git-add --intent-to-add (-N)

This adds "--intent-to-add" option to "git add".  This is to let the
system know that you will tell it the final contents to be staged later,
iow, just be aware of the presense of the path with the type of the blob
for now.  It is implemented by staging an empty blob as the content.

With this sequence:

    $ git reset --hard
    $ edit newfile
    $ git add -N newfile
    $ edit newfile oldfile
    $ git diff

the diff will show all changes relative to the current commit.  Then you
can do:

    $ git commit -a ;# commit everything

or

    $ git commit oldfile ;# only oldfile, newfile not yet added

to pretend you are working with an index-free system like CVS.

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

4 files changed, 65 insertions, 6 deletions

diff --git a/builtin-add.c b/builtin-add.c
index 7c874e311..ea4e77169 100644
--- a/builtin-add.c
+++ b/builtin-add.c
@@ -166,7 +166,7 @@ static const char ignore_error[] =
 "The following paths are ignored by one of your .gitignore files:\n";
 
 static int verbose = 0, show_only = 0, ignored_too = 0, refresh_only = 0;
-static int ignore_add_errors, addremove;
+static int ignore_add_errors, addremove, intent_to_add;
 
 static struct option builtin_add_options[] = {
 	OPT__DRY_RUN(&show_only),
@@ -176,6 +176,7 @@ static struct option builtin_add_options[] = {
 	OPT_BOOLEAN('p', "patch", &patch_interactive, "interactive patching"),
 	OPT_BOOLEAN('f', "force", &ignored_too, "allow adding otherwise ignored files"),
 	OPT_BOOLEAN('u', "update", &take_worktree_changes, "update tracked files"),
+	OPT_BOOLEAN('N', "intent-to-add", &intent_to_add, "record only the fact that the path will be added later"),
 	OPT_BOOLEAN('A', "all", &addremove, "add all, noticing removal of tracked files"),
 	OPT_BOOLEAN( 0 , "refresh", &refresh_only, "don't add, only refresh the index"),
 	OPT_BOOLEAN( 0 , "ignore-errors", &ignore_add_errors, "just skip files which cannot be added because of errors"),
@@ -246,6 +247,7 @@ int cmd_add(int argc, const char **argv, const char *prefix)
 
 	flags = ((verbose ? ADD_CACHE_VERBOSE : 0) |
 		 (show_only ? ADD_CACHE_PRETEND : 0) |
+		 (intent_to_add ? ADD_CACHE_INTENT : 0) |
 		 (ignore_add_errors ? ADD_CACHE_IGNORE_ERRORS : 0) |
 		 (!(addremove || take_worktree_changes)
 		  ? ADD_CACHE_IGNORE_REMOVAL : 0));
diff --git a/cache.h b/cache.h
index de8c2b626..f725783b8 100644
--- a/cache.h
+++ b/cache.h
@@ -371,6 +371,7 @@ extern int index_name_pos(const struct index_state *, const char *name, int name
 #define ADD_CACHE_OK_TO_REPLACE 2	/* Ok to replace file/directory */
 #define ADD_CACHE_SKIP_DFCHECK 4	/* Ok to skip DF conflict checks */
 #define ADD_CACHE_JUST_APPEND 8		/* Append only; tree.c::read_tree() */
+#define ADD_CACHE_NEW_ONLY 16		/* Do not replace existing ones */
 extern int add_index_entry(struct index_state *, struct cache_entry *ce, int option);
 extern struct cache_entry *refresh_cache_entry(struct cache_entry *ce, int really);
 extern void rename_index_entry_at(struct index_state *, int pos, const char *new_name);
@@ -380,6 +381,7 @@ extern int remove_file_from_index(struct index_state *, const char *path);
 #define ADD_CACHE_PRETEND 2
 #define ADD_CACHE_IGNORE_ERRORS	4
 #define ADD_CACHE_IGNORE_REMOVAL 8
+#define ADD_CACHE_INTENT 16
 extern int add_to_index(struct index_state *, const char *path, struct stat *, int flags);
 extern int add_file_to_index(struct index_state *, const char *path, int flags);
 extern struct cache_entry *make_cache_entry(unsigned int mode, const unsigned char *sha1, const char *path, int stage, int refresh);
diff --git a/read-cache.c b/read-cache.c
index 5150c1e14..276b09e66 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -13,6 +13,7 @@
 #include "diff.h"
 #include "diffcore.h"
 #include "revision.h"
+#include "blob.h"
 
