virtualfilesystem: fix case where directories not handled correctly

[jamill]

The vfs does not correctly handle the case when there is a file
that begins with the same prefix as a directory. For example, the
following setup would encounter this issue:

A directory contains a file named `dir1.sln` and a directory
named `dir1/`.

The directory `dir1` contains other files.

The directory `dir1` is in the virtual file system list

The contents of dir1 should be in the virtual file system, but
it is not. The contents of this directory do not have the skip
worktree bit cleared as expected. The problem is in the
apply_virtualfilesystem(…) function where it does not include
the trailing slash of the directory name when looking up the
position in the index to start clearing the skip worktree bit.

This fix is it include the trailing slash when finding the first
index entry from index_name_pos(...).

[jamill]

It appears the problem is that when we have both a file and a directory, where the name of the directory is a prefix of the name of the file (i.e. dir1 and dir1.sln), then the logic to clear the CE_SKIP_WORKTREE bit does not clear the bit for the files in the directory.

In this case, index_name_pos(...) will return the position of the file in the directory (e.g. the index position for dir1.sln), but the condition for the follow while will be false from fspathncmp(...)

[benpeart]

It appears the problem is that when we have both a file and a directory, where the name of the directory is a prefix of the name of the file (i.e. dir1 and dir1.sln), then the logic to clear the CE_SKIP_WORKTREE bit does not clear the bit for the files in the directory.

In this case, index_name_pos(...) will return the position of the file in the directory (e.g. the index position for dir1.sln), but the condition for the follow while will be false from fspathncmp(...)

Thanks for finding this! As you have determined, the problem here is that the file (dir1.sln) is found by the call to index_name_pos() instead of the first path with dir1 as the directory name. The fix is to include the trailing slash when calling index_name_pos() so that the while loop is starting on the correct entry. The following patch will fix the issue:

diff --git a/virtualfilesystem.c b/virtualfilesystem.c
index d70f10c310..424680b437 100644
--- a/virtualfilesystem.c
+++ b/virtualfilesystem.c
@@ -273,7 +273,7 @@ void apply_virtualfilesystem(struct index_state *istate)
                        if (buf[i - 1] == '/') {
                                if (ignore_case)
                                        adjust_dirname_case(istate, entry);
-                               pos = index_name_pos(istate, entry, len - 1);
+                               pos = index_name_pos(istate, entry, len);
                                if (pos < 0) {
                                        pos = -pos - 1;
                                        while (pos < istate->cache_nr && !fspathncmp(istate->cache[pos]->name,
 entry, len)) {

[jamill]

@benpeart - I included your proposed fix and tweaked the test to not make permanent changes to the test repository.

[benpeart]

The test and code fix look good. The commit message is awkwardly worded.