Auto merge of rust-lang#8398 - Jarcho:unordered_transmute, r=llogiq

Add lint `transmute_undefined_repr`

Partially implements rust-lang#3999 and rust-lang#546

This doesn't consider `enum`s at all right now as those are going to be a pain to deal with. This also allows `#[repr(Rust)]` structs with only one non-zero sized fields. I think those are technically undefined when transmuted.

changelog: Add lint `transmute_undefined_repr`

Author: bors

CHANGELOG.md

@@ -3475,6 +3475,7 @@ Released 2018-09-13
 [`transmute_num_to_bytes`]: https://rust-lang.github.io/rust-clippy/master/index.html#transmute_num_to_bytes
 [`transmute_ptr_to_ptr`]: https://rust-lang.github.io/rust-clippy/master/index.html#transmute_ptr_to_ptr
 [`transmute_ptr_to_ref`]: https://rust-lang.github.io/rust-clippy/master/index.html#transmute_ptr_to_ref
+[`transmute_undefined_repr`]: https://rust-lang.github.io/rust-clippy/master/index.html#transmute_undefined_repr
 [`transmutes_expressible_as_ptr_casts`]: https://rust-lang.github.io/rust-clippy/master/index.html#transmutes_expressible_as_ptr_casts
 [`transmuting_null`]: https://rust-lang.github.io/rust-clippy/master/index.html#transmuting_null
 [`trivial_regex`]: https://rust-lang.github.io/rust-clippy/master/index.html#trivial_regex

clippy_lints/src/lib.register_all.rs

@@ -277,6 +277,7 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
     LintId::of(transmute::TRANSMUTE_INT_TO_FLOAT),
     LintId::of(transmute::TRANSMUTE_NUM_TO_BYTES),
     LintId::of(transmute::TRANSMUTE_PTR_TO_REF),
+    LintId::of(transmute::TRANSMUTE_UNDEFINED_REPR),
     LintId::of(transmute::UNSOUND_COLLECTION_TRANSMUTE),
     LintId::of(transmute::WRONG_TRANSMUTE),
     LintId::of(transmuting_null::TRANSMUTING_NULL),

clippy_lints/src/lib.register_correctness.rs

@@ -58,6 +58,7 @@ store.register_group(true, "clippy::correctness", Some("clippy_correctness"), ve
     LintId::of(size_of_in_element_count::SIZE_OF_IN_ELEMENT_COUNT),
     LintId::of(swap::ALMOST_SWAPPED),
     LintId::of(to_string_in_display::TO_STRING_IN_DISPLAY),
+    LintId::of(transmute::TRANSMUTE_UNDEFINED_REPR),
     LintId::of(transmute::UNSOUND_COLLECTION_TRANSMUTE),
     LintId::of(transmute::WRONG_TRANSMUTE),
     LintId::of(transmuting_null::TRANSMUTING_NULL),

clippy_lints/src/lib.register_lints.rs

@@ -473,6 +473,7 @@ store.register_lints(&[
     transmute::TRANSMUTE_NUM_TO_BYTES,
     transmute::TRANSMUTE_PTR_TO_PTR,
     transmute::TRANSMUTE_PTR_TO_REF,
+    transmute::TRANSMUTE_UNDEFINED_REPR,
     transmute::UNSOUND_COLLECTION_TRANSMUTE,
     transmute::USELESS_TRANSMUTE,
     transmute::WRONG_TRANSMUTE,

clippy_lints/src/lib.rs

@@ -5,6 +5,7 @@
 #![feature(control_flow_enum)]
 #![feature(drain_filter)]
 #![feature(iter_intersperse)]
+#![feature(let_chains)]
 #![feature(let_else)]
 #![feature(once_cell)]
 #![feature(rustc_private)]

clippy_lints/src/transmute/mod.rs

@@ -7,6 +7,7 @@ mod transmute_num_to_bytes;
 mod transmute_ptr_to_ptr;
 mod transmute_ptr_to_ref;
 mod transmute_ref_to_ref;
+mod transmute_undefined_repr;
 mod transmutes_expressible_as_ptr_casts;
 mod unsound_collection_transmute;
 mod useless_transmute;
@@ -355,6 +356,30 @@ declare_clippy_lint! {
     "transmute between collections of layout-incompatible types"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for transmutes either to or from a type which does not have a defined representation.
+    ///
+    /// ### Why is this bad?
+    /// The results of such a transmute are not defined.
+    ///
+    /// ### Example
+    /// ```rust
+    /// struct Foo<T>(u32, T);
+    /// let _ = unsafe { core::mem::transmute::<Foo<u32>, Foo<i32>>(Foo(0u32, 0u32)) };
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// #[repr(C)]
+    /// struct Foo<T>(u32, T);
+    /// let _ = unsafe { core::mem::transmute::<Foo<u32>, Foo<i32>>(Foo(0u32, 0u32)) };
+    /// ```
+    #[clippy::version = "1.60.0"]
+    pub TRANSMUTE_UNDEFINED_REPR,
+    correctness,
+    "transmute to or from a type with an undefined representation"
+}
+
 declare_lint_pass!(Transmute => [
     CROSSPOINTER_TRANSMUTE,
     TRANSMUTE_PTR_TO_REF,
@@ -369,13 +394,13 @@ declare_lint_pass!(Transmute => [
     TRANSMUTE_NUM_TO_BYTES,
     UNSOUND_COLLECTION_TRANSMUTE,
     TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
+    TRANSMUTE_UNDEFINED_REPR,
 ]);
 
