Add MVP suggestion for unsafe_op_in_unsafe_fn

Nemo157 rebase notes: Migrated the changes to the lint into fluent

compiler/rustc_mir_transform/messages.ftl

@@ -55,6 +55,7 @@ mir_transform_unaligned_packed_ref = reference to packed field is unaligned
 mir_transform_union_access_label = access to union field
 mir_transform_union_access_note = the field may not be properly initialized: using uninitialized data will cause undefined behavior
 mir_transform_unsafe_op_in_unsafe_fn = {$details} is unsafe and requires unsafe block (error E0133)
+    .suggestion = consider wrapping the function body in an unsafe block
 
 mir_transform_unused_unsafe = unnecessary `unsafe` block
     .label = because it's nested under this `unsafe` block

compiler/rustc_mir_transform/src/check_unsafety.rs

@@ -527,6 +527,8 @@ pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) {
     }
 
     let UnsafetyCheckResult { violations, unused_unsafes, .. } = tcx.unsafety_check_result(def_id);
+    // Only suggest wrapping the entire function body in an unsafe block once
+    let mut suggest_unsafe_block = true;
 
     for &UnsafetyViolation { source_info, lint_root, kind, details } in violations.iter() {
         let details = errors::RequiresUnsafeDetail { violation: details, span: source_info.span };
@@ -561,12 +563,24 @@ pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) {
                     op_in_unsafe_fn_allowed,
                 });
             }
-            UnsafetyViolationKind::UnsafeFn => tcx.emit_spanned_lint(
+            UnsafetyViolationKind::UnsafeFn => {
+                tcx.emit_spanned_lint(
                     UNSAFE_OP_IN_UNSAFE_FN,
                     lint_root,
                     source_info.span,
-                errors::UnsafeOpInUnsafeFn { details },
-            ),
+                    errors::UnsafeOpInUnsafeFn {
+                        details,
+                        suggest_unsafe_block: suggest_unsafe_block.then(|| {
+                            let body = tcx.hir().body_owned_by(def_id);
+                            let body_span = tcx.hir().body(body).value.span;
+                            let start = tcx.sess.source_map().start_point(body_span).shrink_to_hi();
+                            let end = tcx.sess.source_map().end_point(body_span).shrink_to_lo();
+                            (start, end)
+                        }),
+                    },
+                );
+                suggest_unsafe_block = false;
+            }
         }
     }
 

compiler/rustc_mir_transform/src/errors.rs

@@ -1,5 +1,6 @@
 use rustc_errors::{
-    DecorateLint, DiagnosticBuilder, DiagnosticMessage, EmissionGuarantee, Handler, IntoDiagnostic,
+    Applicability, DecorateLint, DiagnosticBuilder, DiagnosticMessage, EmissionGuarantee, Handler,
+    IntoDiagnostic,
 };
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
 use rustc_middle::mir::{AssertKind, UnsafetyViolationDetails};
@@ -130,6 +131,7 @@ impl RequiresUnsafeDetail {
 
 pub(crate) struct UnsafeOpInUnsafeFn {
     pub details: RequiresUnsafeDetail,
+    pub suggest_unsafe_block: Option<(Span, Span)>,
 }
 
 impl<'a> DecorateLint<'a, ()> for UnsafeOpInUnsafeFn {
@@ -138,13 +140,20 @@ impl<'a> DecorateLint<'a, ()> for UnsafeOpInUnsafeFn {
         self,
         diag: &'b mut DiagnosticBuilder<'a, ()>,
     ) -> &'b mut DiagnosticBuilder<'a, ()> {
-        let desc = diag
-            .handler()
-            .expect("lint should not yet be emitted")
-            .eagerly_translate_to_string(self.details.label(), [].into_iter());
+        let handler = diag.handler().expect("lint should not yet be emitted");
+        let desc = handler.eagerly_translate_to_string(self.details.label(), [].into_iter());
         diag.set_arg("details", desc);
         diag.span_label(self.details.span, self.details.label());
         diag.note(self.details.note());
+
+        if let Some((start, end)) = self.suggest_unsafe_block {
+            diag.multipart_suggestion_verbose(
+                crate::fluent_generated::mir_transform_suggestion,
+                vec![(start, " unsafe {".into()), (end, "}".into())],
+                Applicability::MaybeIncorrect,
+            );
+        }
+
         diag
     }
 

tests/ui/unsafe/rfc-2585-unsafe_op_in_unsafe_fn.mir.stderr

@@ -10,6 +10,14 @@ note: the lint level is defined here
    |
 LL | #![deny(unsafe_op_in_unsafe_fn)]
    |         ^^^^^^^^^^^^^^^^^^^^^^
+help: consider wrapping the function body in an unsafe block
+   |
+LL ~ unsafe fn deny_level() { unsafe {
+LL |     unsf();
+ ...
+LL |
+LL ~ }}
+   |
 
 error: dereference of raw pointer is unsafe and requires unsafe block (error E0133)
   --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:15:5
@@ -52,6 +60,14 @@ note: the lint level is defined here
 LL | #[deny(warnings)]
    |        ^^^^^^^^
    = note: `#[deny(unsafe_op_in_unsafe_fn)]` implied by `#[deny(warnings)]`
+help: consider wrapping the function body in an unsafe block
+   |
+LL ~ unsafe fn warning_level() { unsafe {
+LL |     unsf();
+ ...
+LL |
+LL ~ }}
+   |
 
 error: dereference of raw pointer is unsafe and requires unsafe block (error E0133)
   --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:31:5

tests/ui/unsafe/wrapping-unsafe-block-sugg.fixed

@@ -0,0 +1,12 @@
+// run-rustfix
+
+#![deny(unsafe_op_in_unsafe_fn)]
+
+unsafe fn unsf() {}
+
+pub unsafe fn foo() { unsafe {
+    unsf(); //~ ERROR call to unsafe function is unsafe
+    unsf(); //~ ERROR call to unsafe function is unsafe
+}}
+
+fn main() {}

tests/ui/unsafe/wrapping-unsafe-block-sugg.rs

@@ -0,0 +1,12 @@
+// run-rustfix
+
+#![deny(unsafe_op_in_unsafe_fn)]
+
+unsafe fn unsf() {}
+
+pub unsafe fn foo() {
+    unsf(); //~ ERROR call to unsafe function is unsafe
+    unsf(); //~ ERROR call to unsafe function is unsafe
+}
+
+fn main() {}

tests/ui/unsafe/wrapping-unsafe-block-sugg.stderr

@@ -0,0 +1,30 @@
+error: call to unsafe function is unsafe and requires unsafe block (error E0133)
+  --> $DIR/wrapping-unsafe-block-sugg.rs:8:5
+   |
+LL |     unsf();
+   |     ^^^^^^ call to unsafe function
+   |
+   = note: consult the function's documentation for information on how to avoid undefined behavior
+note: the lint level is defined here
+  --> $DIR/wrapping-unsafe-block-sugg.rs:3:9
+   |
+LL | #![deny(unsafe_op_in_unsafe_fn)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+help: consider wrapping the function body in an unsafe block
+   |
+LL ~ pub unsafe fn foo() { unsafe {
+LL |     unsf();
+LL |     unsf();
+LL ~ }}
+   |
+
+error: call to unsafe function is unsafe and requires unsafe block (error E0133)
+  --> $DIR/wrapping-unsafe-block-sugg.rs:9:5
+   |
+LL |     unsf();
+   |     ^^^^^^ call to unsafe function
+   |
+   = note: consult the function's documentation for information on how to avoid undefined behavior
+
+error: aborting due to 2 previous errors
+