git/unpack-trees.h
Elijah Newren 7af7a25853 unpack-trees: add a new update_sparsity() function
Previously, the only way to update the SKIP_WORKTREE bits for various
paths was invoking `git read-tree -mu HEAD` or calling the same code
that this codepath invoked.  This however had a number of problems if
the index or working directory were not clean.  First, let's consider
the case:

  Flipping SKIP_WORKTREE -> !SKIP_WORKTREE (materializing files)

If the working tree was clean this was fine, but if there were files or
directories or symlinks or whatever already present at the given path
then the operation would abort with an error.  Let's label this case
for later discussion:

    A) There is an untracked path in the way

Now let's consider the opposite case:

  Flipping !SKIP_WORKTREE -> SKIP_WORKTREE (removing files)

If the index and working tree was clean this was fine, but if there were
any unclean paths we would run into problems.  There are three different
cases to consider:

    B) The path is unmerged
    C) The path has unstaged changes
    D) The path has staged changes (differs from HEAD)

If any path fell into case B or C, then the whole operation would be
aborted with an error.  With sparse-checkout, the whole operation would
be aborted for case D as well, but for its predecessor of using `git
read-tree -mu HEAD` directly, any paths that fell into case D would be
removed from the working copy and the index entry for that path would be
reset to match HEAD -- which looks and feels like data loss to users
(only a few are even aware to ask whether it can be recovered, and even
then it requires walking through loose objects trying to match up the
right ones).

Refusing to remove files that have unsaved user changes is good, but
refusing to work on any other paths is very problematic for users.  If
the user is in the middle of a rebase or has made modifications to files
that bring in more dependencies, then for their build to work they need
to update the sparse paths.  This logic has been preventing them from
doing so.  Sometimes in response, the user will stage the files and
re-try, to no avail with sparse-checkout or to the horror of losing
their changes if they are using its predecessor of `git read-tree -mu
HEAD`.

Add a new update_sparsity() function which will not error out in any of
these cases but behaves as follows for the special cases:
    A) Leave the file in the working copy alone, clear the SKIP_WORKTREE
       bit, and print a warning (thus leaving the path in a state where
       status will report the file as modified, which seems logical).
    B) Do NOT mark this path as SKIP_WORKTREE, and leave it as unmerged.
    C) Do NOT mark this path as SKIP_WORKTREE and print a warning about
       the dirty path.
    D) Mark the path as SKIP_WORKTREE, but do not revert the version
       stored in the index to match HEAD; leave the contents alone.

I tried a different behavior for A (leave the SKIP_WORKTREE bit set),
but found it very surprising and counter-intuitive (e.g. the user sees
it is present along with all the other files in that directory, tries to
stage it, but git add ignores it since the SKIP_WORKTREE bit is set).  A
& C seem like optimal behavior to me.  B may be as well, though I wonder
if printing a warning would be an improvement.  Some might be slightly
surprised by D at first, but given that it does the right thing with
`git commit` and even `git commit -a` (`git add` ignores entries that
are marked SKIP_WORKTREE and thus doesn't delete them, and `commit -a`
is similar), it seems logical to me.

Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-03-27 11:33:30 -07:00

113 lines
2.9 KiB
C

#ifndef UNPACK_TREES_H
#define UNPACK_TREES_H
#include "cache.h"
#include "argv-array.h"
#include "string-list.h"
#include "tree-walk.h"
#define MAX_UNPACK_TREES MAX_TRAVERSE_TREES
struct cache_entry;
struct unpack_trees_options;
struct pattern_list;
typedef int (*merge_fn_t)(const struct cache_entry * const *src,
struct unpack_trees_options *options);
enum unpack_trees_error_types {
ERROR_WOULD_OVERWRITE = 0,
ERROR_NOT_UPTODATE_FILE,
ERROR_NOT_UPTODATE_DIR,
ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN,
ERROR_WOULD_LOSE_UNTRACKED_REMOVED,
ERROR_BIND_OVERLAP,
ERROR_SPARSE_NOT_UPTODATE_FILE,
ERROR_WOULD_LOSE_ORPHANED_OVERWRITTEN,
ERROR_WOULD_LOSE_SUBMODULE,
NB_UNPACK_TREES_ERROR_TYPES
};
/*
* Sets the list of user-friendly error messages to be used by the
* command "cmd" (either merge or checkout), and show_all_errors to 1.
*/
void setup_unpack_trees_porcelain(struct unpack_trees_options *opts,
const char *cmd);
/*
* Frees resources allocated by setup_unpack_trees_porcelain().
*/
void clear_unpack_trees_porcelain(struct unpack_trees_options *opts);
struct unpack_trees_options {
unsigned int reset,
merge,
update,
clone,
index_only,
nontrivial_merge,
trivial_merges_only,
verbose_update,
aggressive,
skip_unmerged,
initial_checkout,
diff_index_cached,
debug_unpack,
skip_sparse_checkout,
quiet,
exiting_early,
show_all_errors,
dry_run;
const char *prefix;
int cache_bottom;
struct dir_struct *dir;
struct pathspec *pathspec;
merge_fn_t fn;
const char *msgs[NB_UNPACK_TREES_ERROR_TYPES];
struct argv_array msgs_to_free;
/*
* Store error messages in an array, each case
* corresponding to a error message type
*/
struct string_list unpack_rejects[NB_UNPACK_TREES_ERROR_TYPES];
int head_idx;
int merge_size;
struct cache_entry *df_conflict_entry;
void *unpack_data;
struct index_state *dst_index;
struct index_state *src_index;
struct index_state result;
struct pattern_list *pl; /* for internal use */
};
int unpack_trees(unsigned n, struct tree_desc *t,
struct unpack_trees_options *options);
enum update_sparsity_result {
UPDATE_SPARSITY_SUCCESS = 0,
UPDATE_SPARSITY_WARNINGS = 1,
UPDATE_SPARSITY_INDEX_UPDATE_FAILURES = -1,
UPDATE_SPARSITY_WORKTREE_UPDATE_FAILURES = -2
};
enum update_sparsity_result update_sparsity(struct unpack_trees_options *options);
int verify_uptodate(const struct cache_entry *ce,
struct unpack_trees_options *o);
int threeway_merge(const struct cache_entry * const *stages,
struct unpack_trees_options *o);
int twoway_merge(const struct cache_entry * const *src,
struct unpack_trees_options *o);
int bind_merge(const struct cache_entry * const *src,
struct unpack_trees_options *o);
int oneway_merge(const struct cache_entry * const *src,
struct unpack_trees_options *o);
#endif