fix: "Follow symlink" to work with arbitrary links (#12246)

This change introduces a Path method on the TreeEntry struct, that
collects the path by moving upwards in the tree.

The existing FollowSymlink(s) methods interface has been changed, the
previously returned string has been removed, as after the fix it wasn't
used anywhere.

Fixes: #9931

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/12246
Reviewed-by: Gusted <gusted@noreply.codeberg.org>

modules/git/tree_entry.go

@@ -5,6 +5,7 @@
 package git
 
 import (
+	"fmt"
 	"io"
 	"sort"
 	"strings"
@@ -136,11 +137,11 @@ func (te *TreeEntry) LinkTarget() (string, error) {
 }
 
 // FollowLink returns the entry pointed to by a symlink
-func (te *TreeEntry) FollowLink() (*TreeEntry, string, error) {
+func (te *TreeEntry) FollowLink() (*TreeEntry, error) {
 	// read the link
 	lnk, err := te.LinkTarget()
 	if err != nil {
-		return nil, "", err
+		return nil, err
 	}
 
 	t := te.ptree
@@ -151,35 +152,33 @@ func (te *TreeEntry) FollowLink() (*TreeEntry, string, error) {
 	}
 
 	if t == nil {
-		return nil, "", ErrBadLink{te.Name(), "points outside of repo"}
+		return nil, ErrBadLink{te.Name(), "points outside of repo"}
 	}
 
 	target, err := t.GetTreeEntryByPath(lnk)
 	if err != nil {
 		if IsErrNotExist(err) {
-			return nil, "", ErrBadLink{te.Name(), "broken link"}
+			return nil, ErrBadLink{te.Name(), "broken link"}
 		}
-		return nil, "", err
+		return nil, err
 	}
-	return target, lnk, nil
+	return target, nil
 }
 
 // FollowLinks returns the entry ultimately pointed to by a symlink
-func (te *TreeEntry) FollowLinks() (*TreeEntry, string, error) {
+func (te *TreeEntry) FollowLinks() (*TreeEntry, error) {
 	if !te.IsLink() {
-		return nil, "", ErrBadLink{te.Name(), "not a symlink"}
+		return nil, ErrBadLink{te.Name(), "not a symlink"}
 	}
 	entry := te
-	entryLink := ""
 	for range 999 {
 		if entry.IsLink() {
-			next, link, err := entry.FollowLink()
-			entryLink = link
+			next, err := entry.FollowLink()
 			if err != nil {
-				return nil, "", err
+				return nil, err
 			}
 			if next.ID == entry.ID {
-				return nil, "", ErrBadLink{
+				return nil, ErrBadLink{
 					entry.Name(),
 					"recursive link",
 				}
@@ -190,12 +189,12 @@ func (te *TreeEntry) FollowLinks() (*TreeEntry, string, error) {
 		}
 	}
 	if entry.IsLink() {
-		return nil, "", ErrBadLink{
+		return nil, ErrBadLink{
 			te.Name(),
 			"too many levels of symbolic links",
 		}
 	}
-	return entry, entryLink, nil
+	return entry, nil
 }
 
 // returns the Tree pointed to by this TreeEntry, or nil if this is not a tree
@@ -208,6 +207,42 @@ func (te *TreeEntry) Tree() *Tree {
 	return t
 }
 
+// returns the calulcated path within the tree of this TreeEntry, or an error if it can be determined
+func (te *TreeEntry) Path() (string, error) {
+	targetPath := te.Name()
+	parentTree := te.ptree
+	if parentTree == nil {
+		return "", fmt.Errorf("couldn't find the parent tree of the entry")
+	}
+
+	prevID := parentTree.ID
+	parentTree = parentTree.ptree
+	for parentTree != nil {
+		entries, err := parentTree.ListEntries()
+		if err != nil {
+			return "", fmt.Errorf("couldn't list entries: %v", err)
+		}
+
+		var matchingEntry *TreeEntry
+		for _, entry := range entries {
+			if entry.ID == prevID {
+				matchingEntry = entry
+				break
+			}
+		}
+
+		if matchingEntry == nil {
+			return "", fmt.Errorf("this shouldn't happen: couldn't find entry (ID: %s) in tree (ID: %s)", prevID, parentTree.ID)
+		}
+
+		targetPath = matchingEntry.name + "/" + targetPath
+		prevID = parentTree.ID
+		parentTree = parentTree.ptree
+	}
+
+	return targetPath, nil
+}
+
 // GetSubJumpablePathName return the full path of subdirectory jumpable ( contains only one directory )
 func (te *TreeEntry) GetSubJumpablePathName() string {
 	if te.IsSubmodule() || !te.IsDir() {

modules/git/tree_entry_test.go

@@ -0,0 +1,46 @@
+// Copyright 2015 The Gogs Authors. All rights reserved.
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package git_test
+
+import (
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestTreeEntry_Path(t *testing.T) {
+	repo, err := openRepositoryWithDefaultContext(filepath.Join(testReposDir, "templates_repo"))
+	require.NoError(t, err)
+	defer repo.Close()
+
+	tests := []struct {
+		name string // description of this test case
+		path string
+	}{
+		{
+			name: "Top level dir",
+			path: ".forgejo",
+		},
+		{
+			name: "File in subdir",
+			path: ".forgejo/default_merge_message/MERGE_TEMPLATE.md",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			tree, err := repo.GetTree("HEAD^{tree}")
+			require.NoError(t, err)
+
+			te, err := tree.GetTreeEntryByPath(tt.path)
+			require.NoError(t, err)
+
+			got, gotErr := te.Path()
+			require.NoError(t, gotErr, "Path() failed: %v", gotErr)
+			assert.Equal(t, tt.path, got, "Path() = %v, want %v", got, tt.path)
+		})
+	}
+}