Eliminate the "input callback queue"

This was a sort of side channel that was only used to propagate redraws
after universal variable changes. We can eliminate it and handle these
more directly.

src/env.cpp

@@ -61,7 +61,7 @@ static latch_t<env_universal_t> s_universal_variables;
 /// Getter for universal variables.
 static env_universal_t *uvars() { return s_universal_variables; }
 
-void env_universal_barrier() { env_stack_t::principal().universal_barrier(); }
+bool env_universal_barrier() { return env_stack_t::principal().universal_barrier(); }
 
 // A typedef for a set of constant strings. Note our sets are typically on the order of 6 elements,
 // so we don't bother to sort them.
@@ -498,9 +498,9 @@ env_scoped_t::env_scoped_t(std::unique_ptr<var_stack_t> vars) : vars_(std::move(
 env_scoped_t::env_scoped_t(env_scoped_t &&) = default;
 env_scoped_t::~env_scoped_t() = default;
 
-void env_stack_t::universal_barrier() {
+bool env_stack_t::universal_barrier() {
     ASSERT_IS_MAIN_THREAD();
-    if (!uvars()) return;
+    if (!uvars()) return false;
 
     callback_data_list_t callbacks;
     bool changed = uvars()->sync(callbacks);
@@ -509,6 +509,7 @@ void env_stack_t::universal_barrier() {
     }
 
     env_universal_callbacks(this, callbacks);
+    return changed || !callbacks.empty();
 }
 
 /// If they don't already exist initialize the `COLUMNS` and `LINES` env vars to reasonable

src/env.h

@@ -271,7 +271,8 @@ class env_stack_t final : public env_scoped_t {
     void pop();
 
     /// Synchronizes all universal variable changes: writes everything out, reads stuff in.
-    void universal_barrier();
+    /// \return true if something changed, false otherwise.
+    bool universal_barrier();
 
     /// Returns an array containing all exported variables in a format suitable for execv
     const char *const *export_arr();
@@ -302,7 +303,8 @@ extern bool g_use_posix_spawn;
 extern bool term_has_xn;  // does the terminal have the "eat_newline_glitch"
 
 /// Synchronizes all universal variable changes: writes everything out, reads stuff in.
-void env_universal_barrier();
+/// \return true if any value changed.
+bool env_universal_barrier();
 
 /// Returns true if we think the terminal supports setting its title.
 bool term_supports_setting_title();

src/input_common.cpp

@@ -36,11 +36,6 @@ static int wait_on_escape_ms = WAIT_ON_ESCAPE_DEFAULT;
 /// Events which have been read and returned by the sequence matching code.
 static std::deque<char_event_t> lookahead_list;
 
-// Queue of pairs of (function pointer, argument) to be invoked. Expected to be mostly empty.
-typedef std::list<std::function<void(void)>> callback_queue_t;
-static callback_queue_t callback_queue;
-static void input_flush_callbacks();
-
 static bool has_lookahead() { return !lookahead_list.empty(); }
 
 static char_event_t lookahead_pop() {
@@ -78,9 +73,6 @@ static char_event_t readb() {
     bool do_loop;
 
     do {
-        // Flush callbacks.
-        input_flush_callbacks();
-
         fd_set fdset;
         int fd_max = 0;
         int ioport = iothread_port();
@@ -139,7 +131,12 @@ static char_event_t readb() {
                 barrier_from_readability = notifier.notification_fd_became_readable(notifier_fd);
             }
             if (barrier_from_poll || barrier_from_readability) {
-                env_universal_barrier();
+                if (env_universal_barrier()) {
+                    // A variable change may have triggered a repaint, etc.
+                    if (auto mc = lookahead_pop_evt()) {
+                        return *mc;
+                    }
+                }
             }
 
             if (ioport > 0 && FD_ISSET(ioport, &fdset)) {
@@ -245,19 +242,3 @@ char_event_t input_common_readch_timed(bool dequeue_timeouts) {
 void input_common_queue_ch(char_event_t ch) { lookahead_push_back(ch); }
 
 void input_common_next_ch(char_event_t ch) { lookahead_push_front(ch); }
-
-void input_common_add_callback(std::function<void(void)> callback) {
-    ASSERT_IS_MAIN_THREAD();
-    callback_queue.push_back(std::move(callback));
-}
-
-static void input_flush_callbacks() {
-    // We move the queue into a local variable, so that events queued up during a callback don't get
-    // fired until next round.
-    ASSERT_IS_MAIN_THREAD();
-    callback_queue_t local_queue;
-    std::swap(local_queue, callback_queue);
-    for (auto &f : local_queue) {
-        f();
-    }
-}

src/input_common.h

@@ -2,13 +2,11 @@
 #ifndef INPUT_COMMON_H
 #define INPUT_COMMON_H
 
-#include <stddef.h>
-
-#include <functional>
-
 #include "common.h"
 #include "maybe.h"
 
+#include <stddef.h>
+
 enum class readline_cmd_t {
     beginning_of_line,
     end_of_line,
@@ -172,8 +170,4 @@ void input_common_queue_ch(char_event_t ch);
 /// once).
 void input_common_next_ch(char_event_t ch);
 
-/// Adds a callback to be invoked at the next turn of the "event loop." The callback function will
-/// be invoked and passed arg.
-void input_common_add_callback(std::function<void(void)>);
-
 #endif

src/reader.cpp

@@ -3436,7 +3436,7 @@ void reader_react_to_color_change() {
     if (!data->repaint_needed || !data->screen_reset_needed) {
         data->repaint_needed = true;
         data->screen_reset_needed = true;
-        input_common_add_callback(reader_repaint_if_needed);
+        input_common_queue_ch(readline_cmd_t::repaint);
     }
 }