From 382b3083932a0f9068d0327899b98a6209d30184 Mon Sep 17 00:00:00 2001
From: Moritz Neeb <nt4u@kpvn.de>
Date: Sat, 22 Jul 2023 11:48:48 +0200
Subject: [PATCH 1/3] allow empty css variables

fixes #1849

Co-authored-by: @eliasdorneles
---
 src/textual/css/parse.py |  2 ++
 tests/css/test_parse.py  | 16 ++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/src/textual/css/parse.py b/src/textual/css/parse.py
index 13aeea488..a604fed01 100644
--- a/src/textual/css/parse.py
+++ b/src/textual/css/parse.py
@@ -287,6 +287,8 @@ def substitute_references(
                     variables.setdefault(variable_name, []).append(token)
                     yield token
                 elif token.name == "variable_value_end":
+                    # in case of an empty variable, avoid not referenced error
+                    variables.setdefault(variable_name, [])
                     yield token
                     break
                 # For variables referring to other variables
diff --git a/tests/css/test_parse.py b/tests/css/test_parse.py
index fea7b3dad..cb6e6aad0 100644
--- a/tests/css/test_parse.py
+++ b/tests/css/test_parse.py
@@ -220,6 +220,22 @@ class TestVariableReferenceSubstitution:
         with pytest.raises(UnresolvedVariableError):
             list(substitute_references(tokenize(css, "")))
 
+    def test_empty_variable(self):
+        css = "$x:\n* { background:$x; }"
+        result = list(substitute_references(tokenize(css, "")))
+        assert [(t.name, t.value) for t in result] == [
+            ("variable_name", "$x:"),
+            ("variable_value_end", "\n"),
+            ("selector_start_universal", "*"),
+            ("whitespace", " "),
+            ("declaration_set_start", "{"),
+            ("whitespace", " "),
+            ("declaration_name", "background:"),
+            ("declaration_end", ";"),
+            ("whitespace", " "),
+            ("declaration_set_end", "}"),
+        ]
+
     def test_transitive_reference(self):
         css = "$x: 1\n$y: $x\n.thing { border: $y }"
         assert list(substitute_references(tokenize(css, ""))) == [

From 2ab6ca364f3401aacd340fb7409e88954745d291 Mon Sep 17 00:00:00 2001
From: Moritz Neeb <nt4u@kpvn.de>
Date: Sat, 22 Jul 2023 11:54:21 +0200
Subject: [PATCH 2/3] explain change on changelog

---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index bf9a3b79b..ec1c24b51 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Fixed a crash when a `SelectionList` had a prompt wider than itself https://github.com/Textualize/textual/issues/2900
 - Fixed a bug where `Click` events were bubbling up from `Switch` widgets https://github.com/Textualize/textual/issues/2366
+- Fixed a crash when using empty CSS variables https://github.com/Textualize/textual/issues/1849
 
 ## [0.30.0] - 2023-07-17
 

From 7770f8de82b2fc20a31e97f00ef45ce6e3cab682 Mon Sep 17 00:00:00 2001
From: Moritz Neeb <nt4u@kpvn.de>
Date: Sat, 22 Jul 2023 12:24:03 +0200
Subject: [PATCH 3/3] refactor: simplify css variable table creation

---
 src/textual/css/parse.py | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/src/textual/css/parse.py b/src/textual/css/parse.py
index a604fed01..1b31e8b66 100644
--- a/src/textual/css/parse.py
+++ b/src/textual/css/parse.py
@@ -269,6 +269,7 @@ def substitute_references(
             break
         if token.name == "variable_name":
             variable_name = token.value[1:-1]  # Trim the $ and the :, i.e. "$x:" -> "x"
+            variable_tokens = variables.setdefault(variable_name, [])
             yield token
 
             while True:
@@ -284,18 +285,15 @@ def substitute_references(
                 if not token:
                     break
                 elif token.name == "whitespace":
-                    variables.setdefault(variable_name, []).append(token)
+                    variable_tokens.append(token)
                     yield token
                 elif token.name == "variable_value_end":
-                    # in case of an empty variable, avoid not referenced error
-                    variables.setdefault(variable_name, [])
                     yield token
                     break
                 # For variables referring to other variables
                 elif token.name == "variable_ref":
                     ref_name = token.value[1:]
                     if ref_name in variables:
-                        variable_tokens = variables.setdefault(variable_name, [])
                         reference_tokens = variables[ref_name]
                         variable_tokens.extend(reference_tokens)
                         ref_location = token.location
@@ -309,7 +307,7 @@ def substitute_references(
                     else:
                         _unresolved(ref_name, variables.keys(), token)
                 else:
-                    variables.setdefault(variable_name, []).append(token)
+                    variable_tokens.append(token)
                     yield token
                 token = next(iter_tokens, None)
         elif token.name == "variable_ref":