cmd/goyacc: add flags for enabling debug and verbose error messages

Currently, there is no way of enabling debug/verbose error messages
using the goyacc command, despite already having support for them.
This patch adds two flags for enabling both of these during parser
generation.

cmd/goyacc/yacc.go

@@ -159,6 +159,8 @@ var fmtImported bool // output file has recorded an import of "fmt"
 var oflag string  // -o [y.go]		- y.go file
 var vflag string  // -v [y.output]	- y.output file
 var lflag bool    // -l			- disable line directives
+var tflag int     // -t			- set debug message level
+var eflag bool    // -e			- enable verbose error messages
 var prefix string // name prefix for identifiers, default yy
 
 func init() {
@@ -166,6 +168,8 @@ func init() {
 	flag.StringVar(&prefix, "p", "yy", "name prefix to use in generated code")
 	flag.StringVar(&vflag, "v", "y.output", "create parsing tables")
 	flag.BoolVar(&lflag, "l", false, "disable line directives")
+	flag.IntVar(&tflag, "t", 0, "set debug message level")
+	flag.BoolVar(&eflag, "e", false, "enable verbose error messages")
 }
 
 var initialstacksize = 16
@@ -385,6 +389,8 @@ func setup() {
 		usage()
 	}
 	yaccpar = strings.Replace(yaccpartext, "$$", prefix, -1)
+	yaccpar = strings.Replace(yaccpar, "$tflag", strconv.Itoa(tflag), 1)
+	yaccpar = strings.Replace(yaccpar, "$eflag", strconv.FormatBool(eflag), 1)
 	openup()
 
 	fmt.Fprintf(ftable, "// Code generated by goyacc %s. DO NOT EDIT.\n", strings.Join(os.Args[1:], " "))
@@ -3094,7 +3100,7 @@ func chcopy(q string) string {
 }
 
 func usage() {
-	fmt.Fprintf(stderr, "usage: yacc [-o output] [-v parsetable] input\n")
+	fmt.Fprintf(stderr, "usage: yacc [-o output] [-v parsetable] [-p prefix] [-l] [-e] [-t debuglevel] input\n")
 	exit(1)
 }
 
@@ -3265,8 +3271,8 @@ var yaccpartext = `
 /*	parser for yacc output	*/
 
 var (
-	$$Debug        = 0
-	$$ErrorVerbose = false
+	$$Debug        = $tflag
+	$$ErrorVerbose = $eflag
 )
 
 type $$Lexer interface {