rust-lang · oli-obk · Aug 30, 2019
diff --git a/src/librustc_mir/transform/qualify_consts.rs b/src/librustc_mir/transform/qualify_consts.rs
@@ -1321,14 +1321,15 @@ impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
                                 // special intrinsic that can be called diretly without an intrinsic
                                 // feature gate needs a language feature gate
                                 "transmute" => {
-                                    if self.mode.requires_const_checking() {
-                                        // const eval transmute calls only with the feature gate
+                                    if let Mode::ConstFn = self.mode {
+                                        // permit transmute calls in const fns only with the feature
+                                        // gate. Anywhere else they are fine
                                         if !self.tcx.features().const_transmute {
                                             emit_feature_err(
                                                 &self.tcx.sess.parse_sess, sym::const_transmute,
                                                 self.span, GateIssue::Language,
                                                 &format!("The use of std::mem::transmute() \
-                                                is gated in {}s", self.mode));
+                                                is gated in const fns"));
                                         }
                                     }
                                 }

diff --git a/src/test/ui/consts/const-eval/double_check.rs b/src/test/ui/consts/const-eval/double_check.rs
@@ -19,4 +19,6 @@ static FOO: (&Foo, &Bar) = unsafe {(
     Union { u8: &BAR }.bar,
 )};
 
+static FOO2: (&Foo, &Bar) = unsafe {(std::mem::transmute(&BAR), std::mem::transmute(&BAR))};
+
 fn main() {}
diff --git a/src/test/ui/consts/const-eval/double_check2.rs b/src/test/ui/consts/const-eval/double_check2.rs
@@ -16,5 +16,7 @@ static FOO: (&Foo, &Bar) = unsafe {( //~ undefined behavior
     Union { u8: &BAR }.foo,
     Union { u8: &BAR }.bar,
 )};
+static FOO2: (&Foo, &Bar) = unsafe {(std::mem::transmute(&BAR), std::mem::transmute(&BAR))};
+//~^ undefined behavior
 
 fn main() {}
diff --git a/src/test/ui/consts/const-eval/double_check2.stderr b/src/test/ui/consts/const-eval/double_check2.stderr
@@ -9,6 +9,14 @@ LL | | )};
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
-error: aborting due to previous error
+error[E0080]: it is undefined behavior to use this value
+  --> $DIR/double_check2.rs:19:1
+   |
+LL | static FOO2: (&Foo, &Bar) = unsafe {(std::mem::transmute(&BAR), std::mem::transmute(&BAR))};
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 5 at .1.<deref>, but expected a valid enum discriminant
+   |
+   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0080`.
diff --git a/src/test/ui/consts/const-eval/ub-enum.rs b/src/test/ui/consts/const-eval/ub-enum.rs
@@ -18,16 +18,26 @@ union TransmuteEnum {
 }
 
 const GOOD_ENUM: Enum = unsafe { TransmuteEnum { in2: 0 }.out1 };
+const GOOD_ENUM_TRANSMUTE: Enum = unsafe { std::mem::transmute(0usize) };
 
 const BAD_ENUM: Enum = unsafe { TransmuteEnum { in2: 1 }.out1 };
 //~^ ERROR is undefined behavior
 
+const BAD_ENUM_TRANSMUTE: Enum = unsafe { std::mem::transmute(1usize) };
+//~^ ERROR is undefined behavior
+
 const BAD_ENUM_PTR: Enum = unsafe { TransmuteEnum { in1: &1 }.out1 };
 //~^ ERROR is undefined behavior
 
+const BAD_ENUM_PTR_TRANSMUTE: Enum = unsafe { std::mem::transmute(&1) };
+//~^ ERROR is undefined behavior
+
 const BAD_ENUM_WRAPPED: Wrap<Enum> = unsafe { TransmuteEnum { in1: &1 }.out2 };
 //~^ ERROR is undefined behavior
 
+const BAD_ENUM_WRAPPED_TRANSMUTE: Wrap<Enum> = unsafe { std::mem::transmute(&1) };
+//~^ ERROR is undefined behavior
+
 // (Potentially) invalid enum discriminant
 #[repr(usize)]
 #[derive(Copy, Clone)]
@@ -45,10 +55,16 @@ union TransmuteEnum2 {
 }
 const BAD_ENUM2: Enum2 = unsafe { TransmuteEnum2 { in1: 0 }.out1 };
 //~^ ERROR is undefined behavior
+const BAD_ENUM2_TRANSMUTE: Enum2 = unsafe { std::mem::transmute(0usize) };
+//~^ ERROR is undefined behavior
 const BAD_ENUM2_PTR: Enum2 = unsafe { TransmuteEnum2 { in2: &0 }.out1 };
 //~^ ERROR is undefined behavior
+const BAD_ENUM2_PTR_TRANSMUTE: Enum2 = unsafe { std::mem::transmute(&0) };
+//~^ ERROR is undefined behavior
 const BAD_ENUM2_WRAPPED: Wrap<Enum2> = unsafe { TransmuteEnum2 { in2: &0 }.out2 };
 //~^ ERROR is undefined behavior
+const BAD_ENUM2_WRAPPED_TRANSMUTE: Wrap<Enum2> = unsafe { std::mem::transmute(&0) };
+//~^ ERROR is undefined behavior
 
