Accept "cd dir/" again instead of using a subdirectory

Commit 69053d962 (Use menu behavior when completing change-directory,
2022-07-19) made ":cd dir/" actually run ":cd dir/first-subdir",
which can be surprising.
This is usually irrelevant because you rarely type the trailing slash.
However it does happen after correcting an error with `<backspace>`
and friends. For for example,

	:cd d<tab>/f<backspace>

results in

	:cd dir/

We should probably fix user expectations here. Do this by adding "dir/"
as valid completion.  This requires us to allow empty candidates in
"RankedMatch" but there's no harm in that. This means we need to
filter out empty completions from shell-script-candidates elsewhere.

Alternative fix: we could revert 69053d962. This would remove the
convenient menu behavior but that wouldn't be a huge deal.

Fixes #4775

1 files changed, 8 insertions, 0 deletions

diff --git a/src/file.cc b/src/file.cc
index ee358be0..c7092209 100644
--- a/src/file.cc
+++ b/src/file.cc
@@ -518,6 +518,14 @@ CandidateList complete_filename(StringView prefix, const Regex& ignored_regex,
         if (RankedMatch match{file, fileprefix})
             matches.push_back(match);
     }
+    // Hack: when completing directories, also echo back the query if it
+    // is a valid directory. This enables menu completion to select the
+    // directory instead of a child.
+    if (only_dirs and not dirname.empty() and dirname.back() == '/' and fileprefix.empty()
+        and /* exists on disk */ not files.empty())
+    {
+        matches.push_back(RankedMatch{fileprefix, fileprefix});
+    }
     std::sort(matches.begin(), matches.end());
     const bool expand = (flags & FilenameFlags::Expand);
     return candidates(matches, expand ? parsed_dirname : dirname);