Rollup merge of rust-lang#159253 - asuto15:suggest-export-name, r=JonathanBrouwer

Add suggestions for using `#[export_name]` instead of `#[link_name]` on static

Fixes rust-lang#159247.

This adds a suggestion for using `#[unsafe(export_name = "...")]` when `#[link_name = "..."]` is applied to a static.

It also handles the existing `#[unsafe(link_name = "...")]` form by replacing only the attribute name.

Tested with:

- `./x test tests/ui/attributes/link-name-on-static.rs`
- `./x test tests/ui/attributes/unsafe-link-name-on-static.rs`

Author: JonathanBrouwer

compiler/rustc_attr_parsing/src/session_diagnostics.rs

@@ -403,6 +403,18 @@ pub(crate) struct InvalidTarget {
 
 #[derive(Subdiagnostic)]
 pub(crate) enum InvalidTargetHelp {
+    #[multipart_suggestion(
+        "did you mean to use `#[export_name]`?",
+        applicability = "maybe-incorrect"
+    )]
+    UseExportName {
+        #[suggestion_part(code = "unsafe(")]
+        unsafe_open: Option<Span>,
+        #[suggestion_part(code = "export_name")]
+        name: Span,
+        #[suggestion_part(code = ")")]
+        unsafe_close: Option<Span>,
+    },
     #[help("use `#[rustc_align(...)]` instead")]
     UseRustcAlign,
     #[help("use `#[rustc_align_static(...)]` instead")]

compiler/rustc_attr_parsing/src/target_checking.rs

@@ -1,6 +1,6 @@
 use std::borrow::Cow;
 
-use rustc_ast::AttrStyle;
+use rustc_ast::{AttrStyle, Safety};
 use rustc_errors::{DiagArgValue, MultiSpan, StashKey};
 use rustc_feature::Features;
 use rustc_hir::attrs::AttributeKind;
@@ -187,6 +187,15 @@ impl<'sess> AttributeParser<'sess> {
         cx: &AcceptContext<'_, '_>,
     ) -> Option<InvalidTargetHelp> {
         match &*cx.attr_path.segments {
+            [sym::link_name] if cx.target == Target::Static => {
+                let needs_unsafe_wrapper = matches!(cx.attr_safety, Safety::Default);
+
+                Some(InvalidTargetHelp::UseExportName {
+                    unsafe_open: needs_unsafe_wrapper.then(|| cx.inner_span.shrink_to_lo()),
+                    name: cx.attr_path.span,
+                    unsafe_close: needs_unsafe_wrapper.then(|| cx.inner_span.shrink_to_hi()),
+                })
+            }
             [sym::repr] if attribute_args == "(align(...))" => match cx.target {
                 Target::Fn | Target::Method(..) if cx.features().fn_align() => {
                     Some(InvalidTargetHelp::UseRustcAlign)

tests/ui/attributes/link-name-on-static.rs

@@ -0,0 +1,17 @@
+#[link_name = "VALUE"]
+//~^ WARN the `link_name` attribute cannot be used on statics
+//~| WARN this was previously accepted by the compiler but is being phased out
+static VALUE_DEFINITION: u8 = 0;
+
+#[unsafe(link_name = "UNSAFE_VALUE")]
+//~^ ERROR `link_name` is not an unsafe attribute
+//~| WARN the `link_name` attribute cannot be used on statics
+//~| WARN this was previously accepted by the compiler but is being phased out
+static UNSAFE_VALUE_DEFINITION: u8 = 0;
+
+unsafe extern "C" {
+    #[link_name = "VALUE"]
+    static VALUE_DECLARATION: u8;
+}
+
+fn main() {}

tests/ui/attributes/link-name-on-static.stderr

@@ -0,0 +1,39 @@
+error: `link_name` is not an unsafe attribute
+  --> $DIR/link-name-on-static.rs:6:3
+   |
+LL | #[unsafe(link_name = "UNSAFE_VALUE")]
+   |   ^^^^^^ this is not an unsafe attribute
+   |
+   = note: extraneous unsafe is not allowed in attributes
+
+warning: the `link_name` attribute cannot be used on statics
+  --> $DIR/link-name-on-static.rs:1:3
+   |
+LL | #[link_name = "VALUE"]
+   |   ^^^^^^^^^
+   |
+   = help: the `link_name` attribute can be applied to foreign functions and foreign statics
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: requested on the command line with `-W unused-attributes`
+help: did you mean to use `#[export_name]`?
+   |
+LL - #[link_name = "VALUE"]
+LL + #[unsafe(export_name = "VALUE")]
+   |
+
+warning: the `link_name` attribute cannot be used on statics
+  --> $DIR/link-name-on-static.rs:6:10
+   |
+LL | #[unsafe(link_name = "UNSAFE_VALUE")]
+   |          ^^^^^^^^^
+   |
+   = help: the `link_name` attribute can be applied to foreign functions and foreign statics
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+help: did you mean to use `#[export_name]`?
+   |
+LL - #[unsafe(link_name = "UNSAFE_VALUE")]
+LL + #[unsafe(export_name = "UNSAFE_VALUE")]
+   |
+
+error: aborting due to 1 previous error; 2 warnings emitted
+