Only lint non-promoted temporaries

Author: Centri3

clippy_lints/src/casts/mod.rs

@@ -18,7 +18,6 @@ mod fn_to_numeric_cast_any;
 mod fn_to_numeric_cast_with_truncation;
 mod ptr_as_ptr;
 mod ptr_cast_constness;
-mod ptr_to_temporary;
 mod unnecessary_cast;
 mod utils;
 
@@ -666,33 +665,6 @@ declare_clippy_lint! {
     "casting a known floating-point NaN into an integer"
 }
 
-declare_clippy_lint! {
-    /// ### What it does
-    /// Checks for raw pointers that point to temporary values.
-    ///
-    /// ### Why is this bad?
-    /// Usage of such a pointer can result in Undefined Behavior, as the pointer will stop pointing
-    /// to valid stack memory once the temporary is dropped.
-    ///
-    /// ### Example
-    /// ```rust,ignore
-    /// const PS: [usize; 3] = [2usize, 3usize, 11usize];
-    /// let mut ps = vec![];
-    ///
-    /// for p in PS {
-    ///     ps.push(&p as *const usize);
-    /// }
-    ///
-    /// for p in ps {
-    ///     unsafe { p.read() }; // ⚠️
-    /// }
-    /// ```
-    #[clippy::version = "1.72.0"]
-    pub PTR_TO_TEMPORARY,
-    correctness,
-    "disallows obtaining a raw pointer to a temporary value"
-}
-
 pub struct Casts {
     msrv: Msrv,
 }
@@ -727,7 +699,6 @@ impl_lint_pass!(Casts => [
     CAST_SLICE_FROM_RAW_PARTS,
     AS_PTR_CAST_MUT,
     CAST_NAN_TO_INT,
-    PTR_TO_TEMPORARY,
 ]);
 
 impl<'tcx> LateLintPass<'tcx> for Casts {
@@ -773,7 +744,6 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
             }
 
             as_underscore::check(cx, expr, cast_to_hir);
-            ptr_to_temporary::check(cx, expr, cast_expr, cast_to_hir);
 
             if self.msrv.meets(msrvs::BORROW_AS_PTR) {
                 borrow_as_ptr::check(cx, expr, cast_expr, cast_to_hir);

clippy_lints/src/casts/ptr_to_temporary.rs

@@ -94,7 +94,6 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::casts::FN_TO_NUMERIC_CAST_WITH_TRUNCATION_INFO,
     crate::casts::PTR_AS_PTR_INFO,
     crate::casts::PTR_CAST_CONSTNESS_INFO,
-    crate::casts::PTR_TO_TEMPORARY_INFO,
     crate::casts::UNNECESSARY_CAST_INFO,
     crate::checked_conversions::CHECKED_CONVERSIONS_INFO,
     crate::cognitive_complexity::COGNITIVE_COMPLEXITY_INFO,
@@ -545,6 +544,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::ptr::MUT_FROM_REF_INFO,
     crate::ptr::PTR_ARG_INFO,
     crate::ptr_offset_with_cast::PTR_OFFSET_WITH_CAST_INFO,
+    crate::ptr_to_temporary::PTR_TO_TEMPORARY_INFO,
     crate::pub_use::PUB_USE_INFO,
     crate::question_mark::QUESTION_MARK_INFO,
     crate::question_mark_used::QUESTION_MARK_USED_INFO,

clippy_lints/src/declared_lints.rs

@@ -262,6 +262,7 @@ mod permissions_set_readonly_false;
 mod precedence;
 mod ptr;
 mod ptr_offset_with_cast;
+mod ptr_to_temporary;
 mod pub_use;
 mod question_mark;
 mod question_mark_used;
@@ -1082,6 +1083,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|_| Box::new(manual_float_methods::ManualFloatMethods));
     store.register_late_pass(|_| Box::new(four_forward_slashes::FourForwardSlashes));
     store.register_late_pass(|_| Box::new(error_impl_error::ErrorImplError));
+    store.register_late_pass(move |_| Box::new(ptr_to_temporary::PtrToTemporary));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
 

