Fix 'printf -v varname %B' overwriting/truncating data

Reproducer:

    typeset  -b foo
    read -N8 foo <<<abcdefghijklmnop
    printf -v got '%s / %B\n' "$foo" foo
    print -rn "$got"

Expected output:

    YWJjZGVmZ2g= / abcdefgh

Actual output:

    YWJjZGVm

Thanks to @JohnoKing for finding the cause, which is a conflicting
use of sh.strbuf2 by the code handling the %B format specifier.

The many formatting specifiers to printf involve code paths into
various parts of the shell, some of which use both sh.strbuf and
sh.strbuf2, so neither of those are safe to use here.

src/cmd/ksh93/bltins/print.c: b_print():
- To avoid the possibility of any conflict, use a dedicated locally
  scoped Sfio string buffer instead of sh.strbuf2.

Resolves: #608

NEWS

@@ -2,6 +2,11 @@ This documents significant changes in the dev branch of ksh 93u+m.
 For full details, see the git log at: https://github.com/ksh93/ksh
 Uppercase BUG_* IDs are shell bug IDs as used by the Modernish shell library.
 
+2023-03-29:
+
+- Fixed a bug in 'printf -v' (added on 2021-11-18) where using the %B format
+  specifier would overwrite any data already written to the variable.
+
 2023-03-26:
 
 - Fixed an intermittent crash in 'command -x' experienced on some arm/arm64

src/cmd/ksh93/bltins/print.c

@@ -307,9 +307,10 @@ int    b_print(int argc, char *argv[], Shbltin_t *context)
 		argv++;
 	if(vname)
 	{
-		if(!sh.strbuf2)
-			sh.strbuf2 = sfstropen();
-		outfile = sh.strbuf2;
+		static Sfio_t *vbuf;
+		if(!vbuf)
+			vbuf = sfstropen();
+		outfile = vbuf;
 		goto printf_v;
 	}
 skip2:

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	"1.1.0-alpha"	/* semantic version number: https://semver.org */
-#define SH_RELEASE_DATE	"2023-03-26"	/* must be in this format for $((.sh.version)) */
+#define SH_RELEASE_DATE	"2023-03-29"	/* must be in this format for $((.sh.version)) */
 #define SH_RELEASE_CPYR	"(c) 2020-2023 Contributors to ksh " SH_RELEASE_FORK
 
 /* Scripts sometimes field-split ${.sh.version}, so don't change amount of whitespace. */

src/cmd/ksh93/tests/builtins.sh

@@ -1655,5 +1655,19 @@ got=$(set +x; { "$SHELL" -c 'read -rd $'\''\200'\'' && echo "$REPLY"';} 2>&1 <<<
 	"(expected status 0, '$exp';" \
 	"got status $e$( ((e>128)) && print -n /SIG && kill -l "$e"), $(printf %q "$got"))"
 
+# ======
+# printf -v varname %B overwrites/truncates data
+# https://github.com/ksh93/ksh/issues/608
+exp='YWJjZGVmZ2g= / abcdefgh'
+got=$(
+	typeset  -b foo
+	read -N8 foo <<<abcdefghijklmnop &&
+	printf -v got '%s / %B\n' "$foo" foo &&
+	print -rn "$got"
+)
+[[ e=$? -eq 0 && $got == "$exp" ]] || err_exit "read -N8 && printf -v %B" \
+	"(expected status 0, '$exp';" \
+	"got status $e$( ((e>128)) && print -n /SIG && kill -l "$e"), $(printf %q "$got"))"
+
 # ======
 exit $((Errors<125?Errors:125))