add --dry-run mode

REFMAIL: 20211130142121.xon5oygrpdfj5s2t@fastmail.com

NEWS

@@ -22,6 +22,8 @@ Added new sync operation 'Old'.
 
 Added support for mirroring deletions more accurately.
 
+Added --dry-run option.
+
 [1.4.0]
 
 The 'isync' compatibility wrapper was removed.

src/common.h

@@ -113,6 +113,8 @@ BIT_ENUM(
 
 	PROGRESS,
 
+	DRYRUN,
+
 	ZERODELAY,
 	KEEPJOURNAL,
 	FORCEJOURNAL,

src/drv_proxy.c

@@ -23,6 +23,8 @@ typedef union proxy_store {
 		gen_cmd_t *pending_cmds, **pending_cmds_append;
 		gen_cmd_t *check_cmds, **check_cmds_append;
 		wakeup_t wakeup;
+		uint fake_nextuid;
+		char is_fake;  // Was "created" by dry-run
 		char force_async;
 
 		void (*expunge_callback)( message_t *msg, void *aux );
@@ -139,8 +141,11 @@ static @type@proxy_@name@( store_t *gctx )
 {
 	proxy_store_t *ctx = (proxy_store_t *)gctx;
 
-	@type@rv = ctx->real_driver->@name@( ctx->real_store );
-	debug( "%sCalled @name@, ret=@fmt@\n", ctx->label, rv );
+	@type@rv;
+	@pre_invoke@
+	@indent_invoke@rv = ctx->real_driver->@name@( ctx->real_store );
+	@post_invoke@
+	debug( "%sCalled @name@@print_fmt_dry@, ret=@fmt@\n", ctx->label@print_pass_dry@, rv );
 	return rv;
 }
 //# END
@@ -151,9 +156,12 @@ static @type@proxy_@name@( store_t *gctx@decl_args@ )
 	proxy_store_t *ctx = (proxy_store_t *)gctx;
 
 	@pre_print_args@
-	debug( "%sEnter @name@@print_fmt_args@\n", ctx->label@print_pass_args@ );
+	debug( "%sEnter @name@@print_fmt_dry@@print_fmt_args@\n", ctx->label@print_pass_dry@@print_pass_args@ );
 	@print_args@
-	@type@rv = ctx->real_driver->@name@( ctx->real_store@pass_args@ );
+	@type@rv;
+	@pre_invoke@
+	@indent_invoke@rv = ctx->real_driver->@name@( ctx->real_store@pass_args@ );
+	@post_invoke@
 	debug( "%sLeave @name@, ret=@print_fmt_ret@\n", ctx->label, @print_pass_ret@ );
 	return rv;
 }
@@ -165,9 +173,11 @@ static @type@proxy_@name@( store_t *gctx@decl_args@ )
 	proxy_store_t *ctx = (proxy_store_t *)gctx;
 
 	@pre_print_args@
-	debug( "%sEnter @name@@print_fmt_args@\n", ctx->label@print_pass_args@ );
+	debug( "%sEnter @name@@print_fmt_dry@@print_fmt_args@\n", ctx->label@print_pass_dry@@print_pass_args@ );
 	@print_args@
-	ctx->real_driver->@name@( ctx->real_store@pass_args@ );
+	@pre_invoke@
+	@indent_invoke@ctx->real_driver->@name@( ctx->real_store@pass_args@ );
+	@post_invoke@
 	debug( "%sLeave @name@\n", ctx->label );
 	@action@
 }
@@ -226,9 +236,11 @@ proxy_do_@name@( gen_cmd_t *gcmd )
 	proxy_store_t *ctx = cmd->ctx;
 
 	@pre_print_args@
-	debug( "%s[% 2d] Enter @name@@print_fmt_args@\n", ctx->label, cmd->tag@print_pass_args@ );
+	debug( "%s[% 2d] Enter @name@@print_fmt_dry@@print_fmt_args@\n", ctx->label, cmd->tag@print_pass_dry@@print_pass_args@ );
 	@print_args@
-	ctx->real_driver->@name@( ctx->real_store@pass_args@, proxy_@name@_cb, cmd );
+	@pre_invoke@
+	@indent_invoke@ctx->real_driver->@name@( ctx->real_store@pass_args@, proxy_@name@_cb, cmd );
+	@post_invoke@
 	debug( "%s[% 2d] Leave @name@\n", ctx->label, cmd->tag );
 }
 
