Revert "fmt: check newline in the end of input"

This change can break real code. There are other newline-related bugs in this code, and fixing them will also break real code. If we're going to break real code, let's fix all the bugs together and just break things once.

This reverts commit 8331f19d.

Change-Id: Ie4b3022f3a305c3e1f78cc208e50beed212608e6
Reviewed-on: https://go-review.googlesource.com/17724Reviewed-by: Rob Pike <r@golang.org>

src/fmt/scan.go

@@ -1108,10 +1108,6 @@ func (s *ss) advance(format string) (i int) {
 			// in the input.
 			inputc := s.getRune()
 			if inputc == eof {
-				if wasNewline {
-					// Newlines are mandatory.
-					return -1
-				}
 				return
 			}
 			if !isSpace(inputc) {
@@ -1152,18 +1148,17 @@ func (s *ss) doScanf(format string, a []interface{}) (numProcessed int, err erro
 	end := len(format) - 1
 	// We process one item per non-trivial format
 	for i := 0; i <= end; {
-		switch w := s.advance(format[i:]); {
-		case w > 0:
+		w := s.advance(format[i:])
+		if w > 0 {
 			i += w
 			continue
-		case w < 0:
-			// Can't advance format. Why not?
-			s.errorString("input does not match format")
 		}
-
-		// Either we have a percent character, or we ran out of input.
-
+		// Either we failed to advance, we have a percent character, or we ran out of input.
 		if format[i] != '%' {
+			// 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
 		}

src/fmt/scan_test.go

@@ -1114,22 +1114,14 @@ func TestScanfNewlineMatchFormat(t *testing.T) {
 		count  int
 		ok     bool
 	}{
-		{"newline in both", "1\n2", "%d\n%d", 2, true},
+		{"newline in both", "1\n2", "%d\n%d\n", 2, true},
 		{"newline in input", "1\n2", "%d %d", 1, false},
-		{"extra newline in format", "1\n2", "%d\n%d\n", 2, false},
-		{"newline-newline in both", "1\n\n2", "%d\n\n%d", 2, true},
-		{"newline-newline in format", "1\n2", "%d\n\n%d", 1, false},
-		{"newline-newline in input", "1\n\n2", "%d\n%d", 1, false},
 		{"space-newline in input", "1 \n2", "%d %d", 1, false},
 		{"newline in format", "1 2", "%d\n%d", 1, false},
 		{"space-newline in format", "1 2", "%d \n%d", 1, false},
 		{"space-newline in both", "1 \n2", "%d \n%d", 2, true},
 		{"extra space in format", "1\n2", "%d\n %d", 2, true},
 		{"two extra spaces in format", "1\n2", "%d \n %d", 2, true},
-		{"newline start in both", "\n1 2", "\n%d %d", 2, true},
-		{"newline start in format", "1 2", "\n%d %d", 0, false},
-		{"newline start in input", "\n1 2", "%d %d", 0, false},
-		{"space-newline start in input", " \n1 2", "\n%d %d", 2, true},
 	}
 	for _, test := range tests {
 		n, err := Sscanf(test.text, test.format, &a, &b)