go/scanner: align line and column limit with the compiler's limit

The compiler disallows line and column numbers > (1<<30)
(cmd/compiler/internal/syntax.PosMax).

Set the go/scanner limit to the same rather than off by one.

For #59180

Change-Id: Ibf9e0e6826d6f6230b0d492543b7e906298a0524
Reviewed-on: https://go-review.googlesource.com/c/go/+/482595
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Damien Neil <dneil@google.com>

src/cmd/compile/internal/syntax/pos.go

@@ -8,6 +8,8 @@ import "fmt"
 
 // PosMax is the largest line or column value that can be represented without loss.
 // Incoming values (arguments) larger than PosMax will be set to PosMax.
+//
+// Keep this consistent with maxLineCol in go/scanner.
 const PosMax = 1 << 30
 
 // A Pos represents an absolute (line, col) source position

src/go/scanner/scanner.go

@@ -255,7 +255,8 @@ func (s *Scanner) updateLineInfo(next, offs int, text []byte) {
 
 	// Put a cap on the maximum size of line and column numbers.
 	// 30 bits allows for some additional space before wrapping an int32.
-	const maxLineCol = 1<<30 - 1
+	// Keep this consistent with cmd/compile/internal/syntax.PosMax.
+	const maxLineCol = 1 << 30
 	var line, col int
 	i2, n2, ok2 := trailingDigits(text[:i-1])
 	if ok2 {