fmt.Scanf: improve error message when input does not match format

R=rsc
CC=golang-dev
https://golang.org/cl/1693043

diff --git a/src/pkg/fmt/scan.go b/src/pkg/fmt/scan.go
index 883a95d34ac3128acd169ec01798a28b35398001..87076e8fc91f90612d7a4d9f6284ca569df11c18 100644 (file)
--- a/src/pkg/fmt/scan.go
+++ b/src/pkg/fmt/scan.go
@@ -885,6 +885,7 @@ func (s *ss) doScan(a []interface{}) (numProcessed int, err os.Error) {
 // either input or format behave as a single space. This routine also
 // handles the %% case.  If the return value is zero, either format
 // starts with a % (with no following %) or the input is empty.
+// If it is negative, the input did not match the string.
 func (s *ss) advance(format string) (i int) {
        for i < len(format) {
                fmtc, w := utf8.DecodeRuneInString(format[i:])
@@ -919,7 +920,7 @@ func (s *ss) advance(format string) (i int) {
                inputc := s.mustGetRune()
                if fmtc != inputc {
                        s.UngetRune(inputc)
-                       return
+                       return -1
                }
                i += w
        }
@@ -940,10 +941,11 @@ func (s *ss) doScanf(format string, a []interface{}) (numProcessed int, err os.E
                }
                // Either we failed to advance, we have a percent character, or we ran out of input.
                if format[i] != '%' {
-                       // Can't advance format.  Do we have arguments still to process?
-                       if i < len(a) {
-                               s.errorString("too many arguments for format")
+                       // Can't advance format.  Why not?
+                       if w < 0 {
+                               s.errorString("input does not match format")
                        }
+                       // Otherwise at EOF; "too many operands" error handled below
                        break
                }
                i++ // % is one byte

diff --git a/src/pkg/fmt/scan_test.go b/src/pkg/fmt/scan_test.go
index d316f2e4a339701c3d8116dd28ff024a570a2192..f195c0317c95da48dc1c336bb67883d8db911e7d 100644 (file)
--- a/src/pkg/fmt/scan_test.go
+++ b/src/pkg/fmt/scan_test.go
@@ -303,6 +303,7 @@ var multiTests = []ScanfMultiTest{
        ScanfMultiTest{"%d %d %d", "23 18", args(&i, &j), args(23, 18), "too few operands"},
        ScanfMultiTest{"%d %d", "23 18 27", args(&i, &j, &k), args(23, 18), "too many operands"},
        ScanfMultiTest{"%c", "\u0100", args(&int8Val), nil, "overflow"},
+       ScanfMultiTest{"X%d", "10X", args(&intVal), nil, "input does not match format"},
 
        // Bad UTF-8: should see every byte.
        ScanfMultiTest{"%c%c%c", "\xc2X\xc2", args(&i, &j, &k), args(utf8.RuneError, 'X', utf8.RuneError), ""},