On nightly, dump ICE backtraces to disk

Implement rust-lang/compiler-team#578.

When an ICE is encountered on nightly releases, the new rustc panic
handler will also write the contents of the backtrace to disk. If any
`delay_span_bug`s are encountered, their backtrace is also added to the
file. The platform and rustc version will also be collected.

Cargo.lock

@@ -3488,6 +3488,7 @@ dependencies = [
  "rustc_trait_selection",
  "rustc_ty_utils",
  "serde_json",
+ "time",
  "tracing",
  "windows",
 ]
@@ -5142,6 +5143,33 @@ dependencies = [
 name = "tier-check"
 version = "0.1.0"
 
+[[package]]
+name = "time"
+version = "0.3.22"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ea9e1b3cf1243ae005d9e74085d4d542f3125458f3a81af210d901dcd7411efd"
+dependencies = [
+ "itoa",
+ "serde",
+ "time-core",
+ "time-macros",
+]
+
+[[package]]
+name = "time-core"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7300fbefb4dadc1af235a9cef3737cea692a9d97e1b9cbcd4ebdae6f8868e6fb"
+
+[[package]]
+name = "time-macros"
+version = "0.2.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "372950940a5f07bf38dbe211d7283c9e6d7327df53794992d293e534c733d09b"
+dependencies = [
+ "time-core",
+]
+
 [[package]]
 name = "tinystr"
 version = "0.7.1"

compiler/rustc_codegen_ssa/src/back/write.rs

@@ -362,7 +362,7 @@ pub struct CodegenContext<B: WriteBackendMethods> {
 
 impl<B: WriteBackendMethods> CodegenContext<B> {
     pub fn create_diag_handler(&self) -> Handler {
-        Handler::with_emitter(true, None, Box::new(self.diag_emitter.clone()))
+        Handler::with_emitter(true, None, Box::new(self.diag_emitter.clone()), None)
     }
 
     pub fn config(&self, kind: ModuleKind) -> &ModuleConfig {

compiler/rustc_driver_impl/Cargo.toml

@@ -6,6 +6,7 @@ edition = "2021"
 [lib]
 
 [dependencies]
+time = { version = "0.3", default-features = false, features = ["formatting", ] }
 tracing = { version = "0.1.35" }
 serde_json = "1.0.59"
 rustc_log = { path = "../rustc_log" }

compiler/rustc_driver_impl/messages.ftl

@@ -3,7 +3,11 @@ driver_impl_ice_bug_report = we would appreciate a bug report: {$bug_report_url}
 driver_impl_ice_exclude_cargo_defaults = some of the compiler flags provided by cargo are hidden
 
 driver_impl_ice_flags = compiler flags: {$flags}
+driver_impl_ice_path = please attach the file at `{$path}` to your bug report
+driver_impl_ice_path_error = the ICE couldn't be written to `{$path}`: {$error}
+driver_impl_ice_path_error_env = the environment variable `RUSTC_ICE` is set to `{$env_var}`
 driver_impl_ice_version = rustc {$version} running on {$triple}
+
 driver_impl_rlink_empty_version_number = The input does not contain version number
 
 driver_impl_rlink_encoding_version_mismatch = .rlink file was produced with encoding version `{$version_array}`, but the current version is `{$rlink_version}`

compiler/rustc_driver_impl/src/lib.rs

@@ -7,6 +7,8 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(lazy_cell)]
 #![feature(decl_macro)]
+#![feature(ice_to_disk)]
+#![feature(let_chains)]
 #![recursion_limit = "256"]
 #![allow(rustc::potential_query_instability)]
 #![deny(rustc::untranslatable_diagnostic)]
@@ -57,8 +59,11 @@ use std::panic::{self, catch_unwind};
 use std::path::PathBuf;
 use std::process::{self, Command, Stdio};
 use std::str;
+use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::OnceLock;
-use std::time::Instant;
+use std::time::{Instant, SystemTime};
+use time::format_description::well_known::Rfc3339;
+use time::OffsetDateTime;
 