clippy_lints/src/lib.rs

@@ -0,0 +1,70 @@
+use clippy_utils::{consts::is_promotable, diagnostics::span_lint_and_note, is_from_proc_macro};
+use rustc_hir::{BorrowKind, Expr, ExprKind, ItemKind, OwnerNode};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::lint::in_external_macro;
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for raw pointers pointing to temporary values that will **not** be promoted to a
+    /// constant through
+    /// [constant promotion](https://doc.rust-lang.org/stable/reference/destructors.html#constant-promotion).
+    ///
+    /// ### Why is this bad?
+    /// Usage of such a pointer can result in Undefined Behavior, as the pointer will stop pointing
+    /// to valid stack memory once the temporary is dropped.
+    ///
+    /// ### Example
+    /// ```rust,ignore
+    /// fn x() -> *const i32 {
+    ///     let x = 0;
+    ///     &x as *const i32
+    /// }
+    ///
+    /// let x = x();
+    /// unsafe { *x }; // ⚠️
+    /// ```
+    #[clippy::version = "1.72.0"]
+    pub PTR_TO_TEMPORARY,
+    correctness,
+    "disallows returning a raw pointer to a temporary value"
+}
+declare_lint_pass!(PtrToTemporary => [PTR_TO_TEMPORARY]);
+
+impl<'tcx> LateLintPass<'tcx> for PtrToTemporary {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
+        if in_external_macro(cx.sess(), expr.span) {
+            return;
+        }
+
+        // Get the final return statement if this is a return statement, or don't lint
+        let expr = if let ExprKind::Ret(Some(expr)) = expr.kind {
+            expr
+        } else if let OwnerNode::Item(parent) = cx.tcx.hir().owner(cx.tcx.hir().get_parent_item(expr.hir_id))
+            && let ItemKind::Fn(_, _, body) = parent.kind
+            && let block = cx.tcx.hir().body(body).value
+            && let ExprKind::Block(block, _) = block.kind
+            && let Some(final_block_expr) = block.expr
+            && final_block_expr.hir_id == expr.hir_id
+        {
+            expr
+        } else {
+            return;
+        };
+
+        if let ExprKind::Cast(cast_expr, _) = expr.kind
+            && let ExprKind::AddrOf(BorrowKind::Ref, _, e) = cast_expr.kind
+            && !is_promotable(cx, e)
+            && !is_from_proc_macro(cx, expr)
+        {
+            span_lint_and_note(
+                cx,
+                PTR_TO_TEMPORARY,
+                expr.span,
+                "returning a raw pointer to a temporary value that cannot be promoted to a constant",
+                None,
+                "usage of this pointer by callers will cause Undefined Behavior",
+            );
+        }
+    }
+}

clippy_lints/src/ptr_to_temporary.rs

@@ -1,7 +1,8 @@
 #![allow(clippy::float_cmp)]
 
 use crate::source::{get_source_text, walk_span_to_context};
-use crate::{clip, is_direct_expn_of, sext, unsext};
+use crate::visitors::for_each_expr;
+use crate::{clip, is_ctor_or_promotable_const_function, is_direct_expn_of, path_res, sext, unsext};
 use if_chain::if_chain;
 use rustc_ast::ast::{self, LitFloatType, LitKind};
 use rustc_data_structures::sync::Lrc;
@@ -17,6 +18,7 @@ use rustc_span::SyntaxContext;
 use std::cmp::Ordering::{self, Equal};
 use std::hash::{Hash, Hasher};
 use std::iter;
+use std::ops::ControlFlow;
 
