os, syscall: implement Stat and Lstat

File.Stat is left as a stub for now.

Tests are a bit stubbed down because os.ReadDir, os.Symlink, and t.TempDir are not yet (fully) implemented.
TODO: reimport tests from upstream as those materialize.

src/os/stat_test.go

@@ -0,0 +1,96 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os_test
+
+import (
+	"io/fs"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// testStatAndLstat verifies that all os.Stat, os.Lstat os.File.Stat and os.Readdir work.
+func testStatAndLstat(t *testing.T, path string, isLink bool, statCheck, lstatCheck func(*testing.T, string, fs.FileInfo)) {
+	// TODO: revert to upstream test once fstat and readdir are implemented
+	// test os.Stat
+	sfi, err := os.Stat(path)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	statCheck(t, path, sfi)
+
+	// test os.Lstat
+	lsfi, err := os.Lstat(path)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	lstatCheck(t, path, lsfi)
+
+	if isLink {
+		if os.SameFile(sfi, lsfi) {
+			t.Errorf("stat and lstat of %q should not be the same", path)
+		}
+	} else {
+		if !os.SameFile(sfi, lsfi) {
+			t.Errorf("stat and lstat of %q should be the same", path)
+		}
+	}
+}
+
+// testIsDir verifies that fi refers to directory.
+func testIsDir(t *testing.T, path string, fi fs.FileInfo) {
+	t.Helper()
+	if !fi.IsDir() {
+		t.Errorf("%q should be a directory", path)
+	}
+	if fi.Mode()&fs.ModeSymlink != 0 {
+		t.Errorf("%q should not be a symlink", path)
+	}
+}
+
+// testIsFile verifies that fi refers to file.
+func testIsFile(t *testing.T, path string, fi fs.FileInfo) {
+	t.Helper()
+	if fi.IsDir() {
+		t.Errorf("%q should not be a directory", path)
+	}
+	if fi.Mode()&fs.ModeSymlink != 0 {
+		t.Errorf("%q should not be a symlink", path)
+	}
+}
+
+func testDirStats(t *testing.T, path string) {
+	testStatAndLstat(t, path, false, testIsDir, testIsDir)
+}
+
+func testFileStats(t *testing.T, path string) {
+	testStatAndLstat(t, path, false, testIsFile, testIsFile)
+}
+
+func TestDirAndSymlinkStats(t *testing.T) {
+	// TODO: revert to upstream test once symlinks and t.TempDir are implemented
+	tmpdir := os.TempDir()
+	dir := filepath.Join(tmpdir, "dir")
+	os.Remove(dir)
+	if err := os.Mkdir(dir, 0777); err != nil {
+		t.Fatal(err)
+		return
+	}
+	testDirStats(t, dir)
+
+}
+
+func TestFileAndSymlinkStats(t *testing.T) {
+	// TODO: revert to upstream test once symlinks and t.TempDir are implemented
+	tmpdir := os.TempDir()
+	file := filepath.Join(tmpdir, "file")
+	if err := os.WriteFile(file, []byte("abcdefg"), 0644); err != nil {
+		t.Fatal(err)
+		return
+	}
+	testFileStats(t, file)
+}