ls: Rework and simplify logic

This commit introduces two functions: withinDir() and
approachingMatchingTree()

Both bind the list of directories with a closure, so we don't need to
iterate over the list in the function passed to Walk(). This reduces the
indentation level and since we can just use return, we don't need the
breaks any more.

The case that len(dirs) == 0 can also be handled by the functions with a
return, which saves another indentation level.

The main function body of the function passed to Walk() was reduced to
three cases:

 * Within one of the dirs: Print the node, and if recursive operation is
   requested, directly return, so the walker continues recursive
   traversal

 * Approaching one of the dirs: don't print anything, but continue
   recursive traversal.

 * Nothing of the two: abort walking this branch of the tree.

cmd/restic/cmd_ls.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"context"
-	"path"
 	"strings"
 
 	"github.com/spf13/cobra"
@@ -76,6 +75,40 @@ func runLs(opts LsOptions, gopts GlobalOptions, args []string) error {
 		}
 	}
 
+	withinDir := func(nodepath string) bool {
+		if len(dirs) == 0 {
+			return true
+		}
+
+		for _, dir := range dirs {
+			// we're within one of the selected dirs, example:
+			//   nodepath: "/test/foo"
+			//   dir:      "/test"
+			if fs.HasPathPrefix(dir, nodepath) {
+				return true
+			}
+		}
+		return false
+	}
+
+	approachingMatchingTree := func(nodepath string) bool {
+		if len(dirs) == 0 {
+			return true
+		}
+
+		for _, dir := range dirs {
+			// the current node path is a prefix for one of the
+			// directories, so we're interested in something deeper in the
+			// tree. Example:
+			//   nodepath: "/test"
+			//   dir:      "/test/foo"
+			if fs.HasPathPrefix(nodepath, dir) {
+				return true
+			}
+		}
+		return false
+	}
+
 	repo, err := OpenRepository(gopts)
 	if err != nil {
 		return err
@@ -98,85 +131,31 @@ func runLs(opts LsOptions, gopts GlobalOptions, args []string) error {
 				return false, nil
 			}
 
-			// apply any directory filters
+			if withinDir(nodepath) {
-			if len(dirs) > 0 {
+				// if we're within a dir, print the node
-				nodeDir := path.Dir(nodepath)
-
-				// this first iteration ensures we do not traverse branches that
-				// are not in matching trees or will not lead us to matching trees
-				var walk bool
-				for _, dir := range dirs {
-
-					// the current node path is a prefix for one of the
-					// directories, so we're interested in something deeper in the
-					// tree. Example:
-					//   nodepath: "/test"
-					//   dir:      "/test/foo"
-					approachingMatchingTree := fs.HasPathPrefix(nodepath, dir)
-
-					// we're within one of the selected dirs, example:
-					//   nodepath: "/test/foo"
-					//   dir:      "/test"
-					inMatchingTree := fs.HasPathPrefix(dir, nodepath)
-
-					// this condition is complex, but it basically requires that we
-					// are either approaching a matching tree (not yet deep enough)
-					// or: if recursive, we have entered a matching tree; if non-
-					// recursive, then that we are at exactly the right depth
-					// (we can do the walk correctly by just using the condition of
-					// "approachingMatchingTree || inMatchingTree", but it will be
-					// much slower for non-recursive queries since it will continue
-					// to traverse subtrees that are too deep and won't match -- this
-					// extra check allows us to return SkipNode if we've gone TOO deep,
-					// which skips all its subfolders)
-					if approachingMatchingTree || opts.Recursive || (inMatchingTree && dir == nodeDir) {
-						walk = true
-						break
-					}
-				}
-				if !walk {
-					if node.Type == "dir" {
-						// signal Walk() that it should not descend into the tree.
-						return false, walker.SkipNode
-					}
-
-					// we must not return SkipNode for non-dir nodes because
-					// then the remaining nodes in the same tree would be
-					// skipped, so return nil instead
-					return false, nil
-				}
-
-				// this second iteration ensures that we get an exact match
-				// according to the filter and whether we should match subfolders
-				var match bool
-				for _, dir := range dirs {
-					if nodepath == dir {
-						// special case: match the directory filter exactly,
-						// which may or may not be desirable depending on your
-						// use case (for example, this is unnecessary when
-						// wanting to simply list the contents of a folder,
-						// rather than all files matching a directory prefix)
-						match = true
-						break
-					}
-					if opts.Recursive && fs.HasPathPrefix(dir, nodepath) {
-						match = true
-						break
-					}
-					if !opts.Recursive && nodeDir == dir {
-						match = true
-						break
-					}
-				}
-				if !match {
-					return false, nil
-				}
-			}
-
 				Printf("%s\n", formatNode(nodepath, node, lsOptions.ListLong))
 
+				// if recursive listing is requested, signal the walker that it
+				// should continue walking recursively
+				if opts.Recursive {
+					return false, nil
+				}
+			}
+
+			// if there's an upcoming match deeper in the tree (but we're not
+			// there yet), signal the walker to descend into any subdirs
+			if approachingMatchingTree(nodepath) {
+				return false, nil
+			}
+
+			// otherwise, signal the walker to not walk recursively into any
+			// subdirs
+			if node.Type == "dir" {
+				return false, walker.SkipNode
+			}
 			return false, nil
 		})
+
 		if err != nil {
 			return err
 		}