Rollup merge of rust-lang#48221 - rkruppe:improve-ctypes-lint, r=estebank

Overhaul improper_ctypes output

This snowballed into a rather big set of improvements to the diagnostics of the improper_ctypes lint. See commits for details, including effects of each change on the `compile-fail/improper-ctypes.rs` test (now a UI test), which is pretty gnarly and hopefully not representative of real code, but covers a lot of different error cases.

Fixes rust-lang#42050

Author: Manishearth

src/librustc_lint/types.rs

@@ -37,13 +37,13 @@ struct D {
 }
 
 extern "C" {
-    fn foo(x: A); //~ ERROR found struct without foreign-function-safe
-    fn bar(x: B); //~ ERROR foreign-function-safe
+    fn foo(x: A); //~ ERROR type `A` which is not FFI-safe
+    fn bar(x: B); //~ ERROR type `A`
     fn baz(x: C);
-    fn qux(x: A2); //~ ERROR foreign-function-safe
-    fn quux(x: B2); //~ ERROR foreign-function-safe
+    fn qux(x: A2); //~ ERROR type `A`
+    fn quux(x: B2); //~ ERROR type `A`
     fn corge(x: C2);
-    fn fred(x: D); //~ ERROR foreign-function-safe
+    fn fred(x: D); //~ ERROR type `A`
 }
 
 fn main() { }

src/test/compile-fail/issue-14309.rs

@@ -13,7 +13,7 @@
 pub struct Foo;
 
 extern {
-    pub fn foo(x: (Foo)); //~ ERROR found struct without
+    pub fn foo(x: (Foo)); //~ ERROR unspecified layout
 }
 
 fn main() {

src/test/compile-fail/issue-16250.rs

@@ -16,11 +16,23 @@ enum U { A }
 enum B { C, D }
 enum T { E, F, G }
 
+#[repr(C)]
+enum ReprC { A, B, C }
+
+#[repr(u8)]
+enum U8 { A, B, C }
+
+#[repr(isize)]
+enum Isize { A, B, C }
+
 extern {
    fn zf(x: Z);
-   fn uf(x: U); //~ ERROR found enum without foreign-function-safe
-   fn bf(x: B); //~ ERROR found enum without foreign-function-safe
-   fn tf(x: T); //~ ERROR found enum without foreign-function-safe
+   fn uf(x: U); //~ ERROR enum has no representation hint
+   fn bf(x: B); //~ ERROR enum has no representation hint
+   fn tf(x: T); //~ ERROR enum has no representation hint
+   fn reprc(x: ReprC);
+   fn u8(x: U8);
+   fn isize(x: Isize);
 }
 
 pub fn main() { }

src/test/compile-fail/lint-ctypes-enum.rs

@@ -22,7 +22,7 @@ union W {
 
 extern "C" {
     static FOREIGN1: U; // OK
-    static FOREIGN2: W; //~ ERROR found union without foreign-function-safe representation
+    static FOREIGN2: W; //~ ERROR union has unspecified layout
 }
 
 fn main() {}

src/test/compile-fail/union/union-repr-c.rs

@@ -51,27 +51,27 @@ pub struct TransparentCustomZst(i32, ZeroSize);
 pub struct ZeroSizeWithPhantomData(::std::marker::PhantomData<i32>);
 
