lint ImproperCTypes: message tweaks and refactoring from code review

niacdoial · niacdoial · commit c1898b182694 · 2024-12-03T23:57:56.000+01:00
diff --git a/compiler/rustc_lint/messages.ftl b/compiler/rustc_lint/messages.ftl
@@ -391,7 +391,7 @@ lint_improper_ctypes_pat_help = consider using the base type instead
 lint_improper_ctypes_pat_reason = pattern types have no C equivalent
 
 lint_improper_ctypes_sized_ptr_to_unsafe_type =
-    this reference (`{$ty}`) is can safely be translated into a C pointer, but `{$inner_ty}` itself is not FFI-safe
+    this reference (`{$ty}`) is ABI-compatible with a C pointer, but `{$inner_ty}` itself does not have a C layout
 
 lint_improper_ctypes_slice_help = consider using a raw pointer to the slice's first element (and a length) instead
 
@@ -419,9 +419,9 @@ lint_improper_ctypes_union_layout_help = consider adding a `#[repr(C)]` or `#[re
 lint_improper_ctypes_union_layout_reason = this union has unspecified layout
 lint_improper_ctypes_union_non_exhaustive = this union is non-exhaustive
 
-lint_improper_ctypes_unsized_box = this box for an unsized rust type contains metadata, which makes it incompatible with a C pointer
-lint_improper_ctypes_unsized_ptr = this pointer to an unsized rust type contains metadata, which makes it incompatible with a C pointer
-lint_improper_ctypes_unsized_ref = this reference to an unsized rust type contains metadata, which makes it incompatible with a C pointer
+lint_improper_ctypes_unsized_box = this box for an unsized type contains metadata, which makes it incompatible with a C pointer
+lint_improper_ctypes_unsized_ptr = this pointer to an unsized type contains metadata, which makes it incompatible with a C pointer
+lint_improper_ctypes_unsized_ref = this reference to an unsized type contains metadata, which makes it incompatible with a C pointer
 
 lint_incomplete_include =
     include macro expected single expression in source
diff --git a/compiler/rustc_lint/src/types.rs b/compiler/rustc_lint/src/types.rs
@@ -614,10 +614,10 @@ enum FfiResult<'tcx> {
 /// Determine if a type is sized or not, and wether it affects references/pointers/boxes to it
 #[derive(Clone, Copy)]
 enum TypeSizedness {
-    /// sized type (pointers are C-compatible)
-    Sized,
+    /// type of definite size (pointers are C-compatible)
+    Definite,
     /// unsized type because it includes an opaque/foreign type (pointers are C-compatible)
-    UnsizedBecauseForeign,
+    UnsizedWithExternType,
     /// unsized type for other reasons (slice, string, dyn Trait, closure, ...) (pointers are not C-compatible)
     UnsizedWithMetadata,
 }
@@ -628,13 +628,13 @@ fn get_type_sizedness<'tcx, 'a>(cx: &'a LateContext<'tcx>, ty: Ty<'tcx>) -> Type
     let tcx = cx.tcx;
 
     if ty.is_sized(tcx, cx.typing_env()) {
-        TypeSizedness::Sized
+        TypeSizedness::Definite
     } else {
         match ty.kind() {
             ty::Slice(_) => TypeSizedness::UnsizedWithMetadata,
             ty::Str => TypeSizedness::UnsizedWithMetadata,
             ty::Dynamic(..) => TypeSizedness::UnsizedWithMetadata,
-            ty::Foreign(..) => TypeSizedness::UnsizedBecauseForeign,
+            ty::Foreign(..) => TypeSizedness::UnsizedWithExternType,
             // While opaque types are checked for earlier, if a projection in a struct field
             // normalizes to an opaque type, then it will reach this branch.
             ty::Alias(ty::Opaque, ..) => todo!("We... don't know enough about this type yet?"),
@@ -668,8 +668,8 @@ fn get_type_sizedness<'tcx, 'a>(cx: &'a LateContext<'tcx>, ty: Ty<'tcx>) -> Type
                             .unwrap_or(field_ty);
                         match get_type_sizedness(cx, field_ty) {
                             s @ (TypeSizedness::UnsizedWithMetadata
-                            | TypeSizedness::UnsizedBecauseForeign) => s,
-                            TypeSizedness::Sized => {
+                            | TypeSizedness::UnsizedWithExternType) => s,
+                            TypeSizedness::Definite => {
                                 bug!("failed to find the reason why struct `{:?}` is unsized", ty)
                             }
                         }
@@ -687,16 +687,16 @@ fn get_type_sizedness<'tcx, 'a>(cx: &'a LateContext<'tcx>, ty: Ty<'tcx>) -> Type
                     .unwrap_or(field_ty);
                 match get_type_sizedness(cx, field_ty) {
                     s @ (TypeSizedness::UnsizedWithMetadata
-                    | TypeSizedness::UnsizedBecauseForeign) => s,
-                    TypeSizedness::Sized => {
+                    | TypeSizedness::UnsizedWithExternType) => s,
+                    TypeSizedness::Definite => {
                         bug!("failed to find the reason why tuple `{:?}` is unsized", ty)
                     }
                 }
             }
-            t => {
+            ty => {
                 bug!(
                     "we shouldn't be trying to determine if this is unsized for a reason or another: `{:?}`",
-                    t
+                    ty
                 )
             }
         }
@@ -1006,7 +1006,7 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
         match *ty.kind() {
             ty::Adt(def, args) => {
                 if let Some(inner_ty) = ty.boxed_ty() {
-                    if let TypeSizedness::UnsizedBecauseForeign | TypeSizedness::Sized =
+                    if let TypeSizedness::UnsizedWithExternType | TypeSizedness::Definite =
                         get_type_sizedness(self.cx, inner_ty)
                     {
                         // discussion on declaration vs definition:
@@ -1211,24 +1211,27 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
             }
 
