Basic Darcs support (ignoring VCS dir)

Darcs <https://darcs.net> is a decentralized version control system.
Advanced support would be adding .boring file support like .gitignore.

src/tup/path.c

@@ -124,7 +124,7 @@ static int watch_path_internal(tupid_t dt, const char *file,
 			if(subtent) {
 				tupid_tree_remove(&root, subtent->tnode.tupid);
 			}
-			if(f.filename[0] == '.') {
+			if(f.filename[0] == '.' || f.filename[0] == '_') {
 				if(pel_ignored(f.filename, -1))
 					continue;
 			}

src/tup/pel_group.c

@@ -47,6 +47,8 @@ int pel_ignored(const char *path, int len)
 		return 1;
 	if(len == 4 && strncmp(path, ".svn", 4) == 0)
 		return 1;
+	if(len == 6 && strncmp(path, "_darcs", 6) == 0)
+		return 1;
 	if(len == 7 && strncmp(path, ".ccache", 7) == 0)
 		return 1;
 	/* See also fuse_fs.c:is_hidden() */
@@ -169,7 +171,7 @@ int get_path_elements(const char *path, struct pel_group *pg)
 	}
 
 	TAILQ_FOREACH(pel, &pg->path_list, list) {
-		if(pel->path[0] == '.') {
+		if(pel->path[0] == '.' || pel->path[0] == '_') {
 			if(pel->len == 2 && strncmp(pel->path, "..", 2) == 0) {
 				/* .. paths are ignored */
 			} else if(pel_ignored(pel->path,  pel->len)) {

src/tup/server/fuse_fs.c

@@ -101,6 +101,8 @@ static int is_hidden(const char *path)
 		return 1;
 	if(strstr(path, "/.bzr") != NULL)
 		return 1;
+	if(strstr(path, "/_darcs") != NULL)
+		return 1;
 	if(is_ccache_path(path))
 		return 1;
 	return 0;

tup.1

@@ -320,7 +320,7 @@ Set to '1' to keep building as much as possible even if errors are encountered.
 Set to '1' to track dependencies on files outside of the tup hierarchy. The default is '0', which only tracks dependencies within the tup hierarchy. For example, if you want all C files to be re-compiled when gcc is updated on your system, you should set this to '1'. In Linux and OSX, using full dependencies requires that the tup binary is suid as root so that it can run sub-processes in a chroot environment. Alternatively on Linux, if your kernel supports user namespaces, then you don't need to make the binary suid. Note that if this value is set to '1' from '0', tup will rebuild the entire project. Disabling this option when it was previously enabled does not require a full rebuild, but does take some time since the nodes representing external files are cleared out. NOTE: This does not currently work with ccache or other programs that may write to external files due to issues with locking. This may be fixed in the future.
 .TP
 .B updater.warnings (defaults to '1')
-Set to '0' to disable warnings about writing to hidden files. Tup doesn't track files that are hidden. If a sub-process writes to a hidden file, then by default tup will display a warning that this file was created. By disabling this option, those warnings are not displayed. Hidden filenames (or directories) include: ., .., .tup, .git, .hg, .bzr, .svn.
+Set to '0' to disable warnings about writing to hidden files. Tup doesn't track files that are hidden. If a sub-process writes to a hidden file, then by default tup will display a warning that this file was created. By disabling this option, those warnings are not displayed. Hidden filenames (or directories) include: ., .., .tup, .git, .hg, .bzr, .svn, _darcs.
 .TP
 .B display.color (default 'auto')
 Set to 'never' to disable ANSI escape codes for colored output, or 'always' to always use ANSI escape codes for colored output. The default is 'auto', which displays uses colored output if stdout is connected to a tty, and uses no colors otherwise (ie: if stdout is redirected to a file).