@@ -252,10 +264,51 @@ static @type@proxy_@name@( store_t *gctx@decl_args@, void (*cb)( @decl_cb_args@v
 		debug( "  %s\n", box->string );
 //# END
 
+//# DEFINE select_box_pre_invoke
+	ctx->is_fake = 0;
+//# END
+
+//# DEFINE create_box_driable 1
+//# DEFINE create_box_fake_invoke
+	ctx->is_fake = 1;
+//# END
 //# DEFINE create_box_counted 1
 
+//# DEFINE open_box_fakeable 1
+//# DEFINE open_box_fake_invoke
+	ctx->fake_nextuid = 1;
+//# END
+//# DEFINE open_box_fake_cb_args , 1
+
+//# DEFINE get_uidnext_fakeable 1
+//# DEFINE get_uidnext_fake_invoke
+	rv = ctx->fake_nextuid;
+//# END
+//# DEFINE get_uidnext_post_real_invoke
+	ctx->fake_nextuid = rv;
+//# END
+
+//# DEFINE get_supported_flags_fakeable 1
+//# DEFINE get_supported_flags_fake_invoke
+	rv = 255;
+//# END
+
+//# DEFINE confirm_box_empty_fakeable 1
+//# DEFINE confirm_box_empty_fake_invoke
+	rv = 1;
+//# END
+
+//# DEFINE delete_box_driable 1
+//# DEFINE delete_box_fake_invoke
+	ctx->is_fake = 0;
+//# END
 //# DEFINE delete_box_counted 1
 
+//# DEFINE finish_delete_box_driable 1
+//# DEFINE finish_delete_box_fake_invoke
+	rv = DRV_OK;
+//# END
+
 //# DEFINE prepare_load_box_print_fmt_args , opts=%s
 //# DEFINE prepare_load_box_print_pass_args , fmt_opts( opts ).str
 //# DEFINE prepare_load_box_print_fmt_ret %s
@@ -274,6 +327,8 @@ static @type@proxy_@name@( store_t *gctx@decl_args@, void (*cb)( @decl_cb_args@v
 		debug( "\n" );
 	}
 //# END
+//# DEFINE load_box_fakeable 1
+//# DEFINE load_box_fake_cb_args , NULL, 0, 0
 //# DEFINE load_box_print_fmt_cb_args , total=%d, recent=%d
 //# DEFINE load_box_print_pass_cb_args , total_msgs, recent_msgs
 //# DEFINE load_box_print_cb_args
@@ -297,6 +352,11 @@ static @type@proxy_@name@( store_t *gctx@decl_args@, void (*cb)( @decl_cb_args@v
 
 //# DEFINE fetch_msg_print_fmt_args , uid=%u, want_flags=%s, want_date=%s
 //# DEFINE fetch_msg_print_pass_args , cmd->msg->uid, !(cmd->msg->status & M_FLAGS) ? "yes" : "no", cmd->data->date ? "yes" : "no"
+//# DEFINE fetch_msg_driable 1
+//# DEFINE fetch_msg_fake_invoke
+	cmd->data->data = strdup( "" );
+	cmd->data->len = 0;
+//# END
 //# DEFINE fetch_msg_print_fmt_cb_args , flags=%s, date=%lld, size=%u
 //# DEFINE fetch_msg_print_pass_cb_args , fmt_flags( cmd->data->flags ).str, (long long)cmd->data->date, cmd->data->len
 //# DEFINE fetch_msg_print_cb_args
@@ -318,17 +378,23 @@ static @type@proxy_@name@( store_t *gctx@decl_args@, void (*cb)( @decl_cb_args@v
 		fflush( stdout );
 	}
 //# END
+//# DEFINE store_msg_driable 1
+//# DEFINE store_msg_fake_cb_args , cmd->to_trash ? 0 : ctx->fake_nextuid++
 //# DEFINE store_msg_counted 1
 
