Rollup merge of rust-lang#64377 - GuillaumeGomez:E0493, r=estebank

Add long error explanation for E0493

Part of rust-lang#61137.

Author: tmandry

src/librustc_mir/error_codes.rs

@@ -1128,6 +1128,51 @@ Remember this solution is unsafe! You will have to ensure that accesses to the
 cell are synchronized.
 "##,
 
+E0493: r##"
+A type with a `Drop` implementation was destructured when trying to initialize
+a static item.
+
+Erroneous code example:
+
+```compile_fail,E0493
+enum DropType {
+    A,
+}
+
+impl Drop for DropType {
+    fn drop(&mut self) {}
+}
+
+struct Foo {
+    field1: DropType,
+}
+
+static FOO: Foo = Foo { ..Foo { field1: DropType::A } }; // error!
+```
+
+The problem here is that if the given type or one of its fields implements the
+`Drop` trait, this `Drop` implementation cannot be called during the static
+type initialization which might cause a memory leak. To prevent this issue,
+you need to instantiate all the static type's fields by hand.
+
+```
+enum DropType {
+    A,
+}
+
+impl Drop for DropType {
+    fn drop(&mut self) {}
+}
+
+struct Foo {
+    field1: DropType,
+}
+
+static FOO: Foo = Foo { field1: DropType::A }; // We initialize all fields
+                                               // by hand.
+```
+"##,
+
 E0499: r##"
 A variable was borrowed as mutable more than once. Erroneous code example:
 
@@ -2454,7 +2499,6 @@ There are some known bugs that trigger this message.
 //  E0299, // mismatched types between arms
 //  E0471, // constant evaluation error (in pattern)
 //  E0385, // {} in an aliasable location
-    E0493, // destructors cannot be evaluated at compile-time
     E0521, // borrowed data escapes outside of closure
     E0526, // shuffle indices are not constant
     E0594, // cannot assign to {}

src/test/ui/check-static-values-constraints.stderr

@@ -108,5 +108,5 @@ LL |     let y = { static x: Box<isize> = box 3; x };
 
 error: aborting due to 17 previous errors
 
-Some errors have detailed explanations: E0010, E0015, E0019, E0507.
+Some errors have detailed explanations: E0010, E0015, E0019, E0493, E0507.
 For more information about an error, try `rustc --explain E0010`.

src/test/ui/consts/const-eval/const_let.stderr

@@ -24,3 +24,4 @@ LL | const Z2: () = { let mut x; x = None; x = Some(FakeNeedsDrop); };
 
 error: aborting due to 4 previous errors
 
+For more information about this error, try `rustc --explain E0493`.

src/test/ui/consts/min_const_fn/min_const_fn.stderr

@@ -324,5 +324,5 @@ LL | const fn no_fn_ptrs2() -> fn() { fn foo() {} foo }
 
 error: aborting due to 37 previous errors
 
-Some errors have detailed explanations: E0515, E0723.
-For more information about an error, try `rustc --explain E0515`.
+Some errors have detailed explanations: E0493, E0515, E0723.
+For more information about an error, try `rustc --explain E0493`.

src/test/ui/consts/miri_unleashed/feature-gate-unleash_the_miri_inside_of_you.stderr

@@ -6,3 +6,4 @@ LL |     const F: u32 = (U::X, 42).1;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0493`.

src/test/ui/span/E0493.stderr

@@ -6,3 +6,4 @@ LL | const F : Foo = (Foo { a : 0 }, Foo { a : 1 }).1;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0493`.

src/test/ui/static/static-drop-scope.stderr

@@ -68,4 +68,5 @@ LL | const EARLY_DROP_C_OPTION_CONSTANT: i32 = (HELPER, 0).1;
 
 error: aborting due to 10 previous errors
 
-For more information about this error, try `rustc --explain E0716`.
+Some errors have detailed explanations: E0493, E0716.
+For more information about an error, try `rustc --explain E0493`.