 #[allow(unused_macros)]
 macro do_not_use_print($($t:tt)*) {
@@ -294,6 +299,7 @@ fn run_compiler(
         input: Input::File(PathBuf::new()),
         output_file: ofile,
         output_dir: odir,
+        ice_file: ice_path().clone(),
         file_loader,
         locale_resources: DEFAULT_LOCALE_RESOURCES,
         lint_caps: Default::default(),
@@ -1292,9 +1298,29 @@ pub fn catch_with_exit_code(f: impl FnOnce() -> interface::Result<()>) -> i32 {
     }
 }
 
-/// Stores the default panic hook, from before [`install_ice_hook`] was called.
+pub static ICE_PATH: OnceLock<Option<PathBuf>> = OnceLock::new();
-static DEFAULT_HOOK: OnceLock<Box<dyn Fn(&panic::PanicInfo<'_>) + Sync + Send + 'static>> =
+
-    OnceLock::new();
+pub fn ice_path() -> &'static Option<PathBuf> {
+    ICE_PATH.get_or_init(|| {
+        if !rustc_feature::UnstableFeatures::from_environment(None).is_nightly_build() {
+            return None;
+        }
+        if let Ok("0") = std::env::var("RUST_BACKTRACE").as_deref() {
+            return None;
+        }
+        let mut path = match std::env::var("RUSTC_ICE").as_deref() {
+            // Explicitly opting out of writing ICEs to disk.
+            Ok("0") => return None,
+            Ok(s) => PathBuf::from(s),
+            Err(_) => std::env::current_dir().unwrap_or_default(),
+        };
+        let now: OffsetDateTime = SystemTime::now().into();
+        let file_now = now.format(&Rfc3339).unwrap_or(String::new());
+        let pid = std::process::id();
+        path.push(format!("rustc-ice-{file_now}-{pid}.txt"));
+        Some(path)
+    })
+}
 
 /// Installs a panic hook that will print the ICE message on unexpected panics.
 ///
@@ -1318,8 +1344,6 @@ pub fn install_ice_hook(bug_report_url: &'static str, extra_info: fn(&Handler))
         std::env::set_var("RUST_BACKTRACE", "full");
     }
 
-    let default_hook = DEFAULT_HOOK.get_or_init(panic::take_hook);
-
     panic::set_hook(Box::new(move |info| {
         // If the error was caused by a broken pipe then this is not a bug.
         // Write the error and return immediately. See #98700.
@@ -1336,7 +1360,7 @@ pub fn install_ice_hook(bug_report_url: &'static str, extra_info: fn(&Handler))
         // Invoke the default handler, which prints the actual panic message and optionally a backtrace
         // Don't do this for delayed bugs, which already emit their own more useful backtrace.
         if !info.payload().is::<rustc_errors::DelayedBugPanic>() {
-            (*default_hook)(info);
+            std::panic_hook_with_disk_dump(info, ice_path().as_deref());
 
             // Separate the output with an empty line
             eprintln!();
@@ -1368,7 +1392,7 @@ pub fn report_ice(info: &panic::PanicInfo<'_>, bug_report_url: &str, extra_info:
         false,
         TerminalUrl::No,
     ));
-    let handler = rustc_errors::Handler::with_emitter(true, None, emitter);
+    let handler = rustc_errors::Handler::with_emitter(true, None, emitter, None);
 
     // a .span_bug or .bug call has already printed what
     // it wants to print.
@@ -1379,10 +1403,40 @@ pub fn report_ice(info: &panic::PanicInfo<'_>, bug_report_url: &str, extra_info:
     }
 
     handler.emit_note(session_diagnostics::IceBugReport { bug_report_url });
-    handler.emit_note(session_diagnostics::IceVersion {
+
-        version: util::version_str!().unwrap_or("unknown_version"),
+    let version = util::version_str!().unwrap_or("unknown_version");
-        triple: config::host_triple(),
+    let triple = config::host_triple();
-    });
+
+    static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
+
+    let file = if let Some(path) = ice_path().as_ref() {
+        // Create the ICE dump target file.
+        match crate::fs::File::options().create(true).append(true).open(&path) {
+            Ok(mut file) => {
+                handler
+                    .emit_note(session_diagnostics::IcePath { path: path.display().to_string() });
+                if FIRST_PANIC.swap(false, Ordering::SeqCst) {
+                    let _ = write!(file, "\n\nrustc version: {version}\nplatform: {triple}");
+                }
+                Some(file)
+            }
+            Err(err) => {
+                // The path ICE couldn't be written to disk, provide feedback to the user as to why.
+                handler.emit_warning(session_diagnostics::IcePathError {
+                    path: path.display().to_string(),
+                    error: err.to_string(),
+                    env_var: std::env::var("RUSTC_ICE")
+                        .ok()
+                        .map(|env_var| session_diagnostics::IcePathErrorEnv { env_var }),
+                });
+                handler.emit_note(session_diagnostics::IceVersion { version, triple });
+                None
+            }
+        }
+    } else {
+        handler.emit_note(session_diagnostics::IceVersion { version, triple });
+        None
+    };
 
