Add diagnostics for unsafe_op_in_unsafe_fn

Turns out it's pretty easy, but I did have to add support for allowed-by-default lints.

Author: ChayimFriedman2

src/tools/rust-analyzer/crates/hir-ty/src/diagnostics/unsafe_check.rs

@@ -13,7 +13,10 @@ use crate::{
     db::HirDatabase, utils::is_fn_unsafe_to_call, InferenceResult, Interner, TyExt, TyKind,
 };
 
-pub fn missing_unsafe(db: &dyn HirDatabase, def: DefWithBodyId) -> Vec<ExprId> {
+/// Returns `(unsafe_exprs, fn_is_unsafe)`.
+///
+/// If `fn_is_unsafe` is false, `unsafe_exprs` are hard errors. If true, they're `unsafe_op_in_unsafe_fn`.
+pub fn missing_unsafe(db: &dyn HirDatabase, def: DefWithBodyId) -> (Vec<ExprId>, bool) {
     let _p = tracing::info_span!("missing_unsafe").entered();
 
     let mut res = Vec::new();
@@ -24,9 +27,6 @@ pub fn missing_unsafe(db: &dyn HirDatabase, def: DefWithBodyId) -> Vec<ExprId> {
         | DefWithBodyId::VariantId(_)
         | DefWithBodyId::InTypeConstId(_) => false,
     };
-    if is_unsafe {
-        return res;
-    }
 
     let body = db.body(def);
     let infer = db.infer(def);
@@ -36,7 +36,7 @@ pub fn missing_unsafe(db: &dyn HirDatabase, def: DefWithBodyId) -> Vec<ExprId> {
         }
     });
 
-    res
+    (res, is_unsafe)
 }
 
 pub struct UnsafeExpr {

src/tools/rust-analyzer/crates/hir/src/diagnostics.rs

@@ -258,6 +258,8 @@ pub struct PrivateField {
 #[derive(Debug)]
 pub struct MissingUnsafe {
     pub expr: InFile<AstPtr<ast::Expr>>,
+    /// If true, the diagnostics is an `unsafe_op_in_unsafe_fn` lint instead of a hard error.
+    pub only_lint: bool,
 }
 
 #[derive(Debug)]

src/tools/rust-analyzer/crates/hir/src/lib.rs

@@ -1884,9 +1884,10 @@ impl DefWithBody {
             );
         }
 
-        for expr in hir_ty::diagnostics::missing_unsafe(db, self.into()) {
+        let (unafe_exprs, only_lint) = hir_ty::diagnostics::missing_unsafe(db, self.into());
+        for expr in unafe_exprs {
             match source_map.expr_syntax(expr) {
-                Ok(expr) => acc.push(MissingUnsafe { expr }.into()),
+                Ok(expr) => acc.push(MissingUnsafe { expr, only_lint }.into()),
                 Err(SyntheticSyntax) => {
                     // FIXME: Here and elsewhere in this file, the `expr` was
                     // desugared, report or assert that this doesn't happen.

src/tools/rust-analyzer/crates/ide-diagnostics/src/handlers/missing_unsafe.rs

@@ -11,9 +11,14 @@ use crate::{fix, Diagnostic, DiagnosticCode, DiagnosticsContext};
 //
 // This diagnostic is triggered if an operation marked as `unsafe` is used outside of an `unsafe` function or block.
 pub(crate) fn missing_unsafe(ctx: &DiagnosticsContext<'_>, d: &hir::MissingUnsafe) -> Diagnostic {
+    let code = if d.only_lint {
+        DiagnosticCode::RustcLint("unsafe_op_in_unsafe_fn")
+    } else {
+        DiagnosticCode::RustcHardError("E0133")
+    };
     Diagnostic::new_with_syntax_node_ptr(
         ctx,
-        DiagnosticCode::RustcHardError("E0133"),
+        code,
         "this operation is unsafe and requires an unsafe function or block",
         d.expr.map(|it| it.into()),
     )
@@ -562,6 +567,30 @@ fn main() {
     ed2021::safe();
     ed2024::not_safe();
   //^^^^^^^^^^^^^^^^^^💡 error: this operation is unsafe and requires an unsafe function or block
+}
+            "#,
+        )
+    }
+
+    #[test]
+    fn unsafe_op_in_unsafe_fn_allowed_by_default() {
+        check_diagnostics(
+            r#"
+unsafe fn foo(p: *mut i32) {
+    *p = 123;
+}
+            "#,
+        )
+    }
+
+    #[test]
+    fn unsafe_op_in_unsafe_fn() {
+        check_diagnostics(
+            r#"
+#![warn(unsafe_op_in_unsafe_fn)]
+unsafe fn foo(p: *mut i32) {
+    *p = 123;
+  //^^💡 warn: this operation is unsafe and requires an unsafe function or block
 }
             "#,
         )

src/tools/rust-analyzer/crates/ide-diagnostics/src/lib.rs

@@ -491,7 +491,7 @@ pub fn semantic_diagnostics(
 
     // The edition isn't accurate (each diagnostics may have its own edition due to macros),
     // but it's okay as it's only being used for error recovery.
-    handle_lint_attributes(
+    handle_lints(
         &ctx.sema,
         &mut FxHashMap::default(),
         &mut lints,
@@ -551,14 +551,27 @@ fn build_group_dict(
     map_with_prefixes.into_iter().map(|(k, v)| (k.strip_prefix(prefix).unwrap(), v)).collect()
 }
 
-fn handle_lint_attributes(
+/// Thd default severity for lints that are not warn by default.
+// FIXME: Autogenerate this instead of write manually.
+static LINTS_DEFAULT_SEVERITY: LazyLock<FxHashMap<&str, Severity>> =
+    LazyLock::new(|| FxHashMap::from_iter([("unsafe_op_in_unsafe_fn", Severity::Allow)]));
+
+fn handle_lints(
     sema: &Semantics<'_, RootDatabase>,
     cache: &mut FxHashMap<HirFileId, FxHashMap<SmolStr, SeverityAttr>>,
     diagnostics: &mut [(InFile<SyntaxNode>, &mut Diagnostic)],
     cache_stack: &mut Vec<HirFileId>,
     edition: Edition,
 ) {
     for (node, diag) in diagnostics {
+        let lint = match diag.code {
+            DiagnosticCode::RustcLint(lint) | DiagnosticCode::Clippy(lint) => lint,
+            _ => panic!("non-lint passed to `handle_lints()`"),
+        };
+        if let Some(&default_severity) = LINTS_DEFAULT_SEVERITY.get(lint) {
+            diag.severity = default_severity;
+        }
+
         let mut diag_severity = fill_lint_attrs(sema, node, cache, cache_stack, diag, edition);
 
         if let outline_diag_severity @ Some(_) =