From bdef1b1eb45e2953e1ff68f0cc9a68ec83573e57 Mon Sep 17 00:00:00 2001
From: Benjamin Coe <ben@npmjs.com>
Date: Thu, 9 Aug 2018 16:52:41 -0700
Subject: [PATCH] fs: implement mkdir recursive (mkdirp)

Implements mkdirp functionality in node_file.cc. The Benefit
of implementing in C++ layer is that the logic is more easily
shared between the Promise and callback implementation and
there are notable performance improvements.

This commit is part of the Tooling Group Initiative.

Refs: https://github.com/nodejs/user-feedback/pull/70

PR-URL: https://github.com/nodejs/node/pull/21875
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Ron Korving <ron@ronkorving.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Sam Ruby <rubys@intertwingly.net>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
---
 benchmark/fs/bench-mkdirp.js      |  23 +++++
 doc/api/fs.md                     |  35 +++++--
 lib/fs.js                         |  45 ++++++---
 lib/internal/fs/promises.js       |  18 +++-
 src/node_file.cc                  | 158 ++++++++++++++++++++++++++++--
 src/node_file.h                   |  42 ++++++++
 test/parallel/test-fs-mkdir.js    | 107 +++++++++++++++++++-
 test/parallel/test-fs-promises.js |  49 ++++++++-
 8 files changed, 441 insertions(+), 36 deletions(-)
 create mode 100644 benchmark/fs/bench-mkdirp.js

diff --git a/benchmark/fs/bench-mkdirp.js b/benchmark/fs/bench-mkdirp.js
new file mode 100644
index 00000000000000..96a792c35a48e4
--- /dev/null
+++ b/benchmark/fs/bench-mkdirp.js
@@ -0,0 +1,23 @@
+'use strict';
+
+const common = require('../common');
+const fs = require('fs');
+const tmpdir = require('../../test/common/tmpdir');
+tmpdir.refresh();
+let dirc = 0;
+
+const bench = common.createBenchmark(main, {
+  n: [1e4],
+});
+
+function main({ n }) {
+  bench.start();
+  (function r(cntr) {
+    if (cntr-- <= 0)
+      return bench.end(n);
+    const pathname = `${tmpdir.path}/${++dirc}/${++dirc}/${++dirc}/${++dirc}`;
+    fs.mkdir(pathname, { createParents: true }, (err) => {
+      r(cntr);
+    });
+  }(n));
+}
diff --git a/doc/api/fs.md b/doc/api/fs.md
index d0348d45c93f04..1f71a537e3eb46 100644
--- a/doc/api/fs.md
+++ b/doc/api/fs.md
@@ -2047,7 +2047,7 @@ changes:
 
 Synchronous lstat(2).
 
-## fs.mkdir(path[, mode], callback)
+## fs.mkdir(path[, options], callback)
 <!-- YAML
 added: v0.1.8
 changes:
@@ -2066,16 +2066,29 @@ changes:
 -->
 
 * `path` {string|Buffer|URL}
-* `mode` {integer} Not supported on Windows. **Default:** `0o777`.
+* `options` {Object|integer}
+  * `recursive` {boolean} **Default:** `false`
+  * `mode` {integer} Not supported on Windows. **Default:** `0o777`.
 * `callback` {Function}
   * `err` {Error}
 
 Asynchronously creates a directory. No arguments other than a possible exception
 are given to the completion callback.
 
+The optional `options` argument can be an integer specifying mode (permission
+and sticky bits), or an object with a `mode` property and a `recursive`
+property indicating whether parent folders should be created.
+
+```js
+// Creates /tmp/a/apple, regardless of whether `/tmp` and /tmp/a exist.
+fs.mkdir('/tmp/a/apple', { recursive: true }, (err) => {
+  if (err) throw err;
+});
+```
+
 See also: mkdir(2).
 