 //# DEFINE set_msg_flags_checked 1
 //# DEFINE set_msg_flags_print_fmt_args , uid=%u, add=%s, del=%s
 //# DEFINE set_msg_flags_print_pass_args , cmd->uid, fmt_flags( cmd->add ).str, fmt_flags( cmd->del ).str
+//# DEFINE set_msg_flags_driable 1
 //# DEFINE set_msg_flags_counted 1
 
 //# DEFINE trash_msg_print_fmt_args , uid=%u
 //# DEFINE trash_msg_print_pass_args , cmd->msg->uid
+//# DEFINE trash_msg_driable 1
 //# DEFINE trash_msg_counted 1
 
+//# DEFINE close_box_driable 1
+//# DEFINE close_box_fake_cb_args , 0
 //# DEFINE close_box_counted 1
 
 //# DEFINE commit_cmds_print_args

src/drv_proxy_gen.pl

@@ -175,15 +175,49 @@ for (@ptypes) {
 		$replace{'print_pass_args'} = $replace{'pass_args'} = $pass_args;
 		$replace{'print_fmt_args'} = make_format($cmd_args);
 	}
+	my ($fake_cond, $fake_invoke, $fake_cb_args, $post_invoke) = (undef, "", "", "");
 	for (keys %defines) {
 		next if (!/^${cmd_name}_(.*)$/);
 		my ($key, $val) = ($1, delete $defines{$_});
 		if ($key eq 'counted') {
 			$replace{count_step} = "countStep();\n";
+		} elsif ($key eq 'fakeable') {
+			$fake_cond = "ctx->is_fake";
+			$replace{print_pass_dry} = ', '.$fake_cond.' ? " [FAKE]" : ""';
+		} elsif ($key eq 'driable') {
+			$fake_cond = "DFlags & DRYRUN";
+			$replace{print_pass_dry} = ', ('.$fake_cond.') ? " [DRY]" : ""';
+		} elsif ($key eq 'fake_invoke') {
+			$fake_invoke = $val;
+		} elsif ($key eq 'fake_cb_args') {
+			$fake_cb_args = $val;
+		} elsif ($key eq 'post_real_invoke') {
+			$post_invoke = $val;
 		} else {
 			$replace{$key} = $val;
 		}
 	}
+	if (defined($fake_cond)) {
+		$replace{print_fmt_dry} = '%s';
+		if ($inc_tpl eq 'CALLBACK_STS') {
+			$fake_invoke .= "proxy_${cmd_name}_cb( DRV_OK${fake_cb_args}, cmd );\n";
+		} elsif (length($fake_cb_args)) {
+			die("Unexpected fake callback arguments to $cmd_name\n");
+		}
+		my $num_fake = $fake_invoke =~ s/^(?=.)/\t/gsm;
+		my $num_real = $post_invoke =~ s/^(?=.)/\t/gsm;
+		my $pre_invoke = "if (".$fake_cond.")";
+		if ($num_fake > 1 || $num_real) {
+			$pre_invoke .= " {";
+			$fake_invoke .= "} else {\n";
+			$post_invoke .= "}\n";
+		} else {
+			$fake_invoke .= "else\n";
+		}
+		$replace{pre_invoke} = $pre_invoke."\n".$fake_invoke;
+		$replace{indent_invoke} = "\t";
+		$replace{post_invoke} = $post_invoke;
+	}
 	my %used;
 	my $text = $templates{$template};
 	if ($inc_tpl) {

