improve inspect output for arglists with 1 arg

src/value/mod.rs

@@ -291,6 +291,14 @@ impl Value {
             )),
             Value::Dimension(num, unit) => Cow::owned(format!("{}{}", num, unit)),
             Value::ArgList(args) if args.is_empty() => Cow::const_str("()"),
+            Value::ArgList(args) if args.len() == 1 => Cow::owned(format!(
+                "({},)",
+                args.iter()
+                    .filter(|x| !x.is_null())
+                    .map(|a| Ok(a.node.inspect(span)?))
+                    .collect::<SassResult<Vec<Cow<'static, str>>>>()?
+                    .join(", "),
+            )),
             Value::ArgList(args) => Cow::owned(
                 args.iter()
                     .filter(|x| !x.is_null())

tests/arglist.rs

@@ -62,3 +62,14 @@ test!(
     }",
     "a {\n  color: null;\n}\n"
 );
+test!(
+    inspect_arglist_with_one_arg,
+    "@function foo($a...) {
+        @return inspect($a);
+    }
+    
+    a {
+        color: inspect(foo(1));
+    }",
+    "a {\n  color: (1,);\n}\n"
+);

tests/inspect.rs

@@ -129,5 +129,5 @@ test!(
     a {
         color: foo((a: b));
     }",
-    "a {\n  color: (a: b);\n}\n"
+    "a {\n  color: ((a: b),);\n}\n"
 );