1. Check if the argument is an empty string in `path.format`. (#4064)

2. Avoid duplicating '/' at the beginning of the path.
Close: #4005

2 files changed, 213 insertions, 67 deletions

diff --git a/src/bun.js/node/types.zig b/src/bun.js/node/types.zig
index c858c9b04..02bfe8757 100644
--- a/src/bun.js/node/types.zig
+++ b/src/bun.js/node/types.zig
@@ -1861,14 +1861,17 @@ pub const Path = struct {
         var insert_separator = true;
         if (path_object.getTruthy(globalThis, "dir")) |prop| {
             prop.toZigString(&dir, globalThis);
-            insert_separator = !dir.isEmpty();
-        } else if (path_object.getTruthy(globalThis, "root")) |prop| {
-            prop.toZigString(&dir, globalThis);
+        }
+        if (dir.isEmpty()) {
+            if (path_object.getTruthy(globalThis, "root")) |prop| {
+                prop.toZigString(&dir, globalThis);
+            }
         }
 
         if (path_object.getTruthy(globalThis, "base")) |prop| {
             prop.toZigString(&name_with_ext, globalThis);
-        } else {
+        }
+        if (name_with_ext.isEmpty()) {
             var had_ext = false;
             if (path_object.getTruthy(globalThis, "ext")) |prop| {
                 prop.toZigString(&ext, globalThis);
@@ -1897,6 +1900,16 @@ pub const Path = struct {
             defer allocator.free(out);
 
             return JSC.ZigString.init(out).withEncoding().toValueGC(globalThis);
+        } else {
+            if (!isWindows) {
+                if (dir.eqlComptime("/")) {
+                    insert_separator = false;
+                }
+            } else {
+                if (dir.eqlComptime("\\")) {
+                    insert_separator = false;
+                }
+            }
         }
 
         if (insert_separator) {
diff --git a/test/js/node/path/path.test.js b/test/js/node/path/path.test.js
index 47d16fee0..3c8a04d72 100644
--- a/test/js/node/path/path.test.js
+++ b/test/js/node/path/path.test.js
@@ -627,71 +627,204 @@ it("path.resolve", () => {
   strictEqual(failures.length, 0, failures.join("\n"));
 });
 
