reset: introduce dry-run mode

In a subsequent commit we'll add add another caller to `reset_head()`
that wants to perform a dry-run check of whether it would be possible to
udpate the index and working tree when moving to a new commit. Introduce
a new flag that lets the caller perform this operation.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/reset.c b/reset.c
index 9ff14f5ed168affacbf45b370a611495056f2ae5..a8d7eea4d6fb3f4f8618d77f3c4a4df298b292fe 100644 (file)
--- a/reset.c
+++ b/reset.c
@@ -92,11 +92,14 @@ int reset_head(struct repository *r, const struct reset_head_opts *opts)
        unsigned reset_hard = opts->flags & RESET_HEAD_HARD;
        unsigned refs_only = opts->flags & RESET_HEAD_REFS_ONLY;
        unsigned update_orig_head = opts->flags & RESET_HEAD_ORIG_HEAD;
+       unsigned dry_run = opts->flags & RESET_HEAD_DRY_RUN;
        struct object_id *head = NULL, head_oid;
        struct tree_desc desc[2] = { { NULL }, { NULL } };
        struct lock_file lock = LOCK_INIT;
        struct unpack_trees_options unpack_tree_opts = { 0 };
        struct tree *tree;
+       struct index_state scratch_index = INDEX_STATE_INIT(r);
+       struct index_state *istate;
        const char *action;
        int ret = 0, nr = 0;
 
@@ -109,7 +112,7 @@ int reset_head(struct repository *r, const struct reset_head_opts *opts)
        if (opts->branch_msg && !opts->branch)
                BUG("branch reflog message given without a branch");
 
-       if (!refs_only && repo_hold_locked_index(r, &lock, LOCK_REPORT_ON_ERROR) < 0) {
+       if (!refs_only && !dry_run && repo_hold_locked_index(r, &lock, LOCK_REPORT_ON_ERROR) < 0) {
                ret = -1;
                goto leave_reset_head;
        }
@@ -124,16 +127,36 @@ int reset_head(struct repository *r, const struct reset_head_opts *opts)
        if (!oid)
                oid = &head_oid;
 
-       if (refs_only)
-               return update_refs(r, opts, oid, head);
+       if (refs_only) {
+               if (!dry_run)
+                       return update_refs(r, opts, oid, head);
+               return 0;
+       }
+
+       if (dry_run) {
+               if (read_index_from(&scratch_index, r->index_file, r->gitdir) < 0 ||
+                   index_state_unmerged_to_stage0(&scratch_index) < 0) {
+                       ret = error(_("could not read index"));
+                       goto leave_reset_head;
+               }
+
+               istate = &scratch_index;
+       } else {
+               if (repo_read_index_unmerged(r) < 0) {
+                       ret = error(_("could not read index"));
+                       goto leave_reset_head;
+               }
+               istate = r->index;
+       }
 
        action = reset_hard ? "reset" : "checkout";
        setup_unpack_trees_porcelain(&unpack_tree_opts, action);
        unpack_tree_opts.head_idx = 1;
-       unpack_tree_opts.src_index = r->index;
-       unpack_tree_opts.dst_index = r->index;
+       unpack_tree_opts.src_index = istate;
+       unpack_tree_opts.dst_index = istate;
        unpack_tree_opts.fn = reset_hard ? oneway_merge : twoway_merge;
-       unpack_tree_opts.update = 1;
+       unpack_tree_opts.update = !dry_run;
+       unpack_tree_opts.dry_run = dry_run;
        unpack_tree_opts.merge = 1;
        unpack_tree_opts.preserve_ignored = 0; /* FIXME: !overwrite_ignore */
        unpack_tree_opts.skip_cache_tree_update = 1;
@@ -141,11 +164,6 @@ int reset_head(struct repository *r, const struct reset_head_opts *opts)
        if (reset_hard)
                unpack_tree_opts.reset = UNPACK_RESET_PROTECT_UNTRACKED;
 
-       if (repo_read_index_unmerged(r) < 0) {
-               ret = error(_("could not read index"));
-               goto leave_reset_head;
-       }
-
        if (!reset_hard && !fill_tree_descriptor(r, &desc[nr++], &head_oid)) {
                ret = error(_("failed to find tree of %s"),
                            oid_to_hex(&head_oid));
@@ -162,6 +180,9 @@ int reset_head(struct repository *r, const struct reset_head_opts *opts)
                goto leave_reset_head;
        }
 
+       if (dry_run)
+               goto leave_reset_head;
+
        tree = repo_parse_tree_indirect(r, oid);
        if (!tree) {
                ret = error(_("unable to read tree (%s)"), oid_to_hex(oid));
@@ -181,6 +202,7 @@ int reset_head(struct repository *r, const struct reset_head_opts *opts)
 leave_reset_head:
        rollback_lock_file(&lock);
        clear_unpack_trees_porcelain(&unpack_tree_opts);
+       release_index(&scratch_index);
        while (nr)
                free((void *)desc[--nr].buffer);
        return ret;

diff --git a/reset.h b/reset.h
index 97ced2601e35efed5672657333edc6926385a060..9f696382c1a4f890858877af392b0adc94663c24 100644 (file)
--- a/reset.h
+++ b/reset.h
@@ -21,6 +21,12 @@ enum reset_head_flags {
 
        /* Update ORIG_HEAD as well as HEAD */
        RESET_HEAD_ORIG_HEAD = (1 << 4),
+
+       /*
+        * Perform a dry-run by performing the operation without updating
+        * any user-visible state.
+        */
+       RESET_HEAD_DRY_RUN = (1 << 5),
 };
 
 struct reset_head_opts {