Rollup merge of rust-lang#66027 - Mark-Simulacrum:panic-handler-query, r=alexcrichton

Move has_panic_handler to query

Moves us off of a global Once instead re-querying the lang item each time. The conditions on when we set it to true change a little (previously we'd make sure a few more lang items were `Some`) but I think they in practice don't matter, we won't compile later on if we don't have them.

Author: Centril

src/librustc/session/mod.rs

@@ -148,9 +148,6 @@ pub struct Session {
     /// Metadata about the allocators for the current crate being compiled.
     pub has_global_allocator: Once<bool>,
 
-    /// Metadata about the panic handlers for the current crate being compiled.
-    pub has_panic_handler: Once<bool>,
-
     /// Cap lint level specified by a driver specifically.
     pub driver_lint_caps: FxHashMap<lint::LintId, lint::Level>,
 
@@ -1211,7 +1208,6 @@ fn build_session_(
         print_fuel,
         jobserver: jobserver::client(),
         has_global_allocator: Once::new(),
-        has_panic_handler: Once::new(),
         driver_lint_caps,
         trait_methods_not_found: Lock::new(Default::default()),
         confused_type_with_std_module: Lock::new(Default::default()),

src/librustc/ty/context.rs

@@ -3045,4 +3045,9 @@ pub fn provide(providers: &mut ty::query::Providers<'_>) {
         assert_eq!(cnum, LOCAL_CRATE);
         attr::contains_name(tcx.hir().krate_attrs(), sym::compiler_builtins)
     };
+    providers.has_panic_handler = |tcx, cnum| {
+        assert_eq!(cnum, LOCAL_CRATE);
+        // We want to check if the panic handler was defined in this crate
+        tcx.lang_items().panic_impl().map_or(false, |did| did.is_local())
+    };
 }

src/librustc_metadata/encoder.rs

@@ -542,7 +542,6 @@ impl<'tcx> EncodeContext<'tcx> {
         let attrs = tcx.hir().krate_attrs();
         let has_default_lib_allocator = attr::contains_name(&attrs, sym::default_lib_allocator);
         let has_global_allocator = *tcx.sess.has_global_allocator.get();
-        let has_panic_handler = *tcx.sess.has_panic_handler.try_get().unwrap_or(&false);
 
         let root = self.lazy(CrateRoot {
             name: tcx.crate_name(LOCAL_CRATE),
@@ -553,7 +552,7 @@ impl<'tcx> EncodeContext<'tcx> {
             panic_strategy: tcx.sess.panic_strategy(),
             edition: tcx.sess.edition(),
             has_global_allocator: has_global_allocator,
-            has_panic_handler: has_panic_handler,
+            has_panic_handler: tcx.has_panic_handler(LOCAL_CRATE),
             has_default_lib_allocator: has_default_lib_allocator,
             plugin_registrar_fn: tcx.plugin_registrar_fn(LOCAL_CRATE).map(|id| id.index),
             proc_macro_decls_static: if is_proc_macro {

src/librustc_typeck/check/mod.rs

@@ -1267,11 +1267,6 @@ fn check_fn<'a, 'tcx>(
     if let Some(panic_impl_did) = fcx.tcx.lang_items().panic_impl() {
         if panic_impl_did == fcx.tcx.hir().local_def_id(fn_id) {
             if let Some(panic_info_did) = fcx.tcx.lang_items().panic_info() {
-                // at this point we don't care if there are duplicate handlers or if the handler has
-                // the wrong signature as this value we'll be used when writing metadata and that
-                // only happens if compilation succeeded
-                fcx.tcx.sess.has_panic_handler.try_set_same(true);
-
                 if declared_ret_ty.kind != ty::Never {
                     fcx.tcx.sess.span_err(
                         decl.output.span(),