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+A struct, enum, or union with the `repr(transparent)` representation hint
+contains a zero-sized field that requires non-trivial alignment.
+
+Erroneous code example:
+
+```compile_fail,E0691
+#![feature(repr_align)]
+
+#[repr(align(32))]
+struct ForceAlign32;
+
+#[repr(transparent)]
+struct Wrapper(f32, ForceAlign32); // error: zero-sized field in transparent
+                                   //        struct has alignment larger than 1
+```
+
+A transparent struct, enum, or union is supposed to be represented exactly like
+the piece of data it contains. Zero-sized fields with different alignment
+requirements potentially conflict with this property. In the example above,
+`Wrapper` would have to be aligned to 32 bytes even though `f32` has a smaller
+alignment requirement.
+
+Consider removing the over-aligned zero-sized field:
+
+```
+#[repr(transparent)]
+struct Wrapper(f32);
+```
+
+Alternatively, `PhantomData<T>` has alignment 1 for all `T`, so you can use it
+if you need to keep the field for some reason:
+
+```
+#![feature(repr_align)]
+
+use std::marker::PhantomData;
+
+#[repr(align(32))]
+struct ForceAlign32;
+
+#[repr(transparent)]
+struct Wrapper(f32, PhantomData<ForceAlign32>);
+```
+
+Note that empty arrays `[T; 0]` have the same alignment requirement as the
+element type `T`. Also note that the error is conservatively reported even when
+the alignment of the zero-sized type is less than or equal to the data field's
+alignment.