 /* Index extensions.
  *
@@ -511,6 +512,14 @@ static struct cache_entry *create_alias_ce(struct cache_entry *ce, struct cache_
 	return new;
 }
 
+static void record_intent_to_add(struct cache_entry *ce)
+{
+	unsigned char sha1[20];
+	if (write_sha1_file("", 0, blob_type, sha1))
+		die("cannot create an empty blob in the object database");
+	hashcpy(ce->sha1, sha1);
+}
+
 int add_to_index(struct index_state *istate, const char *path, struct stat *st, int flags)
 {
 	int size, namelen, was_same;
@@ -519,6 +528,9 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 	unsigned ce_option = CE_MATCH_IGNORE_VALID|CE_MATCH_RACY_IS_DIRTY;
 	int verbose = flags & (ADD_CACHE_VERBOSE | ADD_CACHE_PRETEND);
 	int pretend = flags & ADD_CACHE_PRETEND;
+	int intent_only = flags & ADD_CACHE_INTENT;
+	int add_option = (ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE|
+			  (intent_only ? ADD_CACHE_NEW_ONLY : 0));
 
 	if (!S_ISREG(st_mode) && !S_ISLNK(st_mode) && !S_ISDIR(st_mode))
 		return error("%s: can only add regular files, symbolic links or git-directories", path);
@@ -532,7 +544,8 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 	ce = xcalloc(1, size);
 	memcpy(ce->name, path, namelen);
 	ce->ce_flags = namelen;
-	fill_stat_cache_info(ce, st);
+	if (!intent_only)
+		fill_stat_cache_info(ce, st);
 
 	if (trust_executable_bit && has_symlinks)
 		ce->ce_mode = create_ce_mode(st_mode);
@@ -555,8 +568,12 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 		alias->ce_flags |= CE_ADDED;
 		return 0;
 	}
-	if (index_path(ce->sha1, path, st, 1))
-		return error("unable to index file %s", path);
+	if (!intent_only) {
+		if (index_path(ce->sha1, path, st, 1))
+			return error("unable to index file %s", path);
+	} else
+		record_intent_to_add(ce);
+
 	if (ignore_case && alias && different_name(ce, alias))
 		ce = create_alias_ce(ce, alias);
 	ce->ce_flags |= CE_ADDED;
@@ -569,7 +586,7 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 
 	if (pretend)
 		;
-	else if (add_index_entry(istate, ce, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE))
+	else if (add_index_entry(istate, ce, add_option))
 		return error("unable to add %s to index",path);
 	if (verbose && !was_same)
 		printf("add '%s'\n", path);
@@ -848,13 +865,15 @@ static int add_index_entry_with_check(struct index_state *istate, struct cache_e
 	int ok_to_add = option & ADD_CACHE_OK_TO_ADD;
 	int ok_to_replace = option & ADD_CACHE_OK_TO_REPLACE;
 	int skip_df_check = option & ADD_CACHE_SKIP_DFCHECK;
+	int new_only = option & ADD_CACHE_NEW_ONLY;
 
 	cache_tree_invalidate_path(istate->cache_tree, ce->name);
 	pos = index_name_pos(istate, ce->name, ce->ce_flags);
 
 	/* existing match? Just replace it. */
 	if (pos >= 0) {
-		replace_index_entry(istate, pos, ce);
+		if (!new_only)
+			replace_index_entry(istate, pos, ce);
 		return 0;
 	}
 	pos = -pos-1;
diff --git a/t/t2203-add-intent.sh b/t/t2203-add-intent.sh
new file mode 100755
index 000000000..d4de35ea0
--- /dev/null
+++ b/t/t2203-add-intent.sh
@@ -0,0 +1,36 @@
+#!/bin/sh
+
+test_description='Intent to add'
+
+. ./test-lib.sh
+
+test_expect_success 'intent to add' '
+	echo hello >file &&
+	echo hello >elif &&
+	git add -N file &&
+	git add elif
+'
+
+test_expect_success 'check result of "add -N"' '
+	git ls-files -s file >actual &&
+	empty=$(git hash-object --stdin </dev/null) &&
+	echo "100644 $empty 0	file" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'intent to add is just an ordinary empty blob' '
+	git add -u &&
+	git ls-files -s file >actual &&
+	git ls-files -s elif | sed -e "s/elif/file/" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'intent to add does not clobber existing paths' '
+	git add -N file elif &&
+	empty=$(git hash-object --stdin </dev/null) &&
+	git ls-files -s >actual &&
+	! grep "$empty" actual
+'
+
+test_done
+