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improper ctypes: normalize return types and transparent structs #72890

Merged
merged 3 commits into from
Jun 11, 2020
Merged

improper ctypes: normalize return types and transparent structs #72890

merged 3 commits into from
Jun 11, 2020

Commits on Jun 9, 2020

  1. improper_ctypes: add test for rust-lang#66202 

    This commit adds a test of the improper ctypes lint, checking that
return type are normalized bethat return types are normalized before
being checked for FFI-safety, and that transparent newtype wrappers
are FFI-safe if the type being wrapped is FFI-safe.

Signed-off-by: David Wood <david@davidtw.co>
    @davidtwco
    davidtwco committed Jun 9, 2020
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  2. lint: check for unit ret type after normalization 

    This commit moves the check that skips unit return types to after
where the return type has been normalized - therefore ensuring that
FFI-safety lints are not emitted for types which normalize to unit.

Signed-off-by: David Wood <david@davidtw.co>
    @davidtwco
    davidtwco committed Jun 9, 2020
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  3. lint: transitive FFI-safety for transparent types 

    This commit ensures that if a `repr(transparent)` newtype's only
non-zero-sized field is FFI-safe then the newtype is also FFI-safe.

Previously, ZSTs were ignored for the purposes of linting FFI-safety
in transparent structs - thus, only the single non-ZST would be checked
for FFI-safety. However, if the non-zero-sized field is a generic
parameter, and is substituted for a ZST, then the type would be
considered FFI-unsafe (as when every field is thought to be zero-sized,
the type is considered to be "composed only of `PhantomData`" which is
FFI-unsafe).

In this commit, for transparent structs, the non-zero-sized field is
identified (before any substitutions are applied, necessarily) and then
that field's type (now with substitutions) is checked for FFI-safety
(where previously it would have been skipped for being zero-sized in
this case).

To handle the case where the non-zero-sized field is a generic
parameter, which is substituted for `()` (a ZST), and is being used
as a return type - the `FfiUnsafe` result (previously `FfiPhantom`) is
caught and silenced.

Signed-off-by: David Wood <david@davidtw.co>
    @davidtwco
    davidtwco committed Jun 9, 2020
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