     if let Some((flags, excluded_cargo_defaults)) = extra_compiler_flags() {
         handler.emit_note(session_diagnostics::IceFlags { flags: flags.join(" ") });
@@ -1396,7 +1450,7 @@ pub fn report_ice(info: &panic::PanicInfo<'_>, bug_report_url: &str, extra_info:
 
     let num_frames = if backtrace { None } else { Some(2) };
 
-    interface::try_print_query_stack(&handler, num_frames);
+    interface::try_print_query_stack(&handler, num_frames, file);
 
     // We don't trust this callback not to panic itself, so run it at the end after we're sure we've
     // printed all the relevant info.

compiler/rustc_driver_impl/src/session_diagnostics.rs

@@ -1,4 +1,4 @@
-use rustc_macros::Diagnostic;
+use rustc_macros::{Diagnostic, Subdiagnostic};
 
 #[derive(Diagnostic)]
 #[diag(driver_impl_rlink_unable_to_read)]
@@ -56,6 +56,27 @@ pub(crate) struct IceVersion<'a> {
     pub triple: &'a str,
 }
 
+#[derive(Diagnostic)]
+#[diag(driver_impl_ice_path)]
+pub(crate) struct IcePath {
+    pub path: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(driver_impl_ice_path_error)]
+pub(crate) struct IcePathError {
+    pub path: String,
+    pub error: String,
+    #[subdiagnostic]
+    pub env_var: Option<IcePathErrorEnv>,
+}
+
+#[derive(Subdiagnostic)]
+#[note(driver_impl_ice_path_error_env)]
+pub(crate) struct IcePathErrorEnv {
+    pub env_var: String,
+}
+
 #[derive(Diagnostic)]
 #[diag(driver_impl_ice_flags)]
 pub(crate) struct IceFlags {

compiler/rustc_error_messages/src/lib.rs

@@ -354,6 +354,13 @@ impl DiagnosticMessage {
             }
         }
     }
+
+    pub fn as_str(&self) -> Option<&str> {
+        match self {
+            DiagnosticMessage::Eager(s) | DiagnosticMessage::Str(s) => Some(s),
+            DiagnosticMessage::FluentIdentifier(_, _) => None,
+        }
+    }
 }
 
 impl From<String> for DiagnosticMessage {

compiler/rustc_errors/src/json/tests.rs

@@ -64,7 +64,7 @@ fn test_positions(code: &str, span: (u32, u32), expected_output: SpanTestData) {
         );
 
         let span = Span::with_root_ctxt(BytePos(span.0), BytePos(span.1));
-        let handler = Handler::with_emitter(true, None, Box::new(je));
+        let handler = Handler::with_emitter(true, None, Box::new(je), None);
         handler.span_err(span, "foo");
 
         let bytes = output.lock().unwrap();

compiler/rustc_errors/src/lib.rs

@@ -47,9 +47,10 @@ use std::borrow::Cow;
 use std::error::Report;
 use std::fmt;
 use std::hash::Hash;
+use std::io::Write;
 use std::num::NonZeroUsize;
 use std::panic;
-use std::path::Path;
+use std::path::{Path, PathBuf};
 
 use termcolor::{Color, ColorSpec};
 
@@ -461,6 +462,10 @@ struct HandlerInner {
     ///
     /// [RFC-2383]: https://rust-lang.github.io/rfcs/2383-lint-reasons.html
     fulfilled_expectations: FxHashSet<LintExpectationId>,
+
+    /// The file where the ICE information is stored. This allows delayed_span_bug backtraces to be
+    /// stored along side the main panic backtrace.
+    ice_file: Option<PathBuf>,
 }
 
