[gjs: 1/3] console: Catch Ctrl+C in interactive prompt

[Philip Chimento <pchimento src gnome org>]

commit 772c31e5d8440861f892d888f126db2f7367af7e
Author: Philip Chimento <philip chimento gmail com>
Date:   Sat Feb 20 12:34:42 2021 -0800

    console: Catch Ctrl+C in interactive prompt
    
    Instead of exiting outright, Ctrl+C clears anything that's been typed so
    far in the buffer and goes back to the interactive prompt.
    
    (This is not really possible to test other than manually, so no tests.)
    
    Closes: #98

 modules/console.cpp | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 56 insertions(+), 3 deletions(-)
---
diff --git a/modules/console.cpp b/modules/console.cpp
index da0b9115..944dec26 100644
--- a/modules/console.cpp
+++ b/modules/console.cpp
@@ -5,6 +5,11 @@
 
 #include <config.h>  // for HAVE_READLINE_READLINE_H
 
+#ifdef HAVE_SIGNAL_H
+#    include <setjmp.h>
+#    include <signal.h>
+#endif
+
 #ifdef HAVE_READLINE_READLINE_H
 #    include <stdio.h>  // include before readline/readline.h
 
@@ -80,6 +85,37 @@ public:
     }
 };
 
+#ifdef HAVE_SIGNAL_H
+
+// Adapted from https://stackoverflow.com/a/17035073/172999
+class AutoCatchCtrlC {
+    void (*m_prev_handler)(int);
+
+    static void handler(int signal) {
+        if (signal == SIGINT)
+            siglongjmp(jump_buffer, 1);
+    }
+
+ public:
+    static sigjmp_buf jump_buffer;
+
+    AutoCatchCtrlC() {
+        m_prev_handler = signal(SIGINT, &AutoCatchCtrlC::handler);
+    }
+
+    ~AutoCatchCtrlC() {
+        if (m_prev_handler != SIG_ERR)
+            signal(SIGINT, m_prev_handler);
+    }
+};
+sigjmp_buf AutoCatchCtrlC::jump_buffer;
+
+#else  // !HAVE_SIGNAL_H
+
+struct AutoCatchCtrlC {};
+
+#endif  // !HAVE_SIGNAL_H
+
 [[nodiscard]] static bool gjs_console_readline(char** bufp,
                                                const char* prompt) {
 #ifdef HAVE_READLINE_READLINE_H
@@ -139,15 +175,20 @@ gjs_console_interact(JSContext *context,
                      JS::Value *vp)
 {
     JS::CallArgs argv = JS::CallArgsFromVp(argc, vp);
-    bool eof = false;
+    bool eof;
     JS::RootedObject global(context, gjs_get_import_global(context));
-    char *temp_buf = NULL;
+    char* temp_buf;
     int lineno;
     int startline;
 
     JS::SetWarningReporter(context, gjs_console_warning_reporter);
 
-        /* It's an interactive filehandle; drop into read-eval-print loop. */
+    AutoCatchCtrlC ctrl_c;
+
+    // Separate initialization from declaration because of possible overwriting
+    // when siglongjmp() jumps into this function
+    eof = false;
+    temp_buf = nullptr;
     lineno = 1;
     do {
         /*
@@ -159,6 +200,18 @@ gjs_console_interact(JSContext *context,
         startline = lineno;
         std::string buffer;
         do {
+#ifdef HAVE_SIGNAL_H
+            // sigsetjmp() returns 0 if control flow encounters it normally, and
+            // nonzero if it's been jumped to. In the latter case, use a while
+            // loop so that we call sigsetjmp() a second time to reinit the jump
+            // buffer.
+            while (sigsetjmp(AutoCatchCtrlC::jump_buffer, 1) != 0) {
+                g_fprintf(stdout, "\n");
+                buffer.clear();
+                startline = lineno = 1;
+            }
+#endif  // HAVE_SIGNAL_H
+
             if (!gjs_console_readline(
                     &temp_buf, startline == lineno ? "gjs> " : ".... ")) {
                 eof = true;