go/expect: rewrite the expectation parser

The expectation langauge is LL(1) but the scanner does not support true
lookahead
This change adds a true LL(1) token stream and rewrites the parser in terms of
it.
Also clean up the error handling and use the behaviour to fix all the broken
edge cases, and then change the tests to cover the now correct behaviour.

Change-Id: If3d602cda490ed2f4732efce400eb8eabce8a8ec
Reviewed-on: https://go-review.googlesource.com/c/151998
Run-TryBot: Ian Cottrell <iancottrell@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

go/expect/extract.go

@@ -73,153 +73,191 @@ func Extract(fset *token.FileSet, file *ast.File) ([]*Note, error) {
 	return notes, nil
 }
 
+const invalidToken rune = 0
+
+type tokens struct {
+	scanner scanner.Scanner
+	current rune
+	err     error
+	base    token.Pos
+}
+
+func (t *tokens) Init(base token.Pos, text string) *tokens {
+	t.base = base
+	t.scanner.Init(strings.NewReader(text))
+	t.scanner.Mode = scanner.GoTokens
+	t.scanner.Whitespace ^= 1 << '\n' // don't skip new lines
+	t.scanner.Error = func(s *scanner.Scanner, msg string) {
+		t.Errorf("%v", msg)
+	}
+	return t
+}
+
+func (t *tokens) Consume() string {
+	t.current = invalidToken
+	return t.scanner.TokenText()
+}
+
+func (t *tokens) Token() rune {
+	if t.err != nil {
+		return scanner.EOF
+	}
+	if t.current == invalidToken {
+		t.current = t.scanner.Scan()
+	}
+	return t.current
+}
+
+func (t *tokens) Skip(r rune) int {
+	i := 0
+	for t.Token() == '\n' {
+		t.Consume()
+		i++
+	}
+	return i
+}
+
+func (t *tokens) TokenString() string {
+	return scanner.TokenString(t.Token())
+}
+
+func (t *tokens) Pos() token.Pos {
+	return t.base + token.Pos(t.scanner.Position.Offset)
+}
+
+func (t *tokens) Errorf(msg string, args ...interface{}) {
+	if t.err != nil {
+		return
+	}
+	t.err = fmt.Errorf(msg, args...)
+}
+
 func parse(fset *token.FileSet, base token.Pos, text string) ([]*Note, error) {
-	var scanErr error
-	s := new(scanner.Scanner).Init(strings.NewReader(text))
-	s.Mode = scanner.GoTokens
-	s.Whitespace ^= 1 << '\n' // don't skip new lines
-	s.Error = func(s *scanner.Scanner, msg string) {
-		scanErr = fmt.Errorf("%v:%s", fset.Position(base+token.Pos(s.Position.Offset)), msg)
-	}
-	notes, err := parseComment(s)
-	if err != nil {
-		return nil, fmt.Errorf("%v:%s", fset.Position(base+token.Pos(s.Position.Offset)), err)
-	}
-	if scanErr != nil {
-		return nil, scanErr
-	}
-	for _, n := range notes {
-		n.Pos += base
+	t := new(tokens).Init(base, text)
+	notes := parseComment(t)
+	if t.err != nil {
+		return nil, fmt.Errorf("%v:%s", fset.Position(t.Pos()), t.err)
 	}
 	return notes, nil
 }
 
-func parseComment(s *scanner.Scanner) ([]*Note, error) {
+func parseComment(t *tokens) []*Note {
 	var notes []*Note
 	for {
-		n, err := parseNote(s)
-		if err != nil {
-			return nil, err
-		}
-		var tok rune = scanner.EOF
-		if n != nil {
-			notes = append(notes, n)
-			tok = s.Scan()
-		}
-		switch tok {
-		case ',', '\n':
-			// continue
+		t.Skip('\n')
+		switch t.Token() {
 		case scanner.EOF:
-			return notes, nil
+			return notes
+		case scanner.Ident:
+			notes = append(notes, parseNote(t))
 		default:
-			return nil, fmt.Errorf("unexpected %s parsing comment", scanner.TokenString(tok))
+			t.Errorf("unexpected %s parsing comment, expect identifier", t.TokenString())
+			return nil
+		}
+		switch t.Token() {
+		case scanner.EOF:
+			return notes
+		case ',', '\n':
+			t.Consume()
+		default:
+			t.Errorf("unexpected %s parsing comment, expect separator", t.TokenString())
+			return nil
 		}
 	}
 }
 