 // Undef enum discriminant.
 const BAD_ENUM2_UNDEF : Enum2 = unsafe { TransmuteEnum2 { in3: () }.out1 };
@@ -57,6 +73,8 @@ const BAD_ENUM2_UNDEF : Enum2 = unsafe { TransmuteEnum2 { in3: () }.out1 };
 // Pointer value in an enum with a niche that is not just 0.
 const BAD_ENUM2_OPTION_PTR: Option<Enum2> = unsafe { TransmuteEnum2 { in2: &0 }.out3 };
 //~^ ERROR is undefined behavior
+const BAD_ENUM2_OPTION_PTR_TRANSMUTE: Option<Enum2> = unsafe { std::mem::transmute(&0) };
+//~^ ERROR is undefined behavior
 
 // Invalid enum field content (mostly to test printing of paths for enum tuple
 // variants and tuples).
@@ -67,6 +85,9 @@ union TransmuteChar {
 // Need to create something which does not clash with enum layout optimizations.
 const BAD_OPTION_CHAR: Option<(char, char)> = Some(('x', unsafe { TransmuteChar { a: !0 }.b }));
 //~^ ERROR is undefined behavior
+const BAD_OPTION_CHAR_TRANSMUTE: Option<(char, char)> =
+    Some(('x', unsafe { std::mem::transmute(!0) }));
+//~^^ ERROR is undefined behavior
 