 /// A `LitKind`-like enum to fold constant `Expr`s into.
 #[derive(Debug, Clone)]
@@ -736,3 +738,29 @@ fn field_of_struct<'tcx>(
         None
     }
 }
+
+/// Returns whether a certain `Expr` will be promoted to a constant.
+pub fn is_promotable<'tcx>(cx: &LateContext<'tcx>, start: &'tcx Expr<'tcx>) -> bool {
+    let ty = cx.typeck_results().expr_ty(start);
+    for_each_expr(start, |expr| {
+        match expr.kind {
+            ExprKind::Binary(_, _, _) => ControlFlow::Break(()),
+            ExprKind::Unary(UnOp::Deref, e) if !matches!(path_res(cx, e), Res::Def(DefKind::Const, _)) => {
+                ControlFlow::Break(())
+            },
+            ExprKind::Call(_, _) if !is_ctor_or_promotable_const_function(cx, expr) => ControlFlow::Break(()),
+            ExprKind::MethodCall(..) if let Some(def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id)
+                && !cx.tcx.is_promotable_const_fn(def_id) =>
+            {
+                ControlFlow::Break(())
+            },
+            ExprKind::Path(qpath) if let Res::Local(_) = cx.qpath_res(&qpath, expr.hir_id) => {
+                ControlFlow::Break(())
+            },
+            _ => ControlFlow::Continue(()),
+        }
+    })
+    .is_none()
+        && ty.is_freeze(cx.tcx, cx.param_env)
+        && !ty.needs_drop(cx.tcx, cx.param_env)
+}

clippy_utils/src/consts.rs

@@ -1,34 +1,65 @@
-#![allow(clippy::explicit_auto_deref, clippy::unnecessary_cast, clippy::useless_vec)]
+//@aux-build:proc_macros.rs
+#![allow(clippy::borrow_deref_ref, clippy::deref_addrof, clippy::identity_op, unused)]
+#![warn(clippy::ptr_to_temporary)]
+#![no_main]
 
-use std::ptr::addr_of;
+#[macro_use]
+extern crate proc_macros;
 
-fn a() -> i32 {
-    0
+fn bad_1() -> *const i32 {
+    &(100 + *&0) as *const i32
 }
 
-struct Vec3 {
-    x: f32,
-    y: f32,
-    z: f32,
+fn bad_2() -> *const i32 {
+    let a = 0i32;
+    &(*&a) as *const i32
 }
 
-fn main() {
-    let _p = &0 as *const i32;
-    let _p = &a() as *const i32;
-    let vec = vec![1];
-    let _p = &vec.len() as *const usize;
-    let x = &(1 + 2) as *const i32;
-    let x = &(x as *const i32) as *const *const i32;
+fn bad_3() -> *const i32 {
+    let a = 0i32;
+    &a as *const i32
+}
+
+fn bad_4() -> *const i32 {
+    let mut a = 0i32;
+    &a as *const i32
+}
+
+fn bad_5() -> *const i32 {
+    const A: &i32 = &1i32;
+    let mut a = 0i32;
 
-    // Do not lint...
-    let ptr = &Vec3 { x: 1.0, y: 2.0, z: 3.0 };
-    let some_variable = 1i32;
-    let x = &(*ptr).x as *const f32;
-    let x = &(some_variable) as *const i32;
+    if true {
+        return &(*A) as *const i32;
+    }
+    &a as *const i32
+}
+
+fn fine_1() -> *const i32 {
+    &100 as *const i32
+}
+
+fn fine_2() -> *const i32 {
+    const A: &i32 = &0i32;
+    A as *const i32
+}
+
+fn fine_3() -> *const i32 {
+    const A: &i32 = &0i32;
+    &(*A) as *const i32
+}
+
+external! {
+    fn fine_external() -> *const i32 {
+        let a = 0i32;
+        &a as *const i32
+    }
+}
 
-    // ...As `addr_of!` does not report anything out of the ordinary
-    let ptr = &Vec3 { x: 1.0, y: 2.0, z: 3.0 };
-    let some_variable = 1i32;
-    let x = addr_of!((*ptr).x) as *const f32;
-    let x = addr_of!(some_variable);
+with_span! {
+    span
+    fn fine_proc_macro() -> *const i32 {
+        let a = 0i32;
+        &a as *const i32
+    }
 }