Initial investigation and issue reproduction

Co-authored-by: nzakas <[email protected]>

Author: Copilot

tests/reproduce-issue.test.js

@@ -0,0 +1,78 @@
+/**
+ * @fileoverview Test to reproduce the parsing error with @apply outline-ring/50
+ */
+
+import assert from "node:assert";
+import { tailwind3 } from "../src/tailwind3.js";
+import { tailwind4 } from "../src/tailwind4.js";
+import { fork } from "@eslint/css-tree";
+
+describe("Issue Reproduction", function () {
+    describe("@apply with slash notation", () => {
+        const problematicCSS = `
+@layer base {
+  * {
+    @apply border-border outline-ring/50;
+  }
+  body {
+    @apply bg-background text-foreground;
+  }
+}
+        `;
+
+        const simpleCase = `a { @apply outline-ring/50; }`;
+
+        it("should parse @apply with slash notation in Tailwind 3", () => {
+            const { parse, toPlainObject } = fork(tailwind3);
+            try {
+                const result = parse(simpleCase);
+                console.log("Tailwind 3 result:", JSON.stringify(toPlainObject(result), null, 2));
+                assert.ok(result, "Should parse successfully");
+            } catch (error) {
+                console.error("Tailwind 3 error:", error.message);
+                throw error;
+            }
+        });
+
+        it("should parse @apply with slash notation in Tailwind 4", () => {
+            const { parse, toPlainObject } = fork(tailwind4);
+            try {
+                const result = parse(simpleCase);
+                console.log("Tailwind 4 result:", JSON.stringify(toPlainObject(result), null, 2));
+                assert.ok(result, "Should parse successfully");
+            } catch (error) {
+                console.error("Tailwind 4 error:", error.message);
+                throw error;
+            }
+        });
+
+        it("should test @apply border-border outline-ring/50 specifically", () => {
+            const specificCase = "* { @apply border-border outline-ring/50; }";
+            
+            console.log("Testing:", specificCase);
+            
+            const { parse, toPlainObject } = fork(tailwind3);
+            try {
+                const result = parse(specificCase);
+                console.log("Parsed successfully:", JSON.stringify(toPlainObject(result), null, 2));
+                assert.ok(result, "Should parse successfully");
+            } catch (error) {
+                console.error("Parse error:", error.message);
+                console.error("Full error:", error);
+                throw error;
+            }
+        });
+
+        it("should parse complex @apply with slash notation in Tailwind 3", () => {
+            const { parse } = fork(tailwind3);
+            const result = parse(problematicCSS);
+            assert.ok(result, "Should parse successfully");
+        });
+
+        it("should parse complex @apply with slash notation in Tailwind 4", () => {
+            const { parse } = fork(tailwind4);
+            const result = parse(problematicCSS);
+            assert.ok(result, "Should parse successfully");
+        });
+    });
+});