Auto merge of #18350 - roife:safe-kw-1, r=lnicola

feat: initial support for safe_kw in extern blocks

This PR adds initial support for `safe` keywords in external blocks.

## Changes

1. Parsing static declarations with `safe` kw and `unsafe` kw, as well as functions with `safe` kw in extern_blocks
2. Add `HAS_SAFE_KW ` to `FnFlags`
3. Handle `safe` kw in `is_fn_unsafe_to_call` query
4. Handle safe_kw in unsafe diagnostics

crates/hir-def/src/data.rs

@@ -148,6 +148,10 @@ impl FunctionData {
         self.flags.contains(FnFlags::HAS_UNSAFE_KW)
     }
 
+    pub fn is_safe(&self) -> bool {
+        self.flags.contains(FnFlags::HAS_SAFE_KW)
+    }
+
     pub fn is_varargs(&self) -> bool {
         self.flags.contains(FnFlags::IS_VARARGS)
     }
@@ -567,6 +571,8 @@ pub struct StaticData {
     pub visibility: RawVisibility,
     pub mutable: bool,
     pub is_extern: bool,
+    pub has_safe_kw: bool,
+    pub has_unsafe_kw: bool,
 }
 
 impl StaticData {
@@ -581,6 +587,8 @@ impl StaticData {
             visibility: item_tree[statik.visibility].clone(),
             mutable: statik.mutable,
             is_extern: matches!(loc.container, ItemContainerId::ExternBlockId(_)),
+            has_safe_kw: statik.has_safe_kw,
+            has_unsafe_kw: statik.has_unsafe_kw,
         })
     }
 }

crates/hir-def/src/item_tree.rs

@@ -754,6 +754,7 @@ bitflags::bitflags! {
         const HAS_ASYNC_KW = 1 << 4;
         const HAS_UNSAFE_KW = 1 << 5;
         const IS_VARARGS = 1 << 6;
+        const HAS_SAFE_KW = 1 << 7;
     }
 }
 
@@ -822,7 +823,10 @@ pub struct Const {
 pub struct Static {
     pub name: Name,
     pub visibility: RawVisibilityId,
+    // TODO: use bitflags when we have more flags
     pub mutable: bool,
+    pub has_safe_kw: bool,
+    pub has_unsafe_kw: bool,
     pub type_ref: Interned<TypeRef>,
     pub ast_id: FileAstId<ast::Static>,
 }

crates/hir-def/src/item_tree/lower.rs

@@ -440,6 +440,9 @@ impl<'a> Ctx<'a> {
         if func.unsafe_token().is_some() {
             flags |= FnFlags::HAS_UNSAFE_KW;
         }
+        if func.safe_token().is_some() {
+            flags |= FnFlags::HAS_SAFE_KW;
+        }
         if has_var_args {
             flags |= FnFlags::IS_VARARGS;
         }
@@ -484,8 +487,11 @@ impl<'a> Ctx<'a> {
         let type_ref = self.lower_type_ref_opt(static_.ty());
         let visibility = self.lower_visibility(static_);
         let mutable = static_.mut_token().is_some();
+        let has_safe_kw = static_.safe_token().is_some();
+        let has_unsafe_kw = static_.unsafe_token().is_some();
         let ast_id = self.source_ast_id_map.ast_id(static_);
-        let res = Static { name, visibility, mutable, type_ref, ast_id };
+        let res =
+            Static { name, visibility, mutable, type_ref, ast_id, has_safe_kw, has_unsafe_kw };
         Some(id(self.data().statics.alloc(res)))
     }
 

crates/hir-def/src/item_tree/pretty.rs

@@ -278,6 +278,9 @@ impl Printer<'_> {
                 if flags.contains(FnFlags::HAS_UNSAFE_KW) {
                     w!(self, "unsafe ");
                 }
+                if flags.contains(FnFlags::HAS_SAFE_KW) {
+                    w!(self, "safe ");
+                }
                 if let Some(abi) = abi {
                     w!(self, "extern \"{}\" ", abi);
                 }
@@ -379,9 +382,23 @@ impl Printer<'_> {
                 wln!(self, " = _;");
             }
             ModItem::Static(it) => {
-                let Static { name, visibility, mutable, type_ref, ast_id } = &self.tree[it];
+                let Static {
+                    name,
+                    visibility,
+                    mutable,
+                    type_ref,
+                    ast_id,
+                    has_safe_kw,
+                    has_unsafe_kw,
+                } = &self.tree[it];
                 self.print_ast_id(ast_id.erase());
                 self.print_visibility(*visibility);
+                if *has_safe_kw {
+                    w!(self, "safe ");
+                }
+                if *has_unsafe_kw {
+                    w!(self, "unsafe ");
+                }
                 w!(self, "static ");
                 if *mutable {
                     w!(self, "mut ");