 impl<'tcx> LateLintPass<'tcx> for Transmute {
-    #[allow(clippy::similar_names, clippy::too_many_lines)]
     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
         if_chain! {
-            if let ExprKind::Call(path_expr, args) = e.kind;
+            if let ExprKind::Call(path_expr, [arg]) = e.kind;
             if let ExprKind::Path(ref qpath) = path_expr.kind;
             if let Some(def_id) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id();
             if cx.tcx.is_diagnostic_item(sym::transmute, def_id);
@@ -385,28 +410,31 @@ impl<'tcx> LateLintPass<'tcx> for Transmute {
                 // And see https://github.com/rust-lang/rust/issues/51911 for dereferencing raw pointers.
                 let const_context = in_constant(cx, e.hir_id);
 
-                let from_ty = cx.typeck_results().expr_ty(&args[0]);
+                let from_ty = cx.typeck_results().expr_ty(arg);
                 let to_ty = cx.typeck_results().expr_ty(e);
 
                 // If useless_transmute is triggered, the other lints can be skipped.
-                if useless_transmute::check(cx, e, from_ty, to_ty, args) {
+                if useless_transmute::check(cx, e, from_ty, to_ty, arg) {
                     return;
                 }
 
-                let mut linted = wrong_transmute::check(cx, e, from_ty, to_ty);
-                linted |= crosspointer_transmute::check(cx, e, from_ty, to_ty);
-                linted |= transmute_ptr_to_ref::check(cx, e, from_ty, to_ty, args, qpath);
-                linted |= transmute_int_to_char::check(cx, e, from_ty, to_ty, args);
-                linted |= transmute_ref_to_ref::check(cx, e, from_ty, to_ty, args, const_context);
-                linted |= transmute_ptr_to_ptr::check(cx, e, from_ty, to_ty, args);
-                linted |= transmute_int_to_bool::check(cx, e, from_ty, to_ty, args);
-                linted |= transmute_int_to_float::check(cx, e, from_ty, to_ty, args, const_context);
-                linted |= transmute_float_to_int::check(cx, e, from_ty, to_ty, args, const_context);
-                linted |= transmute_num_to_bytes::check(cx, e, from_ty, to_ty, args, const_context);
-                linted |= unsound_collection_transmute::check(cx, e, from_ty, to_ty);
+                let linted = wrong_transmute::check(cx, e, from_ty, to_ty)
+                    | crosspointer_transmute::check(cx, e, from_ty, to_ty)
+                    | transmute_ptr_to_ref::check(cx, e, from_ty, to_ty, arg, qpath)
+                    | transmute_int_to_char::check(cx, e, from_ty, to_ty, arg)
+                    | transmute_ref_to_ref::check(cx, e, from_ty, to_ty, arg, const_context)
+                    | transmute_ptr_to_ptr::check(cx, e, from_ty, to_ty, arg)
+                    | transmute_int_to_bool::check(cx, e, from_ty, to_ty, arg)
+                    | transmute_int_to_float::check(cx, e, from_ty, to_ty, arg, const_context)
+                    | transmute_float_to_int::check(cx, e, from_ty, to_ty, arg, const_context)
+                    | transmute_num_to_bytes::check(cx, e, from_ty, to_ty, arg, const_context)
+                    | (
+                        unsound_collection_transmute::check(cx, e, from_ty, to_ty)
+                        || transmute_undefined_repr::check(cx, e, from_ty, to_ty)
+                    );
 
                 if !linted {
-                    transmutes_expressible_as_ptr_casts::check(cx, e, from_ty, to_ty, args);
+                    transmutes_expressible_as_ptr_casts::check(cx, e, from_ty, to_ty, arg);
                 }
             }
         }

clippy_lints/src/transmute/transmute_float_to_int.rs

@@ -15,7 +15,7 @@ pub(super) fn check<'tcx>(
     e: &'tcx Expr<'_>,
     from_ty: Ty<'tcx>,
     to_ty: Ty<'tcx>,
-    args: &'tcx [Expr<'_>],
+    mut arg: &'tcx Expr<'_>,
     const_context: bool,
 ) -> bool {
     match (&from_ty.kind(), &to_ty.kind()) {
@@ -26,37 +26,36 @@ pub(super) fn check<'tcx>(
                 e.span,
                 &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
                 |diag| {
-                    let mut expr = &args[0];
-                    let mut arg = sugg::Sugg::hir(cx, expr, "..");
+                    let mut sugg = sugg::Sugg::hir(cx, arg, "..");
 
