cmd/go: support walking through overlay directories

Change-Id: I7d9d75aa1dbc34fec5073ca36091c626b9dd4920
Reviewed-on: https://go-review.googlesource.com/c/go/+/261537
Trust: Michael Matloob <matloob@golang.org>
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

5 files changed, 434 insertions, 14 deletions

diff --git a/src/cmd/go/internal/fsys/fsys.go b/src/cmd/go/internal/fsys/fsys.go
index d64ce0aba1..489af93496 100644
--- a/src/cmd/go/internal/fsys/fsys.go
+++ b/src/cmd/go/internal/fsys/fsys.go
@@ -208,8 +208,8 @@ func IsDir(path string) (bool, error) {
 }
 
 // parentIsOverlayFile returns whether name or any of
-// its parents are directories in the overlay, and the first parent found,
-// including name itself, that's a directory in the overlay.
+// its parents are files in the overlay, and the first parent found,
+// including name itself, that's a file in the overlay.
 func parentIsOverlayFile(name string) (string, bool) {
 	if overlay != nil {
 		// Check if name can't possibly be a directory because
@@ -385,6 +385,80 @@ func IsDirWithGoFiles(dir string) (bool, error) {
 	return false, firstErr
 }
 
+// walk recursively descends path, calling walkFn. Copied, with some
+// modifications from path/filepath.walk.
+func walk(path string, info os.FileInfo, walkFn filepath.WalkFunc) error {
+	if !info.IsDir() {
+		return walkFn(path, info, nil)
+	}
+
+	fis, readErr := ReadDir(path)
+	walkErr := walkFn(path, info, readErr)
+	// If readErr != nil, walk can't walk into this directory.
+	// walkErr != nil means walkFn want walk to skip this directory or stop walking.
+	// Therefore, if one of readErr and walkErr isn't nil, walk will return.
+	if readErr != nil || walkErr != nil {
+		// The caller's behavior is controlled by the return value, which is decided
+		// by walkFn. walkFn may ignore readErr and return nil.
+		// If walkFn returns SkipDir, it will be handled by the caller.
+		// So walk should return whatever walkFn returns.
+		return walkErr
+	}
+
+	for _, fi := range fis {
+		filename := filepath.Join(path, fi.Name())
+		if walkErr = walk(filename, fi, walkFn); walkErr != nil {
+			if !fi.IsDir() || walkErr != filepath.SkipDir {
+				return walkErr
+			}
+		}
+	}
+	return nil
+}
+
+// Walk walks the file tree rooted at root, calling walkFn for each file or
+// directory in the tree, including root.
+func Walk(root string, walkFn filepath.WalkFunc) error {
+	info, err := lstat(root)
+	if err != nil {
+		err = walkFn(root, nil, err)
+	} else {
+		err = walk(root, info, walkFn)
+	}
+	if err == filepath.SkipDir {
+		return nil
+	}
+	return err
+}
+
+// lstat implements a version of os.Lstat that operates on the overlay filesystem.
+func lstat(path string) (os.FileInfo, error) {
+	cpath := canonicalize(path)
+
+	if _, ok := parentIsOverlayFile(filepath.Dir(cpath)); ok {
+		return nil, &os.PathError{Op: "lstat", Path: cpath, Err: os.ErrNotExist}
+	}
+
+	node, ok := overlay[cpath]
+	if !ok {
+		// The file or directory is not overlaid.
+		return os.Lstat(cpath)
+	}
+
+	switch {
+	case node.isDeleted():
+		return nil, &os.PathError{Op: "lstat", Path: cpath, Err: os.ErrNotExist}
+	case node.isDir():
+		return fakeDir(filepath.Base(cpath)), nil
+	default:
+		fi, err := os.Lstat(node.actualFilePath)
+		if err != nil {
+			return nil, err
+		}
+		return fakeFile{name: filepath.Base(cpath), real: fi}, nil
+	}
+}
+
 // fakeFile provides an os.FileInfo implementation for an overlaid file,
 // so that the file has the name of the overlaid file, but takes all
 // other characteristics of the replacement file.
diff --git a/src/cmd/go/internal/fsys/fsys_test.go b/src/cmd/go/internal/fsys/fsys_test.go
index 4b53059427..0c3069a6a2 100644
--- a/src/cmd/go/internal/fsys/fsys_test.go
+++ b/src/cmd/go/internal/fsys/fsys_test.go
@@ -3,10 +3,12 @@ package fsys
 import (
 	"cmd/go/internal/txtar"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"reflect"
 	"testing"
 )
 
