fix nil-deref bug; improve error messages; fix confusing comment in protoprint

desc/protoparse/ast.go

@@ -462,6 +462,12 @@ type fieldNode struct {
 }
 
 func (n *fieldNode) fieldLabel() node {
+	// proto3 fields and fields inside one-ofs will not have a label and we need
+	// this check in order to return a nil node -- otherwise we'd return a
+	// non-nil node that has a nil pointer value in it :/
+	if n.label == nil {
+		return nil
+	}
 	return n.label
 }
 

desc/protoparse/parser.go

@@ -23,6 +23,49 @@ import (
 
 func init() {
 	protoErrorVerbose = true
+
+	// fix up the generated "token name" array so that error messages are nicer
+	setTokenName(_STRING_LIT, "string literal")
+	setTokenName(_INT_LIT, "int literal")
+	setTokenName(_FLOAT_LIT, "float literal")
+	setTokenName(_NAME, "identifier")
+	setTokenName(_FQNAME, "fully-qualified name")
+	setTokenName(_TYPENAME, "type name")
+	setTokenName(_TYPENAME, "error")
+	// for keywords, just show the keyword itself wrapped in quotes
+	for str, i := range keywords {
+		setTokenName(i, fmt.Sprintf(`"%s"`, str))
+	}
+}
+
+func setTokenName(token int, text string) {
+	// NB: this is based on logic in generated parse code that translates the
+	// int returned from the lexer into an internal token number.
+	var intern int
+	if token < len(protoTok1) {
+		intern = protoTok1[token]
+	} else {
+		if token >= protoPrivate {
+			if token < protoPrivate+len(protoTok2) {
+				intern = protoTok2[token-protoPrivate]
+			}
+		}
+		if intern == 0 {
+			for i := 0; i+1 < len(protoTok3); i += 2 {
+				if protoTok3[i] == token {
+					intern = protoTok3[i+1]
+					break
+				}
+			}
+		}
+	}
+
+	if intern >= 1 && intern-1 < len(protoToknames) {
+		protoToknames[intern-1] = text
+		return
+	}
+
+	panic(fmt.Sprintf("Unknown token value: %d", token))
 }
 
 // FileAccessor is an abstraction for opening proto source files. It takes the

desc/protoprint/print.go

@@ -313,7 +313,7 @@ func (p *Printer) printMessageBody(md *desc.MessageDescriptor, mf *dynamic.Messa
 	for i, el := range elements.addrs {
 		d := elements.at(el)
 		// skip[d] will panic if d is a slice (which it could be for []option),
-		// so just ignore since don't try to skip options
+		// so just ignore it since we don't try to skip options
 		if reflect.TypeOf(d).Kind() != reflect.Slice && skip[d] {
 			// skip this element
 			continue