[pull] master from golang:master

src/cmd/go/testdata/script/gofmt_with_symlink.txt

@@ -0,0 +1,31 @@
+# Test that gofmt-ing a symlink works correctly. See #79735.
+
+# Skip on systems without unix-style symlinks
+[GOOS:windows] skip
+
+cd $WORK/a
+cp issue-original.go issue-expected.go
+exec go fmt issue-expected.go
+! cmp -q issue-expected.go issue-original.go
+
+# Create that symlink.
+exec ln -s issue-original.go issue-symlink.go
+
+# Now go fmt it.
+exec go fmt issue-symlink.go
+
+# Ensure that the symlinked file is equal to the expected.
+cmp issue-expected.go issue-symlink.go
+
+# Our source code and setup.
+-- $WORK/a/go.mod --
+module gofmt_symlink
+
+-- $WORK/a/issue-original.go --
+package main;
+
+import "fmt"
+
+func main() {
+       fmt.Println(  "Hello, world!!!"  )
+}

src/cmd/gofmt/gofmt.go

@@ -280,7 +280,7 @@ func processFile(filename string, info fs.FileInfo, in io.Reader, r *reporter) e
 			}
 
 			perm := info.Mode().Perm()
-			if err := writeFile(filename, src, res, perm, info.Size()); err != nil {
+			if err := writeFile(filename, src, res, perm); err != nil {
 				return err
 			}
 		}
@@ -465,7 +465,7 @@ func fileWeight(path string, info fs.FileInfo) int64 {
 }
 
 // writeFile updates a file with the new formatted data.
-func writeFile(filename string, orig, formatted []byte, perm fs.FileMode, size int64) error {
+func writeFile(filename string, orig, formatted []byte, perm fs.FileMode) error {
 	// Make a temporary backup file before rewriting the original file.
 	bakname, err := backupFile(filename, orig, perm)
 	if err != nil {
@@ -489,7 +489,7 @@ func writeFile(filename string, orig, formatted []byte, perm fs.FileMode, size i
 	}
 
 	n, err := fout.Write(formatted)
-	if err == nil && int64(n) < size {
+	if err == nil {
 		err = fout.Truncate(int64(n))
 	}
 

src/os/file.go

@@ -839,7 +839,13 @@ func (dir dirFS) ReadLink(name string) (string, error) {
 	if err != nil {
 		return "", &PathError{Op: "readlink", Path: name, Err: err}
 	}
-	return Readlink(fullname)
+	f, err := Readlink(fullname)
+	if err != nil {
+		// See comment in dirFS.Open.
+		err.(*PathError).Path = name
+		return "", err
+	}
+	return f, nil
 }
 
 // join returns the path for name in dir.

src/os/file_test.go

@@ -49,6 +49,19 @@ func TestDirFSReadLink(t *testing.T) {
 			t.Errorf("fs.ReadLink(fsys, %q) = %q, %v; want %q, <nil>", name, got, err, want)
 		}
 	}
+
+	const nonesuch = "dir/nonesuch"
+	_, err := fs.ReadLink(fsys, nonesuch)
+	if err == nil {
+		t.Fatal("fs.ReadLink of nonexistent file succeeded")
+	}
+	pe, ok := err.(*PathError)
+	if !ok {
+		t.Fatalf("fs.ReadLink error type = %T; want *PathError", err)
+	}
+	if pe.Path != nonesuch {
+		t.Errorf("fs.ReadLink(%q) error path = %q; want %q", nonesuch, pe.Path, nonesuch)
+	}
 }
 
 func TestDirFSLstat(t *testing.T) {
@@ -78,6 +91,19 @@ func TestDirFSLstat(t *testing.T) {
 			t.Errorf("fs.Lstat(fsys, %q).Mode().Type() = %v, %v; want %v, <nil>", name, got, err, want)
 		}
 	}
+
+	const nonesuch = "dir/nonesuch"
+	_, err := fs.Lstat(fsys, nonesuch)
+	if err == nil {
+		t.Fatal("fs.Lstat of nonexistent file succeeded")
+	}
+	pe, ok := err.(*PathError)
+	if !ok {
+		t.Fatalf("fs.Lstat error type = %T; want *PathError", err)
+	}
+	if pe.Path != nonesuch {
+		t.Errorf("fs.Lstat(%q) error path = %q; want %q", nonesuch, pe.Path, nonesuch)
+	}
 }
 
 func TestDirFSWalkDir(t *testing.T) {