aux/getflags: improve flagfmt parser

This makes the flagfmt parser more robust and accepting
a looser input language — namely by allowing whitespace
around specifier fields and ignoring any empty fields.

Long flagfmts can thus be pleasingly displayed:

	flagfmt='
		a, b, c, C:cache,
		m:mtpt mountpoint,
		s:srvn srvname'

sys/src/cmd/aux/getflags.c

@@ -9,13 +9,34 @@ usage(void)
 	exits(0);
 }
 
+char*
+skipspace(char *p)
+{
+	while(isspace(*p))
+		p++;
+	return p;
+}
+
+char*
+nextarg(char *p)
+{
+	char *s;
+
+	s = strchr(p, ',');
+	if(s == nil)
+		return p+strlen(p); /* to \0 */
+	while(*s == ',' || isspace(*s))
+		s++;
+	return s;
+}
+
 char*
 findarg(char *flags, Rune r)
 {
 	char *p;
 	Rune rr;
 
-	for(p=flags; p!=(char*)1; p=strchr(p, ',')+1){
+	for(p=skipspace(flags); *p; p=nextarg(p)){
 		chartorune(&rr, p);
 		if(rr == r)
 			return p;
@@ -44,10 +65,9 @@ countargs(char *p)
 	int n;
 
 	n = 1;
-	while(*p == ' ')
-		p++;
-	for(; *p && *p != ','; p++)
-		if(*p == ' ' && *(p-1) != ' ')
+	print("%s\n", p);
+	for(p=skipspace(p); *p && *p != ','; p++)
+		if(isspace(*p) && !isspace(*(p-1)))
 			n++;
 	return n;
 }
@@ -71,7 +91,7 @@ main(int argc, char *argv[])
 	}
 
 	fmtfdinit(&fmt, 1, buf, sizeof buf);
-	for(p=flags; p!=(char*)1 && *p != 0; p=strchr(p, ',')+1){
+	for(p=skipspace(flags); *p; p=nextarg(p)){
 		s = e = nil;
 		if(p[1] == ':'){
 			s = p + 2;

sys/src/cmd/aux/usage.c

@@ -1,5 +1,6 @@
 #include <u.h>
 #include <libc.h>
+#include <ctype.h>
 
 void
 main(void)
@@ -30,9 +31,11 @@ main(void)
 	if(flags[0]){
 		single = 0;
 		for(p=flags; *p; ){
+			while(isspace(*p))
+				p++;
 			p += chartorune(&r, p);
 			if(*p == ':')
-				while(*p != '\0' && *p != ',' && *p != ' ')
+				while(*p && *p != ',' && !isspace(*p))
 					p++;
 			if(*p == ',' || *p == 0){
 				if(!single){
@@ -44,7 +47,7 @@ main(void)
 					p++;
 				continue;
 			}
-			while(*p == ' ')
+			while(isspace(*p))
 				p++;
 			if(single){
 				fmtprint(&fmt, "]");