 /// A key denoting where from a diagnostic was stashed.
@@ -550,6 +555,7 @@ impl Handler {
         sm: Option<Lrc<SourceMap>>,
         fluent_bundle: Option<Lrc<FluentBundle>>,
         fallback_bundle: LazyFallbackBundle,
+        ice_file: Option<PathBuf>,
     ) -> Self {
         Self::with_tty_emitter_and_flags(
             color_config,
@@ -557,6 +563,7 @@ impl Handler {
             fluent_bundle,
             fallback_bundle,
             HandlerFlags { can_emit_warnings, treat_err_as_bug, ..Default::default() },
+            ice_file,
         )
     }
 
@@ -566,6 +573,7 @@ impl Handler {
         fluent_bundle: Option<Lrc<FluentBundle>>,
         fallback_bundle: LazyFallbackBundle,
         flags: HandlerFlags,
+        ice_file: Option<PathBuf>,
     ) -> Self {
         let emitter = Box::new(EmitterWriter::stderr(
             color_config,
@@ -579,23 +587,26 @@ impl Handler {
             flags.track_diagnostics,
             TerminalUrl::No,
         ));
-        Self::with_emitter_and_flags(emitter, flags)
+        Self::with_emitter_and_flags(emitter, flags, ice_file)
     }
 
     pub fn with_emitter(
         can_emit_warnings: bool,
         treat_err_as_bug: Option<NonZeroUsize>,
         emitter: Box<dyn Emitter + sync::Send>,
+        ice_file: Option<PathBuf>,
     ) -> Self {
         Handler::with_emitter_and_flags(
             emitter,
             HandlerFlags { can_emit_warnings, treat_err_as_bug, ..Default::default() },
+            ice_file,
         )
     }
 
     pub fn with_emitter_and_flags(
         emitter: Box<dyn Emitter + sync::Send>,
         flags: HandlerFlags,
+        ice_file: Option<PathBuf>,
     ) -> Self {
         Self {
             flags,
@@ -618,6 +629,7 @@ impl Handler {
                 check_unstable_expect_diagnostics: false,
                 unstable_expect_diagnostics: Vec::new(),
                 fulfilled_expectations: Default::default(),
+                ice_file,
             }),
         }
     }
@@ -1657,8 +1669,21 @@ impl HandlerInner {
         explanation: impl Into<DiagnosticMessage> + Copy,
     ) {
         let mut no_bugs = true;
+        // If backtraces are enabled, also print the query stack
+        let backtrace = std::env::var_os("RUST_BACKTRACE").map_or(true, |x| &x != "0");
         for bug in bugs {
-            let mut bug = bug.decorate();
+            if let Some(file) = self.ice_file.as_ref()
+                && let Ok(mut out) = std::fs::File::options().append(true).open(file)
+            {
+                let _ = write!(
+                    &mut out,
+                    "\n\ndelayed span bug: {}\n{}",
+                    bug.inner.styled_message().iter().filter_map(|(msg, _)| msg.as_str()).collect::<String>(),
+                    &bug.note
+                );
+            }
+            let mut bug =
+                if backtrace || self.ice_file.is_none() { bug.decorate() } else { bug.inner };
 
             if no_bugs {
                 // Put the overall explanation before the `DelayedBug`s, to

compiler/rustc_expand/src/tests.rs

@@ -161,7 +161,7 @@ fn test_harness(file_text: &str, span_labels: Vec<SpanLabel>, expected_output: &
             false,
             TerminalUrl::No,
         );
-        let handler = Handler::with_emitter(true, None, Box::new(emitter));
+        let handler = Handler::with_emitter(true, None, Box::new(emitter), None);
         #[allow(rustc::untranslatable_diagnostic)]
         handler.span_err(msp, "foo");
 

compiler/rustc_interface/src/interface.rs

@@ -251,6 +251,7 @@ pub struct Config {
     pub input: Input,
     pub output_dir: Option<PathBuf>,
     pub output_file: Option<OutFileName>,
+    pub ice_file: Option<PathBuf>,
     pub file_loader: Option<Box<dyn FileLoader + Send + Sync>>,
     pub locale_resources: &'static [&'static str],
 