src/main.c

@@ -46,6 +46,7 @@ PACKAGE " " VERSION " - mailbox synchronizer\n"
 "  -x, --expunge-solo	expunge deleted messages that are not paired\n"
 "  -c, --config CONFIG	read an alternate config file (default: ~/." EXE "rc)\n"
 "  -D, --debug		debugging modes (see manual)\n"
+"  -y, --dry-run		do not actually modify anything\n"
 "  -V, --verbose		display what is happening\n"
 "  -q, --quiet		don't display progress counters\n"
 "  -v, --version		display version\n"
@@ -217,6 +218,8 @@ main( int argc, char **argv )
 					else
 						goto badopt;
 					DFlags |= op;
+				} else if (!strcmp( opt, "dry-run" )) {
+					DFlags |= DRYRUN;
 				} else if (!strcmp( opt, "pull" )) {
 					cops |= XOP_PULL, mvars->ops[F] |= XOP_HAVE_TYPE;
 				} else if (!strcmp( opt, "push" )) {
@@ -454,6 +457,9 @@ main( int argc, char **argv )
 				op = DEBUG_ALL;
 			DFlags |= op;
 			break;
+		case 'y':
+			DFlags |= DRYRUN;
+			break;
 		case 'T':
 			for (; *ochar; ) {
 				switch (*ochar++) {

src/main_sync.c

@@ -50,10 +50,14 @@ summary( void )
 	printf( "Processed %d box(es) in %d channel(s)", boxes_done, chans_done );
 	for (int t = 2; --t >= 0; ) {
 		if (ops_any[t])
-			printf( ",\n%sed %d new message(s) and %d flag update(s)",
+			printf( (DFlags & DRYRUN) ?
+			            ",\nwould %s %d new message(s) and %d flag update(s)" :
+			            ",\n%sed %d new message(s) and %d flag update(s)",
 			        str_hl[t], new_done[t], flags_done[t] );
 		if (trash_any[t])
-			printf( ",\nmoved %d %s message(s) to trash",
+			printf( (DFlags & DRYRUN) ?
+			            ",\nwould move %d %s message(s) to trash" :
+			            ",\nmoved %d %s message(s) to trash",
 			        trash_done[t], str_fn[t] );
 	}
 	puts( "." );

src/mbsync.1

@@ -74,6 +74,11 @@ Display a summary of command line options.
 \fB-v\fR, \fB--version\fR
 Display version information.
 .TP
+\fB-y\fR, \fB--dry-run\fR
+Enter simulation mode: the Channel status is queried and all required
+operations are determined, but no modifications are actually made
+to either the mailboxes or the state files.
+.TP
 \fB-V\fR, \fB--verbose\fR
 Enable \fIverbose\fR mode, which displays what is currently happening.
 .TP

src/sync_state.c

@@ -77,6 +77,9 @@ lock_state( sync_vars_t *svars )
 {
 	struct flock lck;
 
+	if (DFlags & DRYRUN)
+		return 1;
+
 	if (svars->lfd >= 0)
 		return 1;
 	memset( &lck, 0, sizeof(lck) );
@@ -451,6 +454,8 @@ jFprintf( sync_vars_t *svars, const char *msg, ... )
 	va_list va;
 
 	if (!svars->jfp) {
+		if (DFlags & DRYRUN)
+			goto dryout;
 		create_state( svars );
 		if (!(svars->jfp = fopen( svars->jname, svars->replayed ? "a" : "w" ))) {
 			sys_error( "Error: cannot create journal %s", svars->jname );
@@ -463,6 +468,7 @@ jFprintf( sync_vars_t *svars, const char *msg, ... )
 	va_start( va, msg );
 	vFprintf( svars->jfp, msg, va );
 	va_end( va );
+  dryout:
 	countStep();
 	JCount++;
 }
@@ -474,6 +480,10 @@ save_state( sync_vars_t *svars )
 	if (!svars->jfp && !svars->replayed)
 		return;
 
+	// jfp is NULL in this case anyway, but we might have replayed.
+	if (DFlags & DRYRUN)
+		return;
+
 	if (!svars->nfp)
 		create_state( svars );
 	Fprintf( svars->nfp,
@@ -506,6 +516,9 @@ save_state( sync_vars_t *svars )
 void
 delete_state( sync_vars_t *svars )
 {
+	if (DFlags & DRYRUN)
+		return;
+
 	unlink( svars->nname );
 	unlink( svars->jname );
 	if (unlink( svars->dname ) || unlink( svars->lname )) {