In wc, replace mbrtowc() with new utf8towc() which doesn't have a context struct

or care about locale.

lib/lib.h

@@ -257,6 +257,7 @@ void linestack_addstack(struct linestack **lls, struct linestack *throw,
 void linestack_insert(struct linestack **lls, long pos, char *line, long len);
 void linestack_append(struct linestack **lls, char *line);
 struct linestack *linestack_load(char *name);
+int utf8towc(wchar_t *wc, char *str, unsigned len);
 int crunch_escape(FILE *out, int cols, int wc);
 int crunch_rev_escape(FILE *out, int cols, int wc);
 int crunch_str(char **str, int width, FILE *out, char *escmore,

lib/linestack.c

@@ -80,6 +80,37 @@ struct linestack *linestack_load(char *name)
   return ls;
 }
 
+// Convert utf8 sequence to a unicode wide character
+int utf8towc(wchar_t *wc, char *str, unsigned len)
+{
+  unsigned result, mask, first;
+  char *s, c;
+
+  // fast path ASCII
+  if (len && *str<128) return !!(*wc = *str);
+
+  result = first = *(s = str++);
+  for (mask = 6; (first&0xc0)==0xc0; mask += 5, first <<= 1) {
+    if (!--len) return -2;
+    c = *(str++);
+    if ((c&0xc0) != 0x80) return -1;
+    result = (result<<6)|(c&0x3f);
+  }
+  result &= (1<<mask)-1;
+  c = str-s;
+  if (mask==6 || mask>21) return -1;
+
+  // Avoid overlong encodings
+  if (mask==6 || mask>21 || result<(unsigned []){0x80,0x800,0x10000}[c-2])
+    return -1;
+
+  // Limit unicode so it can't encode anything UTF-16 can't.
+  if (result>0x10ffff || (result>=0xd800 && result<=0xdfff)) return -1;
+  *wc = result;
+
+  return str-s;
+}
+
 // Show width many columns, negative means from right edge, out=0 just measure
 // if escout, send it unprintable chars, otherwise pass through raw data.
 // Returns width in columns, moves *str to end of data consumed.

toys/posix/wc.c

@@ -80,6 +80,7 @@ static void do_wc(int fd, char *name)
 
           // next wide size, don't count invalid, fetch more data if necessary
           clen = mbrtowc(&wchar, toybuf+pos, len-pos, 0);
+          clen = utf8towc(&wchar, toybuf+pos, len-pos);
           if (clen == -1) continue;
           if (clen == -2 && !done) break;