#[deprecated_safe_2024]: Also use the // TODO: hint in the compiler error

This doesn't work for translated compiler error messages.

compiler/rustc_feature/src/builtin_attrs.rs

@@ -643,7 +643,7 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         through unstable paths"
     ),
     rustc_attr!(
-        rustc_deprecated_safe_2024, Normal, template!(List: r#"todo = "...""#),
+        rustc_deprecated_safe_2024, Normal, template!(List: r#"audit_that = "...""#),
         ErrorFollowing, EncodeCrossCrate::Yes,
         "rustc_deprecated_safe_2024 is supposed to be used in libstd only",
     ),

compiler/rustc_mir_build/messages.ftl

@@ -30,7 +30,7 @@ mir_build_call_to_deprecated_safe_fn_requires_unsafe =
     call to deprecated safe function `{$function}` is unsafe and requires unsafe block
     .note = consult the function's documentation for information on how to avoid undefined behavior
     .label = call to unsafe function
-    .suggestion = you can wrap the call in an `unsafe` block if you can guarantee its unsafe preconditions
+    .suggestion = you can wrap the call in an `unsafe` block if you can guarantee {$guarantee}
 
 mir_build_call_to_fn_with_requires_unsafe =
     call to function `{$function}` with `#[target_feature]` is unsafe and requires unsafe block

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -102,18 +102,23 @@ impl<'tcx> UnsafetyVisitor<'_, 'tcx> {
                     .meta_item_list()
                     .unwrap_or_default()
                     .into_iter()
-                    .find(|item| item.has_name(sym::todo))
+                    .find(|item| item.has_name(sym::audit_that))
                     .map(|item| {
                         item.value_str().expect(
-                            "`#[rustc_deprecated_safe_2024(todo)]` must have a string value",
+                            "`#[rustc_deprecated_safe_2024(audit_that)]` must have a string value",
                         )
                     });
 
                 let sm = self.tcx.sess.source_map();
+                let guarantee = suggestion
+                    .as_ref()
+                    .map(|suggestion| format!("that {}", suggestion))
+                    .unwrap_or_else(|| String::from("its unsafe preconditions"));
                 let suggestion = suggestion
                     .and_then(|suggestion| {
-                        sm.indentation_before(span)
-                            .map(|indent| format!("{}// TODO: {}\n", indent, suggestion)) // ignore-tidy-todo
+                        sm.indentation_before(span).map(|indent| {
+                            format!("{}// TODO: Audit that {}.\n", indent, suggestion) // ignore-tidy-todo
+                        })
                     })
                     .unwrap_or_default();
 
@@ -124,6 +129,7 @@ impl<'tcx> UnsafetyVisitor<'_, 'tcx> {
                     CallToDeprecatedSafeFnRequiresUnsafe {
                         span,
                         function: with_no_trimmed_paths!(self.tcx.def_path_str(id)),
+                        guarantee,
                         sub: CallToDeprecatedSafeFnRequiresUnsafeSub {
                             start_of_line_suggestion: suggestion,
                             start_of_line: sm.span_extend_to_line(span).shrink_to_lo(),

compiler/rustc_mir_build/src/errors.rs

@@ -28,6 +28,7 @@ pub(crate) struct CallToDeprecatedSafeFnRequiresUnsafe {
     #[label]
     pub(crate) span: Span,
     pub(crate) function: String,
+    pub(crate) guarantee: String,
     #[subdiagnostic]
     pub(crate) sub: CallToDeprecatedSafeFnRequiresUnsafeSub,
 }

compiler/rustc_span/src/symbol.rs

@@ -472,6 +472,7 @@ symbols! {
         attr,
         attr_literals,
         attributes,
+        audit_that,
         augmented_assignments,
         auto_traits,
         automatically_derived,
@@ -1897,7 +1898,6 @@ symbols! {
         to_string,
         to_string_method,
         to_vec,
-        todo,
         todo_macro,
         tool_attributes,
         tool_lints,

library/std/src/env.rs

@@ -359,7 +359,7 @@ impl Error for VarError {
 #[cfg_attr(
     not(bootstrap),
     rustc_deprecated_safe_2024(
-        todo = "Audit that the environment access only happens in single-threaded code."
+        audit_that = "the environment access only happens in single-threaded code"
     )
 )]
 #[stable(feature = "env", since = "1.0.0")]
@@ -429,7 +429,7 @@ pub unsafe fn set_var<K: AsRef<OsStr>, V: AsRef<OsStr>>(key: K, value: V) {
 #[cfg_attr(
     not(bootstrap),
     rustc_deprecated_safe_2024(
-        todo = "Audit that the environment access only happens in single-threaded code."
+        audit_that = "the environment access only happens in single-threaded code"
     )
 )]
 #[stable(feature = "env", since = "1.0.0")]

tests/ui/rust-2024/unsafe-env-suggestion.stderr

@@ -11,7 +11,7 @@ note: the lint level is defined here
    |
 LL | #![deny(deprecated_safe_2024)]
    |         ^^^^^^^^^^^^^^^^^^^^
-help: you can wrap the call in an `unsafe` block if you can guarantee its unsafe preconditions
+help: you can wrap the call in an `unsafe` block if you can guarantee that the environment access only happens in single-threaded code
    |
 LL +     // TODO: Audit that the environment access only happens in single-threaded code.
 LL ~     unsafe { env::set_var("FOO", "BAR") };
@@ -25,7 +25,7 @@ LL |     env::remove_var("FOO");
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2024!
    = note: for more information, see issue #27970 <https://github.com/rust-lang/rust/issues/27970>
-help: you can wrap the call in an `unsafe` block if you can guarantee its unsafe preconditions
+help: you can wrap the call in an `unsafe` block if you can guarantee that the environment access only happens in single-threaded code
    |
 LL +     // TODO: Audit that the environment access only happens in single-threaded code.
 LL ~     unsafe { env::remove_var("FOO") };