Fix linker error by resolving regions for main return type obligations

compiler/rustc_hir_analysis/src/check/entry.rs

@@ -7,22 +7,23 @@ use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::span_bug;
 use rustc_middle::ty::{self, TyCtxt, TypingMode};
 use rustc_session::config::EntryFnType;
-use rustc_span::Span;
 use rustc_span::def_id::{CRATE_DEF_ID, DefId, LocalDefId};
+use rustc_span::{ErrorGuaranteed, Span};
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
+use rustc_trait_selection::regions::InferCtxtRegionExt;
 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode};
 
 use super::check_function_signature;
 use crate::errors;
 
-pub(crate) fn check_for_entry_fn(tcx: TyCtxt<'_>) {
+pub(crate) fn check_for_entry_fn(tcx: TyCtxt<'_>) -> Result<(), ErrorGuaranteed> {
     match tcx.entry_fn(()) {
         Some((def_id, EntryFnType::Main { .. })) => check_main_fn_ty(tcx, def_id),
-        _ => {}
+        _ => Ok(()),
     }
 }
 
-fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
+fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) -> Result<(), ErrorGuaranteed> {
     let main_fnsig = tcx.fn_sig(main_def_id).instantiate_identity();
     let main_span = tcx.def_span(main_def_id);
 
@@ -87,33 +88,28 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
         }
     }
 
-    let mut error = false;
     let main_diagnostics_def_id = main_fn_diagnostics_def_id(tcx, main_def_id, main_span);
 
     let main_asyncness = tcx.asyncness(main_def_id);
     if main_asyncness.is_async() {
         let asyncness_span = main_fn_asyncness_span(tcx, main_def_id);
-        tcx.dcx()
-            .emit_err(errors::MainFunctionAsync { span: main_span, asyncness: asyncness_span });
-        error = true;
+        return Err(tcx
+            .dcx()
+            .emit_err(errors::MainFunctionAsync { span: main_span, asyncness: asyncness_span }));
     }
 
     if let Some(attr_span) = find_attr!(tcx, main_def_id, TrackCaller(span) => *span) {
-        tcx.dcx().emit_err(errors::TrackCallerOnMain { span: attr_span, annotated: main_span });
-        error = true;
+        return Err(tcx
+            .dcx()
+            .emit_err(errors::TrackCallerOnMain { span: attr_span, annotated: main_span }));
     }
 
     if !tcx.codegen_fn_attrs(main_def_id).target_features.is_empty()
         // Calling functions with `#[target_feature]` is not unsafe on WASM, see #84988
         && !tcx.sess.target.is_like_wasm
         && !tcx.sess.opts.actually_rustdoc
     {
-        tcx.dcx().emit_err(errors::TargetFeatureOnMain { main: main_span });
-        error = true;
-    }
-
-    if error {
-        return;
+        return Err(tcx.dcx().emit_err(errors::TargetFeatureOnMain { main: main_span }));
     }
 
     // Main should have no WC, so empty param env is OK here.
@@ -123,8 +119,9 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
         let return_ty = main_fnsig.output();
         let return_ty_span = main_fn_return_type_span(tcx, main_def_id).unwrap_or(main_span);
         let Some(return_ty) = return_ty.no_bound_vars() else {
-            tcx.dcx().emit_err(errors::MainFunctionReturnTypeGeneric { span: return_ty_span });
-            return;
+            return Err(tcx
+                .dcx()
+                .emit_err(errors::MainFunctionReturnTypeGeneric { span: return_ty_span }));
         };
         let infcx = tcx.infer_ctxt().build(TypingMode::non_body_analysis());
         let cause = traits::ObligationCause::new(
@@ -137,8 +134,16 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
         ocx.register_bound(cause, param_env, norm_return_ty, term_did);
         let errors = ocx.evaluate_obligations_error_on_ambiguity();
         if !errors.is_empty() {
-            infcx.err_ctxt().report_fulfillment_errors(errors);
-            error = true;
+            return Err(infcx.err_ctxt().report_fulfillment_errors(errors));
+        }
+
+        let region_errors =
+            infcx.resolve_regions(main_diagnostics_def_id, param_env, ty::List::empty());
+
+        if !region_errors.is_empty() {
+            return Err(infcx
+                .err_ctxt()
+                .report_region_errors(main_diagnostics_def_id, &region_errors));
         }
         // now we can take the return type of the given main function
         expected_return_type = norm_return_ty;
@@ -147,10 +152,6 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
         expected_return_type = tcx.types.unit;
     }
 
