Introduce sigint_checker_t and use it in wait

Allow a simpler way to check for sigint via sigint_checker_t.
Adopt it in builtin_wait, instead of hooking into the reader.

src/builtin_wait.cpp

@@ -7,7 +7,7 @@
 #include "common.h"
 #include "parser.h"
 #include "proc.h"
-#include "reader.h"
+#include "signal.h"
 #include "wgetopt.h"
 #include "wutil.h"
 
@@ -66,11 +66,11 @@ static bool any_jobs_finished(size_t jobs_len, const parser_t &parser) {
 }
 
 static int wait_for_backgrounds(parser_t &parser, bool any_flag) {
+    sigint_checker_t sigint;
     size_t jobs_len = parser.jobs().size();
-
     while ((!any_flag && !all_jobs_finished(parser)) ||
            (any_flag && !any_jobs_finished(jobs_len, parser))) {
-        if (reader_test_interrupted()) {
+        if (sigint.check()) {
             return 128 + SIGINT;
         }
         proc_wait_any(parser);
@@ -108,9 +108,10 @@ static bool any_specified_jobs_finished(const std::vector<job_id_t> &ids) {
 
 static int wait_for_backgrounds_specified(parser_t &parser, const std::vector<job_id_t> &ids,
                                           bool any_flag) {
+    sigint_checker_t sigint;
     while ((!any_flag && !all_specified_jobs_finished(ids)) ||
            (any_flag && !any_specified_jobs_finished(ids))) {
-        if (reader_test_interrupted()) {
+        if (sigint.check()) {
             return 128 + SIGINT;
         }
         proc_wait_any(parser);

src/signal.cpp

@@ -15,6 +15,7 @@
 #include "parser.h"
 #include "proc.h"
 #include "reader.h"
+#include "signal.h"
 #include "topic_monitor.h"
 #include "wutil.h"  // IWYU pragma: keep
 
@@ -417,3 +418,16 @@ void signal_unblock_all() {
     sigemptyset(&iset);
     sigprocmask(SIG_SETMASK, &iset, NULL);
 }
+
+sigint_checker_t::sigint_checker_t() {
+    // Call check() to update our generation.
+    check();
+}
+
+bool sigint_checker_t::check() {
+    auto &tm = topic_monitor_t::principal();
+    generation_t gen = tm.generation_for_topic(topic_t::sighupint);
+    bool changed = this->gen_ != gen;
+    this->gen_ = gen;
+    return changed;
+}

src/signal.h

@@ -32,4 +32,16 @@ void signal_unblock_all();
 /// Returns signals with non-default handlers.
 void get_signals_with_handlers(sigset_t *set);
 
+/// A sigint_detector_t can be used to check if a SIGINT (or SIGHUP) has been delivered.
+class sigint_checker_t {
+    uint64_t gen_{0};
+
+   public:
+    sigint_checker_t();
+
+    /// Check if a sigint has been delivered since the last call to check(), or since the detector
+    /// was created.
+    bool check();
+};
+
 #endif