-## fs.mkdirSync(path[, mode])
+## fs.mkdirSync(path[, options])
 <!-- YAML
 added: v0.1.21
 changes:
@@ -2086,7 +2099,9 @@ changes:
 -->
 
 * `path` {string|Buffer|URL}
-* `mode` {integer} Not supported on Windows. **Default:** `0o777`.
+* `options` {Object|integer}
+  * `recursive` {boolean} **Default:** `false`
+  * `mode` {integer} Not supported on Windows. **Default:** `0o777`.
 
 Synchronously creates a directory. Returns `undefined`.
 This is the synchronous version of [`fs.mkdir()`][].
@@ -3979,18 +3994,24 @@ changes:
 Asynchronous lstat(2). The `Promise` is resolved with the [`fs.Stats`][] object
 for the given symbolic link `path`.
 
-### fsPromises.mkdir(path[, mode])
+### fsPromises.mkdir(path[, options])
 <!-- YAML
 added: v10.0.0
 -->
 
 * `path` {string|Buffer|URL}
-* `mode` {integer} **Default:** `0o777`
+* `options` {Object|integer}
+  * `recursive` {boolean} **Default:** `false`
+  * `mode` {integer} Not supported on Windows. **Default:** `0o777`.
 * Returns: {Promise}
 
 Asynchronously creates a directory then resolves the `Promise` with no
 arguments upon success.
 
+The optional `options` argument can be an integer specifying mode (permission
+and sticky bits), or an object with a `mode` property and a `recursive`
+property indicating whether parent folders should be created.
+
 ### fsPromises.mkdtemp(prefix[, options])
 <!-- YAML
 added: v10.0.0
@@ -4627,7 +4648,7 @@ the file contents.
 [`fs.ftruncate()`]: #fs_fs_ftruncate_fd_len_callback
 [`fs.futimes()`]: #fs_fs_futimes_fd_atime_mtime_callback
 [`fs.lstat()`]: #fs_fs_lstat_path_options_callback
-[`fs.mkdir()`]: #fs_fs_mkdir_path_mode_callback
+[`fs.mkdir()`]: #fs_fs_mkdir_path_options_callback
 [`fs.mkdtemp()`]: #fs_fs_mkdtemp_prefix_options_callback
 [`fs.open()`]: #fs_fs_open_path_flags_mode_callback
 [`fs.read()`]: #fs_fs_read_fd_buffer_offset_length_position_callback
diff --git a/lib/fs.js b/lib/fs.js
index 7517f275c82ff3..bb8c17bbbb5436 100644
--- a/lib/fs.js
+++ b/lib/fs.js
@@ -721,29 +721,48 @@ function fsyncSync(fd) {
   handleErrorFromBinding(ctx);
 }
 
-function mkdir(path, mode, callback) {
+function mkdir(path, options, callback) {
+  if (typeof options === 'function') {
+    callback = options;
+    options = {};
+  } else if (typeof options === 'number' || typeof options === 'string') {
+    options = { mode: options };
+  }
+  const {
+    recursive = false,
+    mode = 0o777
+  } = options || {};
+  callback = makeCallback(callback);
   path = getPathFromURL(path);
-  validatePath(path);
 
-  if (arguments.length < 3) {
-    callback = makeCallback(mode);
-    mode = 0o777;
-  } else {
-    callback = makeCallback(callback);
-    mode = validateMode(mode, 'mode', 0o777);
-  }
+  validatePath(path);
+  if (typeof recursive !== 'boolean')
+    throw new ERR_INVALID_ARG_TYPE('recursive', 'boolean', recursive);
 
   const req = new FSReqCallback();
   req.oncomplete = callback;
-  binding.mkdir(pathModule.toNamespacedPath(path), mode, req);
+  binding.mkdir(pathModule.toNamespacedPath(path),
+                validateMode(mode, 'mode', 0o777), recursive, req);
 }
 