 extern {
-    pub fn ptr_type1(size: *const Foo); //~ ERROR: found struct without
-    pub fn ptr_type2(size: *const Foo); //~ ERROR: found struct without
-    pub fn slice_type(p: &[u32]); //~ ERROR: found Rust slice type
-    pub fn str_type(p: &str); //~ ERROR: found Rust type
-    pub fn box_type(p: Box<u32>); //~ ERROR found struct without
-    pub fn char_type(p: char); //~ ERROR found Rust type
-    pub fn i128_type(p: i128); //~ ERROR found Rust type
-    pub fn u128_type(p: u128); //~ ERROR found Rust type
-    pub fn trait_type(p: &Clone); //~ ERROR found Rust trait type
-    pub fn tuple_type(p: (i32, i32)); //~ ERROR found Rust tuple type
-    pub fn tuple_type2(p: I32Pair); //~ ERROR found Rust tuple type
-    pub fn zero_size(p: ZeroSize); //~ ERROR found zero-size struct
-    pub fn zero_size_phantom(p: ZeroSizeWithPhantomData); //~ ERROR found zero-sized type
+    pub fn ptr_type1(size: *const Foo); //~ ERROR: uses type `Foo`
+    pub fn ptr_type2(size: *const Foo); //~ ERROR: uses type `Foo`
+    pub fn slice_type(p: &[u32]); //~ ERROR: uses type `[u32]`
+    pub fn str_type(p: &str); //~ ERROR: uses type `str`
+    pub fn box_type(p: Box<u32>); //~ ERROR uses type `std::boxed::Box<u32>`
+    pub fn char_type(p: char); //~ ERROR uses type `char`
+    pub fn i128_type(p: i128); //~ ERROR uses type `i128`
+    pub fn u128_type(p: u128); //~ ERROR uses type `u128`
+    pub fn trait_type(p: &Clone); //~ ERROR uses type `std::clone::Clone`
+    pub fn tuple_type(p: (i32, i32)); //~ ERROR uses type `(i32, i32)`
+    pub fn tuple_type2(p: I32Pair); //~ ERROR uses type `(i32, i32)`
+    pub fn zero_size(p: ZeroSize); //~ ERROR struct has no fields
+    pub fn zero_size_phantom(p: ZeroSizeWithPhantomData); //~ ERROR composed only of PhantomData
     pub fn zero_size_phantom_toplevel()
-        -> ::std::marker::PhantomData<bool>; //~ ERROR: found zero-sized type
-    pub fn fn_type(p: RustFn); //~ ERROR found function pointer with Rust
-    pub fn fn_type2(p: fn()); //~ ERROR found function pointer with Rust
-    pub fn fn_contained(p: RustBadRet); //~ ERROR: found struct without
-    pub fn transparent_i128(p: TransparentI128); //~ ERROR: found Rust type `i128`
-    pub fn transparent_str(p: TransparentStr); //~ ERROR: found Rust type `str`
-    pub fn transparent_fn(p: TransparentBadFn); //~ ERROR: found struct without
+        -> ::std::marker::PhantomData<bool>; //~ ERROR: composed only of PhantomData
+    pub fn fn_type(p: RustFn); //~ ERROR function pointer has Rust-specific
+    pub fn fn_type2(p: fn()); //~ ERROR function pointer has Rust-specific
+    pub fn fn_contained(p: RustBadRet); //~ ERROR: uses type `std::boxed::Box<u32>`
+    pub fn transparent_i128(p: TransparentI128); //~ ERROR: uses type `i128`
+    pub fn transparent_str(p: TransparentStr); //~ ERROR: uses type `str`
+    pub fn transparent_fn(p: TransparentBadFn); //~ ERROR: uses type `std::boxed::Box<u32>`
 
     pub fn good3(fptr: Option<extern fn()>);
     pub fn good4(aptr: &[u8; 4 as usize]);

