Use tcx.require_lang_item

compiler/rustc_error_messages/locales/en-US/monomorphize.ftl

@@ -21,6 +21,3 @@ monomorphize_large_assignments =
     moving {$size} bytes
     .label = value moved from here
     .note = The current maximum size is {$limit}, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
-
-monomorphize_requires_lang_item =
-    requires `{$lang_item}` lang_item

compiler/rustc_monomorphize/src/collector.rs

@@ -201,7 +201,7 @@
 use std::ops::Range;
 use std::path::PathBuf;
 
-use crate::errors::{LargeAssignmentsLint, RecursionLimit, RequiresLangItem, TypeLengthLimit};
+use crate::errors::{LargeAssignmentsLint, RecursionLimit, TypeLengthLimit};
 
 #[derive(PartialEq)]
 pub enum MonoItemCollectionMode {
@@ -1298,14 +1298,7 @@ fn push_extra_entry_roots(&mut self) {
             return;
         };
 
-        let start_def_id = match self.tcx.lang_items().require(LangItem::Start) {
+        let start_def_id = self.tcx.require_lang_item(LangItem::Start, None);
-            Ok(s) => s,
-            Err(lang_item_err) => {
-                self.tcx
-                    .sess
-                    .emit_fatal(RequiresLangItem { lang_item: lang_item_err.0.name().to_string() });
-            }
-        };
         let main_ret_ty = self.tcx.fn_sig(main_def_id).output();
 
         // Given that `main()` has no arguments,

compiler/rustc_monomorphize/src/errors.rs

@@ -32,12 +32,6 @@ pub struct TypeLengthLimit {
     pub type_length: usize,
 }
 
-#[derive(Diagnostic)]
-#[diag(monomorphize_requires_lang_item)]
-pub struct RequiresLangItem {
-    pub lang_item: String,
-}
-
 pub struct UnusedGenericParams {
     pub span: Span,
     pub param_spans: Vec<Span>,