fs: add recursive copy method

Introduces recursive copy method, based on fs-extra implementation

Refs: nodejs/tooling#98

Author: bcoe

lib/internal/fs/copy/copy.js

@@ -394,6 +394,8 @@ function copyDirItem(items, item, src, dest, opts, cb) {
 function onLink(destStat, src, dest, opts, cb) {
   readlink(src, (err, resolvedSrc) => {
     if (err) return cb(err);
+    // TODO(bcoe): I don't know how this could be called, because
+    // getStatsForCopy will have used stat. Ask during review.
     if (opts.dereference) {
       resolvedSrc = resolve(process.cwd(), resolvedSrc);
     }
@@ -428,6 +430,8 @@ function onLink(destStat, src, dest, opts, cb) {
       // Do not copy if src is a subdir of dest since unlinking
       // dest in this case would result in removing src contents
       // and therefore a broken symlink would be created.
+      // TODO(bcoe): I'm having trouble exercising this code in test,
+      // ask about during review.
       if (destStat.isDirectory() &&
           stat.isSrcSubdir(resolvedDest, resolvedSrc)) {
         return cb(new ERR_FS_COPY_SYMLINK_TO_SUBDIRECTORY({
@@ -440,7 +444,6 @@ function onLink(destStat, src, dest, opts, cb) {
       }
       return copyLink(resolvedSrc, dest, cb);
     });
-
   });
 }
 

test/fixtures/copy/files-and-folders/README.md

@@ -0,0 +1 @@
+# Hello

test/fixtures/copy/files-and-folders/sub-folder/hello.mjs

@@ -0,0 +1 @@
+../../README.md

test/fixtures/copy/kitchen-sink/README.md

@@ -0,0 +1 @@
+b