fix SubFolders style Maildir++

turns out i misread the spec in a subtle way: while all other folders
are physically nested under INBOX, the IMAP view puts them at the same
(root) level. to get them shown as subfolders of INBOX, they need to
have _two_ leading dots.

this also implies that the Maildir++ mode has no use for a Path, so
reject attempts to specify one.

src/drv_maildir.c

@@ -113,13 +113,34 @@ maildir_parse_flags( const char *info_prefix, const char *base )
 	return flags;
 }
 
+static int
+maildir_ensure_path( maildir_store_conf_t *conf )
+{
+	if (!conf->gen.path) {
+		error( "Maildir error: store '%s' has no Path\n", conf->gen.name );
+		conf->failed = FAIL_FINAL;
+		return -1;
+	}
+	return 0;
+}
+
+/* Subdirs of INBOX include a leading slash. */
+/* Path includes a trailing slash, Inbox does not. */
 static char *
-maildir_join_path( maildir_store_conf_t *conf, const char *prefix, const char *box )
+maildir_join_path( maildir_store_conf_t *conf, int in_inbox, const char *box )
 {
 	char *out, *p;
-	int pl, bl, n, sub = 0;
+	const char *prefix;
+	int pl, bl, n;
 	char c;
 
+	if (in_inbox || conf->sub_style == SUB_MAILDIRPP) {
+		prefix = conf->inbox;
+	} else {
+		if (maildir_ensure_path( conf ) < 0)
+			return 0;
+		prefix = conf->gen.path;
+	}
 	pl = strlen( prefix );
 	for (bl = 0, n = 0; (c = box[bl]); bl++)
 		if (c == '/') {
@@ -134,24 +155,33 @@ maildir_join_path( maildir_store_conf_t *conf, const char *prefix, const char *b
 			       conf->gen.name, box );
 			return 0;
 		}
+	switch (conf->sub_style) {
+	case SUB_VERBATIM:
+		n = 0;
+		break;
+	case SUB_MAILDIRPP:
+		n = 2;
+		break;
+	default: /* SUB_LEGACY and SUB_UNSET */
+		break;
+	}
 	out = nfmalloc( pl + bl + n + 1 );
 	memcpy( out, prefix, pl );
 	p = out + pl;
+	if (conf->sub_style == SUB_MAILDIRPP) {
+		*p++ = '/';
+		*p++ = '.';
+	}
 	while ((c = *box++)) {
 		if (c == '/') {
 			switch (conf->sub_style) {
 			case SUB_VERBATIM:
 				*p++ = c;
 				break;
-			case SUB_MAILDIRPP:
-				if (!sub) {
-					sub = 1;
-					*p++ = c;
-				}
-				*p++ = '.';
-				break;
 			case SUB_LEGACY:
 				*p++ = c;
+				/* fallthrough */
+			default: /* SUB_MAILDIRPP */
 				*p++ = '.';
 				break;
 			}
@@ -163,17 +193,6 @@ maildir_join_path( maildir_store_conf_t *conf, const char *prefix, const char *b
 	return out;
 }
 
