Auto merge of #8564 - Jarcho:transmute_erase_regions, r=Alexendoo

Don't lint `useless_transmute` on types with erased regions

fixes #6356
fixes #3340
fixes #2906

This should get a proper fix at some point, but this at least gets the lint running on some types.

cc #5343

changelog: Don't lint `useless_transmute` on types with erased regions

3 files changed, 60 insertions, 49 deletions

diff --git a/tests/ui/transmute.rs b/tests/ui/transmute.rs
index 5b688ce4d64..001c910239a 100644
--- a/tests/ui/transmute.rs
+++ b/tests/ui/transmute.rs
@@ -16,7 +16,8 @@ fn my_vec() -> MyVec<i32> {
 #[allow(clippy::needless_lifetimes, clippy::transmute_ptr_to_ptr)]
 #[warn(clippy::useless_transmute)]
 unsafe fn _generic<'a, T, U: 'a>(t: &'a T) {
-    let _: &'a T = core::intrinsics::transmute(t);
+    // FIXME: should lint
+    // let _: &'a T = core::intrinsics::transmute(t);
 
     let _: &'a U = core::intrinsics::transmute(t);
 
@@ -48,6 +49,22 @@ fn useless() {
 
         let _ = (1 + 1_usize) as *const usize;
     }
+
+    unsafe fn _f<'a, 'b>(x: &'a u32) -> &'b u32 {
+        std::mem::transmute(x)
+    }
+
+    unsafe fn _f2<'a, 'b>(x: *const (dyn Iterator<Item = u32> + 'a)) -> *const (dyn Iterator<Item = u32> + 'b) {
+        std::mem::transmute(x)
+    }
+
+    unsafe fn _f3<'a, 'b>(x: fn(&'a u32)) -> fn(&'b u32) {
+        std::mem::transmute(x)
+    }
+
+    unsafe fn _f4<'a, 'b>(x: std::borrow::Cow<'a, str>) -> std::borrow::Cow<'b, str> {
+        std::mem::transmute(x)
+    }
 }
 
 struct Usize(usize);
diff --git a/tests/ui/transmute.stderr b/tests/ui/transmute.stderr
index 72a386e8fa6..008b4a981d7 100644
--- a/tests/ui/transmute.stderr
+++ b/tests/ui/transmute.stderr
@@ -1,73 +1,67 @@
-error: transmute from a type (`&T`) to itself
-  --> $DIR/transmute.rs:19:20
-   |
-LL |     let _: &'a T = core::intrinsics::transmute(t);
-   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: `-D clippy::useless-transmute` implied by `-D warnings`
-
 error: transmute from a reference to a pointer
-  --> $DIR/transmute.rs:23:23
+  --> $DIR/transmute.rs:24:23
    |
 LL |     let _: *const T = core::intrinsics::transmute(t);
    |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `t as *const T`
+   |
+   = note: `-D clippy::useless-transmute` implied by `-D warnings`
 
 error: transmute from a reference to a pointer
-  --> $DIR/transmute.rs:25:21
+  --> $DIR/transmute.rs:26:21
    |
 LL |     let _: *mut T = core::intrinsics::transmute(t);
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `t as *const T as *mut T`
 
 error: transmute from a reference to a pointer
-  --> $DIR/transmute.rs:27:23
+  --> $DIR/transmute.rs:28:23
    |
 LL |     let _: *const U = core::intrinsics::transmute(t);
    |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `t as *const T as *const U`
 
 error: transmute from a type (`std::vec::Vec<i32>`) to itself
-  --> $DIR/transmute.rs:33:27
+  --> $DIR/transmute.rs:34:27
    |
 LL |         let _: Vec<i32> = core::intrinsics::transmute(my_vec());
    |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: transmute from a type (`std::vec::Vec<i32>`) to itself
-  --> $DIR/transmute.rs:35:27
+  --> $DIR/transmute.rs:36:27
    |
 LL |         let _: Vec<i32> = core::mem::transmute(my_vec());
    |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: transmute from a type (`std::vec::Vec<i32>`) to itself
-  --> $DIR/transmute.rs:37:27
+  --> $DIR/transmute.rs:38:27
    |
 LL |         let _: Vec<i32> = std::intrinsics::transmute(my_vec());
    |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: transmute from a type (`std::vec::Vec<i32>`) to itself
-  --> $DIR/transmute.rs:39:27
+  --> $DIR/transmute.rs:40:27
    |
 LL |         let _: Vec<i32> = std::mem::transmute(my_vec());
    |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: transmute from a type (`std::vec::Vec<i32>`) to itself
-  --> $DIR/transmute.rs:41:27
+  --> $DIR/transmute.rs:42:27
    |
 LL |         let _: Vec<i32> = my_transmute(my_vec());
    |                           ^^^^^^^^^^^^^^^^^^^^^^
 
 error: transmute from an integer to a pointer
-  --> $DIR/transmute.rs:43:31
+  --> $DIR/transmute.rs:44:31
    |
 LL |         let _: *const usize = std::mem::transmute(5_isize);
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `5_isize as *const usize`
 