@@ -22,7 +24,10 @@ func initOverlay(t *testing.T, config string) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	cwd = t.TempDir()
+	cwd = filepath.Join(t.TempDir(), "root")
+	if err := os.Mkdir(cwd, 0777); err != nil {
+		t.Fatal(err)
+	}
 	if err := os.Chdir(cwd); err != nil {
 		t.Fatal(err)
 	}
@@ -477,3 +482,334 @@ contents don't matter for this test
 		}
 	}
 }
+
+func TestWalk(t *testing.T) {
+	type file struct {
+		path  string
+		name  string
+		size  int64
+		mode  os.FileMode
+		isDir bool
+	}
+	testCases := []struct {
+		name      string
+		overlay   string
+		root      string
+		wantFiles []file
+	}{
+		{"no overlay", `
+{}
+-- file.txt --
+`,
+			".",
+			[]file{
+				{".", "root", 0, os.ModeDir | 0700, true},
+				{"file.txt", "file.txt", 0, 0600, false},
+			},
+		},
+		{"overlay with different file", `
+{
+	"Replace": {
+		"file.txt": "other.txt"
+	}
+}
+-- file.txt --
+-- other.txt --
+contents of other file
+`,
+			".",
+			[]file{
+				{".", "root", 0, os.ModeDir | 0500, true},
+				{"file.txt", "file.txt", 23, 0600, false},
+				{"other.txt", "other.txt", 23, 0600, false},
+			},
+		},
+		{"overlay with new file", `
+{
+	"Replace": {
+		"file.txt": "other.txt"
+	}
+}
+-- other.txt --
+contents of other file
+`,
+			".",
+			[]file{
+				{".", "root", 0, os.ModeDir | 0500, true},
+				{"file.txt", "file.txt", 23, 0600, false},
+				{"other.txt", "other.txt", 23, 0600, false},
+			},
+		},
+		{"overlay with new directory", `
+{
+	"Replace": {
+		"dir/file.txt": "other.txt"
+	}
+}
+-- other.txt --
+contents of other file
+`,
+			".",
+			[]file{
+				{".", "root", 0, os.ModeDir | 0500, true},
+				{"dir", "dir", 0, os.ModeDir | 0500, true},
+				{"dir" + string(filepath.Separator) + "file.txt", "file.txt", 23, 0600, false},
+				{"other.txt", "other.txt", 23, 0600, false},
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			initOverlay(t, tc.overlay)
+
+			var got []file
+			Walk(tc.root, func(path string, info os.FileInfo, err error) error {
+				got = append(got, file{path, info.Name(), info.Size(), info.Mode(), info.IsDir()})
+				return nil
+			})
+
+			if len(got) != len(tc.wantFiles) {
+				t.Errorf("Walk: saw %#v in walk; want %#v", got, tc.wantFiles)
+			}
+			for i := 0; i < len(got) && i < len(tc.wantFiles); i++ {
+				if got[i].path != tc.wantFiles[i].path {
+					t.Errorf("path of file #%v in walk, got %q, want %q", i, got[i].path, tc.wantFiles[i].path)
+				}
+				if got[i].name != tc.wantFiles[i].name {
+					t.Errorf("name of file #%v in walk, got %q, want %q", i, got[i].name, tc.wantFiles[i].name)
+				}
+				if got[i].mode&(os.ModeDir|0700) != tc.wantFiles[i].mode {
+					t.Errorf("mode&(os.ModeDir|0700) for mode of file #%v in walk, got %v, want %v", i, got[i].mode&(os.ModeDir|0700), tc.wantFiles[i].mode)
+				}
+				if got[i].isDir != tc.wantFiles[i].isDir {
