tty driver ignore lnext (\cV) and werase (\cW)

Configure the tty driver to ignore the lnext (\cV) and werase (\cW) characters
so they can be bound to fish functions.

Correct the `fish_key_bindings` program to initialize the tty in the same
manner as the `fish` program.

Fixes #3064

src/fish_key_reader.cpp

@@ -16,7 +16,6 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/time.h>
-#include <termios.h>
 #include <wctype.h>
 #include <string>
 
@@ -25,15 +24,16 @@
 #include "fallback.h"  // IWYU pragma: keep
 #include "input.h"
 #include "input_common.h"
+#include "proc.h"
+#include "reader.h"
 
 struct config_paths_t determine_config_directory_paths(const char *argv0);
 
-static struct termios saved_modes;  // so we can reset the modes when we're done
 static long long int prev_tstamp = 0;
 static const char *ctrl_equivalents[] = {NULL,  NULL,  NULL,  NULL,  NULL,  NULL,  NULL, "\\a",
-    "\\b", "\\t", "\\n", "\\v", "\\f", "\\r", NULL, NULL,
-    NULL,  NULL,  NULL,  NULL,  NULL,  NULL,  NULL, NULL,
-    NULL,  NULL,  NULL,  "\\e", NULL,  NULL,  NULL, NULL};
+                                         "\\b", "\\t", "\\n", "\\v", "\\f", "\\r", NULL, NULL,
+                                         NULL,  NULL,  NULL,  NULL,  NULL,  NULL,  NULL, NULL,
+                                         NULL,  NULL,  NULL,  "\\e", NULL,  NULL,  NULL, NULL};
 
 /// Return true if the recent sequence of characters indicates the user wants to exit the program.
 bool should_exit(unsigned char c) {
@@ -47,7 +47,7 @@ bool should_exit(unsigned char c) {
 }
 
 /// Return the key name if the recent sequence of characters matches a known terminfo sequence.
-char * const key_name(unsigned char c) {
+char *const key_name(unsigned char c) {
     static char recent_chars[8] = {0};
 
     recent_chars[0] = recent_chars[1];
@@ -121,7 +121,7 @@ void process_input(bool continuous_mode) {
             printf("%6lld usec  dec: %3u  hex: %2x  char: %c\n", delta_tstamp, c, c, c);
         }
 
-        char * const name = key_name(c);
+        char *const name = key_name(c);
         if (name) {
             printf("FYI: Saw sequence for bind key name \"%s\"\n", name);
             free(name);
@@ -136,48 +136,22 @@ void process_input(bool continuous_mode) {
     }
 }
 
-/// Set the tty modes to not interpret any characters. We want every character to be passed thru to
-/// this program. Including characters such as [ctrl-C] and [ctrl-D] that might normally have
-/// special significance (e.g., terminate the program).
-bool set_tty_modes(void) {
-    struct termios modes;
-
-    tcgetattr(0, &modes);  // get the current tty modes
-    saved_modes = modes;   // save a copy so we can reset them on exit
-
-    modes.c_lflag &= ~ICANON;  // turn off canonical mode
-    modes.c_lflag &= ~ECHO;    // turn off echo mode
-    modes.c_lflag &= ~ISIG;    // turn off recognizing signal generating characters
-    modes.c_iflag &= ~ICRNL;   // turn off mapping CR to NL
-    modes.c_iflag &= ~INLCR;   // turn off mapping NL to CR
-    modes.c_cc[VMIN] = 1;      // return each character as they arrive
-    modes.c_cc[VTIME] = 0;     // wait forever for the next character
-
-    if (tcsetattr(0, TCSANOW, &modes) != 0) {  // set the new modes
-        return false;
-    }
-    return true;
-}
-
-/// Restore the tty modes to what they were before this program was run. This shouldn't be required
-/// but we do it just in case the program that ran us doesn't handle tty modes for external programs
-/// in a sensible manner.
-void reset_tty_modes() { tcsetattr(0, TCSANOW, &saved_modes); }
-
 /// Make sure we cleanup before exiting if we're signaled.
 void signal_handler(int signo) {
     printf("\nExiting on receipt of signal #%d\n", signo);
-    reset_tty_modes();
+    restore_term_mode();
     exit(1);
 }
 
 /// Setup our environment (e.g., tty modes), process key strokes, then reset the environment.
 void setup_and_process_keys(bool continuous_mode) {
+    is_interactive_session = 1;  // by definition this is interactive
     set_main_thread();
     setup_fork_guards();
     wsetlocale(LC_ALL, L"POSIX");
     program_name = L"fish_key_reader";
     env_init();
+    reader_init();
     input_init();
 
