Allow using unsafe on functions inside extern blocks

Author: spastorino

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -522,18 +522,14 @@ impl<'a> AstValidator<'a> {
     fn check_foreign_fn_headerless(
         &self,
         // Deconstruct to ensure exhaustiveness
-        FnHeader { safety, coroutine_kind, constness, ext }: FnHeader,
+        FnHeader { safety: _, coroutine_kind, constness, ext }: FnHeader,
     ) {
         let report_err = |span| {
             self.dcx().emit_err(errors::FnQualifierInExtern {
                 span: span,
                 block: self.current_extern_span(),
             });
         };
-        match safety {
-            Safety::Unsafe(span) => report_err(span),
-            Safety::Default => (),
-        }
         match coroutine_kind {
             Some(knd) => report_err(knd.span()),
             None => (),

tests/ui/parser/fn-header-semantic-fail.rs

@@ -44,11 +44,11 @@ fn main() {
 
     extern "C" {
         async fn fe1(); //~ ERROR functions in `extern` blocks cannot have qualifiers
-        unsafe fn fe2(); //~ ERROR functions in `extern` blocks cannot have qualifiers
+        unsafe fn fe2();
         const fn fe3(); //~ ERROR functions in `extern` blocks cannot have qualifiers
         extern "C" fn fe4(); //~ ERROR functions in `extern` blocks cannot have qualifiers
-        const async unsafe extern "C" fn fe5(); //~ ERROR functions in `extern` blocks
-        //~| ERROR functions in `extern` blocks
+        const async unsafe extern "C" fn fe5();
+        //~^ ERROR functions in `extern` blocks
         //~| ERROR functions in `extern` blocks
         //~| ERROR functions in `extern` blocks
         //~| ERROR functions cannot be both `const` and `async`

tests/ui/parser/fn-header-semantic-fail.stderr

@@ -78,15 +78,6 @@ LL |     extern "C" {
 LL |         async fn fe1();
    |         ^^^^^ help: remove this qualifier
 
-error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/fn-header-semantic-fail.rs:47:9
-   |
-LL |     extern "C" {
-   |     ---------- in this `extern` block
-LL |         async fn fe1();
-LL |         unsafe fn fe2();
-   |         ^^^^^^ help: remove this qualifier
-
 error: functions in `extern` blocks cannot have qualifiers
   --> $DIR/fn-header-semantic-fail.rs:48:9
    |
@@ -105,15 +96,6 @@ LL |     extern "C" {
 LL |         extern "C" fn fe4();
    |         ^^^^^^^^^^ help: remove this qualifier
 
-error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/fn-header-semantic-fail.rs:50:21
-   |
-LL |     extern "C" {
-   |     ---------- in this `extern` block
-...
-LL |         const async unsafe extern "C" fn fe5();
-   |                     ^^^^^^ help: remove this qualifier
-
 error: functions in `extern` blocks cannot have qualifiers
   --> $DIR/fn-header-semantic-fail.rs:50:15
    |
@@ -150,6 +132,6 @@ LL |         const async unsafe extern "C" fn fe5();
    |         |     `async` because of this
    |         `const` because of this
 
-error: aborting due to 17 previous errors
+error: aborting due to 15 previous errors
 
 For more information about this error, try `rustc --explain E0379`.

tests/ui/parser/no-const-fn-in-extern-block.rs

@@ -3,7 +3,6 @@ extern "C" {
     //~^ ERROR functions in `extern` blocks cannot have qualifiers
     const unsafe fn bar();
     //~^ ERROR functions in `extern` blocks cannot have qualifiers
-    //~| ERROR functions in `extern` blocks cannot have qualifiers
 }
 
 fn main() {}

tests/ui/parser/no-const-fn-in-extern-block.stderr

@@ -6,15 +6,6 @@ LL | extern "C" {
 LL |     const fn foo();
    |     ^^^^^ help: remove this qualifier
 
-error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/no-const-fn-in-extern-block.rs:4:11
-   |
-LL | extern "C" {
-   | ---------- in this `extern` block
-...
-LL |     const unsafe fn bar();
-   |           ^^^^^^ help: remove this qualifier
-
 error: functions in `extern` blocks cannot have qualifiers
   --> $DIR/no-const-fn-in-extern-block.rs:4:5
    |
@@ -24,5 +15,5 @@ LL | extern "C" {
 LL |     const unsafe fn bar();
    |     ^^^^^ help: remove this qualifier
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 

tests/ui/parser/unsafe-foreign-mod-2.rs

@@ -1,7 +1,6 @@
 extern "C" unsafe {
     //~^ ERROR expected `{`, found keyword `unsafe`
     unsafe fn foo();
-    //~^ ERROR functions in `extern` blocks cannot have qualifiers
 }
 
 fn main() {}

tests/ui/parser/unsafe-foreign-mod-2.stderr

@@ -4,14 +4,5 @@ error: expected `{`, found keyword `unsafe`
 LL | extern "C" unsafe {
    |            ^^^^^^ expected `{`
 
-error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/unsafe-foreign-mod-2.rs:3:5
-   |
-LL | extern "C" unsafe {
-   | ----------------- in this `extern` block
-LL |
-LL |     unsafe fn foo();
-   |     ^^^^^^ help: remove this qualifier
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 

tests/ui/rust-2024/unsafe-extern-blocks/unsafe-items.rs

@@ -0,0 +1,17 @@
+//@ revisions: edition2021 edition2024
+//@[edition2021] edition:2021
+//@[edition2024] edition:2024
+//@[edition2024] compile-flags: -Zunstable-options
+//@ check-pass
+
+unsafe extern "C" {
+    unsafe fn test1(i: i32);
+}
+
+fn test2(i: i32) {
+    unsafe {
+        test1(i);
+    }
+}
+
+fn main() {}