whatcanGOwrong

go/pkg/mod/golang.org/x/exp@v0.0.0-20230224173230-c95f2b4c22f2/ebnflint/ebnflint.go

@@ -0,0 +1,122 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"go/scanner"
+	"go/token"
+	"io"
+	"os"
+	"path/filepath"
+
+	"golang.org/x/exp/ebnf"
+)
+
+var fset = token.NewFileSet()
+var start = flag.String("start", "Start", "name of start production")
+
+func usage() {
+	fmt.Fprintf(os.Stderr, "usage: go tool ebnflint [flags] [filename]\n")
+	flag.PrintDefaults()
+	os.Exit(1)
+}
+
+// Markers around EBNF sections in .html files
+var (
+	open  = []byte(`<pre class="ebnf">`)
+	close = []byte(`</pre>`)
+)
+
+func report(err error) {
+	scanner.PrintError(os.Stderr, err)
+	os.Exit(1)
+}
+
+func extractEBNF(src []byte) []byte {
+	var buf bytes.Buffer
+
+	for {
+		// i = beginning of EBNF text
+		i := bytes.Index(src, open)
+		if i < 0 {
+			break // no EBNF found - we are done
+		}
+		i += len(open)
+
+		// write as many newlines as found in the excluded text
+		// to maintain correct line numbers in error messages
+		for _, ch := range src[0:i] {
+			if ch == '\n' {
+				buf.WriteByte('\n')
+			}
+		}
+
+		// j = end of EBNF text (or end of source)
+		j := bytes.Index(src[i:], close) // close marker
+		if j < 0 {
+			j = len(src) - i
+		}
+		j += i
+
+		// copy EBNF text
+		buf.Write(src[i:j])
+
+		// advance
+		src = src[j:]
+	}
+
+	return buf.Bytes()
+}
+
+func main() {
+	flag.Parse()
+
+	var (
+		name string
+		r    io.Reader
+	)
+	switch flag.NArg() {
+	case 0:
+		name, r = "<stdin>", os.Stdin
+	case 1:
+		name = flag.Arg(0)
+	default:
+		usage()
+	}
+
+	if err := verify(name, *start, r); err != nil {
+		report(err)
+	}
+}
+
+func verify(name, start string, r io.Reader) error {
+	if r == nil {
+		f, err := os.Open(name)
+		if err != nil {
+			return err
+		}
+		defer f.Close()
+		r = f
+	}
+
+	src, err := io.ReadAll(r)
+	if err != nil {
+		return err
+	}
+
+	if filepath.Ext(name) == ".html" || bytes.Index(src, open) >= 0 {
+		src = extractEBNF(src)
+	}
+
+	grammar, err := ebnf.Parse(name, bytes.NewBuffer(src))
+	if err != nil {
+		return err
+	}
+
+	return ebnf.Verify(grammar, start)
+}