret = indent_define($func, $full_name, $ind);
@@ -532,8 +535,11 @@ sub embed_h {
                     $use_va_list ? ("__VA_ARGS__") : ());
                 $ret = "#${ind}define $func($paramlist) ";
                 add_indent($ret,full_name($func, $flags) . "(aTHX");
-                $ret .= "_ " if $replacelist;
-                $ret .= $replacelist;
+		if ($replacelist) {
+                    $ret .= ($flags =~ /m/) ? "," : "_ ";
+                    $ret .= $replacelist;
+                }
+
                 if ($flags =~ /W/) {
                     if ($replacelist) {
                         $ret .= " comma_aDEPTH";