From: David Bremner <bremner@debian.org>

The simple heuristic relies on the fact that '(' is not part of the
character set used by hex-escape. Since hex-escape is designed to be
OK for pathnames (and shells), this seems like a reasonable
assumption.

In principle the --format argument to notmuch-restore is notmuch
needed at this point, but it adds literally 5 lines of argument
description, so I left it.
---
 dump-restore-private.h |    5 +++--
 notmuch-restore.c      |   45 ++++++++++++++++++++++++++++++++-------------
 2 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/dump-restore-private.h b/dump-restore-private.h
index 34a5022..67795e5 100644
--- a/dump-restore-private.h
+++ b/dump-restore-private.h
@@ -5,8 +5,9 @@
 #include "command-line-arguments.h"
 
 typedef enum dump_formats {
-    DUMP_FORMAT_SUP,
-    DUMP_FORMAT_NOTMUCH
+    DUMP_FORMAT_AUTO,
+    DUMP_FORMAT_NOTMUCH,
+    DUMP_FORMAT_SUP
 } dump_format_t;
 
 #endif
diff --git a/notmuch-restore.c b/notmuch-restore.c
index f618b47..340f31f 100644
--- a/notmuch-restore.c
+++ b/notmuch-restore.c
@@ -36,7 +36,7 @@ notmuch_restore_command (unused (void *ctx), int argc, char *argv[])
     regex_t regex;
     int rerr;
     int opt_index;
-    int input_format = DUMP_FORMAT_SUP;
+    int input_format = DUMP_FORMAT_AUTO;
 
     config = notmuch_config_open (ctx, NULL, NULL);
     if (config == NULL)
@@ -50,7 +50,11 @@ notmuch_restore_command (unused (void *ctx), int argc, char *argv[])
     synchronize_flags = notmuch_config_get_maildir_synchronize_flags (config);
 
     notmuch_opt_desc_t options[] = {
-	FORMAT_DESC (input_format),
+	{ NOTMUCH_OPT_KEYWORD, &input_format, "format", 'f',
+	  (notmuch_keyword_t []){ { "auto", DUMP_FORMAT_AUTO },
+				  { "notmuch", DUMP_FORMAT_NOTMUCH },
+				  { "sup", DUMP_FORMAT_SUP },
+				  {0, 0} } },
 	{ NOTMUCH_OPT_POSITION, &input_file_name, 0, 0, 0 },
 	{ NOTMUCH_OPT_BOOLEAN,  &accumulate, "accumulate", 'a', 0 },
 	{ 0, 0, 0, 0, 0 }
@@ -80,17 +84,6 @@ notmuch_restore_command (unused (void *ctx), int argc, char *argv[])
 	return 1;
     }
 
-    /* Dump output is one line per message. We match a sequence of
-     * non-space characters for the message-id, then one or more
-     * spaces, then a list of space-separated tags as a sequence of
-     * characters within literal '(' and ')'. */
-    if (input_format == DUMP_FORMAT_SUP) {
-	if ( xregcomp (&regex,
-		       "^([^ ]+) \\(([^)]*)\\)$",
-		       REG_EXTENDED) )
-	    INTERNAL_ERROR("compile time constant regex failed.");
-    }
-
 
     /* These are out here to re-use the buffers with hex_decode */
 
@@ -98,6 +91,7 @@ notmuch_restore_command (unused (void *ctx), int argc, char *argv[])
     size_t message_id_size = 0;
     char *tag = NULL;
     size_t tag_size = 0;
+    notmuch_bool_t first_line = TRUE;
 
     while ((line_len = getline (&line, &line_size, input)) != -1) {
 	regmatch_t match[3];
@@ -109,6 +103,30 @@ notmuch_restore_command (unused (void *ctx), int argc, char *argv[])
 	char *db_tags_str;
 
 	chomp_newline (line);
+	if (first_line && input_format == DUMP_FORMAT_AUTO) {
+	    char *p;
+
+	    for (p = line; *p; p++) {
+		if (*p == '(')
+		    input_format = DUMP_FORMAT_SUP;
+	    }
+
+	    if (input_format == DUMP_FORMAT_AUTO)
+		input_format = DUMP_FORMAT_NOTMUCH;
+
+	}
+
+	/* sup dump output is one line per message. We match a
+	 * sequence of non-space characters for the message-id, then
+	 * one or more spaces, then a list of space-separated tags as
+	 * a sequence of characters within literal '(' and ')'. */
+	if (first_line && input_format == DUMP_FORMAT_SUP) {
+	    if ( xregcomp (&regex,
+			   "^([^ ]+) \\(([^)]*)\\)$",
+			   REG_EXTENDED) )
+		INTERNAL_ERROR("compile time constant regex failed.");
+	}
+
 
 	/* Silently ignore blank lines */
 
@@ -141,6 +159,7 @@ notmuch_restore_command (unused (void *ctx), int argc, char *argv[])
 	    file_tags = xstrdup (p);
 	}
 
+	first_line = FALSE;
 
 	status = notmuch_database_find_message (notmuch, message_id, &message);
 	if (status || message == NULL) {
-- 
1.7.7.3