-it("path.parse", () => {
-  expect(path.parse("/tmp/test.txt")).toStrictEqual({
-    root: "/",
-    dir: "/tmp",
-    base: "test.txt",
-    ext: ".txt",
-    name: "test",
-  });
-
-  expect(path.parse("/tmp/test/file.txt")).toStrictEqual({
-    root: "/",
-    dir: "/tmp/test",
-    base: "file.txt",
-    ext: ".txt",
-    name: "file",
-  });
-
-  expect(path.parse("/tmp/test/dir")).toStrictEqual({ root: "/", dir: "/tmp/test", base: "dir", ext: "", name: "dir" });
-  expect(path.parse("/tmp/test/dir/")).toStrictEqual({
-    root: "/",
-    dir: "/tmp/test",
-    base: "dir",
-    ext: "",
-    name: "dir",
-  });
-
-  expect(path.parse(".")).toStrictEqual({ root: "", dir: "", base: ".", ext: "", name: "." });
-  expect(path.parse("./")).toStrictEqual({ root: "", dir: "", base: ".", ext: "", name: "." });
-  expect(path.parse("/.")).toStrictEqual({ root: "/", dir: "/", base: ".", ext: "", name: "." });
-  expect(path.parse("/../")).toStrictEqual({ root: "/", dir: "/", base: "..", ext: ".", name: "." });
-
-  expect(path.parse("./file.txt")).toStrictEqual({ root: "", dir: ".", base: "file.txt", ext: ".txt", name: "file" });
-  expect(path.parse("../file.txt")).toStrictEqual({ root: "", dir: "..", base: "file.txt", ext: ".txt", name: "file" });
-  expect(path.parse("../test/file.txt")).toStrictEqual({
-    root: "",
-    dir: "../test",
-    base: "file.txt",
-    ext: ".txt",
-    name: "file",
-  });
-  expect(path.parse("test/file.txt")).toStrictEqual({
-    root: "",
-    dir: "test",
-    base: "file.txt",
-    ext: ".txt",
-    name: "file",
-  });
+describe("path.parse and path.format", () => {
+  const testCases = [
+    {
+      input: "/tmp/test.txt",
+      expected: {
+        root: "/",
+        dir: "/tmp",
+        base: "test.txt",
+        ext: ".txt",
+        name: "test",
+      },
+    },
+    {
+      input: "/tmp/test/file.txt",
+      expected: {
+        root: "/",
+        dir: "/tmp/test",
+        base: "file.txt",
+        ext: ".txt",
+        name: "file",
+      },
+    },
+    {
+      input: "/tmp/test/dir",
+      expected: {
+        root: "/",
+        dir: "/tmp/test",
+        base: "dir",
+        ext: "",
+        name: "dir",
+      },
+    },
+    {
+      input: "/tmp/test/dir/",
+      expected: {
+        root: "/",
+        dir: "/tmp/test",
+        base: "dir",
+        ext: "",
+        name: "dir",
+      },
+    },
+    {
+      input: ".",
+      expected: {
+        root: "",
+        dir: "",
+        base: ".",
+        ext: "",
+        name: ".",
+      },
+    },
+    {
+      input: "./",
+      expected: {
+        root: "",
+        dir: "",
+        base: ".",
+        ext: "",
+        name: ".",
+      },
+    },
+    {
+      input: "/.",
+      expected: {
+        root: "/",
+        dir: "/",
+        base: ".",
+        ext: "",
+        name: ".",
+      },
+    },
+    {
+      input: "/../",
+      expected: {
+        root: "/",
+        dir: "/",
+        base: "..",
+        ext: ".",
+        name: ".",
+      },
+    },
+    {
+      input: "./file.txt",
+      expected: {
+        root: "",
+        dir: ".",
+        base: "file.txt",
+        ext: ".txt",
+        name: "file",
+      },
+    },
+    {
+      input: "../file.txt",
+      expected: {
+        root: "",
+        dir: "..",
+        base: "file.txt",
+        ext: ".txt",
+        name: "file",
+      },
+    },
+    {
+      input: "../test/file.txt",
+      expected: {
+        root: "",
+        dir: "../test",
+        base: "file.txt",
+        ext: ".txt",
+        name: "file",
+      },
+    },
+    {
+      input: "test/file.txt",
+      expected: {
+        root: "",
+        dir: "test",
+        base: "file.txt",
+        ext: ".txt",
+        name: "file",
+      },
+    },
+    {
+      input: "test/dir",
+      expected: {
+        root: "",
+        dir: "test",
+        base: "dir",
+        ext: "",
+        name: "dir",
+      },
+    },
+    {
+      input: "test/dir/another_dir",
+      expected: {
+        root: "",
+        dir: "test/dir",
+        base: "another_dir",
+        ext: "",
+        name: "another_dir",
+      },
+    },
+    {
+      input: "./dir",
+      expected: {
+        root: "",
+        dir: ".",
+        base: "dir",
+        ext: "",
+        name: "dir",
+      },
+    },
+    {
+      input: "../dir",
+      expected: {
+        root: "",
+        dir: "..",
+        base: "dir",
+        ext: "",
+        name: "dir",
+      },
+    },
+    {
+      input: "../dir/another_dir",
+      expected: {
+        root: "",
+        dir: "../dir",
+        base: "another_dir",
+        ext: "",
+        name: "another_dir",
+      },
+    },
+  ];
+  testCases.forEach(({ input, expected }) => {
+    it(`case ${input}`, () => {
+      const parsed = path.parse(input);
+      expect(parsed).toStrictEqual(expected);
 
-  expect(path.parse("test/dir")).toStrictEqual({ root: "", dir: "test", base: "dir", ext: "", name: "dir" });
-  expect(path.parse("test/dir/another_dir")).toStrictEqual({
-    root: "",
-    dir: "test/dir",
-    base: "another_dir",
-    ext: "",
-    name: "another_dir",
+      const formatted = path.format(parsed);
+      expect(formatted).toStrictEqual(input.slice(-1) === "/" ? input.slice(0, -1) : input);
+    });
   });
-
-  expect(path.parse("./dir")).toStrictEqual({ root: "", dir: ".", base: "dir", ext: "", name: "dir" });
-  expect(path.parse("../dir")).toStrictEqual({ root: "", dir: "..", base: "dir", ext: "", name: "dir" });
-  expect(path.parse("../dir/another_dir")).toStrictEqual({
-    root: "",
-    dir: "../dir",
-    base: "another_dir",
-    ext: "",
-    name: "another_dir",
+  it("empty string arguments, issue #4005", () => {
+    expect(
+      path.format({
+        root: "",
+        dir: "",
+        base: "",
+        name: "foo",
+        ext: ".ts",
+      }),
+    ).toStrictEqual("foo.ts");
+    expect(
+      path.format({
+        name: "foo",
+        ext: ".ts",
+      }),
+    ).toStrictEqual("foo.ts");
   });
 });