src/test/compile-fail/lint-ctypes.rs src/test/ui/lint-ctypes.rs

@@ -0,0 +1,170 @@
+error: `extern` block uses type `Foo` which is not FFI-safe: this struct has unspecified layout
+  --> $DIR/lint-ctypes.rs:54:28
+   |
+54 |     pub fn ptr_type1(size: *const Foo); //~ ERROR: uses type `Foo`
+   |                            ^^^^^^^^^^
+   |
+note: lint level defined here
+  --> $DIR/lint-ctypes.rs:11:9
+   |
+11 | #![deny(improper_ctypes)]
+   |         ^^^^^^^^^^^^^^^
+   = help: consider adding a #[repr(C)] or #[repr(transparent)] attribute to this struct
+note: type defined here
+  --> $DIR/lint-ctypes.rs:32:1
+   |
+32 | pub struct Foo;
+   | ^^^^^^^^^^^^^^^
+
+error: `extern` block uses type `Foo` which is not FFI-safe: this struct has unspecified layout
+  --> $DIR/lint-ctypes.rs:55:28
+   |
+55 |     pub fn ptr_type2(size: *const Foo); //~ ERROR: uses type `Foo`
+   |                            ^^^^^^^^^^
+   |
+   = help: consider adding a #[repr(C)] or #[repr(transparent)] attribute to this struct
+note: type defined here
+  --> $DIR/lint-ctypes.rs:32:1
+   |
+32 | pub struct Foo;
+   | ^^^^^^^^^^^^^^^
+
+error: `extern` block uses type `[u32]` which is not FFI-safe: slices have no C equivalent
+  --> $DIR/lint-ctypes.rs:56:26
+   |
+56 |     pub fn slice_type(p: &[u32]); //~ ERROR: uses type `[u32]`
+   |                          ^^^^^^
+   |
+   = help: consider using a raw pointer instead
+
+error: `extern` block uses type `str` which is not FFI-safe: string slices have no C equivalent
+  --> $DIR/lint-ctypes.rs:57:24
+   |
+57 |     pub fn str_type(p: &str); //~ ERROR: uses type `str`
+   |                        ^^^^
+   |
+   = help: consider using `*const u8` and a length instead
+
+error: `extern` block uses type `std::boxed::Box<u32>` which is not FFI-safe: this struct has unspecified layout
+  --> $DIR/lint-ctypes.rs:58:24
+   |
+58 |     pub fn box_type(p: Box<u32>); //~ ERROR uses type `std::boxed::Box<u32>`
+   |                        ^^^^^^^^
+   |
+   = help: consider adding a #[repr(C)] or #[repr(transparent)] attribute to this struct
+
+error: `extern` block uses type `char` which is not FFI-safe: the `char` type has no C equivalent
+  --> $DIR/lint-ctypes.rs:59:25
+   |
+59 |     pub fn char_type(p: char); //~ ERROR uses type `char`
+   |                         ^^^^
+   |
+   = help: consider using `u32` or `libc::wchar_t` instead
+
+error: `extern` block uses type `i128` which is not FFI-safe: 128-bit integers don't currently have a known stable ABI
+  --> $DIR/lint-ctypes.rs:60:25
+   |
+60 |     pub fn i128_type(p: i128); //~ ERROR uses type `i128`
+   |                         ^^^^
+
+error: `extern` block uses type `u128` which is not FFI-safe: 128-bit integers don't currently have a known stable ABI
+  --> $DIR/lint-ctypes.rs:61:25
+   |
+61 |     pub fn u128_type(p: u128); //~ ERROR uses type `u128`
+   |                         ^^^^
+
+error: `extern` block uses type `std::clone::Clone` which is not FFI-safe: trait objects have no C equivalent
+  --> $DIR/lint-ctypes.rs:62:26
+   |
+62 |     pub fn trait_type(p: &Clone); //~ ERROR uses type `std::clone::Clone`
+   |                          ^^^^^^
+
+error: `extern` block uses type `(i32, i32)` which is not FFI-safe: tuples have unspecified layout
+  --> $DIR/lint-ctypes.rs:63:26
+   |
+63 |     pub fn tuple_type(p: (i32, i32)); //~ ERROR uses type `(i32, i32)`
+   |                          ^^^^^^^^^^
+   |
+   = help: consider using a struct instead
+
