Rollup merge of #65591 - GuillaumeGomez:long-err-explanation-E0588, r=Dylan-DPC

Add long error explanation for E0588

Part of #61137.

r? @kinnison

Author: JohnTitor

src/librustc_typeck/error_codes.rs

@@ -194,7 +194,7 @@ a guard.
 ```compile_fail,E0029
 let string = "salutations !";
 
-// The ordering relation for strings can't be evaluated at compile time,
+// The ordering relation for strings cannot be evaluated at compile time,
 // so this doesn't work:
 match string {
     "hello" ..= "world" => {}
@@ -348,7 +348,7 @@ fn main() {
 "##,
 
 E0044: r##"
-You can't use type or const parameters on foreign items.
+You cannot use type or const parameters on foreign items.
 Example of erroneous code:
 
 ```compile_fail,E0044
@@ -788,7 +788,7 @@ fn some_other_func() {}
 fn some_function() {
     SOME_CONST = 14; // error : a constant value cannot be changed!
     1 = 3; // error : 1 isn't a valid place!
-    some_other_func() = 4; // error : we can't assign value to a function!
+    some_other_func() = 4; // error : we cannot assign value to a function!
     SomeStruct.x = 12; // error : SomeStruct a structure name but it is used
                        // like a variable!
 }
@@ -3891,6 +3891,33 @@ details.
 [issue #33685]: https://github.com/rust-lang/rust/issues/33685
 "##,
 
+E0588: r##"
+A type with `packed` representation hint has a field with `align`
+representation hint.
+
+Erroneous code example:
+
+```compile_fail,E0588
+#[repr(align(16))]
+struct Aligned(i32);
+
+#[repr(packed)] // error!
+struct Packed(Aligned);
+```
+
+Just like you cannot have both `align` and `packed` representation hints on a
+same type, a `packed` type cannot contain another type with the `align`
+representation hint. However, you can do the opposite:
+
+```
+#[repr(packed)]
+struct Packed(i32);
+
+#[repr(align(16))] // ok!
+struct Aligned(Packed);
+```
+"##,
+
 E0592: r##"
 This error occurs when you defined methods or associated functions with same
 name.
@@ -4299,7 +4326,7 @@ extern {
 
 unsafe {
     printf(::std::ptr::null(), 0f32);
-    // error: can't pass an `f32` to variadic function, cast to `c_double`
+    // error: cannot pass an `f32` to variadic function, cast to `c_double`
 }
 ```
 
@@ -5000,7 +5027,7 @@ the future, [RFC 2091] prohibits their implementation without a follow-up RFC.
 //  E0174,
 //  E0182, // merged into E0229
     E0183,
-//  E0187, // can't infer the kind of the closure
+//  E0187, // cannot infer the kind of the closure
 //  E0188, // can not cast an immutable reference to a mutable pointer
 //  E0189, // deprecated: can only cast a boxed pointer to a boxed object
 //  E0190, // deprecated: can only cast a &-pointer to an &-object
@@ -5047,7 +5074,6 @@ the future, [RFC 2091] prohibits their implementation without a follow-up RFC.
 //  E0564, // only named lifetimes are allowed in `impl Trait`,
            // but `{}` was found in the type `{}`
     E0587, // type has conflicting packed and align representation hints
-    E0588, // packed type cannot transitively contain a `[repr(align)]` type
 //  E0611, // merged into E0616
 //  E0612, // merged into E0609
 //  E0613, // Removed (merged with E0609)

src/test/ui/repr/repr-packed-contains-align.stderr

@@ -56,3 +56,4 @@ LL | | }
 
 error: aborting due to 8 previous errors
 
+For more information about this error, try `rustc --explain E0588`.