Switch the input interrupt function to return maybe_t

Allow returning none() to mean do nothing.

src/input.cpp

@@ -249,14 +249,18 @@ void input_mapping_add(const wchar_t *sequence, const wchar_t *command, const wc
 
 /// Handle interruptions to key reading by reaping finshed jobs and propagating the interrupt to the
 /// reader.
-static int interrupt_handler() {
+static maybe_t<int> interrupt_handler() {
     // Fire any pending events.
     event_fire_delayed();
     // Reap stray processes, including printing exit status messages.
     if (job_reap(true)) reader_repaint_needed();
     // Tell the reader an event occured.
     if (reader_reading_interrupted()) {
-        return shell_modes.c_cc[VINTR];
+        auto vintr = shell_modes.c_cc[VINTR];
+        if (vintr == 0) {
+            return none();
+        }
+        return vintr;
     }
 
     return R_NULL;

src/input_common.cpp

@@ -63,9 +63,9 @@ static void lookahead_push_back(char_event_t c) { lookahead_list.push_back(c); }
 static void lookahead_push_front(char_event_t c) { lookahead_list.push_front(c); }
 
 /// Callback function for handling interrupts on reading.
-static int (*interrupt_handler)();
+static interrupt_func_t interrupt_handler;
 
-void input_common_init(int (*ih)()) { interrupt_handler = ih; }
+void input_common_init(interrupt_func_t func) { interrupt_handler = func; }
 
 /// Internal function used by input_common_readch to read one byte from fd 0. This function should
 /// only be called by input_common_readch().
@@ -115,9 +115,9 @@ static maybe_t<wint_t> readb() {
         if (res == -1) {
             if (errno == EINTR || errno == EAGAIN) {
                 if (interrupt_handler) {
-                    int res = interrupt_handler();
-                    if (res) return res;
-                    if (auto mc = lookahead_pop_char()) {
+                    if (auto interrupt_evt = interrupt_handler()) {
+                        return *interrupt_evt;
+                    } else if (auto mc = lookahead_pop_char()) {
                         return *mc;
                     }
                 }

src/input_common.h

@@ -122,8 +122,12 @@ class char_event_t {
     }
 };
 
-/// Init the library.
-void input_common_init(int (*ih)());
+/// A type of function invoked on interrupt.
+/// \return the event which is to be returned to the reader loop, or none if VINTR is 0.
+using interrupt_func_t = maybe_t<int> (*)();
+
+/// Init the library with an interrupt function.
+void input_common_init(interrupt_func_t func);
 
 /// Adjust the escape timeout.
 class environment_t;