resolve-undo: "checkout -m path" uses resolve-undo information

Once you resolved conflicts by "git add path", you cannot recreate the
conflicted state with "git checkout -m path", because you lost information
from higher stages in the index when you resolved them.

Since we record the necessary information in the resolve-undo index
extension these days, we can reproduce the unmerged state in the index and
check it out.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

5 files changed, 77 insertions, 0 deletions

diff --git a/builtin-checkout.c b/builtin-checkout.c
index a0fe7a4e6..bdef1aa38 100644
--- a/builtin-checkout.c
+++ b/builtin-checkout.c
@@ -235,6 +235,10 @@ static int checkout_paths(struct tree *source_tree, const char **pathspec,
 	if (report_path_error(ps_matched, pathspec, 0))
 		return 1;
 
+	/* "checkout -m path" to recreate conflicted state */
+	if (opts->merge)
+		unmerge_cache(pathspec);
+
 	/* Any unmerged paths? */
 	for (pos = 0; pos < active_nr; pos++) {
 		struct cache_entry *ce = active_cache[pos];
diff --git a/cache.h b/cache.h
index 310d9e672..f479f0919 100644
--- a/cache.h
+++ b/cache.h
@@ -338,6 +338,7 @@ static inline void remove_name_hash(struct cache_entry *ce)
 #define cache_name_exists(name, namelen, igncase) index_name_exists(&the_index, (name), (namelen), (igncase))
 #define cache_name_is_other(name, namelen) index_name_is_other(&the_index, (name), (namelen))
 #define resolve_undo_clear() resolve_undo_clear_index(&the_index)
+#define unmerge_cache(pathspec) unmerge_index(&the_index, pathspec)
 #endif
 
 enum object_type {
diff --git a/resolve-undo.c b/resolve-undo.c
index 86e8547ca..37d73cd94 100644
--- a/resolve-undo.c
+++ b/resolve-undo.c
@@ -1,4 +1,5 @@
 #include "cache.h"
+#include "dir.h"
 #include "resolve-undo.h"
 #include "string-list.h"
 
@@ -115,3 +116,61 @@ void resolve_undo_clear_index(struct index_state *istate)
 	istate->resolve_undo = NULL;
 	istate->cache_changed = 1;
 }
+
+int unmerge_index_entry_at(struct index_state *istate, int pos)
+{
+	struct cache_entry *ce;
+	struct string_list_item *item;
+	struct resolve_undo_info *ru;
+	int i, err = 0;
+
+	if (!istate->resolve_undo)
+		return pos;
+
+	ce = istate->cache[pos];
+	if (ce_stage(ce)) {
+		/* already unmerged */
+		while ((pos < istate->cache_nr) &&
+		       ! strcmp(istate->cache[pos]->name, ce->name))
+			pos++;
+		return pos - 1; /* return the last entry processed */
+	}
+	item = string_list_lookup(ce->name, istate->resolve_undo);
+	if (!item)
+		return pos;
+	ru = item->util;
+	if (!ru)
+		return pos;
+	remove_index_entry_at(istate, pos);
+	for (i = 0; i < 3; i++) {
+		struct cache_entry *nce;
+		if (!ru->mode[i])
+			continue;
+		nce = make_cache_entry(ru->mode[i], ru->sha1[i],
+				       ce->name, i + 1, 0);
+		if (add_index_entry(istate, nce, ADD_CACHE_OK_TO_ADD)) {
+			err = 1;
+			error("cannot unmerge '%s'", ce->name);
+		}
+	}
+	if (err)
+		return pos;
+	free(ru);
+	item->util = NULL;
+	return unmerge_index_entry_at(istate, pos);
+}
+
+void unmerge_index(struct index_state *istate, const char **pathspec)
+{
+	int i;
+
+	if (!istate->resolve_undo)
+		return;
+
+	for (i = 0; i < istate->cache_nr; i++) {
+		struct cache_entry *ce = istate->cache[i];
+		if (!match_pathspec(pathspec, ce->name, ce_namelen(ce), 0, NULL))
+			continue;
+		i = unmerge_index_entry_at(istate, i);
+	}
+}
diff --git a/resolve-undo.h b/resolve-undo.h
index 74194d0eb..e4e5c1b1a 100644
--- a/resolve-undo.h
+++ b/resolve-undo.h
@@ -10,5 +10,7 @@ extern void record_resolve_undo(struct index_state *, struct cache_entry *);
 extern void resolve_undo_write(struct strbuf *, struct string_list *);
 extern struct string_list *resolve_undo_read(void *, unsigned long);
 extern void resolve_undo_clear_index(struct index_state *);
+extern int unmerge_index_entry_at(struct index_state *, int);
+extern void unmerge_index(struct index_state *, const char **);
 
 #endif
diff --git a/t/t2030-unresolve-info.sh b/t/t2030-unresolve-info.sh
index 984480271..ea65f391c 100755
--- a/t/t2030-unresolve-info.sh
+++ b/t/t2030-unresolve-info.sh
@@ -97,4 +97,15 @@ test_expect_success 'plumbing clears' '
 	check_resolve_undo cleared
 '
 
+test_expect_success 'add records checkout -m undoes' '
+	prime_resolve_undo &&
+	git diff HEAD &&
+	git checkout --conflict=merge file &&
+	echo checkout used the record and removed it &&
+	check_resolve_undo removed &&
+	echo the index and the work tree is unmerged again &&
+	git diff >actual &&
+	grep "^++<<<<<<<" actual
+'
+
 test_done