!default variables can override if the value is null

src/parse/variable.rs

@@ -41,7 +41,7 @@ impl<'a> Parser<'a> {
         if default {
             let config_val = self.module_config.get(ident);
             if self.at_root && !self.flags.in_control_flow() {
-                if !self.global_scope.var_exists(ident) {
+                if !self.global_scope.default_var_exists(ident) {
                     let value = if let Some(config_val) = config_val {
                         config_val
                     } else {
@@ -57,7 +57,7 @@ impl<'a> Parser<'a> {
                     self.parse_value_from_vec(val_toks, true)?.node
                 };
 
-                if global && !self.global_scope.var_exists(ident) {
+                if global && !self.global_scope.default_var_exists(ident) {
                     self.global_scope.insert_var(ident, value.clone());
                 }
                 self.scopes.insert_default_var(ident, value);

src/scope.rs

@@ -36,6 +36,10 @@ impl Scope {
         }
     }
 
+    fn get_var_no_err(&self, name: Identifier) -> Option<&Value> {
+        self.vars.get(&name)
+    }
+
     pub fn insert_var(&mut self, s: Identifier, v: Value) -> Option<Value> {
         self.vars.insert(s, v)
     }
@@ -83,6 +87,26 @@ impl Scope {
     pub fn merge_module(&mut self, other: Module) {
         self.merge(other.scope);
     }
+
+    pub fn default_var_exists(&mut self, s: Identifier) -> bool {
+        if let Some(default_var) = self.get_var_no_err(s) {
+            if default_var.is_null() {
+                false
+            } else {
+                true
+            }
+        } else {
+            false
+        }
+    }
+
+    pub fn insert_default_var(&mut self, s: Identifier, v: Value) -> Option<Value> {
+        if self.default_var_exists(s) {
+            None
+        } else {
+            self.insert_var(s, v)
+        }
+    }
 }
 
 #[derive(Debug, Default)]
@@ -153,11 +177,7 @@ impl Scopes {
 
     pub fn insert_default_var(&mut self, s: Identifier, v: Value) -> Option<Value> {
         if let Some(scope) = self.0.last_mut() {
-            if scope.var_exists(s) {
+            scope.insert_default_var(s, v)
-                None
-            } else {
-                scope.insert_var(s, v)
-            }
         } else {
             panic!()
         }

tests/meta.rs

@@ -237,6 +237,16 @@ test!(
     "$a: red; a {\n  color: variable-exists('a')\n}\n",
     "a {\n  color: true;\n}\n"
 );
+test!(
+    variable_exists_local_is_null,
+    "a {\n  $a: null; color: variable-exists(a)\n}\n",
+    "a {\n  color: true;\n}\n"
+);
+test!(
+    variable_exists_global_is_null,
+    "$a: null; a {\n  color: variable-exists(a)\n}\n",
+    "a {\n  color: true;\n}\n"
+);
 error!(
     variable_exists_not_string,
     "a {\n  color: variable-exists(12px)\n}\n", "Error: $name: 12px is not a string."

tests/variables.rs

@@ -152,6 +152,36 @@ test!(
     "  /**/  $a  /**/  :  /**/  red  /**/  ;  /**/  ",
     "/**/\n/**/\n"
 );
+test!(
+    default_var_overrides_when_null_declared_global,
+    "$a: null;
+    $a: red !default;
+    
+    a {
+        color: $a;
+    }",
+    "a {\n  color: red;\n}\n"
+);
+test!(
+    default_var_overrides_when_null_declared_local,
+    "a {
+        $a: null;
+        $a: red !default;
+
+        color: $a;
+    }",
+    "a {\n  color: red;\n}\n"
+);
+test!(
+    default_var_overrides_when_null_declared_local_with_global_flags,
+    "a {
+        $a: null !global;
+        $a: red !default !global;
+
+        color: $a;
+    }",
+    "a {\n  color: red;\n}\n"
+);
 // https://github.com/Kixiron/lasso/issues/7
 test!(
     regression_test_for_lasso_0_3_0,