@@ -315,6 +316,7 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
                 config.lint_caps,
                 config.make_codegen_backend,
                 registry.clone(),
+                config.ice_file,
             );
 
             if let Some(parse_sess_created) = config.parse_sess_created {
@@ -346,7 +348,11 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
     )
 }
 
-pub fn try_print_query_stack(handler: &Handler, num_frames: Option<usize>) {
+pub fn try_print_query_stack(
+    handler: &Handler,
+    num_frames: Option<usize>,
+    file: Option<std::fs::File>,
+) {
     eprintln!("query stack during panic:");
 
     // Be careful relying on global state here: this code is called from
@@ -358,7 +364,8 @@ pub fn try_print_query_stack(handler: &Handler, num_frames: Option<usize>) {
                 QueryCtxt::new(icx.tcx),
                 icx.query,
                 handler,
-                num_frames
+                num_frames,
+                file,
             ))
         } else {
             0

compiler/rustc_interface/src/tests.rs

@@ -67,6 +67,7 @@ fn mk_session(handler: &mut EarlyErrorHandler, matches: getopts::Matches) -> (Se
         None,
         None,
         "",
+        None,
     );
     (sess, cfg)
 }

compiler/rustc_interface/src/util.rs

@@ -70,6 +70,7 @@ pub fn create_session(
         Box<dyn FnOnce(&config::Options) -> Box<dyn CodegenBackend> + Send>,
     >,
     descriptions: Registry,
+    ice_file: Option<PathBuf>,
 ) -> (Session, Box<dyn CodegenBackend>) {
     let codegen_backend = if let Some(make_codegen_backend) = make_codegen_backend {
         make_codegen_backend(&sopts)
@@ -111,6 +112,7 @@ pub fn create_session(
         file_loader,
         target_override,
         rustc_version_str().unwrap_or("unknown"),
+        ice_file,
     );
 
     codegen_backend.init(&sess);

compiler/rustc_query_system/src/query/job.rs

@@ -13,6 +13,7 @@ use rustc_session::Session;
 use rustc_span::Span;
 
 use std::hash::Hash;
+use std::io::Write;
 use std::num::NonZeroU64;
 
 #[cfg(parallel_compiler)]
@@ -617,30 +618,50 @@ pub fn print_query_stack<Qcx: QueryContext>(
     mut current_query: Option<QueryJobId>,
     handler: &Handler,
     num_frames: Option<usize>,
+    mut file: Option<std::fs::File>,
 ) -> usize {
     // Be careful relying on global state here: this code is called from
     // a panic hook, which means that the global `Handler` may be in a weird
     // state if it was responsible for triggering the panic.
-    let mut i = 0;
+    let mut count_printed = 0;
+    let mut count_total = 0;
     let query_map = qcx.try_collect_active_jobs();
 
+    if let Some(ref mut file) = file {
+        let _ = writeln!(file, "\n\nquery stack during panic:");
+    }
     while let Some(query) = current_query {
-        if Some(i) == num_frames {
-            break;
-        }
         let Some(query_info) = query_map.as_ref().and_then(|map| map.get(&query)) else {
             break;
         };
-        let mut diag = Diagnostic::new(
+        if Some(count_printed) < num_frames || num_frames.is_none() {
-            Level::FailureNote,
+            // Only print to stderr as many stack frames as `num_frames` when present.
-            format!("#{} [{:?}] {}", i, query_info.query.dep_kind, query_info.query.description),
+            let mut diag = Diagnostic::new(
-        );
+                Level::FailureNote,
-        diag.span = query_info.job.span.into();
+                format!(
-        handler.force_print_diagnostic(diag);
+                    "#{} [{:?}] {}",
+                    count_printed, query_info.query.dep_kind, query_info.query.description
+                ),
+            );
+            diag.span = query_info.job.span.into();
+            handler.force_print_diagnostic(diag);
+            count_printed += 1;
+        }
+
+        if let Some(ref mut file) = file {
+            let _ = writeln!(
+                file,
+                "#{} [{:?}] {}",
+                count_total, query_info.query.dep_kind, query_info.query.description
+            );
+        }
 
         current_query = query_info.job.parent;
-        i += 1;
+        count_total += 1;
     }
 