             ty::RawPtr(inner_ty, _) | ty::Ref(_, inner_ty, _) => {
-                if let TypeSizedness::UnsizedBecauseForeign | TypeSizedness::Sized =
+                if let TypeSizedness::UnsizedWithExternType | TypeSizedness::Definite =
                     get_type_sizedness(self.cx, inner_ty)
                 {
-                    // there's a nuance on what this lint should do for function definitions
-                    // (`extern "C" fn fn_name(...) {...}`) versus declarations (`extern "C" {fn fn_name(...);}`).
-                    // (this is touched upon in https://github.com/rust-lang/rust/issues/66220
-                    // and https://github.com/rust-lang/rust/pull/72700)
+                    // there's a nuance on what this lint should do for
+                    // function definitions (`extern "C" fn fn_name(...) {...}`)
+                    // versus declarations (`unsafe extern "C" {fn fn_name(...);}`).
+                    // This is touched upon in https://github.com/rust-lang/rust/issues/66220
+                    // and https://github.com/rust-lang/rust/pull/72700
                     //
                     // The big question is: what does "ABI safety" mean? if you have something translated to a C pointer
                     // (which has a stable layout) but points to FFI-unsafe type, is it safe?
-                    // on one hand, the function's ABI will match that of a similar C-declared function API,
-                    // on the other, dereferencing the pointer in not-rust will be painful.
-                    // In this code, the opinion is split between function declarations and function definitions.
+                    // On one hand, the function's ABI will match that of a similar C-declared function API,
+                    // on the other, dereferencing the pointer on the other side of the FFI boundary will be painful.
+                    // In this code, the opinion on is split between function declarations and function definitions,
+                    // with the idea that at least one side of the FFI boundary needs to treat the pointee as an opaque type.
                     // For declarations, we see this as unsafe, but for definitions, we see this as safe.
-                    // This is mostly because, for extern function declarations, the actual definition of the function is written somewhere else,
-                    // so the fact that a pointer's pointee should be treated as opaque to one side or the other can be explicitely written out.
-                    // For extern function definitions, however, both callee and some callers can be written in rust,
-                    // so developers need to keep as much typing information as possible.
+                    //
+                    // For extern function declarations, the actual definition of the function is written somewhere else,
+                    // meaning the declaration is free to express this opaqueness with an extern type (opaque caller-side) or a std::ffi::c_void (opaque callee-side)
+                    // For extern function definitions, however, in the case where the type is opaque caller-side, it is not opaque callee-side,
+                    // and having the full type information is necessary to compile the function.
                     if matches!(self.mode, CItemKind::Definition) {
                         return FfiSafe;
                     } else if matches!(ty.kind(), ty::RawPtr(..))
diff --git a/tests/ui/lint/extern-C-fnptr-lints-slices.stderr b/tests/ui/lint/extern-C-fnptr-lints-slices.stderr
@@ -6,7 +6,7 @@ LL | pub type F = extern "C" fn(&[u8]);
    |
    = note: the function pointer to `for<'a> extern "C" fn(&'a [u8])` is FFI-unsafe due to `&[u8]`
    = help: consider using a raw pointer to the slice's first element (and a length) instead
-   = note: this reference to an unsized rust type contains metadata, which makes it incompatible with a C pointer
+   = note: this reference to an unsized type contains metadata, which makes it incompatible with a C pointer
 note: the lint level is defined here
   --> $DIR/extern-C-fnptr-lints-slices.rs:1:8
    |
diff --git a/tests/ui/lint/lint-ctypes-73249-2.stderr b/tests/ui/lint/lint-ctypes-73249-2.stderr
@@ -4,7 +4,7 @@ error: `extern` block uses type `Qux`, which is not FFI-safe
 LL |     fn lint_me() -> A<()>;
    |                     ^^^^^ not FFI-safe
    |
-   = note: this reference (`&Qux`) is can safely be translated into a C pointer, but `Qux` itself is not FFI-safe
+   = note: this reference (`&Qux`) is ABI-compatible with a C pointer, but `Qux` itself does not have a C layout
    = note: opaque types have no C equivalent
 note: the lint level is defined here
   --> $DIR/lint-ctypes-73249-2.rs:2:9
diff --git a/tests/ui/lint/lint-ctypes-cstr.stderr b/tests/ui/lint/lint-ctypes-cstr.stderr
@@ -19,7 +19,7 @@ LL |     fn take_cstr_ref(s: &CStr);
    |                         ^^^^^ not FFI-safe
    |
    = help: consider passing a `*const std::ffi::c_char` instead, and use `CStr::as_ptr()`
-   = note: this reference to an unsized rust type contains metadata, which makes it incompatible with a C pointer
+   = note: this reference to an unsized type contains metadata, which makes it incompatible with a C pointer
 
