[PATCH v2] dir: check for single file cone patterns

From: William Sprent <williams@unity3d.com>

The sparse checkout documentation states that the cone mode pattern set is limited to patterns that either recursively include directories or patterns that match all files in a directory. In the sparse checkout file, the former manifest in the form:

    /A/B/C/

while the latter become a pair of patterns either in the form:

    /A/B/
    !/A/B/*/

or in the special case of matching the toplevel files:

    /*
    !/*/

The 'add_pattern_to_hashsets()' function contains checks which serve to disable cone-mode when non-cone patterns are encountered. However, these do not catch when the pattern list attempts to match a single file or directory, e.g. a pattern in the form:

    /A/B/C

This causes sparse-checkout to exhibit unexpected behaviour when such a pattern is in the sparse-checkout file and cone mode is enabled. Concretely, with the pattern like the above, sparse-checkout, in non-cone mode, will only include the directory or file located at '/A/B/C'. However, with cone mode enabled, sparse-checkout will instead just manifest the toplevel files but not any file located at '/A/B/C'.

Relatedly, issues occur when supplying the same kind of filter when partial cloning with '--filter=sparse:oid=<oid>'. 'upload-pack' will correctly just include the objects that match the non-cone pattern matching. Which means that checking out the newly cloned repo with the same filter, but with cone mode enabled, fails due to missing objects.

To fix these issues, add a cone mode pattern check that asserts that every pattern is either a directory match or the pattern '/*'. Add a test to verify the new pattern check and modify another to reflect that non-directory patterns are caught earlier.

Signed-off-by: William Sprent <williams@unity3d.com>
---
    dir: check for single file cone patterns
    
    Resubmitting this without the superfluous double negation of the
    'strcmp' output.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1446%2Fwilliams-unity%2Fws%2Fsparse-checkout-pattern-match-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1446/williams-unity/ws/sparse-checkout-pattern-match-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/1446

Range-diff vs v1:

 1:  cfb4b75c378 ! 1:  d5406e62f6f dir: check for single file cone patterns
     @@ dir.c: static void add_pattern_to_hashsets(struct pattern_list *pl, struct path_
       	}
       
      +	if (!(given->flags & PATTERN_FLAG_MUSTBEDIR) &&
     -+	    !!strcmp(given->pattern, "/*")) {
     ++	    strcmp(given->pattern, "/*")) {
      +		/* Not a cone pattern. */
      +		warning(_("unrecognized pattern: '%s'"), given->pattern);
      +		goto clear_hashmaps;

 dir.c                              |  7 +++++++
 t/t1091-sparse-checkout-builtin.sh | 11 ++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)