-                    if let ExprKind::Unary(UnOp::Neg, inner_expr) = &expr.kind {
-                        expr = inner_expr;
+                    if let ExprKind::Unary(UnOp::Neg, inner_expr) = &arg.kind {
+                        arg = inner_expr;
                     }
 
                     if_chain! {
                         // if the expression is a float literal and it is unsuffixed then
                         // add a suffix so the suggestion is valid and unambiguous
-                        if let ExprKind::Lit(lit) = &expr.kind;
+                        if let ExprKind::Lit(lit) = &arg.kind;
                         if let ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) = lit.node;
                         then {
-                            let op = format!("{}{}", arg, float_ty.name_str()).into();
-                            match arg {
-                                sugg::Sugg::MaybeParen(_) => arg = sugg::Sugg::MaybeParen(op),
-                                _ => arg = sugg::Sugg::NonParen(op)
+                            let op = format!("{}{}", sugg, float_ty.name_str()).into();
+                            match sugg {
+                                sugg::Sugg::MaybeParen(_) => sugg = sugg::Sugg::MaybeParen(op),
+                                _ => sugg = sugg::Sugg::NonParen(op)
                             }
                         }
                     }
 
-                    arg = sugg::Sugg::NonParen(format!("{}.to_bits()", arg.maybe_par()).into());
+                    sugg = sugg::Sugg::NonParen(format!("{}.to_bits()", sugg.maybe_par()).into());
 
                     // cast the result of `to_bits` if `to_ty` is signed
-                    arg = if let ty::Int(int_ty) = to_ty.kind() {
-                        arg.as_ty(int_ty.name_str().to_string())
+                    sugg = if let ty::Int(int_ty) = to_ty.kind() {
+                        sugg.as_ty(int_ty.name_str().to_string())
                     } else {
-                        arg
+                        sugg
                     };
 
-                    diag.span_suggestion(e.span, "consider using", arg.to_string(), Applicability::Unspecified);
+                    diag.span_suggestion(e.span, "consider using", sugg.to_string(), Applicability::Unspecified);
                 },
             );
             true

clippy_lints/src/transmute/transmute_int_to_bool.rs

@@ -15,7 +15,7 @@ pub(super) fn check<'tcx>(
     e: &'tcx Expr<'_>,
     from_ty: Ty<'tcx>,
     to_ty: Ty<'tcx>,
-    args: &'tcx [Expr<'_>],
+    arg: &'tcx Expr<'_>,
 ) -> bool {
     match (&from_ty.kind(), &to_ty.kind()) {
         (ty::Int(ty::IntTy::I8) | ty::Uint(ty::UintTy::U8), ty::Bool) => {
@@ -25,7 +25,7 @@ pub(super) fn check<'tcx>(
                 e.span,
                 &format!("transmute from a `{}` to a `bool`", from_ty),
                 |diag| {
-                    let arg = sugg::Sugg::hir(cx, &args[0], "..");
+                    let arg = sugg::Sugg::hir(cx, arg, "..");
                     let zero = sugg::Sugg::NonParen(Cow::from("0"));
                     diag.span_suggestion(
                         e.span,

clippy_lints/src/transmute/transmute_int_to_char.rs

@@ -14,7 +14,7 @@ pub(super) fn check<'tcx>(
     e: &'tcx Expr<'_>,
     from_ty: Ty<'tcx>,
     to_ty: Ty<'tcx>,
-    args: &'tcx [Expr<'_>],
+    arg: &'tcx Expr<'_>,
 ) -> bool {
     match (&from_ty.kind(), &to_ty.kind()) {
         (ty::Int(ty::IntTy::I32) | ty::Uint(ty::UintTy::U32), &ty::Char) => {
@@ -24,7 +24,7 @@ pub(super) fn check<'tcx>(
                 e.span,
                 &format!("transmute from a `{}` to a `char`", from_ty),
                 |diag| {
-                    let arg = sugg::Sugg::hir(cx, &args[0], "..");
+                    let arg = sugg::Sugg::hir(cx, arg, "..");
                     let arg = if let ty::Int(_) = from_ty.kind() {
                         arg.as_ty(ast::UintTy::U32.name_str())
                     } else {

