Write index file on any checkout of files

We need to rewrite the index file when we check out files, even if we
haven't modified the blob info by reading from another tree, so that
we get the stat cache to include the fact that we just modified the
file so it doesn't need to be refreshed.

While we're at it, move everything that needs to be done to check out
some paths from a tree (or the current index) into checkout_paths().

Signed-off-by: Daniel Barkalow <barkalow@iabervon.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-checkout.c

@@ -67,17 +67,8 @@ static int update_some(const unsigned char *sha1, const char *base, int baselen,
 
 static int read_tree_some(struct tree *tree, const char **pathspec)
 {
-	int newfd;
-	struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
-	newfd = hold_locked_index(lock_file, 1);
-	read_cache();
-
 	read_tree_recursive(tree, "", 0, 0, pathspec, update_some);
 
-	if (write_cache(newfd, active_cache, active_nr) ||
-	    commit_locked_index(lock_file))
-		die("unable to write new index file");
-
 	/* update the index with the given tree's info
 	 * for all args, expanding wildcards, and exit
 	 * with any non-zero return code.
@@ -85,7 +76,7 @@ static int read_tree_some(struct tree *tree, const char **pathspec)
 	return 0;
 }
 
-static int checkout_paths(const char **pathspec)
+static int checkout_paths(struct tree *source_tree, const char **pathspec)
 {
 	int pos;
 	struct checkout state;
@@ -94,6 +85,15 @@ static int checkout_paths(const char **pathspec)
 	int flag;
 	struct commit *head;
 
+	int newfd;
+	struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
+
+	newfd = hold_locked_index(lock_file, 1);
+	read_cache();
+
+	if (source_tree)
+		read_tree_some(source_tree, pathspec);
+
 	for (pos = 0; pathspec[pos]; pos++)
 		;
 	ps_matched = xcalloc(1, pos);
@@ -116,6 +116,10 @@ static int checkout_paths(const char **pathspec)
 		}
 	}
 
+	if (write_cache(newfd, active_cache, active_nr) ||
+	    commit_locked_index(lock_file))
+		die("unable to write new index file");
+
 	resolve_ref("HEAD", rev, 0, &flag);
 	head = lookup_commit_reference_gently(rev, 1);
 
@@ -558,11 +562,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 			}
 		}
 
-		if (source_tree)
-			read_tree_some(source_tree, pathspec);
-		else
-			read_cache();
-		return checkout_paths(pathspec);
+		return checkout_paths(source_tree, pathspec);
 	}
 
 	if (new.name && !new.commit) {

t/t2009-checkout-statinfo.sh

@@ -0,0 +1,52 @@
+#!/bin/sh
+
+test_description='checkout should leave clean stat info'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+
+	echo hello >world &&
+	git update-index --add world &&
+	git commit -m initial &&
+	git branch side &&
+	echo goodbye >world &&
+	git update-index --add world &&
+	git commit -m second
+
+'
+
+test_expect_success 'branch switching' '
+
+	git reset --hard &&
+	test "$(git diff-files --raw)" = "" &&
+
+	git checkout master &&
+	test "$(git diff-files --raw)" = "" &&
+
+	git checkout side &&
+	test "$(git diff-files --raw)" = "" &&
+
+	git checkout master &&
+	test "$(git diff-files --raw)" = ""
+
+'
+
+test_expect_success 'path checkout' '
+
+	git reset --hard &&
+	test "$(git diff-files --raw)" = "" &&
+
+	git checkout master world &&
+	test "$(git diff-files --raw)" = "" &&
+
+	git checkout side world &&
+	test "$(git diff-files --raw)" = "" &&
+
+	git checkout master world &&
+	test "$(git diff-files --raw)" = ""
+
+'
+
+test_done
+