-function mkdirSync(path, mode) {
+function mkdirSync(path, options) {
+  if (typeof options === 'number' || typeof options === 'string') {
+    options = { mode: options };
+  }
   path = getPathFromURL(path);
+  const {
+    recursive = false,
+    mode = 0o777
+  } = options || {};
+
   validatePath(path);
-  mode = validateMode(mode, 'mode', 0o777);
+  if (typeof recursive !== 'boolean')
+    throw new ERR_INVALID_ARG_TYPE('recursive', 'boolean', recursive);
+
   const ctx = { path };
-  binding.mkdir(pathModule.toNamespacedPath(path), mode, undefined, ctx);
+  binding.mkdir(pathModule.toNamespacedPath(path),
+                validateMode(mode, 'mode', 0o777), recursive, undefined,
+                ctx);
   handleErrorFromBinding(ctx);
 }
 
diff --git a/lib/internal/fs/promises.js b/lib/internal/fs/promises.js
index f38a3e59befc05..e8cb2317fa4288 100644
--- a/lib/internal/fs/promises.js
+++ b/lib/internal/fs/promises.js
@@ -289,11 +289,23 @@ async function fsync(handle) {
   return binding.fsync(handle.fd, kUsePromises);
 }
 
-async function mkdir(path, mode) {
+async function mkdir(path, options) {
+  if (typeof options === 'number' || typeof options === 'string') {
+    options = { mode: options };
+  }
+  const {
+    recursive = false,
+    mode = 0o777
+  } = options || {};
   path = getPathFromURL(path);
+
   validatePath(path);
-  mode = validateMode(mode, 'mode', 0o777);
-  return binding.mkdir(pathModule.toNamespacedPath(path), mode, kUsePromises);
+  if (typeof recursive !== 'boolean')
+    throw new ERR_INVALID_ARG_TYPE('recursive', 'boolean', recursive);
+
+  return binding.mkdir(pathModule.toNamespacedPath(path),
+                       validateMode(mode, 'mode', 0o777), recursive,
+                       kUsePromises);
 }
 
 async function readdir(path, options) {
diff --git a/src/node_file.cc b/src/node_file.cc
index b0effaff7bb746..714dec157bcedc 100644
--- a/src/node_file.cc
+++ b/src/node_file.cc
@@ -76,6 +76,16 @@ using v8::Value;
 # define MIN(a, b) ((a) < (b) ? (a) : (b))
 #endif
 
+#ifndef S_ISDIR
+# define S_ISDIR(mode)  (((mode) & S_IFMT) == S_IFDIR)
+#endif
+
+#ifdef __POSIX__
+const char* kPathSeparator = "/";
+#else
+const char* kPathSeparator = "\\/";
+#endif
+
 #define GET_OFFSET(a) ((a)->IsNumber() ? (a).As<Integer>()->Value() : -1)
 #define TRACE_NAME(name) "fs.sync." #name
 #define GET_TRACE_ENABLED                                                  \
@@ -1148,11 +1158,137 @@ static void RMDir(const FunctionCallbackInfo<Value>& args) {
   }
 }
 
