Auto merge of #134064 - jieyouxu:revert-131669, r=ChrisDenton

Revert #131669 due to ICEs

Revert [lint: change help for pointers to dyn types in FFI #131669](#131669) due to ICE reports:

- <#134059> (real-world)
- <#134060> (fuzzing)

Closes #134060.

The revert criteria I used to assess whether to post this revert was:

1. It's not trivial to fix-forward. (1) The implementation itself is tricky due to `tcx.is_sized` query not being very trivial. (2) It will need more extensive test coverage for different ty kinds.
2. It is impacting real-world crates, i.e. #134059.
3. `improper_ctypes_definitions` is a warn-by-default lint.

This revert is without prejudice to relanding the changes. The changes can be re-landed with those cases addressed and stronger test coverage.

A rough regression test corresponding to the fuzzed example reported in #134060 is added to check that the revert worked, it is not sufficient for the lint test coverage when the lint improvements are to be relanded. Please feel free to improve the test in the reland.

r? `@workingjubilee` (or compiler)
cc `@niacdoial` (PR author)

compiler/rustc_lint/messages.ftl

@@ -359,6 +359,7 @@ lint_improper_ctypes_128bit = 128-bit integers don't currently have a known stab
 lint_improper_ctypes_array_help = consider passing a pointer to the array
 
 lint_improper_ctypes_array_reason = passing raw arrays by value is not FFI-safe
+lint_improper_ctypes_box = box cannot be represented as a single pointer
 
 lint_improper_ctypes_char_help = consider using `u32` or `libc::wchar_t` instead
 
@@ -376,9 +377,7 @@ lint_improper_ctypes_enum_repr_help =
 lint_improper_ctypes_enum_repr_reason = enum has no representation hint
 lint_improper_ctypes_fnptr_help = consider using an `extern fn(...) -> ...` function pointer instead
 
-lint_improper_ctypes_fnptr_indirect_reason = the function pointer to `{$ty}` is FFI-unsafe due to `{$inner_ty}`
 lint_improper_ctypes_fnptr_reason = this function pointer has Rust-specific calling convention
-
 lint_improper_ctypes_non_exhaustive = this enum is non-exhaustive
 lint_improper_ctypes_non_exhaustive_variant = this enum has non-exhaustive variants
 
@@ -389,11 +388,7 @@ lint_improper_ctypes_opaque = opaque types have no C equivalent
 lint_improper_ctypes_pat_help = consider using the base type instead
 
 lint_improper_ctypes_pat_reason = pattern types have no C equivalent
-
-lint_improper_ctypes_sized_ptr_to_unsafe_type =
-    this reference (`{$ty}`) is ABI-compatible with a C pointer, but `{$inner_ty}` itself does not have a C layout
-
-lint_improper_ctypes_slice_help = consider using a raw pointer to the slice's first element (and a length) instead
+lint_improper_ctypes_slice_help = consider using a raw pointer instead
 
 lint_improper_ctypes_slice_reason = slices have no C equivalent
 lint_improper_ctypes_str_help = consider using `*const u8` and a length instead
@@ -419,10 +414,6 @@ lint_improper_ctypes_union_layout_help = consider adding a `#[repr(C)]` or `#[re
 lint_improper_ctypes_union_layout_reason = this union has unspecified layout
 lint_improper_ctypes_union_non_exhaustive = this union is non-exhaustive
 
-lint_improper_ctypes_unsized_box = this box for an unsized type contains metadata, which makes it incompatible with a C pointer
-lint_improper_ctypes_unsized_ptr = this pointer to an unsized type contains metadata, which makes it incompatible with a C pointer
-lint_improper_ctypes_unsized_ref = this reference to an unsized type contains metadata, which makes it incompatible with a C pointer
-
 lint_incomplete_include =
     include macro expected single expression in source
 

compiler/rustc_lint/src/lints.rs

@@ -1851,44 +1851,13 @@ pub(crate) struct UnpredictableFunctionPointerComparisonsSuggestion<'a> {
     pub right: Span,
 }
 
-pub(crate) struct ImproperCTypesLayer<'a> {
-    pub ty: Ty<'a>,
-    pub inner_ty: Option<Ty<'a>>,
-    pub note: DiagMessage,
-    pub span_note: Option<Span>,
-    pub help: Option<DiagMessage>,
-}
-
-impl<'a> Subdiagnostic for ImproperCTypesLayer<'a> {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        f: &F,
-    ) {
-        diag.arg("ty", self.ty);
-        if let Some(ty) = self.inner_ty {
-            diag.arg("inner_ty", ty);
-        }
-
-        if let Some(help) = self.help {
-            let msg = f(diag, help.into());
-            diag.help(msg);
-        }
-
-        let msg = f(diag, self.note.into());
-        diag.note(msg);
-        if let Some(note) = self.span_note {
-            let msg = f(diag, fluent::lint_note.into());
-            diag.span_note(note, msg);
-        };
-    }
-}
-
 pub(crate) struct ImproperCTypes<'a> {
     pub ty: Ty<'a>,
     pub desc: &'a str,
     pub label: Span,
-    pub reasons: Vec<ImproperCTypesLayer<'a>>,
+    pub help: Option<DiagMessage>,
+    pub note: DiagMessage,
+    pub span_note: Option<Span>,
 }
 
 // Used because of the complexity of Option<DiagMessage>, DiagMessage, and Option<Span>
@@ -1898,8 +1867,12 @@ impl<'a> LintDiagnostic<'a, ()> for ImproperCTypes<'_> {
         diag.arg("ty", self.ty);
         diag.arg("desc", self.desc);
         diag.span_label(self.label, fluent::lint_label);
-        for reason in self.reasons.into_iter() {
-            diag.subdiagnostic(reason);
+        if let Some(help) = self.help {
+            diag.help(help);
+        }
+        diag.note(self.note);
+        if let Some(note) = self.span_note {
+            diag.span_note(note, fluent::lint_note);
         }
     }
 }