-    i
+    if let Some(ref mut file) = file {
+        let _ = writeln!(file, "end of query stack");
+    }
+    count_printed
 }

compiler/rustc_session/src/parse.rs

@@ -231,6 +231,7 @@ impl ParseSess {
             Some(sm.clone()),
             None,
             fallback_bundle,
+            None,
         );
         ParseSess::with_span_handler(handler, sm)
     }
@@ -261,12 +262,20 @@ impl ParseSess {
     pub fn with_silent_emitter(fatal_note: Option<String>) -> Self {
         let fallback_bundle = fallback_fluent_bundle(Vec::new(), false);
         let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-        let fatal_handler =
+        let fatal_handler = Handler::with_tty_emitter(
-            Handler::with_tty_emitter(ColorConfig::Auto, false, None, None, None, fallback_bundle);
+            ColorConfig::Auto,
+            false,
+            None,
+            None,
+            None,
+            fallback_bundle,
+            None,
+        );
         let handler = Handler::with_emitter(
             false,
             None,
             Box::new(SilentEmitter { fatal_handler, fatal_note }),
+            None,
         );
         ParseSess::with_span_handler(handler, sm)
     }

compiler/rustc_session/src/session.rs

@@ -1392,6 +1392,7 @@ pub fn build_session(
     file_loader: Option<Box<dyn FileLoader + Send + Sync + 'static>>,
     target_override: Option<Target>,
     cfg_version: &'static str,
+    ice_file: Option<PathBuf>,
 ) -> Session {
     // FIXME: This is not general enough to make the warning lint completely override
     // normal diagnostic warnings, since the warning lint can also be denied and changed
@@ -1440,6 +1441,7 @@ pub fn build_session(
     let span_diagnostic = rustc_errors::Handler::with_emitter_and_flags(
         emitter,
         sopts.unstable_opts.diagnostic_handler_flags(can_emit_warnings),
+        ice_file,
     );
 
     let self_profiler = if let SwitchWithOptPath::Enabled(ref d) = sopts.unstable_opts.self_profile
@@ -1731,7 +1733,7 @@ pub struct EarlyErrorHandler {
 impl EarlyErrorHandler {
     pub fn new(output: ErrorOutputType) -> Self {
         let emitter = mk_emitter(output);
-        Self { handler: rustc_errors::Handler::with_emitter(true, None, emitter) }
+        Self { handler: rustc_errors::Handler::with_emitter(true, None, emitter, None) }
     }
 
     pub fn abort_if_errors(&self) {
@@ -1745,7 +1747,7 @@ impl EarlyErrorHandler {
         self.handler.abort_if_errors();
 
         let emitter = mk_emitter(output);
-        self.handler = Handler::with_emitter(true, None, emitter);
+        self.handler = Handler::with_emitter(true, None, emitter, None);
     }
 
     #[allow(rustc::untranslatable_diagnostic)]

library/std/src/lib.rs

@@ -604,6 +604,9 @@ pub mod alloc;
 // Private support modules
 mod panicking;
 
+#[unstable(feature = "ice_to_disk", issue = "none")]
+pub use panicking::panic_hook_with_disk_dump;
+
 #[path = "../../backtrace/src/lib.rs"]
 #[allow(dead_code, unused_attributes, fuzzy_provenance_casts)]
 mod backtrace_rs;

library/std/src/panicking.rs

@@ -234,7 +234,16 @@ where
     *hook = Hook::Custom(Box::new(move |info| hook_fn(&prev, info)));
 }
 
+/// The default panic handler.
 fn default_hook(info: &PanicInfo<'_>) {
+    panic_hook_with_disk_dump(info, None)
+}
+
+#[unstable(feature = "ice_to_disk", issue = "none")]
+/// The implementation of the default panic handler.
+///
+/// It can also write the backtrace to a given `path`. This functionality is used only by `rustc`.
+pub fn panic_hook_with_disk_dump(info: &PanicInfo<'_>, path: Option<&crate::path::Path>) {
     // If this is a double panic, make sure that we print a backtrace
     // for this panic. Otherwise only print it if logging is enabled.
     let backtrace = if panic_count::get_count() >= 2 {
@@ -256,7 +265,7 @@ fn default_hook(info: &PanicInfo<'_>) {
     let thread = thread_info::current_thread();
     let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>");
 