+int MKDirpSync(uv_loop_t* loop, uv_fs_t* req, const std::string& path, int mode,
+               uv_fs_cb cb = nullptr) {
+  FSContinuationData continuation_data(req, mode, cb);
+  continuation_data.PushPath(std::move(path));
+
+  while (continuation_data.paths.size() > 0) {
+    std::string next_path = continuation_data.PopPath();
+    int err = uv_fs_mkdir(loop, req, next_path.c_str(), mode, nullptr);
+    while (true) {
+      switch (err) {
+        case 0:
+          if (continuation_data.paths.size() == 0) {
+            return 0;
+          }
+          break;
+        case UV_ENOENT: {
+          std::string dirname = next_path.substr(0,
+                                        next_path.find_last_of(kPathSeparator));
+          if (dirname != next_path) {
+            continuation_data.PushPath(std::move(next_path));
+            continuation_data.PushPath(std::move(dirname));
+          } else if (continuation_data.paths.size() == 0) {
+            err = UV_EEXIST;
+            continue;
+          }
+          break;
+        }
+        case UV_EPERM: {
+          return err;
+        }
+        default:
+          uv_fs_req_cleanup(req);
+          err = uv_fs_stat(loop, req, next_path.c_str(), nullptr);
+          if (err == 0 && !S_ISDIR(req->statbuf.st_mode)) return UV_EEXIST;
+          if (err < 0) return err;
+          break;
+      }
+      break;
+    }
+    uv_fs_req_cleanup(req);
+  }
+
+  return 0;
+}
+
+int MKDirpAsync(uv_loop_t* loop,
+                uv_fs_t* req,
+                const char* path,
+                int mode,
+                uv_fs_cb cb) {
+  FSReqBase* req_wrap = FSReqBase::from_req(req);
+  // on the first iteration of algorithm, stash state information.
+  if (req_wrap->continuation_data == nullptr) {
+    req_wrap->continuation_data = std::unique_ptr<FSContinuationData>{
+      new FSContinuationData(req, mode, cb)};
+    req_wrap->continuation_data->PushPath(std::move(path));
+  }
+
+  // on each iteration of algorithm, mkdir directory on top of stack.
+  std::string next_path = req_wrap->continuation_data->PopPath();
+  int err = uv_fs_mkdir(loop, req, next_path.c_str(), mode,
+                        uv_fs_callback_t{[](uv_fs_t* req) {
+    FSReqBase* req_wrap = FSReqBase::from_req(req);
+    Environment* env = req_wrap->env();
+    uv_loop_t* loop = env->event_loop();
+    std::string path = req->path;
+    int err = req->result;
+
+    while (true) {
+      switch (err) {
+        case 0: {
+          if (req_wrap->continuation_data->paths.size() == 0) {
+            req_wrap->continuation_data->Done(0);
+          } else {
+            uv_fs_req_cleanup(req);
+            MKDirpAsync(loop, req, path.c_str(),
+                        req_wrap->continuation_data->mode, nullptr);
+          }
+          break;
+        }
+        case UV_ENOENT: {
+          std::string dirname = path.substr(0,
+                                            path.find_last_of(kPathSeparator));
+          if (dirname != path) {
+            req_wrap->continuation_data->PushPath(std::move(path));
+            req_wrap->continuation_data->PushPath(std::move(dirname));
+          } else if (req_wrap->continuation_data->paths.size() == 0) {
+            err = UV_EEXIST;
+            continue;
+          }
+          uv_fs_req_cleanup(req);
+          MKDirpAsync(loop, req, path.c_str(),
+                      req_wrap->continuation_data->mode, nullptr);
+          break;
+        }
+        case UV_EPERM: {
+          req_wrap->continuation_data->Done(err);
+          break;
+        }
+        default:
+          if (err == UV_EEXIST &&
+              req_wrap->continuation_data->paths.size() > 0) {
+            uv_fs_req_cleanup(req);
+            MKDirpAsync(loop, req, path.c_str(),
+                        req_wrap->continuation_data->mode, nullptr);
+          } else {
+            // verify that the path pointed to is actually a directory.
+            uv_fs_req_cleanup(req);
+            int err = uv_fs_stat(loop, req, path.c_str(),
+                                 uv_fs_callback_t{[](uv_fs_t* req) {
+              FSReqBase* req_wrap = FSReqBase::from_req(req);
+              int err = req->result;
+              if (err == 0 && !S_ISDIR(req->statbuf.st_mode)) err = UV_EEXIST;
+              req_wrap->continuation_data->Done(err);
+            }});
+            if (err < 0) req_wrap->continuation_data->Done(err);
+          }
+          break;
+      }
+      break;
+    }
+  }});
+
+  return err;
+}
+
 static void MKDir(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
 
   const int argc = args.Length();
-  CHECK_GE(argc, 3);
+  CHECK_GE(argc, 4);
 
   BufferValue path(env->isolate(), args[0]);
   CHECK_NOT_NULL(*path);
@@ -1160,16 +1296,24 @@ static void MKDir(const FunctionCallbackInfo<Value>& args) {
   CHECK(args[1]->IsInt32());
   const int mode = args[1].As<Int32>()->Value();
 