 error: `extern` block uses type `CString`, which is not FFI-safe
   --> $DIR/lint-ctypes-cstr.rs:13:24
@@ -36,7 +36,7 @@ error: `extern` block uses type `CString`, which is not FFI-safe
 LL |     fn take_cstring_ref(s: &CString);
    |                            ^^^^^^^^ not FFI-safe
    |
-   = note: this reference (`&CString`) is can safely be translated into a C pointer, but `CString` itself is not FFI-safe
+   = note: this reference (`&CString`) is ABI-compatible with a C pointer, but `CString` itself does not have a C layout
    = help: consider passing a `*const std::ffi::c_char` instead, and use `CStr::as_ptr()`
    = note: `CStr`/`CString` do not have a guaranteed layout
 
@@ -46,7 +46,7 @@ error: `extern` block uses type `CString`, which is not FFI-safe
 LL |     fn no_special_help_for_mut_cstring(s: *mut CString);
    |                                           ^^^^^^^^^^^^ not FFI-safe
    |
-   = note: this reference (`*mut CString`) is can safely be translated into a C pointer, but `CString` itself is not FFI-safe
+   = note: this reference (`*mut CString`) is ABI-compatible with a C pointer, but `CString` itself does not have a C layout
    = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this struct
    = note: this struct has unspecified layout
 
@@ -56,7 +56,7 @@ error: `extern` block uses type `CString`, which is not FFI-safe
 LL |     fn no_special_help_for_mut_cstring_ref(s: &mut CString);
    |                                               ^^^^^^^^^^^^ not FFI-safe
    |
-   = note: this reference (`&mut CString`) is can safely be translated into a C pointer, but `CString` itself is not FFI-safe
+   = note: this reference (`&mut CString`) is ABI-compatible with a C pointer, but `CString` itself does not have a C layout
    = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this struct
    = note: this struct has unspecified layout
 
@@ -67,7 +67,7 @@ LL | extern "C" fn rust_take_cstr_ref(s: &CStr) {}
    |                                     ^^^^^ not FFI-safe
    |
    = help: consider passing a `*const std::ffi::c_char` instead, and use `CStr::as_ptr()`
-   = note: this reference to an unsized rust type contains metadata, which makes it incompatible with a C pointer
+   = note: this reference to an unsized type contains metadata, which makes it incompatible with a C pointer
 note: the lint level is defined here
   --> $DIR/lint-ctypes-cstr.rs:2:26
    |
diff --git a/tests/ui/lint/lint-ctypes-fn.stderr b/tests/ui/lint/lint-ctypes-fn.stderr
@@ -5,7 +5,7 @@ LL | pub extern "C" fn slice_type(p: &[u32]) { }
    |                                 ^^^^^^ not FFI-safe
    |
    = help: consider using a raw pointer to the slice's first element (and a length) instead
-   = note: this reference to an unsized rust type contains metadata, which makes it incompatible with a C pointer
+   = note: this reference to an unsized type contains metadata, which makes it incompatible with a C pointer
 note: the lint level is defined here
   --> $DIR/lint-ctypes-fn.rs:2:9
    |
@@ -19,7 +19,7 @@ LL | pub extern "C" fn str_type(p: &str) { }
    |                               ^^^^ not FFI-safe
    |
    = help: consider using `*const u8` and a length instead
-   = note: this reference to an unsized rust type contains metadata, which makes it incompatible with a C pointer
+   = note: this reference to an unsized type contains metadata, which makes it incompatible with a C pointer
 