-    if error {
-        return;
-    }
-
     let expected_sig = ty::Binder::dummy(tcx.mk_fn_sig(
         [],
         expected_return_type,
@@ -159,7 +160,7 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
         ExternAbi::Rust,
     ));
 
-    if check_function_signature(
+    check_function_signature(
         tcx,
         ObligationCause::new(
             main_span,
@@ -168,26 +169,24 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
         ),
         main_def_id,
         expected_sig,
-    )
-    .is_err()
-    {
-        return;
-    }
+    )?;
 
     let main_fn_generics = tcx.generics_of(main_def_id);
     let main_fn_predicates = tcx.predicates_of(main_def_id);
     if main_fn_generics.count() != 0 || !main_fnsig.bound_vars().is_empty() {
         let generics_param_span = main_fn_generics_params_span(tcx, main_def_id);
-        tcx.dcx().emit_err(errors::MainFunctionGenericParameters {
+        return Err(tcx.dcx().emit_err(errors::MainFunctionGenericParameters {
             span: generics_param_span.unwrap_or(main_span),
             label_span: generics_param_span,
-        });
+        }));
     } else if !main_fn_predicates.predicates.is_empty() {
         // generics may bring in implicit predicates, so we skip this check if generics is present.
         let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
-        tcx.dcx().emit_err(errors::WhereClauseOnMain {
+        return Err(tcx.dcx().emit_err(errors::WhereClauseOnMain {
             span: generics_where_clauses_span.unwrap_or(main_span),
             generics_span: generics_where_clauses_span,
-        });
+        }));
     }
+
+    Ok(())
 }

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -2350,7 +2350,8 @@ pub(super) fn check_type_wf(tcx: TyCtxt<'_>, (): ()) -> Result<(), ErrorGuarante
             }))
             .and(items.par_nested_bodies(|item| tcx.ensure_result().check_well_formed(item)))
             .and(items.par_opaques(|item| tcx.ensure_result().check_well_formed(item)));
-    super::entry::check_for_entry_fn(tcx);
+
+    super::entry::check_for_entry_fn(tcx)?;
 
     res
 }

tests/ui/typeck/main-termination-lifetime-issue-148421.rs

@@ -0,0 +1,17 @@
+// This test checks that the compiler correctly handles lifetime requirements
+// on the `Termination` trait for the `main` function return type.
+// See https://github.com/rust-lang/rust/issues/148421
+
+use std::process::ExitCode;
+use std::process::Termination;
+
+trait IsStatic {}
+impl<'a: 'static> IsStatic for &'a () {}
+
+struct Thing;
+
+impl Termination for Thing where for<'a> &'a (): IsStatic {
+    fn report(self) -> ExitCode { panic!() }
+}
+
+fn main() -> Thing { Thing } //~ ERROR implementation of `IsStatic` is not general enough

tests/ui/typeck/main-termination-lifetime-issue-148421.stderr

@@ -0,0 +1,11 @@
+error: implementation of `IsStatic` is not general enough
+  --> $DIR/main-termination-lifetime-issue-148421.rs:17:14
+   |
+LL | fn main() -> Thing { Thing }
+   |              ^^^^^ implementation of `IsStatic` is not general enough
+   |
+   = note: `IsStatic` would have to be implemented for the type `&'0 ()`, for any lifetime `'0`...
+   = note: ...but `IsStatic` is actually implemented for the type `&'1 ()`, for some specific lifetime `'1`
+
+error: aborting due to 1 previous error
+