-  FSReqBase* req_wrap_async = GetReqWrap(env, args[2]);
+  CHECK(args[2]->IsBoolean());
+  bool mkdirp = args[2]->IsTrue();
+
+  FSReqBase* req_wrap_async = GetReqWrap(env, args[3]);
   if (req_wrap_async != nullptr) {  // mkdir(path, mode, req)
-    AsyncCall(env, req_wrap_async, args, "mkdir", UTF8, AfterNoArgs,
-              uv_fs_mkdir, *path, mode);
+    AsyncCall(env, req_wrap_async, args, "mkdir", UTF8,
+              AfterNoArgs, mkdirp ? MKDirpAsync : uv_fs_mkdir, *path, mode);
   } else {  // mkdir(path, mode, undefined, ctx)
-    CHECK_EQ(argc, 4);
+    CHECK_EQ(argc, 5);
     FSReqWrapSync req_wrap_sync;
     FS_SYNC_TRACE_BEGIN(mkdir);
-    SyncCall(env, args[3], &req_wrap_sync, "mkdir",
-             uv_fs_mkdir, *path, mode);
+    if (mkdirp) {
+      SyncCall(env, args[4], &req_wrap_sync, "mkdir",
+               MKDirpSync, *path, mode);
+    } else {
+      SyncCall(env, args[4], &req_wrap_sync, "mkdir",
+               uv_fs_mkdir, *path, mode);
+    }
     FS_SYNC_TRACE_END(mkdir);
   }
 }
diff --git a/src/node_file.h b/src/node_file.h
index fdd36efc77582b..af62be0feca0d4 100644
--- a/src/node_file.h
+++ b/src/node_file.h
@@ -21,10 +21,50 @@ using v8::Value;
 
 namespace fs {
 
+// structure used to store state during a complex operation, e.g., mkdirp.
+class FSContinuationData : public MemoryRetainer {
+ public:
+  FSContinuationData(uv_fs_t* req, int mode, uv_fs_cb done_cb)
+      : req(req), mode(mode), done_cb(done_cb) {
+  }
+
+  uv_fs_t* req;
+  int mode;
+  std::vector<std::string> paths;
+
+  void PushPath(std::string&& path) {
+    paths.emplace_back(std::move(path));
+  }
+
+  void PushPath(const std::string& path) {
+    paths.push_back(path);
+  }
+
+  std::string PopPath() {
+    CHECK_GT(paths.size(), 0);
+    std::string path = std::move(paths.back());
+    paths.pop_back();
+    return path;
+  }
+
+  void Done(int result) {
+    req->result = result;
+    done_cb(req);
+  }
+
+  void MemoryInfo(MemoryTracker* tracker) const override {
+    tracker->TrackThis(this);
+    tracker->TrackField("paths", paths);
+  }
+
+ private:
+  uv_fs_cb done_cb;
+};
 
 class FSReqBase : public ReqWrap<uv_fs_t> {
  public:
   typedef MaybeStackBuffer<char, 64> FSReqBuffer;
+  std::unique_ptr<FSContinuationData> continuation_data = nullptr;
 
   FSReqBase(Environment* env, Local<Object> req, AsyncWrap::ProviderType type,
             bool use_bigint)
@@ -97,6 +137,7 @@ class FSReqCallback : public FSReqBase {
 
   void MemoryInfo(MemoryTracker* tracker) const override {
     tracker->TrackThis(this);
+    tracker->TrackField("continuation_data", continuation_data);
   }
 
   ADD_MEMORY_INFO_NAME(FSReqCallback)
@@ -162,6 +203,7 @@ class FSReqPromise : public FSReqBase {
   void MemoryInfo(MemoryTracker* tracker) const override {
     tracker->TrackThis(this);
     tracker->TrackField("stats_field_array", stats_field_array_);
+    tracker->TrackField("continuation_data", continuation_data);
   }
 
