Merge branch 'jb/required-filter'

* jb/required-filter:
  Add a setting to require a filter to be successful

Conflicts:
	convert.c

Documentation/gitattributes.txt

@@ -294,16 +294,27 @@ output is used to update the worktree file.  Similarly, the
 `clean` command is used to convert the contents of worktree file
 upon checkin.
 
-A missing filter driver definition in the config is not an error
-but makes the filter a no-op passthru.
-
-The content filtering is done to massage the content into a
-shape that is more convenient for the platform, filesystem, and
-the user to use.  The key phrase here is "more convenient" and not
-"turning something unusable into usable".  In other words, the
-intent is that if someone unsets the filter driver definition,
-or does not have the appropriate filter program, the project
-should still be usable.
+One use of the content filtering is to massage the content into a shape
+that is more convenient for the platform, filesystem, and the user to use.
+For this mode of operation, the key phrase here is "more convenient" and
+not "turning something unusable into usable".  In other words, the intent
+is that if someone unsets the filter driver definition, or does not have
+the appropriate filter program, the project should still be usable.
+
+Another use of the content filtering is to store the content that cannot
+be directly used in the repository (e.g. a UUID that refers to the true
+content stored outside git, or an encrypted content) and turn it into a
+usable form upon checkout (e.g. download the external content, or decrypt
+the encrypted content).
+
+These two filters behave differently, and by default, a filter is taken as
+the former, massaging the contents into more convenient shape.  A missing
+filter driver definition in the config, or a filter driver that exits with
+a non-zero status, is not an error but makes the filter a no-op passthru.
+
+You can declare that a filter turns a content that by itself is unusable
+into a usable content by setting the filter.<driver>.required configuration
+variable to `true`.
 
 For example, in .gitattributes, you would assign the `filter`
 attribute for paths.
@@ -335,6 +346,16 @@ input that is already correctly indented.  In this case, the lack of a
 smudge filter means that the clean filter _must_ accept its own output
 without modifying it.
 
+If a filter _must_ succeed in order to make the stored contents usable,
+you can declare that the filter is `required`, in the configuration:
+
+------------------------
+[filter "crypt"]
+	clean = openssl enc ...
+	smudge = openssl enc -d ...
+	required
+------------------------
+
 Sequence "%f" on the filter command line is replaced with the name of
 the file the filter is working on.  A filter might use this in keyword
 substitution.  For example:

convert.c

@@ -452,6 +452,7 @@ static struct convert_driver {
 	struct convert_driver *next;
 	const char *smudge;
 	const char *clean;
+	int required;
 } *user_convert, **user_convert_tail;
 
 static int read_convert_config(const char *var, const char *value, void *cb)
@@ -495,6 +496,11 @@ static int read_convert_config(const char *var, const char *value, void *cb)
 	if (!strcmp("clean", ep))
 		return git_config_string(&drv->clean, var, value);
 
+	if (!strcmp("required", ep)) {
+		drv->required = git_config_bool(var, value);
+		return 0;
+	}
+
 	return 0;
 }
 
@@ -773,13 +779,19 @@ int convert_to_git(const char *path, const char *src, size_t len,
 {
 	int ret = 0;
 	const char *filter = NULL;
+	int required = 0;
 	struct conv_attrs ca;
 
 	convert_attrs(&ca, path);
-	if (ca.drv)
+	if (ca.drv) {
 		filter = ca.drv->clean;
+		required = ca.drv->required;
+	}
 
 	ret |= apply_filter(path, src, len, dst, filter);
+	if (!ret && required)
+		die("%s: clean filter '%s' failed", path, ca.drv->name);
+
 	if (ret && dst) {
 		src = dst->buf;
 		len = dst->len;
@@ -797,13 +809,16 @@ static int convert_to_working_tree_internal(const char *path, const char *src,
 					    size_t len, struct strbuf *dst,
 					    int normalizing)
 {
-	int ret = 0;
+	int ret = 0, ret_filter = 0;
 	const char *filter = NULL;
+	int required = 0;
 	struct conv_attrs ca;
 
 	convert_attrs(&ca, path);
-	if (ca.drv)
+	if (ca.drv) {
 		filter = ca.drv->smudge;
+		required = ca.drv->required;
+	}
 
 	ret |= ident_to_worktree(path, src, len, dst, ca.ident);
 	if (ret) {
@@ -822,7 +837,12 @@ static int convert_to_working_tree_internal(const char *path, const char *src,
 			len = dst->len;
 		}
 	}
-	return ret | apply_filter(path, src, len, dst, filter);
+
+	ret_filter = apply_filter(path, src, len, dst, filter);
+	if (!ret_filter && required)
+		die("%s: smudge filter %s failed", path, ca.drv->name);
+
+	return ret | ret_filter;
 }
 
 int convert_to_working_tree(const char *path, const char *src, size_t len, struct strbuf *dst)

t/t0021-conversion.sh

@@ -153,4 +153,41 @@ test_expect_success 'filter shell-escaped filenames' '
 	:
 '
 
+test_expect_success 'required filter success' '
+	git config filter.required.smudge cat &&
+	git config filter.required.clean cat &&
+	git config filter.required.required true &&
+
+	echo "*.r filter=required" >.gitattributes &&
+
+	echo test >test.r &&
+	git add test.r &&
+	rm -f test.r &&
+	git checkout -- test.r
+'
+
+test_expect_success 'required filter smudge failure' '
+	git config filter.failsmudge.smudge false &&
+	git config filter.failsmudge.clean cat &&
+	git config filter.failsmudge.required true &&
+
+	echo "*.fs filter=failsmudge" >.gitattributes &&
+
+	echo test >test.fs &&
+	git add test.fs &&
+	rm -f test.fs &&
+	test_must_fail git checkout -- test.fs
+'
+
+test_expect_success 'required filter clean failure' '
+	git config filter.failclean.smudge cat &&
+	git config filter.failclean.clean false &&
+	git config filter.failclean.required true &&
+
+	echo "*.fc filter=failclean" >.gitattributes &&
+
+	echo test >test.fc &&
+	test_must_fail git add test.fc
+'
+
 test_done