 error: transmute from an integer to a pointer
-  --> $DIR/transmute.rs:47:31
+  --> $DIR/transmute.rs:48:31
    |
 LL |         let _: *const usize = std::mem::transmute(1 + 1usize);
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `(1 + 1usize) as *const usize`
 
 error: transmute from a type (`*const Usize`) to the type that it points to (`Usize`)
-  --> $DIR/transmute.rs:62:24
+  --> $DIR/transmute.rs:79:24
    |
 LL |         let _: Usize = core::intrinsics::transmute(int_const_ptr);
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -75,25 +69,25 @@ LL |         let _: Usize = core::intrinsics::transmute(int_const_ptr);
    = note: `-D clippy::crosspointer-transmute` implied by `-D warnings`
 
 error: transmute from a type (`*mut Usize`) to the type that it points to (`Usize`)
-  --> $DIR/transmute.rs:64:24
+  --> $DIR/transmute.rs:81:24
    |
 LL |         let _: Usize = core::intrinsics::transmute(int_mut_ptr);
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: transmute from a type (`Usize`) to a pointer to that type (`*const Usize`)
-  --> $DIR/transmute.rs:66:31
+  --> $DIR/transmute.rs:83:31
    |
 LL |         let _: *const Usize = core::intrinsics::transmute(my_int());
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: transmute from a type (`Usize`) to a pointer to that type (`*mut Usize`)
-  --> $DIR/transmute.rs:68:29
+  --> $DIR/transmute.rs:85:29
    |
 LL |         let _: *mut Usize = core::intrinsics::transmute(my_int());
    |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: transmute from a `u32` to a `char`
-  --> $DIR/transmute.rs:74:28
+  --> $DIR/transmute.rs:91:28
    |
 LL |     let _: char = unsafe { std::mem::transmute(0_u32) };
    |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::char::from_u32(0_u32).unwrap()`
@@ -101,13 +95,13 @@ LL |     let _: char = unsafe { std::mem::transmute(0_u32) };
    = note: `-D clippy::transmute-int-to-char` implied by `-D warnings`
 
 error: transmute from a `i32` to a `char`
-  --> $DIR/transmute.rs:75:28
+  --> $DIR/transmute.rs:92:28
    |
 LL |     let _: char = unsafe { std::mem::transmute(0_i32) };
    |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::char::from_u32(0_i32 as u32).unwrap()`
 
 error: transmute from a `u8` to a `bool`
-  --> $DIR/transmute.rs:84:28
+  --> $DIR/transmute.rs:101:28
    |
 LL |     let _: bool = unsafe { std::mem::transmute(0_u8) };
    |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `0_u8 != 0`
@@ -115,7 +109,7 @@ LL |     let _: bool = unsafe { std::mem::transmute(0_u8) };
    = note: `-D clippy::transmute-int-to-bool` implied by `-D warnings`
 
 error: transmute from a `u32` to a `f32`
-  --> $DIR/transmute.rs:90:31
+  --> $DIR/transmute.rs:107:31
    |
 LL |         let _: f32 = unsafe { std::mem::transmute(0_u32) };
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `f32::from_bits(0_u32)`
@@ -123,25 +117,25 @@ LL |         let _: f32 = unsafe { std::mem::transmute(0_u32) };
    = note: `-D clippy::transmute-int-to-float` implied by `-D warnings`
 
 error: transmute from a `i32` to a `f32`
-  --> $DIR/transmute.rs:91:31
+  --> $DIR/transmute.rs:108:31
    |
 LL |         let _: f32 = unsafe { std::mem::transmute(0_i32) };
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `f32::from_bits(0_i32 as u32)`
 
 error: transmute from a `u64` to a `f64`
-  --> $DIR/transmute.rs:92:31
+  --> $DIR/transmute.rs:109:31
    |
 LL |         let _: f64 = unsafe { std::mem::transmute(0_u64) };
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `f64::from_bits(0_u64)`
 
 error: transmute from a `i64` to a `f64`
-  --> $DIR/transmute.rs:93:31
+  --> $DIR/transmute.rs:110:31
    |
 LL |         let _: f64 = unsafe { std::mem::transmute(0_i64) };
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `f64::from_bits(0_i64 as u64)`
 
 error: transmute from a `u8` to a `[u8; 1]`
-  --> $DIR/transmute.rs:113:30
+  --> $DIR/transmute.rs:130:30
    |
 LL |             let _: [u8; 1] = std::mem::transmute(0u8);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0u8.to_ne_bytes()`
@@ -149,85 +143,85 @@ LL |             let _: [u8; 1] = std::mem::transmute(0u8);
    = note: `-D clippy::transmute-num-to-bytes` implied by `-D warnings`
 
 error: transmute from a `u32` to a `[u8; 4]`
-  --> $DIR/transmute.rs:114:30
+  --> $DIR/transmute.rs:131:30
    |
 LL |             let _: [u8; 4] = std::mem::transmute(0u32);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0u32.to_ne_bytes()`
 
 error: transmute from a `u128` to a `[u8; 16]`
-  --> $DIR/transmute.rs:115:31
+  --> $DIR/transmute.rs:132:31
    |
 LL |             let _: [u8; 16] = std::mem::transmute(0u128);
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0u128.to_ne_bytes()`
 