+					t.Errorf("isDir for file #%v in walk, got %v, want %v", i, got[i].isDir, tc.wantFiles[i].isDir)
+				}
+				if tc.wantFiles[i].isDir {
+					continue // don't check size for directories
+				}
+				if got[i].size != tc.wantFiles[i].size {
+					t.Errorf("size of file #%v in walk, got %v, want %v", i, got[i].size, tc.wantFiles[i].size)
+				}
+			}
+		})
+	}
+}
+
+func TestWalk_SkipDir(t *testing.T) {
+	initOverlay(t, `
+{
+	"Replace": {
+		"skipthisdir/file.go": "dummy.txt",
+		"dontskip/file.go": "dummy.txt",
+		"dontskip/skip/file.go": "dummy.txt"
+	}
+}
+-- dummy.txt --
+`)
+
+	var seen []string
+	Walk(".", func(path string, info os.FileInfo, err error) error {
+		seen = append(seen, path)
+		if path == "skipthisdir" || path == filepath.Join("dontskip", "skip") {
+			return filepath.SkipDir
+		}
+		return nil
+	})
+
+	wantSeen := []string{".", "dontskip", filepath.Join("dontskip", "file.go"), filepath.Join("dontskip", "skip"), "dummy.txt", "skipthisdir"}
+
+	if len(seen) != len(wantSeen) {
+		t.Errorf("paths seen in walk: got %v entries; want %v entries", len(seen), len(wantSeen))
+	}
+
+	for i := 0; i < len(seen) && i < len(wantSeen); i++ {
+		if seen[i] != wantSeen[i] {
+			t.Errorf("path #%v seen walking tree: want %q, got %q", i, seen[i], wantSeen[i])
+		}
+	}
+}
+
+func TestWalk_Error(t *testing.T) {
+	initOverlay(t, "{}")
+
+	alreadyCalled := false
+	err := Walk("foo", func(path string, info os.FileInfo, err error) error {
+		if alreadyCalled {
+			t.Fatal("expected walk function to be called exactly once, but it was called more than once")
+		}
+		alreadyCalled = true
+		return errors.New("returned from function")
+	})
+	if !alreadyCalled {
+		t.Fatal("expected walk function to be called exactly once, but it was never called")
+
+	}
+	if err == nil {
+		t.Fatalf("Walk: got no error, want error")
+	}
+	if err.Error() != "returned from function" {
+		t.Fatalf("Walk: got error %v, want \"returned from function\" error", err)
+	}
+}
+
+func TestWalk_Symlink(t *testing.T) {
+	initOverlay(t, `{
+	"Replace": {"overlay_symlink": "symlink"}
+}
+-- dir/file --`)
+
+	// Create symlink
+	if err := os.Symlink("dir", "symlink"); err != nil {
+		t.Error(err)
+	}
+
+	testCases := []struct {
+		name      string
+		dir       string
+		wantFiles []string
+	}{
+		{"control", "dir", []string{"dir", "dir" + string(filepath.Separator) + "file"}},
+		// ensure Walk doesn't wolk into the directory pointed to by the symlink
+		// (because it's supposed to use Lstat instead of Stat.
+		{"symlink_to_dir", "symlink", []string{"symlink"}},
+		{"overlay_to_symlink_to_dir", "overlay_symlink", []string{"overlay_symlink"}},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			var got []string
+
+			err := Walk(tc.dir, func(path string, info os.FileInfo, err error) error {
+				got = append(got, path)
+				if err != nil {
+					t.Errorf("walkfn: got non nil err argument: %v, want nil err argument", err)
