os: recomment MkdirAll
The internal comments are not completely precise about
what is going on, and they are causing confusion.
Fixes #8283.
LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/151460043
diff --git a/src/os/path.go b/src/os/path.go
index 24a3415..84a3be3 100644
--- a/src/os/path.go
+++ b/src/os/path.go
@@ -17,7 +17,7 @@
// If path is already a directory, MkdirAll does nothing
// and returns nil.
func MkdirAll(path string, perm FileMode) error {
- // If path exists, stop with success or error.
+ // Fast path: if we can tell whether path is a directory or file, stop with success or error.
dir, err := Stat(path)
if err == nil {
if dir.IsDir() {
@@ -26,7 +26,7 @@
return &PathError{"mkdir", path, syscall.ENOTDIR}
}
- // Doesn't already exist; make sure parent does.
+ // Slow path: make sure parent exists and then call Mkdir for path.
i := len(path)
for i > 0 && IsPathSeparator(path[i-1]) { // Skip trailing path separator.
i--
@@ -45,7 +45,7 @@
}
}
- // Now parent exists, try to create.
+ // Parent now exists; invoke Mkdir and use its result.
err = Mkdir(path, perm)
if err != nil {
// Handle arguments like "foo/." by
