restorer: Add test for restore with include filter

[fd0]

What is the purpose of this change? What does it change?

Resolve an error with the restore command when an include filter is used.

Background:

traverseTree() was meant to call enterDir() whenever a directory is selected for restore, either explicitly or implicitly (=contains a file which is to be restored). After restoring a file, leaveDir() is called in reverse order for all intermediate directories so that the metadata can be restored.

When a directory is selected implicitly, the metadata for it is restored. This is different from the previous restorer behavior, which created implicitly selected intermediate directories with permissions 0700 (only user can read/write it).

This PR changes the behavior back to the old one. Only a directory is explicitly selected for restore, enterDir()/leaveDir() are called for it. Otherwise, only visitNode() is called, so visitNode() needs to make sure the parent directory exists. If the directory is explicitly included, leaveDir() will then restore the metadata correctly.

When we decide to change the behavior (restore metadata for all intermediate directories, even if selected implicitly), we should do that in the selection functions, not here.

This finally resolves #1870

Was the change discussed in an issue or in the forum before?

Closes #1870

Checklist

• I have read the Contribution Guidelines
• I have added tests for all changes in this PR
• There's a new file in changelog/unreleased/ that describes the changes for our users (template here)
• I have run gofmt on the code in all commits
• All commit messages are formatted in the same style as the other commits in the repo
• I'm done, this Pull Request is ready for review

[codecov-io]

Codecov Report

Merging #1900 into master will increase coverage by 0.09%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master    #1900      +/-   ##
==========================================
+ Coverage   51.06%   51.15%   +0.09%     
==========================================
  Files         169      169              
  Lines       13097    13083      -14     
==========================================
+ Hits         6688     6693       +5     
+ Misses       5401     5383      -18     
+ Partials     1008     1007       -1

Impacted Files	Coverage Δ
internal/restorer/restorer.go	45.38% <66.66%> (+3.71%)	⬆️
internal/backend/rclone/backend.go	64.32% <0%> (-1.76%)	⬇️
internal/archiver/file_saver.go	88.59% <0%> (+2.63%)	⬆️
internal/archiver/blob_saver.go	100% <0%> (+7.4%)	⬆️

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[ifedorenko]

Minor. I think there is no need to precreate dst directory in RestoreTo any more. By removing that code all created directories will default to the same 0700 permissions, which is both safer and more consistent. /~https://github.com/restic/restic/pull/1900/files#diff-7e901d641519cb52e213a5d339ee6d65L200

I also wonder if it'll be more "symmetrical" if directories and other node types were created in visitNode. This way it should be possible to remove enterDir, which would simplify the code. I can open follow-up PR to illustrate this, if you are interested.

Update: I tried removing enterDir and don't like the result.

[fd0]

I think we should either isolate the (fairly complex) treeVisitor from the restorer, or replace it with the recently introduced walker.Walk(). I'll give this a try so you can have a look.