scm/c++: fix review issues in handler code

- Fix comments and some debug strings (copy-pasta)
- Fix mime-stream destruction (g_object_unref)
- Fix type-checking of scm types

scm/mu-scm-message.cc

@@ -46,7 +46,7 @@ static const Message&
 to_message(SCM scm, const char *func, int pos)
 {
 	if (!SCM_IS_A_P(scm, message_type))
-		throw ScmError{ScmError::Id::WrongType, func, pos, scm, "mesagestore"};
+		throw ScmError{ScmError::Id::WrongType, func, pos, scm, "message"};
 
 	return *reinterpret_cast<Message*>(scm_foreign_object_ref(scm, 0));
 }
@@ -67,16 +67,19 @@ subr_cc_message_make(SCM message_path_scm) try {
 	constexpr auto func{"cc-message-make"};
 
 	// message objects eat fds, tickle the gc... letting it handle it
-	// automatically is not soon enough.
+	// automatically is not soon enough. Note: if a script _holds_
+	// references to this many messages, the map cannot shrink and this
+	// triggers a full GC on each call; slow, but better than running
+	// out of fds.
 	if (message_map.size() >= 0.8 * max_message_map_size)
 		scm_gc();
 
 	std::unique_lock lock{map_lock};
 
-	// qttempt to give an good error message rather then getting something
+	// attempt to give a good error message rather than getting something
 	// from GMime)
 	if (message_map.size() >= max_message_map_size)
-		throw ScmError{"cc-make-message", "too many open messages"};
+		throw ScmError{func, "too many open messages"};
 
 	// if we already have the message in our map, return it.
 	auto path{from_scm<std::string>(message_path_scm, func, 1)};
@@ -103,7 +106,7 @@ subr_cc_message_make(SCM message_path_scm) try {
 static SCM
 subr_cc_message_body(SCM message_scm, SCM html_scm) try {
 
-	constexpr auto func{"cc-message-make"};
+	constexpr auto func{"cc-message-body"};
 
 	const auto& message{to_message(message_scm, func, 1)};
 	const auto html{from_scm<bool>(html_scm, func, 2)};

scm/mu-scm-mime.cc

@@ -80,7 +80,11 @@ make_mime_stream_port_type()
 {
 	auto ptype = scm_make_port_type(const_cast<char*>("mime-stream"), mime_stream_read, {});
 
-	scm_set_port_close(ptype, [](SCM port){g_mime_stream_close(from_scm_port(port));});
+	scm_set_port_close(ptype, [](SCM port){
+		auto stream{from_scm_port(port)};
+		g_mime_stream_close(stream);
+		g_object_unref(stream); // the port owns the stream
+	});
 	scm_set_port_needs_close_on_gc(ptype, true);
 
 	scm_set_port_seek(ptype, mime_stream_seek);
@@ -164,10 +168,10 @@ subr_make_mime_stream_port(SCM mime_part_scm, SCM content_only_scm,
 	GMimeStream *stream{};
 	try {
 		auto part = part_from_scm(mime_part_scm, func, 1);
-		const auto decode{from_scm<bool>(decode_scm,
-						 func, 2)};
 		const auto content_only{from_scm<bool>(content_only_scm,
-						       func, 3)};
+						       func, 2)};
+		const auto decode{from_scm<bool>(decode_scm,
+						 func, 3)};
 		if (decode)
 			stream = get_decoded_stream(part);
 		else

scm/mu-scm-store.cc

@@ -167,9 +167,13 @@ subr_cc_store_mfind(SCM store_scm, SCM query_scm, SCM related_scm, SCM skip_dups
 	SCM msgs{SCM_EOL};
 	// iterate in reverse order, so the message get consed
 	// into the list in the right order.
-	for (auto it{qres->end()}; it-- != qres->begin();)
-		if (auto plist{it.document()->get_data()}; !plist.empty())
+	for (auto it{qres->end()}; it-- != qres->begin();) {
+		const auto doc{it.document()};
+		if (!doc)
+			continue; // e.g., removed since the query ran
+		if (auto plist{doc->get_data()}; !plist.empty())
 			msgs = scm_cons(to_scm(plist), msgs);
+	}
 	return msgs;
 
 } catch (const ScmError& err) {

scm/mu-scm.cc

@@ -160,12 +160,12 @@ maybe_remove_socket_path()
 
 	// opportunistic, so no real warnings, but be careful deleting!
 