-static int
-maildir_ensure_path( maildir_store_conf_t *conf )
-{
-	if (!conf->gen.path) {
-		error( "Maildir error: store '%s' has no Path\n", conf->gen.name );
-		conf->failed = FAIL_FINAL;
-		return -1;
-	}
-	return 0;
-}
-
 static int
 maildir_validate_path( maildir_store_conf_t *conf )
 {
@@ -212,15 +231,9 @@ maildir_connect_store( store_t *gctx,
 		cb( DRV_STORE_BAD, aux );
 		return;
 	}
-	if (conf->gen.trash) {
-		if (maildir_ensure_path( conf ) < 0) {
-			cb( DRV_STORE_BAD, aux );
-			return;
-		}
-		if (!(ctx->trash = maildir_join_path( conf, conf->gen.path, conf->gen.trash ))) {
-			cb( DRV_STORE_BAD, aux );
-			return;
-		}
+	if (conf->gen.trash && !(ctx->trash = maildir_join_path( conf, 0, conf->gen.trash ))) {
+		cb( DRV_STORE_BAD, aux );
+		return;
 	}
 	cb( DRV_OK, aux );
 }
@@ -325,6 +338,8 @@ maildir_list_recurse( store_t *gctx, int isBox, int flags,
 				return -1;
 			}
 		} else {
+			char *effName = name;
+			int nameOff = 0;
 			if (style == SUB_MAILDIRPP || style == SUB_LEGACY) {
 				if (*ent == '.') {
 					if (!isBox)
@@ -334,15 +349,27 @@ maildir_list_recurse( store_t *gctx, int isBox, int flags,
 					if (isBox)
 						continue;
 				}
+				if (style == SUB_MAILDIRPP) {
+					if (*ent == '.') {
+						if (!(flags & LIST_INBOX))
+							continue;
+						ent++;
+					} else {
+						if (!(flags & (LIST_PATH | LIST_PATH_MAYBE)))
+							continue;
+						effName = name + 6;
+						nameOff = 6;
+					}
+				}
 			}
 			nl = nameLen + nfsnprintf( name + nameLen, _POSIX_PATH_MAX - nameLen, "%s", ent );
-			if (style == SUB_MAILDIRPP && isBox) {
+			if (style == SUB_MAILDIRPP) {
 				for (i = nameLen; i < nl; i++) {
 					if (name[i] == '.')
 						name[i] = '/';
 				}
 			}
-			if (!nameLen && equals( name, nl, "INBOX", 5 ) && (!name[5] || name[5] == '/')) {
+			if (nameLen == nameOff && equals( effName, nl - nameOff, "INBOX", 5 ) && (!effName[5] || effName[5] == '/')) {
 				path[pathLen] = 0;
 				warn( "Maildir warning: ignoring INBOX in %s\n", path );
 				continue;
@@ -350,9 +377,9 @@ maildir_list_recurse( store_t *gctx, int isBox, int flags,
 			path[pl++] = '/';
 			nfsnprintf( path + pl, _POSIX_PATH_MAX - pl, "cur" );
 			if (!stat( path, &st ) && S_ISDIR(st.st_mode))
-				add_string_list( &gctx->boxes, name );
-			if (style == SUB_MAILDIRPP && isBox) {
-				/* Maildir++ subfolder - don't recurse further. */
+				add_string_list( &gctx->boxes, effName );
+			if (style == SUB_MAILDIRPP) {
+				/* Maildir++ folder - don't recurse further. */
 				continue;
 			}
 			path[pl] = 0;
@@ -372,7 +399,8 @@ maildir_list_inbox( store_t *gctx, int flags, const char *basePath )
 {
 	char path[_POSIX_PATH_MAX], name[_POSIX_PATH_MAX];
 