crates/hir-ty/src/diagnostics/unsafe_check.rs

@@ -89,7 +89,7 @@ fn walk_unsafe(
             let value_or_partial = resolver.resolve_path_in_value_ns(db.upcast(), path);
             if let Some(ResolveValueResult::ValueNs(ValueNs::StaticId(id), _)) = value_or_partial {
                 let static_data = db.static_data(id);
-                if static_data.mutable || static_data.is_extern {
+                if static_data.mutable || (static_data.is_extern && !static_data.has_safe_kw) {
                     unsafe_expr_cb(UnsafeExpr { expr: current, inside_unsafe_block });
                 }
             }

crates/hir-ty/src/utils.rs

@@ -257,10 +257,12 @@ pub fn is_fn_unsafe_to_call(db: &dyn HirDatabase, func: FunctionId) -> bool {
         return true;
     }
 
-    match func.lookup(db.upcast()).container {
+    let loc = func.lookup(db.upcast());
+    match loc.container {
         hir_def::ItemContainerId::ExternBlockId(block) => {
-            // Function in an `extern` block are always unsafe to call, except when it has
-            // `"rust-intrinsic"` ABI there are a few exceptions.
+            // Function in an `extern` block are always unsafe to call, except when
+            // it is marked as `safe` or it has `"rust-intrinsic"` ABI there are a
+            // few exceptions.
             let id = block.lookup(db.upcast()).id;
 
             let is_intrinsic =
@@ -270,8 +272,8 @@ pub fn is_fn_unsafe_to_call(db: &dyn HirDatabase, func: FunctionId) -> bool {
                 // Intrinsics are unsafe unless they have the rustc_safe_intrinsic attribute
                 !data.attrs.by_key(&sym::rustc_safe_intrinsic).exists()
             } else {
-                // Extern items are always unsafe
-                true
+                // Extern items without `safe` modifier are always unsafe
+                !db.function_data(func).is_safe()
             }
         }
         _ => false,

crates/ide-diagnostics/src/handlers/missing_unsafe.rs

@@ -554,7 +554,7 @@ fn main() {
             r#"
 //- /ed2021.rs crate:ed2021 edition:2021
 #[rustc_deprecated_safe_2024]
-unsafe fn safe() -> u8 {
+unsafe fn safe_fn() -> u8 {
     0
 }
 //- /ed2024.rs crate:ed2024 edition:2024
@@ -564,7 +564,7 @@ unsafe fn not_safe() -> u8 {
 }
 //- /main.rs crate:main deps:ed2021,ed2024
 fn main() {
-    ed2021::safe();
+    ed2021::safe_fn();
     ed2024::not_safe();
   //^^^^^^^^^^^^^^^^^^💡 error: this operation is unsafe and requires an unsafe function or block
 }
@@ -595,4 +595,39 @@ unsafe fn foo(p: *mut i32) {
             "#,
         )
     }
+
+    #[test]
+    fn no_unsafe_diagnostic_with_safe_kw() {
+        check_diagnostics(
+            r#"
+unsafe extern {
+    pub safe fn f();
+
+    pub unsafe fn g();
+
+    pub fn h();
+
+    pub safe static S1: i32;
+
+    pub unsafe static S2: i32;
+
+    pub static S3: i32;
+}
+
+fn main() {
+    f();
+    g();
+  //^^^💡 error: this operation is unsafe and requires an unsafe function or block
+    h();
+  //^^^💡 error: this operation is unsafe and requires an unsafe function or block
+
+    let _ = S1;
+    let _ = S2;
+          //^^💡 error: this operation is unsafe and requires an unsafe function or block
+    let _ = S3;
+          //^^💡 error: this operation is unsafe and requires an unsafe function or block
+}
+"#,
+        );
+    }
 }

crates/parser/src/grammar/items.rs

@@ -135,6 +135,11 @@ pub(super) fn opt_item(p: &mut Parser<'_>, m: Marker) -> Result<(), Marker> {
         has_mods = true;
     }
 
+    if p.at(T![safe]) {
+        p.eat(T![safe]);
+        has_mods = true;
+    }
+
     if p.at(T![extern]) {
         has_extern = true;
         has_mods = true;
@@ -189,6 +194,7 @@ pub(super) fn opt_item(p: &mut Parser<'_>, m: Marker) -> Result<(), Marker> {
         T![fn] => fn_(p, m),
 
         T![const] if p.nth(1) != T!['{'] => consts::konst(p, m),
+        T![static] if matches!(p.nth(1), IDENT | T![_] | T![mut]) => consts::static_(p, m),
 
         T![trait] => traits::trait_(p, m),
         T![impl] => traits::impl_(p, m),