robotframework: fix empty braces being thrown away after list or dict… (#1921)

* robotframework: fix empty braces being thrown away after list or dict variable

* robotframework: add test cases to ensure correct behaviour

2 files changed, 39 insertions, 1 deletions

diff --git a/pygments/lexers/robotframework.py b/pygments/lexers/robotframework.py
index 305cc26f..3c212f5e 100644
--- a/pygments/lexers/robotframework.py
+++ b/pygments/lexers/robotframework.py
@@ -99,7 +99,7 @@ class VariableTokenizer:
         yield var.identifier + '{', SYNTAX
         yield from self.tokenize(var.base, VARIABLE)
         yield '}', SYNTAX
-        if var.index:
+        if var.index is not None:
             yield '[', SYNTAX
             yield from self.tokenize(var.index, VARIABLE)
             yield ']', SYNTAX
diff --git a/tests/test_robotframework_lexer.py b/tests/test_robotframework_lexer.py
new file mode 100644
index 00000000..d768885f
--- /dev/null
+++ b/tests/test_robotframework_lexer.py
@@ -0,0 +1,38 @@
+"""
+    Pygments Robot Framework lexer tests
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    :copyright: Copyright 2006-2021 by the Pygments team, see AUTHORS.
+    :license: BSD, see LICENSE for details.
+"""
+
+import pytest
+
+from pygments.lexers.robotframework import RobotFrameworkLexer
+
+
+@pytest.fixture(scope='module')
+def lexer():
+    yield RobotFrameworkLexer()
+
+
+def assert_same_text(lexer, text):
+    """Show that lexed text does not remove any content. """
+    tokens = list(lexer.get_tokens_unprocessed(text))
+    output = ''.join(t[2] for t in tokens)
+    assert text == output
+
+
+def test_empty_brackets_after_scalar_variable(lexer):
+    assert_same_text(lexer, '*** Variables ***\n'
+                            '${test}[]\n')
+
+
+def test_empty_brackets_after_list_variable(lexer):
+    assert_same_text(lexer, '*** Variables ***\n'
+                            '@{test}[]\n')
+
+
+def test_empty_brackets_after_dict_variable(lexer):
+    assert_same_text(lexer, '*** Variables ***\n'
+                            '&{test}[]\n')