-    let write = |err: &mut dyn crate::io::Write| {
+    let write = |err: &mut dyn crate::io::Write, backtrace: Option<BacktraceStyle>| {
         let _ = writeln!(err, "thread '{name}' panicked at '{msg}', {location}");
 
         static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
@@ -270,10 +279,19 @@ fn default_hook(info: &PanicInfo<'_>) {
             }
             Some(BacktraceStyle::Off) => {
                 if FIRST_PANIC.swap(false, Ordering::SeqCst) {
-                    let _ = writeln!(
+                    if let Some(path) = path {
-                        err,
+                        let _ = writeln!(
-                        "note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace"
+                            err,
-                    );
+                            "note: a backtrace for this error was stored at `{}`",
+                            path.display(),
+                        );
+                    } else {
+                        let _ = writeln!(
+                            err,
+                            "note: run with `RUST_BACKTRACE=1` environment variable to display a \
+                             backtrace"
+                        );
+                    }
                 }
             }
             // If backtraces aren't supported, do nothing.
@@ -281,11 +299,17 @@ fn default_hook(info: &PanicInfo<'_>) {
         }
     };
 
+    if let Some(path) = path
+        && let Ok(mut out) = crate::fs::File::options().create(true).write(true).open(&path)
+    {
+        write(&mut out, BacktraceStyle::full());
+    }
+
     if let Some(local) = set_output_capture(None) {
-        write(&mut *local.lock().unwrap_or_else(|e| e.into_inner()));
+        write(&mut *local.lock().unwrap_or_else(|e| e.into_inner()), backtrace);
         set_output_capture(Some(local));
     } else if let Some(mut out) = panic_output() {
-        write(&mut out);
+        write(&mut out, backtrace);
     }
 }
 

src/librustdoc/core.rs

@@ -176,6 +176,7 @@ pub(crate) fn new_handler(
     rustc_errors::Handler::with_emitter_and_flags(
         emitter,
         unstable_opts.diagnostic_handler_flags(true),
+        None,
     )
 }
 
@@ -296,6 +297,7 @@ pub(crate) fn create_config(
         }),
         make_codegen_backend: None,
         registry: rustc_driver::diagnostics_registry(),
+        ice_file: None,
     }
 }
 

src/librustdoc/doctest.rs

@@ -108,6 +108,7 @@ pub(crate) fn run(options: RustdocOptions) -> Result<(), ErrorGuaranteed> {
         override_queries: None,
         make_codegen_backend: None,
         registry: rustc_driver::diagnostics_registry(),
+        ice_file: None,
     };
 
     let test_args = options.test_args.clone();
@@ -586,7 +587,7 @@ pub(crate) fn make_test(
             );
 
             // FIXME(misdreavus): pass `-Z treat-err-as-bug` to the doctest parser
-            let handler = Handler::with_emitter(false, None, Box::new(emitter));
+            let handler = Handler::with_emitter(false, None, Box::new(emitter), None);
             let sess = ParseSess::with_span_handler(handler, sm);
 
             let mut found_main = false;
@@ -773,7 +774,7 @@ fn check_if_attr_is_complete(source: &str, edition: Edition) -> bool {
                 TerminalUrl::No,
             );
 
-            let handler = Handler::with_emitter(false, None, Box::new(emitter));
+            let handler = Handler::with_emitter(false, None, Box::new(emitter), None);
             let sess = ParseSess::with_span_handler(handler, sm);
             let mut parser =
                 match maybe_new_parser_from_source_str(&sess, filename, source.to_owned()) {

src/librustdoc/passes/lint/check_code_block_syntax.rs

@@ -40,7 +40,7 @@ fn check_rust_syntax(
     let emitter = BufferEmitter { buffer: Lrc::clone(&buffer), fallback_bundle };
 
     let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-    let handler = Handler::with_emitter(false, None, Box::new(emitter));
+    let handler = Handler::with_emitter(false, None, Box::new(emitter), None);
     let source = dox[code_block.code].to_owned();
     let sess = ParseSess::with_span_handler(handler, sm);
 