 fn main() {
 }
diff --git a/src/test/ui/consts/const-eval/ub-enum.stderr b/src/test/ui/consts/const-eval/ub-enum.stderr
@@ -1,75 +1,140 @@
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:22:1
+  --> $DIR/ub-enum.rs:23:1
    |
 LL | const BAD_ENUM: Enum = unsafe { TransmuteEnum { in2: 1 }.out1 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 1, but expected a valid enum discriminant
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:25:1
+  --> $DIR/ub-enum.rs:26:1
+   |
+LL | const BAD_ENUM_TRANSMUTE: Enum = unsafe { std::mem::transmute(1usize) };
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 1, but expected a valid enum discriminant
+   |
+   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
+
+error[E0080]: it is undefined behavior to use this value
+  --> $DIR/ub-enum.rs:29:1
    |
 LL | const BAD_ENUM_PTR: Enum = unsafe { TransmuteEnum { in1: &1 }.out1 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected a valid enum discriminant
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:28:1
+  --> $DIR/ub-enum.rs:32:1
+   |
+LL | const BAD_ENUM_PTR_TRANSMUTE: Enum = unsafe { std::mem::transmute(&1) };
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected a valid enum discriminant
+   |
+   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
+
+error[E0080]: it is undefined behavior to use this value
+  --> $DIR/ub-enum.rs:35:1
    |
 LL | const BAD_ENUM_WRAPPED: Wrap<Enum> = unsafe { TransmuteEnum { in1: &1 }.out2 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected something that cannot possibly fail to be equal to 0
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:46:1
+  --> $DIR/ub-enum.rs:38:1
+   |
+LL | const BAD_ENUM_WRAPPED_TRANSMUTE: Wrap<Enum> = unsafe { std::mem::transmute(&1) };
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected something that cannot possibly fail to be equal to 0
+   |
+   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
+
+error[E0080]: it is undefined behavior to use this value
+  --> $DIR/ub-enum.rs:56:1
    |
 LL | const BAD_ENUM2: Enum2 = unsafe { TransmuteEnum2 { in1: 0 }.out1 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 0, but expected a valid enum discriminant
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:48:1
+  --> $DIR/ub-enum.rs:58:1
+   |
+LL | const BAD_ENUM2_TRANSMUTE: Enum2 = unsafe { std::mem::transmute(0usize) };
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 0, but expected a valid enum discriminant
+   |
+   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
+
+error[E0080]: it is undefined behavior to use this value
+  --> $DIR/ub-enum.rs:60:1
    |
 LL | const BAD_ENUM2_PTR: Enum2 = unsafe { TransmuteEnum2 { in2: &0 }.out1 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected a valid enum discriminant
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:50:1
+  --> $DIR/ub-enum.rs:62:1
+   |
+LL | const BAD_ENUM2_PTR_TRANSMUTE: Enum2 = unsafe { std::mem::transmute(&0) };
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected a valid enum discriminant
+   |
+   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
+
+error[E0080]: it is undefined behavior to use this value
+  --> $DIR/ub-enum.rs:64:1
    |
 LL | const BAD_ENUM2_WRAPPED: Wrap<Enum2> = unsafe { TransmuteEnum2 { in2: &0 }.out2 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected something that cannot possibly fail to be equal to 2
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:54:1
+  --> $DIR/ub-enum.rs:66:1
+   |
+LL | const BAD_ENUM2_WRAPPED_TRANSMUTE: Wrap<Enum2> = unsafe { std::mem::transmute(&0) };
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected something that cannot possibly fail to be equal to 2
+   |
+   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
+
+error[E0080]: it is undefined behavior to use this value
+  --> $DIR/ub-enum.rs:70:1
    |
 LL | const BAD_ENUM2_UNDEF : Enum2 = unsafe { TransmuteEnum2 { in3: () }.out1 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized bytes, but expected a valid enum discriminant
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:58:1
+  --> $DIR/ub-enum.rs:74:1
    |
 LL | const BAD_ENUM2_OPTION_PTR: Option<Enum2> = unsafe { TransmuteEnum2 { in2: &0 }.out3 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected a valid enum discriminant
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:68:1
+  --> $DIR/ub-enum.rs:76:1
+   |
+LL | const BAD_ENUM2_OPTION_PTR_TRANSMUTE: Option<Enum2> = unsafe { std::mem::transmute(&0) };
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected a valid enum discriminant
+   |
+   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
+
+error[E0080]: it is undefined behavior to use this value
+  --> $DIR/ub-enum.rs:86:1
    |
 LL | const BAD_OPTION_CHAR: Option<(char, char)> = Some(('x', unsafe { TransmuteChar { a: !0 }.b }));
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 4294967295 at .<downcast-variant(Some)>.0.1, but expected something less or equal to 1114111
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
-error: aborting due to 9 previous errors
+error[E0080]: it is undefined behavior to use this value
+  --> $DIR/ub-enum.rs:88:1
+   |
+LL | / const BAD_OPTION_CHAR_TRANSMUTE: Option<(char, char)> =
+LL | |     Some(('x', unsafe { std::mem::transmute(!0) }));
+   | |____________________________________________________^ type validation failed: encountered 4294967295 at .<downcast-variant(Some)>.0.1, but expected something less or equal to 1114111
+   |
+   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
+
+error: aborting due to 17 previous errors
 
 For more information about this error, try `rustc --explain E0080`.
diff --git a/src/test/ui/feature-gates/feature-gate-const_transmute.rs b/src/test/ui/feature-gates/feature-gate-const_transmute.rs
@@ -1,9 +1,13 @@
+#![feature(const_fn)]
+
 use std::mem;
 
 #[repr(transparent)]
 struct Foo(u32);
 
 const TRANSMUTED_U32: u32 = unsafe { mem::transmute(Foo(3)) };
-//~^ ERROR The use of std::mem::transmute() is gated in constants
+
+const fn transmute_fn() -> u32 { unsafe { mem::transmute(Foo(3)) } }
+//~^ ERROR The use of std::mem::transmute() is gated in const fns
 
 fn main() {}
diff --git a/src/test/ui/feature-gates/feature-gate-const_transmute.stderr b/src/test/ui/feature-gates/feature-gate-const_transmute.stderr
@@ -1,8 +1,8 @@
-error[E0658]: The use of std::mem::transmute() is gated in constants
-  --> $DIR/feature-gate-const_transmute.rs:6:38
+error[E0658]: The use of std::mem::transmute() is gated in const fns
+  --> $DIR/feature-gate-const_transmute.rs:10:43
    |
-LL | const TRANSMUTED_U32: u32 = unsafe { mem::transmute(Foo(3)) };
-   |                                      ^^^^^^^^^^^^^^^^^^^^^^
+LL | const fn transmute_fn() -> u32 { unsafe { mem::transmute(Foo(3)) } }
+   |                                           ^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: for more information, see /~https://github.com/rust-lang/rust/issues/53605
    = help: add `#![feature(const_transmute)]` to the crate attributes to enable