     // Installing our handler for every signal (e.g., SIGSEGV) is dubious because it means that
@@ -198,13 +172,9 @@ void setup_and_process_keys(bool continuous_mode) {
         set_wait_on_escape_ms(500);
     }
 
-    if (!set_tty_modes()) {
-        printf("Could not set the tty modes. Refusing to continue running.\n");
-        exit(1);
-    }
     // TODO: We really should enable keypad mode but see issue #838.
     process_input(continuous_mode);
-    reset_tty_modes();
+    restore_term_mode();
 }
 
 int main(int argc, char **argv) {

src/reader.cpp

@@ -784,23 +784,19 @@ void reader_init() {
 
     // Set the mode used for the terminal, initialized to the current mode.
     memcpy(&shell_modes, &terminal_mode_on_startup, sizeof shell_modes);
-    shell_modes.c_iflag &= ~ICRNL;   // turn off mapping CR (\cM) to NL (\cJ)
-    shell_modes.c_iflag &= ~INLCR;   // turn off mapping NL (\cJ) to CR (\cM)
+
+    shell_modes.c_iflag &= ~ICRNL;  // disable mapping CR (\cM) to NL (\cJ)
+    shell_modes.c_iflag &= ~INLCR;  // disable mapping NL (\cJ) to CR (\cM)
+    shell_modes.c_iflag &= ~IXON;   // disable flow control
+    shell_modes.c_iflag &= ~IXOFF;  // disable flow control
+
     shell_modes.c_lflag &= ~ICANON;  // turn off canonical mode
     shell_modes.c_lflag &= ~ECHO;    // turn off echo mode
-    shell_modes.c_iflag &= ~IXON;    // disable flow control
-    shell_modes.c_iflag &= ~IXOFF;   // disable flow control
+    shell_modes.c_lflag &= ~IEXTEN;  // turn off handling of discard and lnext characters
+
     shell_modes.c_cc[VMIN] = 1;
     shell_modes.c_cc[VTIME] = 0;
 
-#if defined(_POSIX_VDISABLE)
-// PCA disable VDSUSP (typically control-Y), which is a funny job control. function available only
-// on OS X and BSD systems. This lets us use control-Y for yank instead.
-#ifdef VDSUSP
-    shell_modes.c_cc[VDSUSP] = _POSIX_VDISABLE;
-#endif
-#endif
-
     // We don't use term_steal because this can fail if fd 0 isn't associated with a tty and this
     // function is run regardless of whether stdin is tied to a tty. This is harmless in that case.
     // We do it unconditionally because disabling ICRNL mode (see above) needs to be done at the
@@ -1107,8 +1103,7 @@ wcstring completion_apply_to_command_line(const wcstring &val_str, complete_flag
     // Perform the insertion and compute the new location.
     wcstring result = command_line;
     result.insert(insertion_point, replaced);
-    size_t new_cursor_pos =
-        insertion_point + replaced.size() + (back_into_trailing_quote ? 1 : 0);
+    size_t new_cursor_pos = insertion_point + replaced.size() + (back_into_trailing_quote ? 1 : 0);
     if (add_space) {
         if (quote != L'\0' && unescaped_quote(command_line, insertion_point) != quote) {
             // This is a quoted parameter, first print a quote.

tests/bind.expect

@@ -199,3 +199,23 @@ expect_prompt -re {\r\nmno pqrt\r\n} {
 } unmatched {
     puts stderr "emacs transpose words fail, 100ms timeout: long delay"
 }
+
+# Verify special characters, such as \cV, are not intercepted by the kernel
+# tty driver. Rather, they can be bound and handled by fish.
+send "bind \\cV 'echo ctrl-v seen'\r"
+expect_prompt
+send "\026\r"
+expect_prompt -re {ctrl-v seen} {
+    puts "ctrl-v seen"
+} unmatched {
+    puts stderr "ctrl-v not seen"
+}
+
+send "bind \\cO 'echo ctrl-o seen'\r"
+expect_prompt
+send "\017\r"
+expect_prompt -re {ctrl-o seen} {
+    puts "ctrl-o seen"
+} unmatched {
+    puts stderr "ctrl-o not seen"
+}

tests/bind.expect.out

@@ -13,3 +13,5 @@ default-mode custom timeout set correctly
 emacs transpose words, 100ms timeout: no delay
 emacs transpose words, 100ms timeout: short delay
 emacs transpose words, 100ms timeout: long delay
+ctrl-v seen
+ctrl-o seen