io/fs: add Stat and StatFS

Add Stat helper function, StatFS interface, and test.
Add Stat method to fstest.MapFS.
Add testing of Stat method to fstest.TestFS.

For #41190.

Change-Id: Icf8b6eb1c3fa6f93a9be8405ec5a9468fb1da97b
Reviewed-on: https://go-review.googlesource.com/c/go/+/243913
Trust: Russ Cox <rsc@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

2 files changed, 28 insertions, 1 deletions

diff --git a/src/testing/fstest/mapfs.go b/src/testing/fstest/mapfs.go
index e969ac2bd1..b01911e589 100644
--- a/src/testing/fstest/mapfs.go
+++ b/src/testing/fstest/mapfs.go
@@ -120,6 +120,10 @@ func (fsys MapFS) ReadFile(name string) ([]byte, error) {
 	return fs.ReadFile(fsOnly{fsys}, name)
 }
 
+func (fsys MapFS) Stat(name string) (fs.FileInfo, error) {
+	return fs.Stat(fsOnly{fsys}, name)
+}
+
 // A mapFileInfo implements fs.FileInfo and fs.DirEntry for a given map file.
 type mapFileInfo struct {
 	name string
diff --git a/src/testing/fstest/testfs.go b/src/testing/fstest/testfs.go
index 66725ca2a4..290d2596cc 100644
--- a/src/testing/fstest/testfs.go
+++ b/src/testing/fstest/testfs.go
@@ -230,7 +230,30 @@ func (t *fsTester) checkStat(path string, entry fs.DirEntry) {
 	fentry := formatEntry(entry)
 	finfo := formatInfoEntry(info)
 	if fentry != finfo {
-		t.errorf("%s: mismatch:\n\tentry = %v\n\tfile.Stat() = %v", path, fentry, finfo)
+		t.errorf("%s: mismatch:\n\tentry = %s\n\tfile.Stat() = %s", path, fentry, finfo)
+	}
+
+	info2, err := fs.Stat(t.fsys, path)
+	if err != nil {
+		t.errorf("%s: fs.Stat: %v", path, err)
+		return
+	}
+	finfo = formatInfo(info)
+	finfo2 := formatInfo(info2)
+	if finfo2 != finfo {
+		t.errorf("%s: fs.Stat(...) = %s\n\twant %s", path, finfo2, finfo)
+	}
+
+	if fsys, ok := t.fsys.(fs.StatFS); ok {
+		info2, err := fsys.Stat(path)
+		if err != nil {
+			t.errorf("%s: fsys.Stat: %v", path, err)
+			return
+		}
+		finfo2 := formatInfo(info2)
+		if finfo2 != finfo {
+			t.errorf("%s: fsys.Stat(...) = %s\n\twant %s", path, finfo2, finfo)
+		}
 	}
 }