 error: transmute from a `i8` to a `[u8; 1]`
-  --> $DIR/transmute.rs:116:30
+  --> $DIR/transmute.rs:133:30
    |
 LL |             let _: [u8; 1] = std::mem::transmute(0i8);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0i8.to_ne_bytes()`
 
 error: transmute from a `i32` to a `[u8; 4]`
-  --> $DIR/transmute.rs:117:30
+  --> $DIR/transmute.rs:134:30
    |
 LL |             let _: [u8; 4] = std::mem::transmute(0i32);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0i32.to_ne_bytes()`
 
 error: transmute from a `i128` to a `[u8; 16]`
-  --> $DIR/transmute.rs:118:31
+  --> $DIR/transmute.rs:135:31
    |
 LL |             let _: [u8; 16] = std::mem::transmute(0i128);
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0i128.to_ne_bytes()`
 
 error: transmute from a `f32` to a `[u8; 4]`
-  --> $DIR/transmute.rs:119:30
+  --> $DIR/transmute.rs:136:30
    |
 LL |             let _: [u8; 4] = std::mem::transmute(0.0f32);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0.0f32.to_ne_bytes()`
 
 error: transmute from a `f64` to a `[u8; 8]`
-  --> $DIR/transmute.rs:120:30
+  --> $DIR/transmute.rs:137:30
    |
 LL |             let _: [u8; 8] = std::mem::transmute(0.0f64);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0.0f64.to_ne_bytes()`
 
 error: transmute from a `u8` to a `[u8; 1]`
-  --> $DIR/transmute.rs:125:30
+  --> $DIR/transmute.rs:142:30
    |
 LL |             let _: [u8; 1] = std::mem::transmute(0u8);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0u8.to_ne_bytes()`
 
 error: transmute from a `u32` to a `[u8; 4]`
-  --> $DIR/transmute.rs:126:30
+  --> $DIR/transmute.rs:143:30
    |
 LL |             let _: [u8; 4] = std::mem::transmute(0u32);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0u32.to_ne_bytes()`
 
 error: transmute from a `u128` to a `[u8; 16]`
-  --> $DIR/transmute.rs:127:31
+  --> $DIR/transmute.rs:144:31
    |
 LL |             let _: [u8; 16] = std::mem::transmute(0u128);
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0u128.to_ne_bytes()`
 
 error: transmute from a `i8` to a `[u8; 1]`
-  --> $DIR/transmute.rs:128:30
+  --> $DIR/transmute.rs:145:30
    |
 LL |             let _: [u8; 1] = std::mem::transmute(0i8);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0i8.to_ne_bytes()`
 
 error: transmute from a `i32` to a `[u8; 4]`
-  --> $DIR/transmute.rs:129:30
+  --> $DIR/transmute.rs:146:30
    |
 LL |             let _: [u8; 4] = std::mem::transmute(0i32);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0i32.to_ne_bytes()`
 
 error: transmute from a `i128` to a `[u8; 16]`
-  --> $DIR/transmute.rs:130:31
+  --> $DIR/transmute.rs:147:31
    |
 LL |             let _: [u8; 16] = std::mem::transmute(0i128);
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0i128.to_ne_bytes()`
 
 error: transmute from a `&[u8]` to a `&str`
-  --> $DIR/transmute.rs:140:28
+  --> $DIR/transmute.rs:157:28
    |
 LL |     let _: &str = unsafe { std::mem::transmute(B) };
    |                            ^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::str::from_utf8(B).unwrap()`
@@ -235,16 +229,16 @@ LL |     let _: &str = unsafe { std::mem::transmute(B) };
    = note: `-D clippy::transmute-bytes-to-str` implied by `-D warnings`
 
 error: transmute from a `&mut [u8]` to a `&mut str`
-  --> $DIR/transmute.rs:141:32
+  --> $DIR/transmute.rs:158:32
    |
 LL |     let _: &mut str = unsafe { std::mem::transmute(mb) };
    |                                ^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::str::from_utf8_mut(mb).unwrap()`
 
 error: transmute from a `&[u8]` to a `&str`
-  --> $DIR/transmute.rs:142:30
+  --> $DIR/transmute.rs:159:30
    |
 LL |     const _: &str = unsafe { std::mem::transmute(B) };
    |                              ^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::str::from_utf8_unchecked(B)`
 
-error: aborting due to 39 previous errors
+error: aborting due to 38 previous errors
 
diff --git a/tests/ui/transmute_undefined_repr.rs b/tests/ui/transmute_undefined_repr.rs
index b06ed4a9173..ebcaa7a84cf 100644
--- a/tests/ui/transmute_undefined_repr.rs
+++ b/tests/ui/transmute_undefined_repr.rs
@@ -1,5 +1,5 @@
 #![warn(clippy::transmute_undefined_repr)]
-#![allow(clippy::unit_arg, clippy::transmute_ptr_to_ref)]
+#![allow(clippy::unit_arg, clippy::transmute_ptr_to_ref, clippy::useless_transmute)]
 
 use core::any::TypeId;
 use core::ffi::c_void;