+error: `extern` block uses type `(i32, i32)` which is not FFI-safe: tuples have unspecified layout
+  --> $DIR/lint-ctypes.rs:64:27
+   |
+64 |     pub fn tuple_type2(p: I32Pair); //~ ERROR uses type `(i32, i32)`
+   |                           ^^^^^^^
+   |
+   = help: consider using a struct instead
+
+error: `extern` block uses type `ZeroSize` which is not FFI-safe: this struct has no fields
+  --> $DIR/lint-ctypes.rs:65:25
+   |
+65 |     pub fn zero_size(p: ZeroSize); //~ ERROR struct has no fields
+   |                         ^^^^^^^^
+   |
+   = help: consider adding a member to this struct
+note: type defined here
+  --> $DIR/lint-ctypes.rs:28:1
+   |
+28 | pub struct ZeroSize;
+   | ^^^^^^^^^^^^^^^^^^^^
+
+error: `extern` block uses type `ZeroSizeWithPhantomData` which is not FFI-safe: composed only of PhantomData
+  --> $DIR/lint-ctypes.rs:66:33
+   |
+66 |     pub fn zero_size_phantom(p: ZeroSizeWithPhantomData); //~ ERROR composed only of PhantomData
+   |                                 ^^^^^^^^^^^^^^^^^^^^^^^
+
+error: `extern` block uses type `std::marker::PhantomData<bool>` which is not FFI-safe: composed only of PhantomData
+  --> $DIR/lint-ctypes.rs:68:12
+   |
+68 |         -> ::std::marker::PhantomData<bool>; //~ ERROR: composed only of PhantomData
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: `extern` block uses type `fn()` which is not FFI-safe: this function pointer has Rust-specific calling convention
+  --> $DIR/lint-ctypes.rs:69:23
+   |
+69 |     pub fn fn_type(p: RustFn); //~ ERROR function pointer has Rust-specific
+   |                       ^^^^^^
+   |
+   = help: consider using an `fn "extern"(...) -> ...` function pointer instead
+
+error: `extern` block uses type `fn()` which is not FFI-safe: this function pointer has Rust-specific calling convention
+  --> $DIR/lint-ctypes.rs:70:24
+   |
+70 |     pub fn fn_type2(p: fn()); //~ ERROR function pointer has Rust-specific
+   |                        ^^^^
+   |
+   = help: consider using an `fn "extern"(...) -> ...` function pointer instead
+
+error: `extern` block uses type `std::boxed::Box<u32>` which is not FFI-safe: this struct has unspecified layout
+  --> $DIR/lint-ctypes.rs:71:28
+   |
+71 |     pub fn fn_contained(p: RustBadRet); //~ ERROR: uses type `std::boxed::Box<u32>`
+   |                            ^^^^^^^^^^
+   |
+   = help: consider adding a #[repr(C)] or #[repr(transparent)] attribute to this struct
+
+error: `extern` block uses type `i128` which is not FFI-safe: 128-bit integers don't currently have a known stable ABI
+  --> $DIR/lint-ctypes.rs:72:32
+   |
+72 |     pub fn transparent_i128(p: TransparentI128); //~ ERROR: uses type `i128`
+   |                                ^^^^^^^^^^^^^^^
+
+error: `extern` block uses type `str` which is not FFI-safe: string slices have no C equivalent
+  --> $DIR/lint-ctypes.rs:73:31
+   |
+73 |     pub fn transparent_str(p: TransparentStr); //~ ERROR: uses type `str`
+   |                               ^^^^^^^^^^^^^^
+   |
+   = help: consider using `*const u8` and a length instead
+
+error: `extern` block uses type `std::boxed::Box<u32>` which is not FFI-safe: this struct has unspecified layout
+  --> $DIR/lint-ctypes.rs:74:30
+   |
+74 |     pub fn transparent_fn(p: TransparentBadFn); //~ ERROR: uses type `std::boxed::Box<u32>`
+   |                              ^^^^^^^^^^^^^^^^
+   |
+   = help: consider adding a #[repr(C)] or #[repr(transparent)] attribute to this struct
+
+error: aborting due to 20 previous errors
+