-func parseNote(s *scanner.Scanner) (*Note, error) {
-	tok := s.Scan()
-	if tok == scanner.EOF || tok == '\n' {
-		return nil, nil
-	}
-	if tok != scanner.Ident {
-		return nil, fmt.Errorf("expected identifier, got %s", scanner.TokenString(tok))
-	}
+func parseNote(t *tokens) *Note {
 	n := &Note{
-		Pos:  token.Pos(s.Position.Offset),
-		Name: s.TokenText(),
+		Pos:  t.Pos(),
+		Name: t.Consume(),
 	}
-	switch s.Peek() {
+
+	switch t.Token() {
 	case ',', '\n', scanner.EOF:
 		// no argument list present
-		return n, nil
+		return n
 	case '(':
-		s.Scan() // consume the '('
-		for s.Peek() == '\n' {
-			s.Scan() // consume all '\n'
-		}
-		// special case the empty argument list
-		if s.Peek() == ')' {
-			s.Scan()                 // consume the ')'
-			n.Args = []interface{}{} // @name() is represented by a non-nil empty slice.
-			return n, nil
-		}
-		// handle a normal argument list
-		for {
-			arg, err := parseArgument(s)
-			if err != nil {
-				return nil, err
-			}
-			n.Args = append(n.Args, arg)
-			switch s.Peek() {
-			case ')':
-				s.Scan() // consume the ')'
-				return n, nil
-			case ',':
-				s.Scan() // consume the ','
-				for s.Peek() == '\n' {
-					s.Scan() // consume all '\n'
-				}
-			default:
-				return nil, fmt.Errorf("unexpected %s parsing argument list", scanner.TokenString(s.Scan()))
-			}
-		}
+		n.Args = parseArgumentList(t)
+		return n
 	default:
-		return nil, fmt.Errorf("unexpected %s parsing note", scanner.TokenString(s.Scan()))
+		t.Errorf("unexpected %s parsing note", t.TokenString())
+		return nil
 	}
 }
 
-func parseArgument(s *scanner.Scanner) (interface{}, error) {
-	tok := s.Scan()
-	switch tok {
+func parseArgumentList(t *tokens) []interface{} {
+	args := []interface{}{} // @name() is represented by a non-nil empty slice.
+	t.Consume()             // '('
+	t.Skip('\n')
+	for t.Token() != ')' {
+		args = append(args, parseArgument(t))
+		if t.Token() != ',' {
+			break
+		}
+		t.Consume()
+		t.Skip('\n')
+	}
+	if t.Token() != ')' {
+		t.Errorf("unexpected %s parsing argument list", t.TokenString())
+		return nil
+	}
+	t.Consume() // ')'
+	return args
+}
+
+func parseArgument(t *tokens) interface{} {
+	switch t.Token() {
 	case scanner.Ident:
-		v := s.TokenText()
+		v := t.Consume()
 		switch v {
 		case "true":
-			return true, nil
+			return true
 		case "false":
-			return false, nil
+			return false
 		case "nil":
-			return nil, nil
+			return nil
 		case "re":
-			tok := s.Scan()
-			switch tok {
-			case scanner.String, scanner.RawString:
-				pattern, _ := strconv.Unquote(s.TokenText()) // can't fail
-				re, err := regexp.Compile(pattern)
-				if err != nil {
-					return nil, fmt.Errorf("invalid regular expression %s: %v", pattern, err)
-				}
-				return re, nil
-			default:
-				return nil, fmt.Errorf("re must be followed by string, got %s", scanner.TokenString(tok))
+			if t.Token() != scanner.String && t.Token() != scanner.RawString {
+				t.Errorf("re must be followed by string, got %s", t.TokenString())
+				return nil
 			}
+			pattern, _ := strconv.Unquote(t.Consume()) // can't fail
+			re, err := regexp.Compile(pattern)
+			if err != nil {
+				t.Errorf("invalid regular expression %s: %v", pattern, err)
+				return nil
+			}
+			return re
 		default:
-			return Identifier(v), nil
+			return Identifier(v)
 		}
 
 	case scanner.String, scanner.RawString:
-		v, _ := strconv.Unquote(s.TokenText()) // can't fail
-		return v, nil
+		v, _ := strconv.Unquote(t.Consume()) // can't fail
+		return v
 
 	case scanner.Int:
-		v, err := strconv.ParseInt(s.TokenText(), 0, 0)
+		s := t.Consume()
+		v, err := strconv.ParseInt(s, 0, 0)
 		if err != nil {
-			return nil, fmt.Errorf("cannot convert %v to int: %v", s.TokenText(), err)
+			t.Errorf("cannot convert %v to int: %v", s, err)
 		}
-		return v, nil
+		return v
 
 	case scanner.Float:
-		v, err := strconv.ParseFloat(s.TokenText(), 64)
+		s := t.Consume()
+		v, err := strconv.ParseFloat(s, 64)
 		if err != nil {
-			return nil, fmt.Errorf("cannot convert %v to float: %v", s.TokenText(), err)
+			t.Errorf("cannot convert %v to float: %v", s, err)
 		}
-		return v, nil
+		return v
 
 	case scanner.Char:
-		return nil, fmt.Errorf("unexpected char literal %s", s.TokenText())
+		t.Errorf("unexpected char literal %s", t.Consume())
+		return nil
 
 	default:
-		return nil, fmt.Errorf("unexpected %s parsing argument", scanner.TokenString(tok))
+		t.Errorf("unexpected %s parsing argument", t.TokenString())
+		return nil
 	}
 }

go/expect/testdata/test.go

@@ -25,6 +25,13 @@ func someFunc(a, b int) int {
 }
 
 // And some extra checks for interesting action parameters
-//@check(αSimpleMarker)
-//@check(StringAndInt, "Number %d", 12)
-//@check(Bool, true)
+// Also checks for multi-line expectations
+/*@
+check(αSimpleMarker)
+check(StringAndInt,
+	"Number %d",
+	12,
+)
+
+check(Bool, true)
+*/