Install a panic handler to avoid dropping crash stacktraces

When fish crashes due to a panic, the terminal window is closed.  Some
terminals keep the window around when the crash is due to a fatal signal,
but today we don't exit via fatal signal on panic.

There is the option to set «panic = "abort"» in Cargo.toml, which
would give us coredumps but also worse stacktraces on stderr.
More importantly it means that we don't unwind, so destructors are skipped
I don't think we want that because we should use destructors to
restore the terminal state.

On crash in interactive fish, read one more line before exiting, so the
stack trace is always visible.

In future, we should move this "read one line before exiting" logic to where
we call "panic!", so I can attach a debugger and see the stacktrace.

src/bin/fish.rs

@@ -32,18 +32,18 @@ use fish::{
         scoped_push_replacer, str2wcstring, wcs2string, PACKAGE_NAME, PROFILING_ACTIVE,
         PROGRAM_NAME,
     },
-    env::Statuses,
     env::{
         environment::{env_init, EnvStack, Environment},
-        ConfigPaths, EnvMode,
+        ConfigPaths, EnvMode, Statuses,
     },
     eprintf,
     event::{self, Event},
     flog::{self, activate_flog_categories_by_pattern, set_flog_file_fd, FLOG, FLOGF},
-    fprintf, function, future_feature_flags as features, history,
-    history::start_private_mode,
+    fprintf, function, future_feature_flags as features,
+    history::{self, start_private_mode},
     io::IoChain,
     nix::{getpid, isatty},
+    panic::panic_handler,
     parse_constants::{ParseErrorList, ParseTreeFlags},
     parse_tree::ParsedSource,
     parse_util::parse_util_detect_errors_in_ast,
@@ -465,6 +465,10 @@ fn cstr_from_osstr(s: &OsStr) -> CString {
 }
 
 fn main() {
+    panic_handler(throwing_main)
+}
+
+fn throwing_main() {
     let mut args: Vec<WString> = env::args_os()
         .map(|osstr| str2wcstring(osstr.as_bytes()))
         .collect();

src/bin/fish_indent.rs

@@ -11,6 +11,7 @@ use std::io::{stdin, Read, Write};
 use std::os::unix::ffi::OsStrExt;
 use std::sync::atomic::Ordering;
 
+use fish::panic::panic_handler;
 use libc::{LC_ALL, STDOUT_FILENO};
 
 use fish::ast::{
@@ -737,8 +738,11 @@ fn char_is_escaped(text: &wstr, idx: usize) -> bool {
 }
 
 fn main() {
-    PROGRAM_NAME.set(L!("fish_indent")).unwrap();
+    panic_handler(throwing_main)
+}
 
+fn throwing_main() {
+    PROGRAM_NAME.set(L!("fish_indent")).unwrap();
     topic_monitor_init();
     threads::init();
     // Using the user's default locale could be a problem if it doesn't use UTF-8 encoding. That's

src/bin/fish_key_reader.rs

@@ -25,6 +25,7 @@ use fish::{
     fprintf,
     input::input_terminfo_get_name,
     input_common::{CharEvent, InputEventQueue, InputEventQueuer},
+    panic::panic_handler,
     print_help::print_help,
     printf,
     proc::set_interactive_session,
@@ -364,6 +365,10 @@ fn parse_flags(continuous_mode: &mut bool, verbose: &mut bool) -> bool {
 }
 
 fn main() {
+    panic_handler(throwing_main)
+}
+
+fn throwing_main() {
     PROGRAM_NAME.set(L!("fish_key_reader")).unwrap();
     let mut continuous_mode = false;
     let mut verbose = false;

src/lib.rs

@@ -68,6 +68,7 @@ pub mod null_terminated_array;
 pub mod operation_context;
 pub mod output;
 pub mod pager;
+pub mod panic;
 pub mod parse_constants;
 pub mod parse_execution;
 pub mod parse_tree;

src/panic.rs

@@ -0,0 +1,33 @@
+use std::panic::{catch_unwind, UnwindSafe};
+
+use libc::STDIN_FILENO;
+
+use crate::{
+    common::{read_blocked, PROGRAM_NAME},
+    nix::isatty,
+};
+
+pub fn panic_handler(main: impl FnOnce() + UnwindSafe) -> ! {
+    if !isatty(STDIN_FILENO) {
+        main();
+        unreachable!();
+    }
+    if catch_unwind(main).is_ok() {
+        unreachable!();
+    }
+    printf!(
+        "%s with PID %d crashed, please report a bug. Press Enter to exit",
+        PROGRAM_NAME.get().unwrap(),
+        unsafe { libc::getpid() }
+    );
+    let mut buf = [0_u8; 1];
+    loop {
+        let Ok(n) = read_blocked(STDIN_FILENO, &mut buf) else {
+            std::process::exit(110);
+        };
+        if n == 0 || matches!(buf[0], b'q' | b'\n' | b'\r') {
+            printf!("\n");
+            std::process::exit(110);
+        }
+    }
+}