Merge branch 'cb/assume-unchanged-fix' into maint

* cb/assume-unchanged-fix:
  Documentation: git-add does not update files marked "assume unchanged"
  do not overwrite files marked "assume unchanged"

Documentation/git-update-index.txt

@@ -93,8 +93,6 @@ OPTIONS
 This option can be also used as a coarse file-level mechanism
 to ignore uncommitted changes in tracked files (akin to what
 `.gitignore` does for untracked files).
-You should remember that an explicit 'git add' operation will
-still cause the file to be refreshed from the working tree.
 Git will fail (gracefully) in case it needs to modify this file
 in the index e.g. when merging in a commit;
 thus, in case the assumed-untracked file is changed upstream,

t/t2106-update-index-assume-unchanged.sh

@@ -0,0 +1,24 @@
+#!/bin/sh
+
+test_description='git update-index --assume-unchanged test.
+'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' \
+	': >file &&
+	 git add file &&
+	 git commit -m initial &&
+	 git branch other &&
+	 echo upstream >file &&
+	 git add file &&
+	 git commit -m upstream'
+
+test_expect_success 'do not switch branches with dirty file' \
+	'git reset --hard &&
+	 git checkout other &&
+	 echo dirt >file &&
+	 git update-index --assume-unchanged file &&
+	 test_must_fail git checkout master'
+
+test_done

unpack-trees.c

@@ -862,7 +862,7 @@ static int verify_uptodate_1(struct cache_entry *ce,
 {
 	struct stat st;
 
-	if (o->index_only || (!ce_skip_worktree(ce) && (o->reset || ce_uptodate(ce))))
+	if (o->index_only || (!((ce->ce_flags & CE_VALID) || ce_skip_worktree(ce)) && (o->reset || ce_uptodate(ce))))
 		return 0;
 
 	if (!lstat(ce->name, &st)) {