blib.pm dont shell out to "cmd.exe" on Win32+Win32.pm

-document Internals::getcwd() enough, with scary warnings, for future
 core devs, or CPAN devs.  A permanent reason for Internals::getcwd() to
 exist on Win32 full perl was found. See code comments.
-optimize a bit the built-in perl core cwd() XSUBs, use TARG, and group
 stack manipulation together for C compiler variable liveness reasons aka
 less variables to save in non-vol regs or on C stack around function
 calls.

dist/PathTools/Cwd.pm

@@ -3,7 +3,7 @@ use strict;
 use Exporter;
 
 
-our $VERSION = '3.92';
+our $VERSION = '3.93';
 my $xs_version = $VERSION;
 $VERSION =~ tr/_//d;
 

dist/PathTools/Cwd.xs

@@ -302,6 +302,7 @@ int Perl_getcwd_sv(pTHX_ SV *sv)
 	/* Some getcwd()s automatically allocate a buffer of the given
 	 * size from the heap if they are given a NULL buffer pointer.
 	 * The problem is that this behaviour is not portable. */
+	/* XXX bug use PerlEnv_get_childdir/PerlEnv_free_childenv all OSes? */
 	if (getcwd(buf, sizeof(buf) - 1)) {
 	    STRLEN len = strlen(buf);
 	    sv_setpvn(sv, buf, len);

lib/Internals.pod

@@ -57,6 +57,22 @@ to implement higher-level behavior which should be used instead.
 See the core implementation for the exact meaning of the readonly flag for
 each internal variable type.
 
+=item Internals::getcwd()
+
+Internally core maintained version of L<Cwd::getcwd()|Cwd/getcwd> or
+L<Win32::GetCwd()|Win32/Win32::GetCwd()>. Only for use if loading L<Cwd::|Cwd> or
+calling C<Win32::GetCwd()> and its C<AUTOLOAD> to L<Win32.pm|Win32> will
+somehow break a TAP test in a C<.t>.
+
+Not defined on all platforms and all perl build flag configs.  May not set
+C<PWD> env var.  May disappear at any time.  Probe for the sub's existance
+before calling it and write C<if>/C<else> if C<Internals::getcwd> is
+unavailable.  Although this would be a bug, there is no guarentee it will
+return the same identical string as L<Cwd::getcwd()|Cwd/getcwd> or
+L<Win32::GetCwd()|Win32/Win32::GetCwd()>.  The public implementations can get patched
+in the future for some future discovered bug while this sub keeps the buggy
+return value.
+
 =item hv_clear_placeholders(%hash)
 
 Clear any placeholders from a locked hash. Should not be used directly.

lib/blib.pm

@@ -39,7 +39,7 @@ Nick Ing-Simmons [email protected]
 use Cwd;
 use File::Spec;
 
-our $VERSION = '1.07';
+our $VERSION = '1.08';
 our $Verbose = 0;
 
 sub import
@@ -52,7 +52,11 @@ sub import
      # That means that it would not be possible to run `make test`
      # for the Win32 module because blib.pm would always load the
      # installed version before @INC gets updated with the blib path.
-     chomp($dir = `cd`);
+     if(defined &Internals::getcwd) {
+       $dir = Internals::getcwd();
+     } else {
+       chomp($dir = `cd`);
+     }
  }
  else {
      $dir = getcwd;

pod/perldelta.pod

@@ -123,11 +123,13 @@ XXX Remove this section if F<Porting/corelist-perldelta.pl> did not add any cont
 
 =over 4
 
-=item *
-
-L<XXX> has been upgraded from version A.xx to B.yy.
+=item blib.pm
 
-XXX If there was something important to note about this change, include that here.
+C<blib.pm> was updated from 1.07 to 1.08. Previously when L<Win32.pm|Win32>,
+and only that module, the C<cwd()> was obtained through inefficiently
+shelling out to a new C<cmd.exe>, this was fixed and the C<cwd> when using
+C<blib.pm> and L<Win32.pm|Win32> is obtained with a fast same-process API
+function call the way C<Win32::GetCwd()> and C<Cwd::> do it.
 
 =back
 
@@ -346,9 +348,12 @@ well.
 
 =over 4
 
-=item *
+=item Internals::getcwd() is documented as very limited platform availability
 
-XXX
+C<Internals::getcwd()> is documented as experimental, unsupported, not-bug-free
+and removeable in the future, and very limited availability on random
+platforms and perl core build flags. Basically C<Win32> only, and only for
+esoteric C<.t> TAP situations and esoteric internal core reasons.
 