clippy_lints/src/transmute/transmute_int_to_float.rs

@@ -13,7 +13,7 @@ pub(super) fn check<'tcx>(
     e: &'tcx Expr<'_>,
     from_ty: Ty<'tcx>,
     to_ty: Ty<'tcx>,
-    args: &'tcx [Expr<'_>],
+    arg: &'tcx Expr<'_>,
     const_context: bool,
 ) -> bool {
     match (&from_ty.kind(), &to_ty.kind()) {
@@ -24,7 +24,7 @@ pub(super) fn check<'tcx>(
                 e.span,
                 &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
                 |diag| {
-                    let arg = sugg::Sugg::hir(cx, &args[0], "..");
+                    let arg = sugg::Sugg::hir(cx, arg, "..");
                     let arg = if let ty::Int(int_ty) = from_ty.kind() {
                         arg.as_ty(format!(
                             "u{}",

clippy_lints/src/transmute/transmute_num_to_bytes.rs

@@ -13,7 +13,7 @@ pub(super) fn check<'tcx>(
     e: &'tcx Expr<'_>,
     from_ty: Ty<'tcx>,
     to_ty: Ty<'tcx>,
-    args: &'tcx [Expr<'_>],
+    arg: &'tcx Expr<'_>,
     const_context: bool,
 ) -> bool {
     match (&from_ty.kind(), &to_ty.kind()) {
@@ -33,7 +33,7 @@ pub(super) fn check<'tcx>(
                 e.span,
                 &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
                 |diag| {
-                    let arg = sugg::Sugg::hir(cx, &args[0], "..");
+                    let arg = sugg::Sugg::hir(cx, arg, "..");
                     diag.span_suggestion(
                         e.span,
                         "consider using `to_ne_bytes()`",

clippy_lints/src/transmute/transmute_ptr_to_ptr.rs

@@ -13,7 +13,7 @@ pub(super) fn check<'tcx>(
     e: &'tcx Expr<'_>,
     from_ty: Ty<'tcx>,
     to_ty: Ty<'tcx>,
-    args: &'tcx [Expr<'_>],
+    arg: &'tcx Expr<'_>,
 ) -> bool {
     match (&from_ty.kind(), &to_ty.kind()) {
         (ty::RawPtr(_), ty::RawPtr(to_ty)) => {
@@ -23,7 +23,7 @@ pub(super) fn check<'tcx>(
                 e.span,
                 "transmute from a pointer to a pointer",
                 |diag| {
-                    if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
+                    if let Some(arg) = sugg::Sugg::hir_opt(cx, arg) {
                         let sugg = arg.as_ty(cx.tcx.mk_ptr(*to_ty));
                         diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
                     }

clippy_lints/src/transmute/transmute_ptr_to_ref.rs

@@ -14,7 +14,7 @@ pub(super) fn check<'tcx>(
     e: &'tcx Expr<'_>,
     from_ty: Ty<'tcx>,
     to_ty: Ty<'tcx>,
-    args: &'tcx [Expr<'_>],
+    arg: &'tcx Expr<'_>,
     qpath: &'tcx QPath<'_>,
 ) -> bool {
     match (&from_ty.kind(), &to_ty.kind()) {
@@ -28,7 +28,7 @@ pub(super) fn check<'tcx>(
                     from_ty, to_ty
                 ),
                 |diag| {
-                    let arg = sugg::Sugg::hir(cx, &args[0], "..");
+                    let arg = sugg::Sugg::hir(cx, arg, "..");
                     let (deref, cast) = if *mutbl == Mutability::Mut {
                         ("&mut *", "*mut")
                     } else {

clippy_lints/src/transmute/transmute_ref_to_ref.rs

@@ -15,7 +15,7 @@ pub(super) fn check<'tcx>(
     e: &'tcx Expr<'_>,
     from_ty: Ty<'tcx>,
     to_ty: Ty<'tcx>,
-    args: &'tcx [Expr<'_>],
+    arg: &'tcx Expr<'_>,
     const_context: bool,
 ) -> bool {
     let mut triggered = false;
@@ -41,7 +41,7 @@ pub(super) fn check<'tcx>(
                     format!(
                         "std::str::from_utf8{}({}).unwrap()",
                         postfix,
-                        snippet(cx, args[0].span, ".."),
+                        snippet(cx, arg.span, ".."),
                     ),
                     Applicability::Unspecified,
                 );
@@ -54,7 +54,7 @@ pub(super) fn check<'tcx>(
                         TRANSMUTE_PTR_TO_PTR,
                         e.span,
                         "transmute from a reference to a reference",
-                        |diag| if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
+                        |diag| if let Some(arg) = sugg::Sugg::hir_opt(cx, arg) {
                             let ty_from_and_mut = ty::TypeAndMut {
                                 ty: ty_from,
                                 mutbl: *from_mutbl