Change fmt to preserve width, flags, and
precision, and change the logic of
fmt[v]print appropriately.  That
__fmtdispatch discards the flags of the
Fmt structure it receives, is broken
behaviour.  I see no present code in
sources that relies on this behaviour,
and I have been running my Plan 9 boxes
with these changes for a while (having
rebuilt the whole source tree and
kernel).  Moreover, the Go compilers
[568]g rely on the preservation of
flags.

Reference: /n/sources/patch/applied/fmt-preserve
Date: Tue Apr 24 23:02:34 CES 2012
Signed-off-by: akumar@mail.nanosouffle.net

--- /sys/src/libc/fmt/fmt.c	Tue Apr 24 22:19:21 2012
+++ /sys/src/libc/fmt/fmt.c	Tue Apr 24 22:19:18 2012
@@ -124,7 +124,13 @@
 _fmtdispatch(Fmt *f, void *fmt, int isrunes)
 {
 	Rune rune, r;
-	int i, n;
+	int i, n, w, p;
+	ulong fl;
+	void *ret;
+
+	w = f->width;
+	p = f->prec;
+	fl = f->flags;
 
 	f->flags = 0;
 	f->width = f->prec = 0;
@@ -140,7 +146,8 @@
 		f->r = r;
 		switch(r){
 		case '\0':
-			return nil;
+			ret = nil;
+			goto end;
 		case '.':
 			f->flags |= FmtWidth|FmtPrec;
 			continue;
@@ -194,9 +201,18 @@
 			goto numflag;
 		}
 		n = (*fmtfmt(r))(f);
-		if(n < 0)
-			return nil;
-		if(n == 0)
-			return fmt;
+		if(n < 0){
+			ret = nil;
+			break;
+		}
+		if(n == 0){
+			ret = fmt;
+			break;
+		}
 	}
+end:
+	f->width = w;
+	f->prec = p;
+	f->flags = fl;
+	return ret;
 }
--- /sys/src/libc/fmt/fmtprint.c	Tue Apr 24 22:19:25 2012
+++ /sys/src/libc/fmt/fmtprint.c	Tue Apr 24 22:19:22 2012
@@ -5,8 +5,7 @@
 
 /*
  * format a string into the output buffer
- * designed for formats which themselves call fmt,
- * but ignore any width flags
+ * designed for formats which themselves call fmt
  */
 int
 fmtprint(Fmt *f, char *fmt, ...)
@@ -14,19 +13,9 @@
 	va_list va;
 	int n;
 
-	f->flags = 0;
-	f->width = 0;
-	f->prec = 0;
-	va = f->args;
-	va_start(f->args, fmt);
-	n = dofmt(f, fmt);
-	va_end(f->args);
-	f->flags = 0;
-	f->width = 0;
-	f->prec = 0;
-	f->args = va;
-	if(n >= 0)
-		return 0;
+	va_start(va, fmt);
+	n = fmtvprint(f, fmt, va);
+	va_end(va);
 	return n;
 }
 
--- /sys/src/libc/fmt/fmtvprint.c	Tue Apr 24 22:19:29 2012
+++ /sys/src/libc/fmt/fmtvprint.c	Tue Apr 24 22:19:26 2012
@@ -5,8 +5,7 @@
 
 /*
  * format a string into the output buffer
- * designed for formats which themselves call fmt,
- * but ignore any width flags
+ * designed for formats which themselves call fmt
  */
 int
 fmtvprint(Fmt *f, char *fmt, va_list args)
@@ -14,15 +13,9 @@
 	va_list va;
 	int n;
 
-	f->flags = 0;
-	f->width = 0;
-	f->prec = 0;
 	va = f->args;
 	f->args = args;
 	n = dofmt(f, fmt);
-	f->flags = 0;
-	f->width = 0;
-	f->prec = 0;
 	f->args = va;
 	if(n >= 0)
 		return 0;
--- /sys/src/ape/lib/fmt/fmt.c	Tue Apr 24 22:19:33 2012
+++ /sys/src/ape/lib/fmt/fmt.c	Tue Apr 24 22:19:31 2012
@@ -143,7 +143,13 @@
 __fmtdispatch(Fmt *f, void *fmt, int isrunes)
 {
 	Rune rune, r;
-	int i, n;
+	int i, n, w, p;
+	ulong fl;
+	void *ret;
+
+	w = f->width;
+	p = f->prec;
+	fl = f->flags;
 
 	f->flags = 0;
 	f->width = f->prec = 0;
@@ -159,7 +165,8 @@
 		f->r = r;
 		switch(r){
 		case '\0':
-			return nil;
+			ret = nil;
+			goto end;
 		case '.':
 			f->flags |= FmtWidth|FmtPrec;
 			continue;
@@ -213,9 +220,18 @@
 			goto numflag;
 		}
 		n = (*fmtfmt(r))(f);
-		if(n < 0)
-			return nil;
-		if(n == 0)
-			return fmt;
+		if(n < 0){
+			ret = nil;
+			break;
+		}
+		if(n == 0){
+			ret = fmt;
+			break;
+		}
 	}
+end:
+	f->width = w;
+	f->prec = p;
+	f->flags = fl;
+	return ret;
 }
--- /sys/src/ape/lib/fmt/fmtprint.c	Tue Apr 24 22:19:38 2012
+++ /sys/src/ape/lib/fmt/fmtprint.c	Tue Apr 24 22:19:35 2012
@@ -20,8 +20,7 @@
 
 /*
  * format a string into the output buffer
- * designed for formats which themselves call fmt,
- * but ignore any width flags
+ * designed for formats which themselves call fmt
  */
 int
 fmtprint(Fmt *f, char *fmt, ...)
@@ -29,19 +28,9 @@
 	va_list va;
 	int n;
 
-	f->flags = 0;
-	f->width = 0;
-	f->prec = 0;
-	va = f->args;
 	va_start(f->args, fmt);
-	n = dofmt(f, fmt);
+	n = fmtvprint(f, fmt, va);
 	va_end(f->args);
-	f->flags = 0;
-	f->width = 0;
-	f->prec = 0;
-	f->args = va;
-	if(n >= 0)
-		return 0;
 	return n;
 }
 
--- /sys/src/ape/lib/fmt/fmtvprint.c	Tue Apr 24 22:19:44 2012
+++ /sys/src/ape/lib/fmt/fmtvprint.c	Tue Apr 24 22:19:41 2012
@@ -20,8 +20,7 @@
 
 /*
  * format a string into the output buffer
- * designed for formats which themselves call fmt,
- * but ignore any width flags
+ * designed for formats which themselves call fmt
  */
 int
 fmtvprint(Fmt *f, char *fmt, va_list args)
@@ -29,15 +28,9 @@
 	va_list va;
 	int n;
 
-	f->flags = 0;
-	f->width = 0;
-	f->prec = 0;
 	va = f->args;
 	f->args = args;
 	n = dofmt(f, fmt);
-	f->flags = 0;
-	f->width = 0;
-	f->prec = 0;
 	f->args = va;
 	if(n >= 0)
 		return 0;
--- /sys/man/2/fmtinstall	Tue Apr 24 22:19:48 2012
+++ /sys/man/2/fmtinstall	Tue Apr 24 22:19:46 2012
@@ -266,7 +266,7 @@
 .IR fmtvprint
 may be called to
 help prepare output in custom conversion routines.
-However, these functions clear the width, precision, and flags.
+These functions will preserve width, precision, and flags.
 Both functions return 0 for success and \-1 for failure.
 .PP
 The functions