Merge branch 'jc/maint-checkout-keep-remove' into maint

* jc/maint-checkout-keep-remove:
  checkout: do not lose staged removal

Author: gitster

Documentation/git-read-tree.txt

@@ -160,7 +160,10 @@ Here are the "carry forward" rules:
       0 nothing             nothing  nothing  (does not happen)
       1 nothing             nothing  exists   use M
       2 nothing             exists   nothing  remove path from index
-      3 nothing             exists   exists   use M
+      3 nothing             exists   exists,  use M if "initial checkout"
+				     H == M   keep index otherwise
+				     exists   fail
+				     H != M
 
         clean I==H  I==M
        ------------------
@@ -207,6 +210,12 @@ you picked it up via e-mail in a patch form), `git diff-index
 merge, but it would not show in `git diff-index --cached $M`
 output after two-tree merge.
 
+Case #3 is slightly tricky and needs explanation.  The result from this
+rule logically should be to remove the path if the user staged the removal
+of the path and then swiching to a new branch.  That however will prevent
+the initial checkout from happening, so the rule is modified to use M (new
+tree) only when the contents of the index is empty.  Otherwise the removal
+of the path is kept as long as $H and $M are the same.
 
 3-Way Merge
 ~~~~~~~~~~~

builtin-checkout.c

@@ -269,6 +269,8 @@ static int merge_working_tree(struct checkout_opts *opts,
 		}
 
 		/* 2-way merge to the new branch */
+		topts.initial_checkout = (!active_nr &&
+					  (old->commit == new->commit));
 		topts.update = 1;
 		topts.merge = 1;
 		topts.gently = opts->merge;

builtin-read-tree.c

@@ -206,6 +206,7 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
 			break;
 		case 2:
 			opts.fn = twoway_merge;
+			opts.initial_checkout = !active_nr;
 			break;
 		case 3:
 		default:

unpack-trees.c

@@ -941,8 +941,17 @@ int twoway_merge(struct cache_entry **src, struct unpack_trees_options *o)
 			return -1;
 		}
 	}
-	else if (newtree)
+	else if (newtree) {
+		if (oldtree && !o->initial_checkout) {
+			/*
+			 * deletion of the path was staged;
+			 */
+			if (same(oldtree, newtree))
+				return 1;
+			return reject_merge(oldtree, o);
+		}
 		return merged_entry(newtree, current, o);
+	}
 	return deleted_entry(oldtree, current, o);
 }
 

unpack-trees.h

@@ -26,6 +26,7 @@ struct unpack_trees_options {
 		     verbose_update:1,
 		     aggressive:1,
 		     skip_unmerged:1,
+		     initial_checkout:1,
 		     gently:1;
 	const char *prefix;
 	int pos;