conf.tab: Support //UNC/paths by default on Cygwin

In the Cygwin port for ksh 93u+m/1.0.8, Roland Mainz had patched
astconf(3) to hardcode a value 1 for PATH_LEADING_SLASHES, which
is necessary to enable the built-in support for the double initial
slash used for UNC network paths on Windows.

Previously, enabling this support required manually adding the
value triplet "PATH_LEADING_SLASHES - 1" to the _AST_FEATURES
environment variable, but the documentation for that was so obscure
and indirect it might as well have been undocuemnted (it would
require reading the --man self-doc of the getconf, dirname and
basename path-bound built-ins).

This commit adds a PATH_LEADING_SLASHES entry to conf.tab that will
cause this value to be hardcoded to 1 in the generated conftab.c
file on Cygwin, causing UNC path support to always be enabled on
that system.

NEWS

@@ -2,6 +2,10 @@ This documents significant changes in the 1.0 branch of ksh 93u+m.
 For full details, see the git log at: https://github.com/ksh93/ksh/tree/1.0
 Uppercase BUG_* IDs are shell bug IDs as used by the Modernish shell library.
 
+2024-07-02:
+
+- Support for UNC paths (//server/dir) is now enabled by default on Cygwin.
+
 2024-06-30:
 
 - Fixed: the 'hash' and 'alias -t' commands no longer autoload functions

src/cmd/ksh93/include/version.h

@@ -18,7 +18,7 @@
 
 #define SH_RELEASE_FORK	"93u+m"		/* only change if you develop a new ksh93 fork */
 #define SH_RELEASE_SVER	"1.0.9-beta"	/* semantic version number: https://semver.org */
-#define SH_RELEASE_DATE	"2024-06-30"	/* must be in this format for $((.sh.version)) */
+#define SH_RELEASE_DATE	"2024-07-02"	/* must be in this format for $((.sh.version)) */
 #define SH_RELEASE_CPYR	"(c) 2020-2024 Contributors to ksh " SH_RELEASE_FORK
 
 /* Scripts sometimes field-split ${.sh.version}, so don't change amount of whitespace. */

src/lib/libast/comp/conf.tab

@@ -1,9 +1,9 @@
 #
 # posix { getconf limits } macro table
 #
-# @(#)conf.tab (AT&T Research) 2010-06-28
+# @(#)conf.tab (ksh 93u+m) 2024-07-01
 #
-# name standard section call flags [ header ... ] [ value ... ]
+# name standard call section flags [ header ... ] [ value ... ]
 #
 # name:		sans prefix
 # standard:	AST, C, POSIX, SVID, XOPEN, <vendor> { SCO, SGI, SUN, ... }
@@ -342,6 +342,12 @@ PATH				AST	CS 1 MU		sh{
 	# DEFPATH should have been exported from package(1)
 	echo "\\"$DEFPATH\\""
 }
+PATH_LEADING_SLASHES		AST	CS 1 M		sh{
+	# HOSTTYPE should have been exported from package(1)
+	case $HOSTTYPE in
+	cygwin.*)	echo "\\"1\\"" ;;  # support UNC paths (with two leading slashes)
+	esac
+}
 PATH_MAX			POSIX	PC 1 CDLMUX	MAXPATHLEN 1024
 PBS				POSIX	SC 2 FUW
 PBS_ACCOUNTING			POSIX	SC 2 FUW