Merge pull request #7459 from roc-lang/ayaz/panic-catcher

Catch panics that happen within repl step executions

.github/workflows/ci_manager.yml

@@ -124,11 +124,6 @@ jobs:
         if: needs.check-changes.outputs.run_tests == 'full'
         uses: ./.github/workflows/benchmarks.yml
 
-    start-panic-check:
-        needs: check-changes
-        if: needs.check-changes.outputs.run_tests == 'full'
-        uses: ./.github/workflows/improve_panics.yml
-
     ran-full:
         runs-on: ubuntu-22.04
         needs: [
@@ -142,7 +137,6 @@ jobs:
                 start-windows-release-build-test,
                 start-windows-tests,
                 start-roc-benchmarks,
-                start-panic-check
             ]
         steps:
             - run: echo "all workflows succeeded!"

crates/repl_cli/src/lib.rs

@@ -17,7 +17,11 @@ use rustyline::highlight::{Highlighter, PromptInfo};
 use rustyline::validate::{self, ValidationContext, ValidationResult, Validator};
 use rustyline::Config;
 use rustyline_derive::{Completer, Helper, Hinter};
+use std::any::Any;
+use std::backtrace::Backtrace;
 use std::borrow::Cow;
+use std::panic::{AssertUnwindSafe, PanicInfo};
+use std::sync::{Arc, Mutex, OnceLock};
 use target_lexicon::Triple;
 
 use crate::cli_gen::eval_llvm;
@@ -37,10 +41,27 @@ pub struct ReplHelper {
     state: ReplState,
 }
 
+static BACKTRACE: OnceLock<Arc<Mutex<Option<String>>>> = OnceLock::new();
+
+fn init_backtrace_storage() {
+    BACKTRACE.get_or_init(|| Arc::new(Mutex::new(None)));
+}
+
+fn panic_hook(_: &PanicInfo) {
+    if let Some(storage) = BACKTRACE.get() {
+        let _ = storage.lock().map(|ref mut storage| {
+            **storage = Some(Backtrace::force_capture().to_string());
+        });
+    }
+}
+
 pub fn main(has_color: bool, has_header: bool) -> i32 {
     use rustyline::error::ReadlineError;
     use rustyline::Editor;
 
+    init_backtrace_storage();
+    std::panic::set_hook(Box::new(panic_hook));
+
     let strip_colors_if_necessary = |s: &str| {
         if has_color {
             s.to_string()
@@ -85,7 +106,13 @@ pub fn main(has_color: bool, has_header: bool) -> i32 {
                     .state;
 
                 arena.reset();
-                match repl_state.step(&arena, line, target, DEFAULT_PALETTE) {
+
+                let action = std::panic::catch_unwind(AssertUnwindSafe(|| {
+                    repl_state.step(&arena, line, target, DEFAULT_PALETTE)
+                }))
+                .unwrap_or_else(|e| notify_repl_panic(target, e));
+
+                match action {
                     ReplAction::Eval { opt_mono, problems } => {
                         let output = evaluate(opt_mono, problems, target);
                         // If there was no output, don't print a blank line!
@@ -129,6 +156,37 @@ pub fn main(has_color: bool, has_header: bool) -> i32 {
     }
 }
 
+fn notify_repl_panic(target: Target, e: Box<dyn Any + Send>) -> ReplAction<'static> {
+    let message = if let Some(s) = e.downcast_ref::<&str>() {
+        s.to_string()
+    } else if let Some(s) = e.downcast_ref::<String>() {
+        s.clone()
+    } else {
+        "Unknown error".to_string()
+    };
+
+    let backtrace = BACKTRACE
+        .get()
+        .and_then(|storage| storage.lock().ok().as_deref_mut().and_then(Option::take))
+        .unwrap_or_else(|| "<Backtrace not found>".to_string());
+
+    println!(
+        "\
+The Roc compiler had an internal error.
+Please file a bug report at
+    https://github.com/roc-lang/roc/issues/new
+Please include the following data:
+
+Error message: {}
+Stack backtrace:
+{}
+Machine Target: {:#?}
+",
+        message, backtrace, target
+    );
+    ReplAction::Nothing
+}
+
 pub fn evaluate(
     opt_mono: Option<MonomorphizedModule<'_>>,
     problems: Problems,