 =back
 

universal.c

@@ -1136,16 +1136,17 @@ XS(XS_re_regexp_pattern)
 XS(XS_Internals_getcwd)
 {
     dXSARGS;
-    SV *sv = sv_newmortal();
-
     if (items != 0)
         croak_xs_usage(cv, "");
+    EXTEND(SP,1);
+    dXSTARG;
+    PUSHs(TARG);
+    PUTBACK;
 
-    (void)getcwd_sv(sv);
+    (void)getcwd_sv(TARG);
 
-    SvTAINTED_on(sv);
-    PUSHs(sv);
-    XSRETURN(1);
+    SvTAINTED_on(TARG);
+    SvSETMAGIC(TARG);
 }
 
 #endif
@@ -1314,6 +1315,10 @@ struct xsub_details {
     int ix;
 };
 
+#ifdef WIN32
+    XS_EXTERNAL(w32_GetCwd);
+#endif
+
 static const struct xsub_details these_details[] = {
     {"UNIVERSAL::isa", XS_UNIVERSAL_isa, NULL, 0 },
     {"UNIVERSAL::can", XS_UNIVERSAL_can, NULL, 0 },
@@ -1344,6 +1349,11 @@ static const struct xsub_details these_details[] = {
     {"re::regexp_pattern", XS_re_regexp_pattern, "$", 0 },
 #if defined(HAS_GETCWD) && defined(PERL_IS_MINIPERL)
     {"Internals::getcwd", XS_Internals_getcwd, "", 0 },
+#elif defined(WIN32)
+    /* Always offer backup, Win32CORE.c vs AUTOLOAD vs Win32.pm
+       vs Win32.dll vs loading a .pm or .dll at all, has rare dep/recursion
+       problems in certain modules or .t files. See w32_GetCwd() . */
+    {"Internals::getcwd", w32_GetCwd, "", 0 },
 #endif
     {"Tie::Hash::NamedCapture::_tie_it", XS_NamedCapture_tie_it, NULL, 0 },
     {"Tie::Hash::NamedCapture::TIEHASH", XS_NamedCapture_TIEHASH, NULL, 0 },

util.c

@@ -4124,6 +4124,7 @@ Perl_getcwd_sv(pTHX_ SV *sv)
         /* Some getcwd()s automatically allocate a buffer of the given
          * size from the heap if they are given a NULL buffer pointer.
          * The problem is that this behaviour is not portable. */
+        /* XXX bug use PerlEnv_get_childdir/PerlEnv_free_childenv all OSes? */
         if (getcwd(buf, sizeof(buf) - 1)) {
             sv_setpv(sv, buf);
             return TRUE;

win32/win32.c

@@ -5016,12 +5016,17 @@ XS(w32_SetChildShowWindow)
 }
 
 
-#ifdef PERL_IS_MINIPERL
-/* shelling out is much slower, full perl uses Win32.pm */
-XS(w32_GetCwd)
+
+/* Shelling out is much slower, full perl uses Win32.pm.
+   So for miniperl install "Win32::GetCwd", and for mini and full perl
+   install this as "Internals::getcwd". On Win32 platform, because of
+   Win32CORE.c AUTOLOAD vs DynaLoader.pm vs Win32.pm, race and recursion
+   and dependency problems can happen in rare cases. For example, see blib.pm
+   Offer Internals::getcwd as a backup at all times. */
+XS_EXTERNAL(w32_GetCwd)
 {
-    dXSARGS;
-    PERL_UNUSED_VAR(items);
+
+    SV *sv;
     /* Make the host for current directory */
     char* ptr = PerlEnv_get_childdir();
     /*
@@ -5030,20 +5035,28 @@ XS(w32_GetCwd)
      *   else return 'undef'
      */
     if (ptr) {
-        SV *sv = sv_newmortal();
+        dXSTARG;
+        sv = TARG;
         sv_setpv(sv, ptr);
         PerlEnv_free_childdir(ptr);
 
 #ifndef INCOMPLETE_TAINTS
         SvTAINTED_on(sv);
 #endif
-
-        ST(0) = sv;
-        XSRETURN(1);
+        SvSETMAGIC(sv);
     }
-    XSRETURN_UNDEF;
+    else {
+      sv = &PL_sv_undef;
+    }
+    {
+      dXSARGS;
+      PERL_UNUSED_VAR(items);
+      XSprePUSH;
+      XPUSHs(sv);
+      PUTBACK;
+    }
+    return;
 }
-#endif
 
 void
 Perl_init_os_extras(void)