+				}
+				return nil
+			})
+			if err != nil {
+				t.Errorf("Walk: got error %q, want nil", err)
+			}
+
+			if !reflect.DeepEqual(got, tc.wantFiles) {
+				t.Errorf("files examined by walk: got %v, want %v", got, tc.wantFiles)
+			}
+		})
+	}
+
+}
+
+func TestLstat(t *testing.T) {
+	type file struct {
+		name  string
+		size  int64
+		mode  os.FileMode // mode & (os.ModeDir|0x700): only check 'user' permissions
+		isDir bool
+	}
+
+	testCases := []struct {
+		name    string
+		overlay string
+		path    string
+
+		want    file
+		wantErr bool
+	}{
+		{
+			"regular_file",
+			`{}
+-- file.txt --
+contents`,
+			"file.txt",
+			file{"file.txt", 9, 0600, false},
+			false,
+		},
+		{
+			"new_file_in_overlay",
+			`{"Replace": {"file.txt": "dummy.txt"}}
+-- dummy.txt --
+contents`,
+			"file.txt",
+			file{"file.txt", 9, 0600, false},
+			false,
+		},
+		{
+			"file_replaced_in_overlay",
+			`{"Replace": {"file.txt": "dummy.txt"}}
+-- file.txt --
+-- dummy.txt --
+contents`,
+			"file.txt",
+			file{"file.txt", 9, 0600, false},
+			false,
+		},
+		{
+			"file_cant_exist",
+			`{"Replace": {"deleted": "dummy.txt"}}
+-- deleted/file.txt --
+-- dummy.txt --
+`,
+			"deleted/file.txt",
+			file{},
+			true,
+		},
+		{
+			"deleted",
+			`{"Replace": {"deleted": ""}}
+-- deleted --
+`,
+			"deleted",
+			file{},
+			true,
+		},
+		{
+			"dir_on_disk",
+			`{}
+-- dir/foo.txt --
+`,
+			"dir",
+			file{"dir", 0, 0700 | os.ModeDir, true},
+			false,
+		},
+		{
+			"dir_in_overlay",
+			`{"Replace": {"dir/file.txt": "dummy.txt"}}
+-- dummy.txt --
+`,
+			"dir",
+			file{"dir", 0, 0500 | os.ModeDir, true},
+			false,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			initOverlay(t, tc.overlay)
+			got, err := lstat(tc.path)
+			if tc.wantErr {
+				if err == nil {
+					t.Errorf("lstat(%q): got no error, want error", tc.path)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("lstat(%q): got error %v, want no error", tc.path, err)
+			}
+			if got.Name() != tc.want.name {
+				t.Errorf("lstat(%q).Name(): got %q, want %q", tc.path, got.Name(), tc.want.name)
+			}
+			if got.Mode()&(os.ModeDir|0700) != tc.want.mode {
+				t.Errorf("lstat(%q).Mode()&(os.ModeDir|0700): got %v, want %v", tc.path, got.Mode()&(os.ModeDir|0700), tc.want.mode)
+			}
+			if got.IsDir() != tc.want.isDir {
+				t.Errorf("lstat(%q).IsDir(): got %v, want %v", tc.path, got.IsDir(), tc.want.isDir)
+			}
+			if tc.want.isDir {
+				return // don't check size for directories
+			}
+			if got.Size() != tc.want.size {
+				t.Errorf("lstat(%q).Size(): got %v, want %v", tc.path, got.Size(), tc.want.size)
+			}
+		})
+	}
+}
diff --git a/src/cmd/go/internal/modload/search.go b/src/cmd/go/internal/modload/search.go
index a9bee0af4e..0f82026732 100644
--- a/src/cmd/go/internal/modload/search.go
+++ b/src/cmd/go/internal/modload/search.go
@@ -12,6 +12,7 @@ import (
 	"strings"
 