   ADD_MEMORY_INFO_NAME(FSReqPromise)
diff --git a/test/parallel/test-fs-mkdir.js b/test/parallel/test-fs-mkdir.js
index 18e9e973f14cce..024fdced9c44ae 100644
--- a/test/parallel/test-fs-mkdir.js
+++ b/test/parallel/test-fs-mkdir.js
@@ -23,12 +23,18 @@
 const common = require('../common');
 const assert = require('assert');
 const fs = require('fs');
+const path = require('path');
 
 const tmpdir = require('../common/tmpdir');
 tmpdir.refresh();
 
+let dirc = 0;
+function nextdir() {
+  return `test${++dirc}`;
+}
+
 {
-  const pathname = `${tmpdir.path}/test1`;
+  const pathname = path.join(tmpdir.path, nextdir());
 
   fs.mkdir(pathname, common.mustCall(function(err) {
     assert.strictEqual(err, null);
@@ -37,7 +43,7 @@ tmpdir.refresh();
 }
 
 {
-  const pathname = `${tmpdir.path}/test2`;
+  const pathname = path.join(tmpdir.path, nextdir());
 
   fs.mkdir(pathname, 0o777, common.mustCall(function(err) {
     assert.strictEqual(err, null);
@@ -46,7 +52,7 @@ tmpdir.refresh();
 }
 
 {
-  const pathname = `${tmpdir.path}/test3`;
+  const pathname = path.join(tmpdir.path, nextdir());
 
   fs.mkdirSync(pathname);
 
@@ -71,6 +77,101 @@ tmpdir.refresh();
   );
 });
 
+// mkdirpSync when both top-level, and sub-folders do not exist.
+{
+  const pathname = path.join(tmpdir.path, nextdir(), nextdir());
+
+  fs.mkdirSync(pathname, { recursive: true });
+
+  const exists = fs.existsSync(pathname);
+  assert.strictEqual(exists, true);
+  assert.strictEqual(fs.statSync(pathname).isDirectory(), true);
+}
+
+// mkdirpSync when folder already exists.
+{
+  const pathname = path.join(tmpdir.path, nextdir(), nextdir());
+
+  fs.mkdirSync(pathname, { recursive: true });
+  // should not cause an error.
+  fs.mkdirSync(pathname, { recursive: true });
+
+  const exists = fs.existsSync(pathname);
+  assert.strictEqual(exists, true);
+  assert.strictEqual(fs.statSync(pathname).isDirectory(), true);
+}
+
+// mkdirpSync ../
+{
+  const pathname = `${tmpdir.path}/${nextdir()}/../${nextdir()}/${nextdir()}`;
+  fs.mkdirSync(pathname, { recursive: true });
+  const exists = fs.existsSync(pathname);
+  assert.strictEqual(exists, true);
+  assert.strictEqual(fs.statSync(pathname).isDirectory(), true);
+}
+
+// mkdirpSync when path is a file.
+{
+  const pathname = path.join(tmpdir.path, nextdir(), nextdir());
+
+  fs.mkdirSync(path.dirname(pathname));
+  fs.writeFileSync(pathname, '', 'utf8');
+
+  try {
+    fs.mkdirSync(pathname, { recursive: true });
+    throw new Error('unreachable');
+  } catch (err) {
+    assert.notStrictEqual(err.message, 'unreachable');
+    assert.strictEqual(err.code, 'EEXIST');
+    assert.strictEqual(err.syscall, 'mkdir');
+  }
+}
+
+// mkdirp when folder does not yet exist.
+{
+  const pathname = path.join(tmpdir.path, nextdir(), nextdir());
+
+  fs.mkdir(pathname, { recursive: true }, common.mustCall(function(err) {
+    assert.strictEqual(err, null);
+    assert.strictEqual(fs.existsSync(pathname), true);
+    assert.strictEqual(fs.statSync(pathname).isDirectory(), true);
+  }));
+}
+
+// mkdirp when path is a file.
+{
+  const pathname = path.join(tmpdir.path, nextdir(), nextdir());
+
+  fs.mkdirSync(path.dirname(pathname));
+  fs.writeFileSync(pathname, '', 'utf8');
+  fs.mkdir(pathname, { recursive: true }, (err) => {
+    assert.strictEqual(err.code, 'EEXIST');
+    assert.strictEqual(err.syscall, 'mkdir');
+    assert.strictEqual(fs.statSync(pathname).isDirectory(), false);
+  });
+}
+
+// mkdirpSync dirname loop
+// XXX: windows and smartos have issues removing a directory that you're in.
+if (common.isMainThread && (common.isLinux || common.isOSX)) {
+  const pathname = path.join(tmpdir.path, nextdir());
+  fs.mkdirSync(pathname);
+  process.chdir(pathname);
+  fs.rmdirSync(pathname);
+  try {
+    fs.mkdirSync('X', { recursive: true });
+    throw new Error('unreachable');
+  } catch (err) {
+    assert.notStrictEqual(err.message, 'unreachable');
+    assert.strictEqual(err.code, 'ENOENT');
+    assert.strictEqual(err.syscall, 'mkdir');
+  }
+  fs.mkdir('X', { recursive: true }, (err) => {
+    assert.strictEqual(err.code, 'ENOENT');
+    assert.strictEqual(err.syscall, 'mkdir');
+  });
+}
+
 // Keep the event loop alive so the async mkdir() requests
 // have a chance to run (since they don't ref the event loop).
 process.nextTick(() => {});
diff --git a/test/parallel/test-fs-promises.js b/test/parallel/test-fs-promises.js
index 6bb3a871406ed2..bcfaaf3890d377 100644
--- a/test/parallel/test-fs-promises.js
+++ b/test/parallel/test-fs-promises.js
@@ -29,11 +29,17 @@ const {
   symlink,
   truncate,
   unlink,
-  utimes
+  utimes,
+  writeFile
 } = fsPromises;
 