-	add_string_list( &gctx->boxes, "INBOX" );
+	if (flags & LIST_INBOX)
+		add_string_list( &gctx->boxes, "INBOX" );
 	return maildir_list_recurse(
 	        gctx, 1, flags, 0, 0, basePath, basePath ? strlen( basePath ) - 1 : 0,
 	        path, nfsnprintf( path, _POSIX_PATH_MAX, "%s/", ((maildir_store_conf_t *)gctx->conf)->inbox ),
@@ -396,9 +424,12 @@ static void
 maildir_list_store( store_t *gctx, int flags,
                     void (*cb)( int sts, void *aux ), void *aux )
 {
-	if ((((flags & LIST_PATH) || ((flags & LIST_PATH_MAYBE) && gctx->conf->path))
-	     && maildir_list_path( gctx, flags, ((maildir_store_conf_t *)gctx->conf)->inbox ) < 0) ||
-	    ((flags & LIST_INBOX) && maildir_list_inbox( gctx, flags, gctx->conf->path ) < 0)) {
+	maildir_store_conf_t *conf = (maildir_store_conf_t *)gctx->conf;
+	if (((((flags & LIST_PATH) && conf->sub_style != SUB_MAILDIRPP)
+	      || ((flags & LIST_PATH_MAYBE) && gctx->conf->path))
+	     && maildir_list_path( gctx, flags, conf->inbox ) < 0) ||
+	    (((flags & LIST_INBOX) || conf->sub_style == SUB_MAILDIRPP)
+	     && maildir_list_inbox( gctx, flags, gctx->conf->path ) < 0)) {
 		maildir_invoke_bad_callback( gctx );
 		cb( DRV_CANCELED, aux );
 	} else {
@@ -1111,14 +1142,16 @@ maildir_select_box( store_t *gctx, const char *name )
 #endif /* USE_DB */
 	ctx->fresh[0] = ctx->fresh[1] = 0;
 	if (starts_with( name, -1, "INBOX", 5 ) && (!name[5] || name[5] == '/')) {
-		gctx->path = maildir_join_path( conf, conf->inbox, name + 5 );
-		ctx->is_inbox = !name[5];
-	} else {
-		if (maildir_ensure_path( conf ) < 0) {
-			gctx->path = 0;
-			return DRV_CANCELED;
+		if (!name[5]) {
+			gctx->path = nfstrdup( conf->inbox );
+			ctx->is_inbox = 1;
+		} else {
+			gctx->path = maildir_join_path( conf, 1, name + 5 );
+			ctx->is_inbox = 0;
 		}
-		gctx->path = maildir_join_path( conf, conf->gen.path, name );
+	} else {
+		if (!(gctx->path = maildir_join_path( conf, 0, name )))
+		    return DRV_CANCELED;
 		ctx->is_inbox = 0;
 	}
 	return gctx->path ? DRV_OK : DRV_BOX_BAD;
@@ -1741,6 +1774,10 @@ maildir_parse_store( conffile_t *cfg, store_conf_t **storep )
 			parse_generic_store( &store->gen, cfg );
 	if (!store->inbox)
 		store->inbox = expand_strdup( "~/Maildir" );
+	if (store->sub_style == SUB_MAILDIRPP && store->gen.path) {
+		error( "Maildir store '%s': Setting Path is incompatible with 'SubFolders Maildir++'\n", store->gen.name );
+		cfg->err = 1;
+	}
 	nfasprintf( &store->info_prefix, "%c2,", store->info_delimiter );
 	nfasprintf( &store->info_stop, "%c,", store->info_delimiter );
 	*storep = &store->gen;

src/mbsync.1

@@ -264,17 +264,18 @@ with DOS/Windows file systems.
 The on-disk folder naming style used for hierarchical mailboxes.
 This has option has no effect when \fBFlatten\fR is used.
 .br
-Suppose a mailbox with the canonical path \fItop/sub/subsub\fR,
-the styles will yield the following on-disk paths:
+Suppose mailboxes with the canonical paths \fBtop/sub/subsub\fR and
+\fBINBOX/sub/subsub\fR, the styles will yield the following on-disk paths:
 .br
-\fBVerbatim\fR - \fItop/sub/subsub\fR
+\fBVerbatim\fR - \fIPath\fB/top/sub/subsub\fR and \fIInbox\fB/sub/subsub\fR
 (this is the style you probably want to use)
 .br
-\fBMaildir++\fR - \fItop/.sub.subsub\fR
+\fBMaildir++\fR - \fIInbox\fB/.top.sub.subsub\fR and \fIInbox\fB/..sub.subsub\fR
 (this style is compatible with Courier and Dovecot - but note that
-the mailbox metadata format is \fInot\fR compatible)
+the mailbox metadata format is \fInot\fR compatible).
+Note that attempts to set \fBPath\fR are rejected in this mode.
 .br
-\fBLegacy\fR - \fItop/.sub/.subsub\fR
+\fBLegacy\fR - \fIPath\fB/top/.sub/.subsub\fR and \fIInbox\fB/.sub/.subsub\fR
 (this is \fBmbsync\fR's historical style)
 .br
 (Default: unset; will error out when sub-folders are encountered)