Revert "checkout branch: prime cache-tree fully"

The logic in 83ae209 (checkout branch: prime cache-tree fully,
2009-04-20) is bogus; checkout can switch branches with a dirty
index and in such a case the tree won't match HEAD.

Add t2014-switch to catch this breakage.

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

builtin-checkout.c

@@ -368,17 +368,14 @@ static int merge_working_tree(struct checkout_opts *opts,
 	int ret;
 	struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
 	int newfd = hold_locked_index(lock_file, 1);
-	int reprime_cache_tree = 0;
 
 	if (read_cache() < 0)
 		return error("corrupt index file");
 
-	cache_tree_free(&active_cache_tree);
 	if (opts->force) {
 		ret = reset_tree(new->commit->tree, opts, 1);
 		if (ret)
 			return ret;
-		reprime_cache_tree = 1;
 	} else {
 		struct tree_desc trees[2];
 		struct tree *tree;
@@ -414,9 +411,7 @@ static int merge_working_tree(struct checkout_opts *opts,
 		init_tree_desc(&trees[1], tree->buffer, tree->size);
 
 		ret = unpack_trees(2, trees, &topts);
-		if (ret != -1) {
-			reprime_cache_tree = 1;
-		} else {
+		if (ret == -1) {
 			/*
 			 * Unpack couldn't do a trivial merge; either
 			 * give up or do a real merge, depending on
@@ -460,8 +455,6 @@ static int merge_working_tree(struct checkout_opts *opts,
 		}
 	}
 
-	if (reprime_cache_tree)
-		prime_cache_tree(&active_cache_tree, new->commit->tree);
 	if (write_cache(newfd, active_cache, active_nr) ||
 	    commit_locked_index(lock_file))
 		die("unable to write new index file");

t/t2014-switch.sh

@@ -0,0 +1,28 @@
+#!/bin/sh
+
+test_description='Peter MacMillan'
+. ./test-lib.sh
+
+test_expect_success setup '
+	echo Hello >file &&
+	git add file &&
+	test_tick &&
+	git commit -m V1 &&
+	echo Hello world >file &&
+	git add file &&
+	git checkout -b other
+'
+
+test_expect_success 'check all changes are staged' '
+	git diff --exit-code
+'
+
+test_expect_success 'second commit' '
+	git commit -m V2
+'
+
+test_expect_success 'check' '
+	git diff --cached --exit-code
+'
+
+test_done