-	if (const int res = ::stat(sock.c_str(), &statbuf); res != 0) {
-		mu_debug("can't stat '{}'; err={}", sock, -res);
+	if (::stat(sock.c_str(), &statbuf) != 0) {
+		mu_debug("can't stat '{}': {}", sock, ::strerror(errno));
 	} else if ((statbuf.st_mode & S_IFMT) != S_IFSOCK) {
 		mu_debug("{} is not a socket", sock);
-	} else if (const int ulres = ::unlink(sock.c_str()); ulres != 0) {
-		mu_debug("failed to unlink '{}'; err={}", sock, -ulres);
+	} else if (::unlink(sock.c_str()) != 0) {
+		mu_debug("failed to unlink '{}': {}", sock, ::strerror(errno));
 	} else {
 		mu_debug("unlinked {}", sock);
 	}
@@ -308,7 +308,7 @@ test_scm_script()
 
 	MemDb mdb;
 	Config conf{mdb};
-;	conf.set<Config::Id::PersonalAddresses>(
+	conf.set<Config::Id::PersonalAddresses>(
 		std::vector<std::string>{"user@example.com"});
 
 	auto store{Store::make_new(tempdir.path(), MuTestMaildir, conf)};

scm/mu-scm.hh

@@ -188,18 +188,22 @@ namespace Mu::Scm {
 			if (!pred)
 				throw ScmError{ScmError::Id::WrongType, func, pos, ARG, expected};
 		};
+		// note: use the C predicates (scm_is_string etc.); the Scheme
+		// predicates (scm_string_p etc.) return an SCM boolean, which
+		// is truthy as a C++ bool even when it is #f.
 		using Type = std::remove_const_t<T>; // *not* std::remove_const
 		if constexpr (std::is_same_v<Type, std::string>) {
-			ensure(scm_string_p(ARG), ARG, "string");
-			auto str{scm_to_utf8_string(ARG)};
-			std::string res{str};
+			ensure(scm_is_string(ARG), ARG, "string");
+			size_t len{};
+			auto str{scm_to_utf8_stringn(ARG, &len)};
+			std::string res{str, len};
 			::free(str);
 			return res;
 		} else if constexpr (std::is_same_v<Type, char>) {
-			ensure(scm_char_p(ARG), ARG, "character");
-			return scm_to_char(ARG);
+			ensure(SCM_CHARP(ARG), ARG, "character");
+			return static_cast<char>(SCM_CHAR(ARG));
 		} else if constexpr (std::is_same_v<Type, bool>) {
-			ensure(scm_boolean_p(ARG), ARG, "bool");
+			ensure(scm_is_bool(ARG), ARG, "bool");
 			return scm_to_bool(ARG);
 		} else if constexpr (std::is_same_v<Type, int>) {
 			ensure(scm_is_signed_integer(ARG, std::numeric_limits<int>::min(),
@@ -292,7 +296,7 @@ namespace Mu::Scm {
 	 */
 	template<typename Key, typename Value, typename... KeyVals>
 	static inline SCM alist_add(SCM alist, const Key& key, const Value& val,
-				    KeyVals... keyvals) {
+				    KeyVals&&... keyvals) {
 		SCM res = scm_acons(to_scm(key), to_scm(val), alist);
 		return alist_add(res, std::forward<KeyVals>(keyvals)...);
 	}