parser: add line number and column to syntax errors

main.go

@@ -2722,19 +2722,36 @@ func (p *parser) advanceOffset(delta int) {
 
 // syntaxError represents a synax error in the Pushup template language.
 type syntaxError struct {
+	// err is the underlying error that caused this syntax error
 	err error
+	// lineNo and column are the positions in the source code where the
+	// error occurred
+	lineNo int
+	column int
 }
 
 func (e syntaxError) Error() string {
-	return e.err.Error()
+	// TODO(paulsmith): add source file name
+	return fmt.Sprintf("%d:%d: %s", e.lineNo, e.column, e.err.Error())
 }
 
 // errorf signals that a syntax error in the Pushup template language has been
 // detected. The Pushup parser uses panic mode error handling, so a function
 // calling the parser higher up in the call stack can recover from the panic
 // and test for a syntax error (syntaxError type).
 func (p *parser) errorf(format string, args ...any) {
-	panic(syntaxError{fmt.Errorf(format, args...)})
+	offset := p.offset
+	if offset >= len(p.src) {
+		offset = len(p.src) - 1
+	}
+	upToErr := p.src[:offset]
+	lineNo := strings.Count(upToErr, "\n") + 1
+	lastNL := strings.LastIndex(upToErr, "\n")
+	column := p.offset + 1
+	if lastNL > -1 {
+		column = p.offset - lastNL
+	}
+	panic(syntaxError{fmt.Errorf(format, args...), lineNo, column})
 }
 
 // htmlParser is the Pushup HTML parser. It wraps the golang.org/x/net/html

main_test.go

@@ -930,8 +930,16 @@ func TestParse(t *testing.T) {
 func TestParseSyntaxErrors(t *testing.T) {
 	tests := []struct {
 		input string
+		// expected error conditions
+		lineNo int
+		column int
 	}{
-		{"^if"},
+		{"^if", 1, 4},
+		{
+			`^if true {
+	<illegal />
+}`, 2, 13,
+		},
 		// FIXME(paulsmith): add more syntax errors
 	}
 
@@ -944,6 +952,13 @@ func TestParseSyntaxErrors(t *testing.T) {
 			if err == nil {
 				t.Errorf("expected parse error, got nil")
 			}
+			serr, ok := err.(syntaxError)
+			if !ok {
+				t.Errorf("expected syntax error type, got %T", err)
+			}
+			if tt.lineNo != serr.lineNo || tt.column != serr.column {
+				t.Errorf("line:column: want %d:%d, got %d:%d", tt.lineNo, tt.column, serr.lineNo, serr.column)
+			}
 		})
 	}
 }