fix url.fileURLToPath test

src/bun.js/bindings/PathInlines.h

@@ -27,11 +27,12 @@ ALWAYS_INLINE bool isAbsolutePath(WTF::String input)
         if (len < 1)
             return false;
         const auto bytes = input.span8().data();
-        if (IS_SLASH(bytes[0]))
+        // On Windows, paths starting with / are not absolute paths
+        // They need to be resolved relative to the current drive
+        // Only paths with drive letters (C:\) or UNC paths (\\) are absolute
+        if (len >= 3 && IS_LETTER(bytes[0]) && bytes[1] == ':' && IS_SLASH(bytes[2]))
             return true;
-        if (len < 2)
-            return false;
-        if (IS_LETTER(bytes[0]) && bytes[1] == ':' && IS_SLASH(bytes[2]))
+        if (len >= 2 && IS_SLASH(bytes[0]) && IS_SLASH(bytes[1]))
             return true;
         return false;
     } else {
@@ -39,11 +40,12 @@ ALWAYS_INLINE bool isAbsolutePath(WTF::String input)
         if (len < 1)
             return false;
         const auto bytes = input.span16().data();
-        if (IS_SLASH(bytes[0]))
+        // On Windows, paths starting with / are not absolute paths
+        // They need to be resolved relative to the current drive
+        // Only paths with drive letters (C:\) or UNC paths (\\) are absolute
+        if (len >= 3 && IS_LETTER(bytes[0]) && bytes[1] == ':' && IS_SLASH(bytes[2]))
             return true;
-        if (len < 2)
-            return false;
-        if (IS_LETTER(bytes[0]) && bytes[1] == ':' && IS_SLASH(bytes[2]))
+        if (len >= 2 && IS_SLASH(bytes[0]) && IS_SLASH(bytes[1]))
             return true;
         return false;
     }

test/js/bun/util/fileUrl.test.js

@@ -4,7 +4,12 @@ import { isWindows } from "harness";
 
 describe("pathToFileURL", () => {
   it("should convert a path to a file url", () => {
-    expect(pathToFileURL("/path/to/file.js").href).toBe("file:///path/to/file.js");
+    if (isWindows) {
+      const result = pathToFileURL("/path/to/file.js").href;
+      expect(result).toMatch(/^file:\/\/\/[A-Z]:\/path\/to\/file\.js$/);
+    } else {
+      expect(pathToFileURL("/path/to/file.js").href).toBe("file:///path/to/file.js");
+    }
   });
 });
 
@@ -12,7 +17,10 @@ describe("fileURLToPath", () => {
   const absoluteErrorMessage = "File URL path must be an absolute";
   it("should convert a file url to a path", () => {
     if (isWindows) {
+      // This is still invalid on Windows because it lacks a drive letter
       expect(() => fileURLToPath("file:///path/to/file.js")).toThrow(absoluteErrorMessage);
+      // But a properly formed Windows file URL should work
+      expect(fileURLToPath("file:///C:/path/to/file.js")).toBe("C:\\path\\to\\file.js");
     } else {
       expect(fileURLToPath("file:///path/to/file.js")).toBe("/path/to/file.js");
     }
@@ -20,7 +28,10 @@ describe("fileURLToPath", () => {
 
   it("should convert a URL to a path", () => {
     if (isWindows) {
+      // This is still invalid on Windows because it lacks a drive letter
       expect(() => fileURLToPath(new URL("file:///path/to/file.js"))).toThrow(absoluteErrorMessage);
+      // But a properly formed Windows file URL should work
+      expect(fileURLToPath(new URL("file:///C:/path/to/file.js"))).toBe("C:\\path\\to\\file.js");
     } else {
       expect(fileURLToPath(new URL("file:///path/to/file.js"))).toBe("/path/to/file.js");
     }
@@ -49,4 +60,22 @@ describe("fileURLToPath", () => {
     expect(fileURLToPath(url)).toBe(import.meta.path);
     expect(fileURLToPath(import.meta.url)).toBe(import.meta.path);
   });
+
+  it("should handle Windows paths starting with / correctly", () => {
+    if (isWindows) {
+      // Test the specific case that was failing with SolidStart
+      const testPaths = ["/test", "/@solid-refresh", "/node_modules/test"];
+
+      for (const testPath of testPaths) {
+        const url = pathToFileURL(testPath);
+        // Should include drive letter
+        expect(url.href).toMatch(/^file:\/\/\/[A-Z]:\//);
+
+        // Should roundtrip correctly
+        const result = fileURLToPath(url);
+        expect(result).toMatch(/^[A-Z]:\\/);
+        expect(result.toLowerCase()).toContain(testPath.replace(/\//g, "\\").toLowerCase());
+      }
+    }
+  });
 });

test/regression/issue/issue-18748-fileURLToPath-windows.test.ts

@@ -0,0 +1,37 @@
+import { expect, test } from "bun:test";
+import { isWindows } from "harness";
+import { fileURLToPath, pathToFileURL } from "node:url";
+
+test("fileURLToPath should handle paths starting with / correctly on all platforms", () => {
+  const testPaths = ["/test", "/@test", "/node_modules/test", "/@solid-refresh"];
+
+  for (const testPath of testPaths) {
+    const url = pathToFileURL(testPath);
+
+    if (isWindows) {
+      expect(url.href).toMatch(/^file:\/\/\/[A-Z]:\//);
+    } else {
+      expect(url.href).toBe(`file://${testPath}`);
+    }
+
+    const result = fileURLToPath(url);
+
+    if (isWindows) {
+      expect(result).toMatch(/^[A-Z]:\\/);
+      expect(result.toLowerCase()).toContain(testPath.replace(/\//g, "\\").toLowerCase());
+    } else {
+      expect(result).toBe(testPath);
+    }
+  }
+});
+
+test.if(isWindows)("Windows absolute paths should still work correctly", () => {
+  const absolutePaths = ["C:\\test", "C:\\Users\\test", "D:\\Projects\\myapp", "\\\\server\\share\\file"];
+
+  for (const absolutePath of absolutePaths) {
+    const url = pathToFileURL(absolutePath);
+    const result = fileURLToPath(url);
+
+    expect(result).toBe(absolutePath);
+  }
+});