Fix var() fallback color minification context in unparsed values

Preserve parsing context when reading var() fallbacks inside unparsed property token lists, so color-ident minification respects function-level whitelisting instead of being reapplied as top-level parsing.

e.g.

Added/updated regression tests in test_custom_properties covering:
non-whitelisted function: foo(var(--c, blue)) should keep blue,

Author: yisibl

src/lib.rs

@@ -23389,6 +23389,23 @@ mod tests {
       ".foo { color: var(--color, rgb(var(--red), var(--green), 0)); }",
       ".foo{color:var(--color,rgb(var(--red), var(--green), 0))}",
     );
+    // 非白名单内的函数颜色值保持原状
+    minify_test(
+      ".foo{background: foo(var(--c, blue))}",
+      ".foo{background:foo(var(--c,blue))}",
+    );
+    minify_test(
+      ".foo2{background: linear-gradient(foo(var(--c, blue)), red)}",
+      ".foo2{background:linear-gradient(foo(var(--c,blue)), red)}",
+    );
+    minify_test(
+      ".foo3{background: linear-gradient(var(--c, blue),red)}",
+      ".foo3{background:linear-gradient(var(--c,#00f),red)}",
+    );
+    minify_test(
+      ".foo4{--x: 90px; background: linear-gradient(red var(--x, white), blue)}",
+      ".foo4{--x:90px;background:linear-gradient(red var(--x,#fff), #00f)}",
+    );
 
     // 非 color 相关的属性颜色值保持原状
     minify_test(

src/properties/custom.rs

@@ -446,7 +446,7 @@ impl<'i> TokenList<'i> {
             tokens.push(TokenOrValue::Url(Url::parse(input)?));
           } else if f == "var" {
             let var = input.parse_nested_block(|input| {
-              let var = Variable::parse(input, options, depth + 1, parse_options.color_ident_mode)?;
+              let var = Variable::parse(input, options, depth + 1, parse_options)?;
               Ok(TokenOrValue::Var(var))
             })?;
             tokens.push(var);
@@ -1351,17 +1351,12 @@ impl<'i> Variable<'i> {
     input: &mut Parser<'i, 't>,
     options: &ParserOptions<'_, 'i>,
     depth: usize,
-    color_ident_mode: ColorIdentMode,
+    parse_options: TokenListParseOptions,
   ) -> Result<Self, ParseError<'i, ParserError<'i>>> {
     let name = DashedIdentReference::parse_with_options(input, options)?;
 
     let fallback = if input.try_parse(|input| input.expect_comma()).is_ok() {
-      Some(TokenList::parse_with_color_idents(
-        input,
-        options,
-        depth,
-        color_ident_mode,
-      )?)
+      Some(TokenList::read_token_list(input, options, depth, parse_options)?)
     } else {
       None
     };