Stop mentioning internal lang items in no_std binary errors

When writing a no_std binary, you'll be greeted with nonsensical errors
mentioning lang items like eh_personality and start. That's pretty bad
because it makes you think that you need to define them somewhere! But
oh no, now you're getting the `internal_features` lint telling you that
you shouldn't use them! But you need a no_std binary! What now?

No problem! Writing a no_std binary is super easy. Just use panic=abort
and supply your own platform specific entrypoint symbol (like `main`)
and you're good to go. Would be nice if the compiler told you that,
right?

This makes it so that it does do that.

2 files changed, 11 insertions, 1 deletions

diff --git a/compiler/rustc_passes/src/errors.rs b/compiler/rustc_passes/src/errors.rs
index d934e959a41..cf3c7cc4ace 100644
--- a/compiler/rustc_passes/src/errors.rs
+++ b/compiler/rustc_passes/src/errors.rs
@@ -813,6 +813,12 @@ pub struct UnknownExternLangItem {
 pub struct MissingPanicHandler;
 
 #[derive(Diagnostic)]
+#[diag(passes_panic_unwind_without_std)]
+#[help]
+#[note]
+pub struct PanicUnwindWithoutStd;
+
+#[derive(Diagnostic)]
 #[diag(passes_missing_lang_item)]
 #[note]
 #[help]
diff --git a/compiler/rustc_passes/src/weak_lang_items.rs b/compiler/rustc_passes/src/weak_lang_items.rs
index db3d442676e..4eb0c6c275e 100644
--- a/compiler/rustc_passes/src/weak_lang_items.rs
+++ b/compiler/rustc_passes/src/weak_lang_items.rs
@@ -9,7 +9,9 @@ use rustc_middle::middle::lang_items::required;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::config::CrateType;
 
-use crate::errors::{MissingLangItem, MissingPanicHandler, UnknownExternLangItem};
+use crate::errors::{
+    MissingLangItem, MissingPanicHandler, PanicUnwindWithoutStd, UnknownExternLangItem,
+};
 
 /// Checks the crate for usage of weak lang items, returning a vector of all the
 /// language items required by this crate, but not defined yet.
@@ -76,6 +78,8 @@ fn verify(tcx: TyCtxt<'_>, items: &lang_items::LanguageItems) {
         if missing.contains(&item) && required(tcx, item) && items.get(item).is_none() {
             if item == LangItem::PanicImpl {
                 tcx.dcx().emit_err(MissingPanicHandler);
+            } else if item == LangItem::EhPersonality {
+                tcx.dcx().emit_err(PanicUnwindWithoutStd);
             } else {
                 tcx.dcx().emit_err(MissingLangItem { name: item.name() });
             }