 const tmpDir = tmpdir.path;
 
+let dirc = 0;
+function nextdir() {
+  return `test${++dirc}`;
+}
+
 // fs.promises should not be enumerable as long as it causes a warning to be
 // emitted.
 assert.strictEqual(Object.keys(fs).includes('promises'), false);
@@ -201,12 +207,49 @@ function verifyStatObject(stat) {
     await mkdir(newdir);
     stats = await stat(newdir);
     assert(stats.isDirectory());
-
     const list = await readdir(tmpDir);
     assert.deepStrictEqual(list, ['baz2.js', 'dir']);
-
     await rmdir(newdir);
 
+    // mkdirp when folder does not yet exist.
+    {
+      const dir = path.join(tmpDir, nextdir(), nextdir());
+      await mkdir(dir, { recursive: true });
+      stats = await stat(dir);
+      assert(stats.isDirectory());
+    }
+
+    // mkdirp when path is a file.
+    {
+      const dir = path.join(tmpDir, nextdir(), nextdir());
+      await mkdir(path.dirname(dir));
+      await writeFile(dir);
+      try {
+        await mkdir(dir, { recursive: true });
+        throw new Error('unreachable');
+      } catch (err) {
+        assert.notStrictEqual(err.message, 'unreachable');
+        assert.strictEqual(err.code, 'EEXIST');
+        assert.strictEqual(err.syscall, 'mkdir');
+      }
+    }
+
+    // mkdirp ./
+    {
+      const dir = path.resolve(tmpDir, `${nextdir()}/./${nextdir()}`);
+      await mkdir(dir, { recursive: true });
+      stats = await stat(dir);
+      assert(stats.isDirectory());
+    }
+
+    // mkdirp ../
+    {
+      const dir = path.resolve(tmpDir, `${nextdir()}/../${nextdir()}`);
+      await mkdir(dir, { recursive: true });
+      stats = await stat(dir);
+      assert(stats.isDirectory());
+    }
+
     await mkdtemp(path.resolve(tmpDir, 'FOO'));
     assert.rejects(
       // mkdtemp() expects to get a string prefix.