make sure the msrv for const_ptr_deref is met when linting [missing_const_for_fn]

Author: J-ZhengLi

clippy_config/src/msrvs.rs

@@ -26,7 +26,7 @@ msrv_aliases! {
     1,63,0 { ASSIGNING_CLONES }
     1,62,0 { BOOL_THEN_SOME, DEFAULT_ENUM_ATTRIBUTE }
     1,59,0 { THREAD_LOCAL_INITIALIZER_CAN_BE_MADE_CONST }
-    1,58,0 { FORMAT_ARGS_CAPTURE, PATTERN_TRAIT_CHAR_ARRAY }
+    1,58,0 { FORMAT_ARGS_CAPTURE, PATTERN_TRAIT_CHAR_ARRAY, CONST_RAW_PTR_DEREF }
     1,55,0 { SEEK_REWIND }
     1,54,0 { INTO_KEYS }
     1,53,0 { OR_PATTERNS, MANUAL_BITS, BTREE_MAP_RETAIN, BTREE_SET_RETAIN, ARRAY_INTO_ITERATOR }

clippy_lints/src/missing_const_for_fn.rs

@@ -1,12 +1,16 @@
+use std::ops::ControlFlow;
+
 use clippy_config::msrvs::{self, Msrv};
 use clippy_utils::diagnostics::span_lint;
 use clippy_utils::qualify_min_const_fn::is_min_const_fn;
 use clippy_utils::ty::has_drop;
+use clippy_utils::visitors::for_each_expr;
 use clippy_utils::{fn_has_unsatisfiable_preds, is_entrypoint_fn, is_from_proc_macro, trait_ref_of_method};
+use hir::UnOp;
 use rustc_hir as hir;
 use rustc_hir::def_id::CRATE_DEF_ID;
 use rustc_hir::intravisit::FnKind;
-use rustc_hir::{Body, Constness, FnDecl, GenericParamKind};
+use rustc_hir::{Body, Constness, ExprKind, FnDecl, GenericParamKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::lint::in_external_macro;
 use rustc_session::impl_lint_pass;
@@ -149,6 +153,11 @@ impl<'tcx> LateLintPass<'tcx> for MissingConstForFn {
             return;
         }
 
+        // Skip if there is any pointer deref ops in the body, and the msrv of that feature does not meet.
+        if !self.msrv.meets(msrvs::CONST_RAW_PTR_DEREF) && has_raw_ptr_deref_in_body(cx, body) {
+            return;
+        }
+
         let mir = cx.tcx.optimized_mir(def_id);
 
         if let Err((span, err)) = is_min_const_fn(cx.tcx, mir, &self.msrv) {
@@ -176,3 +185,16 @@ fn method_accepts_droppable(cx: &LateContext<'_>, def_id: LocalDefId) -> bool {
 fn already_const(header: hir::FnHeader) -> bool {
     header.constness == Constness::Const
 }
+
+fn has_raw_ptr_deref_in_body(cx: &LateContext<'_>, body: &Body<'_>) -> bool {
+    for_each_expr(body.value, |expr| {
+        if let ExprKind::Unary(UnOp::Deref, oprand) = expr.kind
+            && cx.typeck_results().expr_ty(oprand).is_unsafe_ptr()
+        {
+            ControlFlow::Break(())
+        } else {
+            ControlFlow::Continue(())
+        }
+    })
+    .is_some()
+}

tests/ui/missing_const_for_fn/could_be_const.rs

@@ -113,3 +113,24 @@ impl const Drop for D {
 // Lint this, since it can be dropped in const contexts
 // FIXME(effects)
 fn d(this: D) {}
+
+#[clippy::msrv = "1.58"]
+mod const_ptr_deref_supported {
+    struct Foo(*const u8);
+    impl Foo {
+        fn can_be_const(self) -> usize {
+            //~^ ERROR: this could be a `const fn`
+            unsafe { *self.0 as usize }
+        }
+    }
+}
+
+#[clippy::msrv = "1.57"]
+mod const_ptr_deref_not_supported {
+    struct Foo(*const u8);
+    impl Foo {
+        fn cannot_be_const(self) -> usize {
+            unsafe { *self.0 as usize }
+        }
+    }
+}

tests/ui/missing_const_for_fn/could_be_const.stderr

@@ -102,5 +102,14 @@ LL | |     46
 LL | | }
    | |_^
 
-error: aborting due to 11 previous errors
+error: this could be a `const fn`
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:121:9
+   |
+LL | /         fn can_be_const(self) -> usize {
+LL | |
+LL | |             unsafe { *self.0 as usize }
+LL | |         }
+   | |_________^
+
+error: aborting due to 12 previous errors