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/fsys"
 	"cmd/go/internal/imports"
 	"cmd/go/internal/search"
 
@@ -53,7 +54,7 @@ func matchPackages(ctx context.Context, m *search.Match, tags map[string]bool, f
 
 	walkPkgs := func(root, importPathRoot string, prune pruning) {
 		root = filepath.Clean(root)
-		err := filepath.Walk(root, func(path string, fi os.FileInfo, err error) error {
+		err := fsys.Walk(root, func(path string, fi os.FileInfo, err error) error {
 			if err != nil {
 				m.AddError(err)
 				return nil
diff --git a/src/cmd/go/internal/search/search.go b/src/cmd/go/internal/search/search.go
index 868dbf5f9d..b1d2a9376b 100644
--- a/src/cmd/go/internal/search/search.go
+++ b/src/cmd/go/internal/search/search.go
@@ -7,6 +7,7 @@ package search
 import (
 	"cmd/go/internal/base"
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/fsys"
 	"fmt"
 	"go/build"
 	"os"
@@ -127,7 +128,7 @@ func (m *Match) MatchPackages() {
 		if m.pattern == "cmd" {
 			root += "cmd" + string(filepath.Separator)
 		}
-		err := filepath.Walk(root, func(path string, fi os.FileInfo, err error) error {
+		err := fsys.Walk(root, func(path string, fi os.FileInfo, err error) error {
 			if err != nil {
 				return err // Likely a permission error, which could interfere with matching.
 			}
@@ -263,8 +264,7 @@ func (m *Match) MatchDirs() {
 		}
 	}
 
-	err := filepath.Walk(dir, func(path string, fi os.FileInfo, err error) error {
-		// TODO(#39958): Handle walk for overlays.
+	err := fsys.Walk(dir, func(path string, fi os.FileInfo, err error) error {
 		if err != nil {
 			return err // Likely a permission error, which could interfere with matching.
 		}
@@ -273,7 +273,7 @@ func (m *Match) MatchDirs() {
 		}
 		top := false
 		if path == dir {
-			// filepath.Walk starts at dir and recurses. For the recursive case,
+			// Walk starts at dir and recurses. For the recursive case,
 			// the path is the result of filepath.Join, which calls filepath.Clean.
 			// The initial case is not Cleaned, though, so we do this explicitly.
 			//
diff --git a/src/cmd/go/testdata/script/list_overlay.txt b/src/cmd/go/testdata/script/list_overlay.txt
index 7d0e3c2c81..1153975345 100644
--- a/src/cmd/go/testdata/script/list_overlay.txt
+++ b/src/cmd/go/testdata/script/list_overlay.txt
@@ -16,8 +16,17 @@ stdout '^\[h.go i.go\]$'
 ! go list ./dir3 # contains a file without a package statement
 go list -overlay overlay.json -f '{{.GoFiles}}' ./dir3 # overlay removes that file
 
+# Walking through an overlay
+go list -overlay overlay.json ./...
+cmp stdout want-list.txt
+
 # TODO(#39958): assembly files, C files, files that require cgo preprocessing
 
+-- want-list.txt --
+m
+m/dir
+m/dir2
+m/dir3
 -- go.mod --
 // TODO(#39958): Support and test overlays including go.mod itself (especially if mod=readonly)
 module m
@@ -34,21 +43,21 @@ package dir3
 -- overlay.json --
 {
     "Replace": {
-        "f.go": "overlay/f.go",
-        "dir/g.go": "overlay/dir_g.go",
-        "dir2/i.go": "overlay/dir2_i.go",
+        "f.go": "overlay/f_go",
+        "dir/g.go": "overlay/dir_g_go",
+        "dir2/i.go": "overlay/dir2_i_go",
         "dir3/bad.go": ""
     }
 }
--- overlay/f.go --
+-- overlay/f_go --
 package m
 
 func f() {
 }
--- overlay/dir_g.go --
+-- overlay/dir_g_go --
 package m
 
 func g() {
 }
--- overlay/dir2_i.go --
+-- overlay/dir2_i_go --
 package dir2