Add helper function dupwcscat().

The wide-string version of dupcat(), with an identical wrapper macro
to automatically append a correctly typed NULL.

misc.h

@@ -29,6 +29,8 @@ char *dupstr(const char *s);
 wchar_t *dupwcs(const wchar_t *s);
 char *dupcat_fn(const char *s1, ...);
 #define dupcat(...) dupcat_fn(__VA_ARGS__, (const char *)NULL)
+wchar_t *dupwcscat_fn(const wchar_t *s1, ...);
+#define dupwcscat(...) dupwcscat_fn(__VA_ARGS__, (const wchar_t *)NULL)
 char *dupprintf(const char *fmt, ...) PRINTF_LIKE(1, 2);
 char *dupvprintf(const char *fmt, va_list ap);
 void burnstr(char *string);

utils/CMakeLists.txt

@@ -29,6 +29,7 @@ add_sources_from_current_dir(utils
   dupprintf.c
   dupstr.c
   dupwcs.c
+  dupwcscat.c
   dup_mb_to_wc.c
   dup_wc_to_mb.c
   encode_utf8.c

utils/dupwcscat.c

@@ -0,0 +1,48 @@
+/*
+ * Implementation function behind dupwcscat() in misc.h.
+ *
+ * This function is called with an arbitrary number of 'const wchar_t
+ * *' parameters, of which the last one is a null pointer. The wrapper
+ * macro puts on the null pointer itself, so normally callers don't
+ * have to.
+ */
+
+#include <stdarg.h>
+#include <wchar.h>
+
+#include "defs.h"
+#include "misc.h"
+
+wchar_t *dupwcscat_fn(const wchar_t *s1, ...)
+{
+    int len;
+    wchar_t *p, *q, *sn;
+    va_list ap;
+
+    len = wcslen(s1);
+    va_start(ap, s1);
+    while (1) {
+        sn = va_arg(ap, wchar_t *);
+        if (!sn)
+            break;
+        len += wcslen(sn);
+    }
+    va_end(ap);
+
+    p = snewn(len + 1, wchar_t);
+    wcscpy(p, s1);
+    q = p + wcslen(p);
+
+    va_start(ap, s1);
+    while (1) {
+        sn = va_arg(ap, wchar_t *);
+        if (!sn)
+            break;
+        wcscpy(q, sn);
+        q += wcslen(q);
+    }
+    va_end(ap);
+
+    return p;
+}
+