git-read-tree: be a lot more careful about merging dirty trees

diff --git a/read-tree.c b/read-tree.c
index 283f4d8577261645d0f5e2d85b7f74f13b848f79..647f501f6aaef961e9f09db461a1051dd5d936ed 100644 (file)
--- a/read-tree.c
+++ b/read-tree.c
@@ -93,11 +93,46 @@ static struct cache_entry *merge_entries(struct cache_entry *a,
        return NULL;
 }
 
+/*
+ * When a CE gets turned into an unmerged entry, we
+ * want it to be up-to-date
+ */
+static void verify_uptodate(struct cache_entry *ce)
+{
+       struct stat st;
+
+       if (!lstat(ce->name, &st)) {
+               unsigned changed = ce_match_stat(ce, &st);
+               if (!changed)
+                       return;
+               errno = 0;
+       }
+       if (errno == ENOENT)
+               return;
+       die("Entry '%s' not uptodate. Cannot merge.", ce->name);
+}
+
+/*
+ * If the old tree contained a CE that isn't even in the
+ * result, that's always a problem, regardless of whether
+ * it's up-to-date or not (ie it can be a file that we
+ * have updated but not committed yet).
+ */
+static void verify_cleared(struct cache_entry *ce)
+{
+       if (ce)
+               die("Entry '%s' would be overwritten by merge. Cannot merge.", ce->name);
+}
+
+static int old_match(struct cache_entry *old, struct cache_entry *a)
+{
+       return old && path_matches(old, a) && same(old, a);
+}
+
 static void trivially_merge_cache(struct cache_entry **src, int nr)
 {
-       static struct cache_entry null_entry;
        struct cache_entry **dst = src;
-       struct cache_entry *old = &null_entry;
+       struct cache_entry *old = NULL;
 
        while (nr) {
                struct cache_entry *ce, *result;
@@ -106,6 +141,7 @@ static void trivially_merge_cache(struct cache_entry **src, int nr)
 
                /* We throw away original cache entries except for the stat information */
                if (!ce_stage(ce)) {
+                       verify_cleared(old);
                        old = ce;
                        src++;
                        nr--;
@@ -117,18 +153,30 @@ static void trivially_merge_cache(struct cache_entry **src, int nr)
                         * See if we can re-use the old CE directly?
                         * That way we get the uptodate stat info.
                         */
-                       if (path_matches(result, old) && same(result, old))
+                       if (old_match(old, result)) {
                                *result = *old;
+                               old = NULL;
+                       }
                        ce = result;
                        ce->ce_flags &= ~htons(CE_STAGEMASK);
                        src += 2;
                        nr -= 2;
                        active_nr -= 2;
                }
+
+               /*
+                * If we had an old entry that we now effectively
+                * overwrite, make sure it wasn't dirty.
+                */
+               if (old_match(old, ce)) {
+                       verify_uptodate(old);
+                       old = NULL;
+               }
                *dst++ = ce;
                src++;
                nr--;
        }
+       verify_cleared(old);
 }
 
 static void merge_stat_info(struct cache_entry **src, int nr)