[PATCH v2 2/2] unpack-trees: support core.allIgnoredFilesArePreciousWhenMerging

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

Ignored files can be marked precious to prevent being overwritten
during a merge (or even a branch switch). If you really want to make
sure no ignored files are overwritten, this config variable is for
you.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/config/core.txt |  6 ++++++
 Documentation/gitignore.txt   |  5 +++--
 unpack-trees.c                | 21 ++++++++++++++++++++-
 3 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index d0e6635fe0..bff5834c13 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -1,3 +1,9 @@
+core.allIgnoredFilesArePreciousWhenMerging::
+	During a merge operation, if "precious" attribute is unset,
+	consider it set. You can explicitly remove "precious"
+	attribute if needed. See linkgit:gitattributes[5] for more
+	information.
+
 core.fileMode::
 	Tells Git if the executable bit of files in the working tree
 	is to be honored.
diff --git a/Documentation/gitignore.txt b/Documentation/gitignore.txt
index 0e9614289e..2832df7178 100644
--- a/Documentation/gitignore.txt
+++ b/Documentation/gitignore.txt
@@ -142,8 +142,9 @@ To stop tracking a file that is currently tracked, use
 'git rm --cached'.
 
 Ignored files are generally considered discardable. See `precious`
-attribute in linkgit:gitattributes[5] to change the behavior regarding
-ignored files.
+attribute in linkgit:gitattributes[5] and
+`core.allIgnoredFilesArePreciousWhenMerging` in linkgit:git-config[1]
+to change the behavior regarding ignored files.
 
 EXAMPLES
 --------
diff --git a/unpack-trees.c b/unpack-trees.c
index 9a5aadc084..df3b163e2e 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1877,6 +1877,25 @@ static int icase_exists(struct unpack_trees_options *o, const char *name, int le
 	return src && !ie_match_stat(o->src_index, src, st, CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE);
 }
 
+static int is_precious_ignored_file(struct index_state *istate, const char *path)
+{
+	static struct attr_check *check;
+	int all_precious;
+
+	if (!check)
+		check = attr_check_initl("precious", NULL);
+	if (!check)
+		return 0;
+
+	git_check_attr(istate, path, check);
+	if (ATTR_UNSET(check->items[0].value) &&
+	    !git_config_get_bool("core.allignoredfilesarepreciouswhenmerging",
+				 &all_precious) &&
+	    all_precious)
+		return 1;
+	return ATTR_TRUE(check->items[0].value);
+}
+
 static int check_ok_to_remove(const char *name, int len, int dtype,
 			      const struct cache_entry *ce, struct stat *st,
 			      enum unpack_trees_error_types error_type,
@@ -1895,7 +1914,7 @@ static int check_ok_to_remove(const char *name, int len, int dtype,
 		return 0;
 
 	if (o->dir &&
-	    !is_precious_file(o->src_index, name) &&
+	    !is_precious_ignored_file(o->src_index, name) &&
 	    is_excluded(o->dir, o->src_index, name, &dtype))
 		/*
 		 * ce->name is explicitly excluded, so it is Ok to
-- 
2.19.1.1327.g328c130451.dirty