 error: `extern` fn uses type `Box<[u8]>`, which is not FFI-safe
   --> $DIR/lint-ctypes-fn.rs:80:34
@@ -28,7 +28,7 @@ LL | pub extern "C" fn boxed_slice(p: Box<[u8]>) { }
    |                                  ^^^^^^^^^ not FFI-safe
    |
    = help: consider using a raw pointer to the slice's first element (and a length) instead
-   = note: this box for an unsized rust type contains metadata, which makes it incompatible with a C pointer
+   = note: this box for an unsized type contains metadata, which makes it incompatible with a C pointer
 
 error: `extern` fn uses type `Box<str>`, which is not FFI-safe
   --> $DIR/lint-ctypes-fn.rs:83:35
@@ -37,15 +37,15 @@ LL | pub extern "C" fn boxed_string(p: Box<str>) { }
    |                                   ^^^^^^^^ not FFI-safe
    |
    = help: consider using `*const u8` and a length instead
-   = note: this box for an unsized rust type contains metadata, which makes it incompatible with a C pointer
+   = note: this box for an unsized type contains metadata, which makes it incompatible with a C pointer
 
 error: `extern` fn uses type `Box<dyn Trait>`, which is not FFI-safe
   --> $DIR/lint-ctypes-fn.rs:86:34
    |
 LL | pub extern "C" fn boxed_trait(p: Box<dyn Trait>) { }
    |                                  ^^^^^^^^^^^^^^ not FFI-safe
    |
-   = note: this box for an unsized rust type contains metadata, which makes it incompatible with a C pointer
+   = note: this box for an unsized type contains metadata, which makes it incompatible with a C pointer
 
 error: `extern` fn uses type `char`, which is not FFI-safe
   --> $DIR/lint-ctypes-fn.rs:89:32
@@ -158,7 +158,7 @@ LL | pub extern "C" fn transparent_str(p: TransparentStr) { }
    |                                      ^^^^^^^^^^^^^^ not FFI-safe
    |
    = help: consider using `*const u8` and a length instead
-   = note: this reference to an unsized rust type contains metadata, which makes it incompatible with a C pointer
+   = note: this reference to an unsized type contains metadata, which makes it incompatible with a C pointer
 
 error: `extern` fn uses type `PhantomData<bool>`, which is not FFI-safe
   --> $DIR/lint-ctypes-fn.rs:172:43
diff --git a/tests/ui/lint/lint-ctypes.stderr b/tests/ui/lint/lint-ctypes.stderr
@@ -4,7 +4,7 @@ error: `extern` block uses type `Foo`, which is not FFI-safe
 LL |     pub fn ptr_type1(size: *const Foo);
    |                            ^^^^^^^^^^ not FFI-safe
    |
-   = note: this reference (`*const Foo`) is can safely be translated into a C pointer, but `Foo` itself is not FFI-safe
+   = note: this reference (`*const Foo`) is ABI-compatible with a C pointer, but `Foo` itself does not have a C layout
    = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this struct
    = note: this struct has unspecified layout
 note: the type is defined here
@@ -24,7 +24,7 @@ error: `extern` block uses type `Foo`, which is not FFI-safe
 LL |     pub fn ptr_type2(size: *const Foo);
    |                            ^^^^^^^^^^ not FFI-safe
    |
-   = note: this reference (`*const Foo`) is can safely be translated into a C pointer, but `Foo` itself is not FFI-safe
+   = note: this reference (`*const Foo`) is ABI-compatible with a C pointer, but `Foo` itself does not have a C layout
    = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this struct
    = note: this struct has unspecified layout
 note: the type is defined here
@@ -39,7 +39,7 @@ error: `extern` block uses type `((),)`, which is not FFI-safe
 LL |     pub fn ptr_tuple(p: *const ((),));
    |                         ^^^^^^^^^^^^ not FFI-safe
    |
-   = note: this reference (`*const ((),)`) is can safely be translated into a C pointer, but `((),)` itself is not FFI-safe
+   = note: this reference (`*const ((),)`) is ABI-compatible with a C pointer, but `((),)` itself does not have a C layout
    = help: consider using a struct instead
    = note: tuples have unspecified layout
 
