Add some basic continue-after-error handling

Updates #24

parser/parser.go

@@ -59,14 +59,28 @@ func (p *parser) tabularExpr() (*TabularExpr, error) {
 	}
 
 	var returnedError error
-	for {
+	for i := 0; ; i++ {
 		pipeToken, ok := p.next()
 		if !ok {
 			break
 		}
 		if pipeToken.Kind != TokenPipe {
 			p.prev()
-			break
+			if i == 0 {
+				returnedError = joinErrors(returnedError, &parseError{
+					source: p.source,
+					span:   pipeToken.Span,
+					err:    errors.New("unknown syntax after table data source"),
+				})
+			} else {
+				returnedError = joinErrors(returnedError, &parseError{
+					source: p.source,
+					span:   pipeToken.Span,
+					err:    errors.New("unknown syntax after operator"),
+				})
+			}
+			p.skipTo(TokenPipe)
+			continue
 		}
 
 		operatorName, ok := p.next()
@@ -76,16 +90,17 @@ func (p *parser) tabularExpr() (*TabularExpr, error) {
 				span:   pipeToken.Span,
 				err:    errors.New("missing operator name after pipe"),
 			})
-			return expr, returnedError
+			p.skipTo(TokenPipe)
+			continue
 		}
 		if operatorName.Kind != TokenIdentifier {
-			// TODO(soon): Skip ahead to next pipe.
 			returnedError = joinErrors(returnedError, &parseError{
 				source: p.source,
 				span:   operatorName.Span,
 				err:    fmt.Errorf("expected operator name, got %s", formatToken(p.source, operatorName)),
 			})
-			return expr, returnedError
+			p.skipTo(TokenPipe)
+			continue
 		}
 		switch operatorName.Value {
 		case "count":
@@ -101,13 +116,12 @@ func (p *parser) tabularExpr() (*TabularExpr, error) {
 			}
 			returnedError = joinErrors(returnedError, err)
 		default:
-			// TODO(soon): Skip ahead to next pipe.
 			returnedError = joinErrors(returnedError, &parseError{
 				source: p.source,
 				span:   operatorName.Span,
 				err:    fmt.Errorf("unknown operator name %q", operatorName.Value),
 			})
-			return expr, returnedError
+			p.skipTo(TokenPipe)
 		}
 	}
 	return expr, returnedError
@@ -308,8 +322,43 @@ func (p *parser) ident() (*Ident, error) {
 	}, nil
 }
 
+// skipTo advances the parser to right before the next token of the given kind.
+// It ignores tokens that are in parenthetical groups after the initial parse position.
+// If no such token is found, skipTo advances to EOF.
+func (p *parser) skipTo(search TokenKind) {
+	parenLevel := 0
+	for {
+		tok, ok := p.next()
+		if !ok {
+			return
+		}
+
+		switch tok.Kind {
+		case TokenLParen:
+			if search == TokenLParen {
+				p.prev()
+				return
+			}
+			parenLevel++
+		case TokenRParen:
+			if parenLevel > 0 {
+				parenLevel--
+			} else if search == TokenRParen {
+				p.prev()
+				return
+			}
+		case search:
+			if parenLevel <= 0 {
+				p.prev()
+				return
+			}
+		}
+	}
+}
+
 func (p *parser) next() (Token, bool) {
 	if p.pos >= len(p.tokens) {
+		p.pos = len(p.tokens) + 1 // Once we produce EOF, don't permit rewinding.
 		return Token{
 			Kind:  TokenError,
 			Span:  indexSpan(len(p.source)),
@@ -322,7 +371,11 @@ func (p *parser) next() (Token, bool) {
 }
 
 func (p *parser) prev() {
-	p.pos--
+	// Only allow rewinding to a previous token if it's in valid range,
+	// and once we produce EOF, we will always produce EOF.
+	if p.pos > 0 && p.pos <= len(p.tokens) {
+		p.pos--
+	}
 }
 
 func formatToken(source string, tok Token) string {

parser/parser_test.go

@@ -11,7 +11,13 @@ func TestParse(t *testing.T) {
 	tests := []struct {
 		query string
 		want  *TabularExpr
+		err   bool
 	}{
+		{
+			query: "",
+			want:  nil,
+			err:   true,
+		},
 		{
 			query: "StormEvents",
 			want: &TabularExpr{
@@ -201,12 +207,44 @@ func TestParse(t *testing.T) {
 				},
 			},
 		},
+		{
+			query: `StormEvents | count x | where true`,
+			err:   true,
+			want: &TabularExpr{
+				Source: &TableRef{
+					Table: &Ident{
+						Name:     "StormEvents",
+						NameSpan: newSpan(0, 11),
+					},
+				},
+				Operators: []TabularOperator{
+					&CountOperator{
+						Pipe:    newSpan(12, 13),
+						Keyword: newSpan(14, 19),
+					},
+					&WhereOperator{
+						Pipe:    newSpan(22, 23),
+						Keyword: newSpan(24, 29),
+						Predicate: &Ident{
+							Name:     "true",
+							NameSpan: newSpan(30, 34),
+						},
+					},
+				},
+			},
+		},
 	}
 	for _, test := range tests {
 		got, err := Parse(test.query)
 		if err != nil {
-			t.Errorf("Parse(%q): %v", test.query, err)
-			continue
+			if test.err {
+				t.Logf("Parse(%q) error (as expected): %v", test.query, err)
+			} else {
+				t.Errorf("Parse(%q) returned unexpected error: %v", test.query, err)
+			}
+		}
+		if err == nil && test.err {
+			t.Errorf("Parse(%q) did not return an error", test.query)
 		}
 		if diff := cmp.Diff(test.want, got, cmpopts.EquateEmpty()); diff != "" {
 			t.Errorf("Parse(%q) (-want +got):\n%s", test.query, diff)