fix: do not tread negative values as identifiers in the animation shorthand (#68)

Author: alexander-akait

src/index.js

@@ -357,7 +357,7 @@ function localizeDeclaration(declaration, context) {
 
     // We don't validate `hex digits`, because we don't need it, it is work of linters.
     const validIdent =
-      /^-?([a-z\u0080-\uFFFF_]|(\\[^\r\n\f])|-)((\\[^\r\n\f])|[a-z\u0080-\uFFFF_0-9-])*$/i;
+      /^-?([a-z\u0080-\uFFFF_]|(\\[^\r\n\f])|-(?![0-9]))((\\[^\r\n\f])|[a-z\u0080-\uFFFF_0-9-])*$/i;
 
     /*
     The spec defines some keywords that you can use to describe properties such as the timing

test/index.test.js

@@ -864,6 +864,21 @@ const tests = [
     options: { mode: "pure" },
     expected: ":export { foo: __foo; }",
   },
+  {
+    name: "handle negative animation-delay in animation shorthand",
+    input: ".foo { animation: 1s -500ms; }",
+    expected: ":local(.foo) { animation: 1s -500ms; }",
+  },
+  {
+    name: "handle negative animation-delay in animation shorthand #1",
+    input: ".foo { animation: 1s -500.0ms; }",
+    expected: ":local(.foo) { animation: 1s -500.0ms; }",
+  },
+  {
+    name: "handle negative animation-delay in animation shorthand #2",
+    input: ".foo { animation: 1s -500.0ms -a_value; }",
+    expected: ":local(.foo) { animation: 1s -500.0ms :local(-a_value); }",
+  },
 ];
 
 function process(css, options) {