@@ -50,7 +50,7 @@ LL |     pub fn slice_type(p: &[u32]);
    |                          ^^^^^^ not FFI-safe
    |
    = help: consider using a raw pointer to the slice's first element (and a length) instead
-   = note: this reference to an unsized rust type contains metadata, which makes it incompatible with a C pointer
+   = note: this reference to an unsized type contains metadata, which makes it incompatible with a C pointer
 
 error: `extern` block uses type `&str`, which is not FFI-safe
   --> $DIR/lint-ctypes.rs:65:24
@@ -59,7 +59,7 @@ LL |     pub fn str_type(p: &str);
    |                        ^^^^ not FFI-safe
    |
    = help: consider using `*const u8` and a length instead
-   = note: this reference to an unsized rust type contains metadata, which makes it incompatible with a C pointer
+   = note: this reference to an unsized type contains metadata, which makes it incompatible with a C pointer
 
 error: `extern` block uses type `char`, which is not FFI-safe
   --> $DIR/lint-ctypes.rs:68:25
@@ -92,7 +92,7 @@ error: `extern` block uses type `&dyn Bar`, which is not FFI-safe
 LL |     pub fn trait_type(p: &dyn Bar);
    |                          ^^^^^^^^ not FFI-safe
    |
-   = note: this reference to an unsized rust type contains metadata, which makes it incompatible with a C pointer
+   = note: this reference to an unsized type contains metadata, which makes it incompatible with a C pointer
 
 error: `extern` block uses type `(i32, i32)`, which is not FFI-safe
   --> $DIR/lint-ctypes.rs:72:26
@@ -180,7 +180,7 @@ LL |     pub fn transparent_str(p: TransparentStr);
    |                               ^^^^^^^^^^^^^^ not FFI-safe
    |
    = help: consider using `*const u8` and a length instead
-   = note: this reference to an unsized rust type contains metadata, which makes it incompatible with a C pointer
+   = note: this reference to an unsized type contains metadata, which makes it incompatible with a C pointer
 
 error: `extern` block uses type `[u8; 8]`, which is not FFI-safe
   --> $DIR/lint-ctypes.rs:85:27
@@ -197,7 +197,7 @@ error: `extern` block uses type `&UnsizedStructBecauseDyn`, which is not FFI-saf
 LL |     pub fn struct_unsized_ptr_has_metadata(p: &UnsizedStructBecauseDyn);
    |                                               ^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
    |
-   = note: this reference to an unsized rust type contains metadata, which makes it incompatible with a C pointer
+   = note: this reference to an unsized type contains metadata, which makes it incompatible with a C pointer
 
 error: `extern` block uses type `Option<UnsafeCell<extern "C" fn()>>`, which is not FFI-safe
   --> $DIR/lint-ctypes.rs:90:26

Original file line number	Diff line number	Diff line change
`@@ -6,7 +6,7 @@ LL \| pub type F = extern "C" fn(&[u8]);`
`6`	`6`	`\|`
`7`	`7`	= note: the function pointer to `for<'a> extern "C" fn(&'a [u8])` is FFI-unsafe due to `&[u8]`
`8`	`8`	`= help: consider using a raw pointer to the slice's first element (and a length) instead`
`9`		`- = note: this reference to an unsized rust type contains metadata, which makes it incompatible with a C pointer`
	`9`	`+ = note: this reference to an unsized type contains metadata, which makes it incompatible with a C pointer`
`10`	`10`	`note: the lint level is defined here`
`11`	`11`	`--> $DIR/extern-C-fnptr-lints-slices.rs:1:8`
`12`	`12`	`\|`
Original file line number	Diff line number	Diff line change
@@ -4,7 +4,7 @@ error: `extern` block uses type `Qux`, which is not FFI-safe
`4`	`4`	`LL \| fn lint_me() -> A<()>;`
`5`	`5`	`\| ^^^^^ not FFI-safe`
`6`	`6`	`\|`
`7`		- = note: this reference (`&Qux`) is can safely be translated into a C pointer, but `Qux` itself is not FFI-safe
	`7`	+ = note: this reference (`&Qux`) is ABI-compatible with a C pointer, but `Qux` itself does not have a C layout
`8`	`8`	`= note: opaque types have no C equivalent`
`9`	`9`	`note: the lint level is defined here`
`10`	`10`	`--> $DIR/lint-ctypes-73249-2.rs:2:9`