Merge #6307

6307: Add whitelist of safe intrinsics r=frazar a=frazar

This PR should fix #5996, where intrinsic operations where all marked as unsafe.

I'm rather new to this codebase, so I might be doing something *very* wrong. Please forgive me!

In particular, I'm not sure how to "check that we are in extern `rust-intrinsics`" as mentioned [in this comment](https://github.com/rust-analyzer/rust-analyzer/issues/5996#issuecomment-709234802). 

Co-authored-by: Francesco Zardi <frazar@users.noreply.github.com>

crates/hir_def/src/item_tree/lower.rs

@@ -3,7 +3,7 @@
 use std::{collections::hash_map::Entry, mem, sync::Arc};
 
 use arena::map::ArenaMap;
-use hir_expand::{ast_id_map::AstIdMap, hygiene::Hygiene, HirFileId};
+use hir_expand::{ast_id_map::AstIdMap, hygiene::Hygiene, name::known, HirFileId};
 use smallvec::SmallVec;
 use syntax::{
     ast::{self, ModuleItemOwner},
@@ -555,7 +555,8 @@ impl Ctx {
                     let id: ModItem = match item {
                         ast::ExternItem::Fn(ast) => {
                             let func = self.lower_function(&ast)?;
-                            self.data().functions[func.index].is_unsafe = true;
+                            self.data().functions[func.index].is_unsafe =
+                                is_intrinsic_fn_unsafe(&self.data().functions[func.index].name);
                             func.into()
                         }
                         ast::ExternItem::Static(ast) => {
@@ -713,3 +714,45 @@ enum GenericsOwner<'a> {
     TypeAlias,
     Impl,
 }
+
+/// Returns `true` if the given intrinsic is unsafe to call, or false otherwise.
+fn is_intrinsic_fn_unsafe(name: &Name) -> bool {
+    // Should be kept in sync with https://github.com/rust-lang/rust/blob/c6e4db620a7d2f569f11dcab627430921ea8aacf/compiler/rustc_typeck/src/check/intrinsic.rs#L68
+    ![
+        known::abort,
+        known::min_align_of,
+        known::needs_drop,
+        known::caller_location,
+        known::size_of_val,
+        known::min_align_of_val,
+        known::add_with_overflow,
+        known::sub_with_overflow,
+        known::mul_with_overflow,
+        known::wrapping_add,
+        known::wrapping_sub,
+        known::wrapping_mul,
+        known::saturating_add,
+        known::saturating_sub,
+        known::rotate_left,
+        known::rotate_right,
+        known::ctpop,
+        known::ctlz,
+        known::cttz,
+        known::bswap,
+        known::bitreverse,
+        known::discriminant_value,
+        known::type_id,
+        known::likely,
+        known::unlikely,
+        known::ptr_guaranteed_eq,
+        known::ptr_guaranteed_ne,
+        known::minnumf32,
+        known::minnumf64,
+        known::maxnumf32,
+        known::rustc_peek,
+        known::maxnumf64,
+        known::type_name,
+        known::variant_count,
+    ]
+    .contains(&name)
+}

crates/hir_expand/src/name.rs

@@ -208,6 +208,42 @@ pub mod known {
         PartialOrd,
         Eq,
         PartialEq,
+        // Safe intrinsics
+        abort,
+        size_of,
+        min_align_of,
+        needs_drop,
+        caller_location,
+        size_of_val,
+        min_align_of_val,
+        add_with_overflow,
+        sub_with_overflow,
+        mul_with_overflow,
+        wrapping_add,
+        wrapping_sub,
+        wrapping_mul,
+        saturating_add,
+        saturating_sub,
+        rotate_left,
+        rotate_right,
+        ctpop,
+        ctlz,
+        cttz,
+        bswap,
+        bitreverse,
+        discriminant_value,
+        type_id,
+        likely,
+        unlikely,
+        ptr_guaranteed_eq,
+        ptr_guaranteed_ne,
+        minnumf32,
+        minnumf64,
+        maxnumf32,
+        rustc_peek,
+        maxnumf64,
+        type_name,
+        variant_count,
     );
 
     // self/Self cannot be used as an identifier

crates/hir_ty/src/diagnostics/unsafe_check.rs

@@ -199,6 +199,24 @@ fn main() {
         let x = STATIC_MUT.a;
     }
 }
+"#,
+        );
+    }
+
+    #[test]
+    fn no_missing_unsafe_diagnostic_with_safe_intrinsic() {
+        check_diagnostics(
+            r#"
+extern "rust-intrinsic" {
+    pub fn bitreverse(x: u32) -> u32; // Safe intrinsic
+    pub fn floorf32(x: f32) -> f32; // Unsafe intrinsic
+}
+
+fn main() {
+    let _ = bitreverse(12);
+    let _ = floorf32(12.0);
+          //^^^^^^^^^^^^^^ This operation is unsafe and requires an unsafe function or block
+}
 "#,
         );
     }