src/tools/clippy/clippy_lints/src/doc.rs

@@ -729,7 +729,7 @@ fn check_code(cx: &LateContext<'_>, text: &str, edition: Edition, span: Span) {
                     false,
                     TerminalUrl::No,
                 );
-                let handler = Handler::with_emitter(false, None, Box::new(emitter));
+                let handler = Handler::with_emitter(false, None, Box::new(emitter), None);
                 let sess = ParseSess::with_span_handler(handler, sm);
 
                 let mut parser = match maybe_new_parser_from_source_str(&sess, filename, code) {

src/tools/compiletest/src/header.rs

@@ -232,7 +232,7 @@ impl TestProps {
             aux_builds: vec![],
             aux_crates: vec![],
             revisions: vec![],
-            rustc_env: vec![],
+            rustc_env: vec![("RUSTC_ICE".to_string(), "0".to_string())],
             unset_rustc_env: vec![],
             exec_env: vec![],
             unset_exec_env: vec![],

src/tools/rustfmt/src/parse/session.rs

@@ -162,6 +162,7 @@ fn default_handler(
             ignore_path_set,
             can_reset,
         }),
+        None,
     )
 }
 
@@ -233,7 +234,7 @@ impl ParseSess {
     }
 
     pub(crate) fn set_silent_emitter(&mut self) {
-        self.parse_sess.span_diagnostic = Handler::with_emitter(true, None, silent_emitter());
+        self.parse_sess.span_diagnostic = Handler::with_emitter(true, None, silent_emitter(), None);
     }
 
     pub(crate) fn span_to_filename(&self, span: Span) -> FileName {

src/tools/tidy/src/deps.rs

@@ -253,6 +253,9 @@ const PERMITTED_RUSTC_DEPENDENCIES: &[&str] = &[
     "thiserror-impl",
     "thorin-dwp",
     "thread_local",
+    "time",
+    "time-core",
+    "time-macros",
     "tinystr",
     "tinyvec",
     "tinyvec_macros",

tests/run-make-fulldeps/issue-19371/foo.rs

@@ -52,6 +52,7 @@ fn compile(code: String, output: PathBuf, sysroot: PathBuf) {
         input,
         output_file: Some(OutFileName::Real(output)),
         output_dir: None,
+        ice_file: None,
         file_loader: None,
         locale_resources: &[],
         lint_caps: Default::default(),

tests/run-make/exit-code/Makefile

@@ -5,7 +5,7 @@ all:
 	$(RUSTC) success.rs; [ $$? -eq 0 ]
 	$(RUSTC) --invalid-arg-foo; [ $$? -eq 1 ]
 	$(RUSTC) compile-error.rs; [ $$? -eq 1 ]
-	$(RUSTC) -Ztreat-err-as-bug compile-error.rs; [ $$? -eq 101 ]
+	RUSTC_ICE=0 $(RUSTC) -Ztreat-err-as-bug compile-error.rs; [ $$? -eq 101 ]
 	$(RUSTDOC) -o $(TMPDIR)/exit-code success.rs; [ $$? -eq 0 ]
 	$(RUSTDOC) --invalid-arg-foo; [ $$? -eq 1 ]
 	$(RUSTDOC) compile-error.rs; [ $$? -eq 1 ]

tests/run-make/short-ice/check.sh

@@ -1,5 +1,5 @@
 #!/bin/sh
-
+export RUSTC_ICE=0
 RUST_BACKTRACE=1 $RUSTC src/lib.rs -Z treat-err-as-bug=1 1>$TMPDIR/rust-test-1.log 2>&1
 RUST_BACKTRACE=full $RUSTC src/lib.rs -Z treat-err-as-bug=1 1>$TMPDIR/rust-test-2.log 2>&1
 

tests/rustdoc-ui/ice-bug-report-url.rs

@@ -1,4 +1,5 @@
 // compile-flags: -Ztreat-err-as-bug
+// rustc-env:RUSTC_ICE=0
 // failure-status: 101
 // error-pattern: aborting due to
 // error-pattern: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-rustdoc&template=ice.md

tests/rustdoc-ui/ice-bug-report-url.stderr

@@ -1,5 +1,5 @@
 error: expected one of `->`, `where`, or `{`, found `<eof>`
-  --> $DIR/ice-bug-report-url.rs:13:10
+  --> $DIR/ice-bug-report-url.rs:14:10
    |
 LL | fn wrong()
    |          ^ expected one of `->`, `where`, or `{`