Rollup merge of #136274 - compiler-errors:sized-wf, r=lcnr

Check Sizedness of return type in WF

Still need to clean this up a bit. This should fix rust-lang/trait-system-refactor-initiative#150.

r? lcnr

Author: matthiaskrgr

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -1065,6 +1065,7 @@ fn check_associated_item(
                 let ty = tcx.type_of(item.def_id).instantiate_identity();
                 let ty = wfcx.normalize(span, Some(WellFormedLoc::Ty(item_id)), ty);
                 wfcx.register_wf_obligation(span, loc, ty.into());
+                check_sized_if_body(wfcx, item.def_id.expect_local(), ty, Some(span));
                 Ok(())
             }
             ty::AssocKind::Fn => {
@@ -1189,7 +1190,7 @@ fn check_type_defn<'tcx>(
                     ),
                     wfcx.param_env,
                     ty,
-                    tcx.require_lang_item(LangItem::Sized, None),
+                    tcx.require_lang_item(LangItem::Sized, Some(hir_ty.span)),
                 );
             }
 
@@ -1314,7 +1315,7 @@ fn check_item_type(
                 ),
                 wfcx.param_env,
                 item_ty,
-                tcx.require_lang_item(LangItem::Sized, None),
+                tcx.require_lang_item(LangItem::Sized, Some(ty_span)),
             );
         }
 
@@ -1644,6 +1645,31 @@ fn check_fn_or_method<'tcx>(
             );
         }
     }
+
+    // If the function has a body, additionally require that the return type is sized.
+    check_sized_if_body(wfcx, def_id, sig.output(), match hir_decl.output {
+        hir::FnRetTy::Return(ty) => Some(ty.span),
+        hir::FnRetTy::DefaultReturn(_) => None,
+    });
+}
+
+fn check_sized_if_body<'tcx>(
+    wfcx: &WfCheckingCtxt<'_, 'tcx>,
+    def_id: LocalDefId,
+    ty: Ty<'tcx>,
+    maybe_span: Option<Span>,
+) {
+    let tcx = wfcx.tcx();
+    if let Some(body) = tcx.hir().maybe_body_owned_by(def_id) {
+        let span = maybe_span.unwrap_or(body.value.span);
+
+        wfcx.register_bound(
+            ObligationCause::new(span, def_id, traits::ObligationCauseCode::SizedReturnType),
+            wfcx.param_env,
+            ty,
+            tcx.require_lang_item(LangItem::Sized, Some(span)),
+        );
+    }
 }
 
 /// The `arbitrary_self_types_pointers` feature implies `arbitrary_self_types`.

compiler/rustc_hir_typeck/src/check.rs

@@ -117,22 +117,17 @@ pub(super) fn check_fn<'a, 'tcx>(
 
     fcx.typeck_results.borrow_mut().liberated_fn_sigs_mut().insert(fn_id, fn_sig);
 
-    let return_or_body_span = match decl.output {
-        hir::FnRetTy::DefaultReturn(_) => body.value.span,
-        hir::FnRetTy::Return(ty) => ty.span,
-    };
-
-    fcx.require_type_is_sized(
-        declared_ret_ty,
-        return_or_body_span,
-        ObligationCauseCode::SizedReturnType,
-    );
-    // We checked the root's signature during wfcheck, but not the child.
+    // We checked the root's ret ty during wfcheck, but not the child.
     if fcx.tcx.is_typeck_child(fn_def_id.to_def_id()) {
+        let return_or_body_span = match decl.output {
+            hir::FnRetTy::DefaultReturn(_) => body.value.span,
+            hir::FnRetTy::Return(ty) => ty.span,
+        };
+
         fcx.require_type_is_sized(
             declared_ret_ty,
             return_or_body_span,
-            ObligationCauseCode::WellFormed(None),
+            ObligationCauseCode::SizedReturnType,
         );
     }