correctly parse idents starting with interpolation

src/value/parse.rs

@@ -722,11 +722,8 @@ impl Value {
                 })
             }
             '#' => {
-                if let Ok(s) = eat_ident(toks, scope, super_selector) {
-                    IntermediateValue::Value(Spanned {
-                        node: Value::Ident(s.node, QuoteKind::None),
-                        span: s.span,
-                    })
+                if let Ok(s) = Self::ident(toks, scope, super_selector) {
+                    s
                 } else {
                     IntermediateValue::Value(match parse_hex(toks, scope, super_selector, span) {
                         Ok(v) => v,

tests/interpolation.rs

@@ -68,3 +68,8 @@ test!(
     "a {\n  color: \"#{\\\"\\'}\";\n}\n",
     "a {\n  color: \"\\\\\\\"\\\\'\";\n}\n"
 );
+test!(
+    interpolated_plain_css_fn,
+    "$f: foo;\na {\n  color: #{$f}(a, 1+2, c);\n}\n",
+    "a {\n  color: foo(a, 3, c);\n}\n"
+);