Auto merge of #108611 - davidtwco:issue-94223-external-abi-fn-ptr-in-internal-abi-fn, r=jackh726

lint/ctypes: ext. abi fn-ptr in internal abi fn

Fixes #94223.

- In the improper ctypes lint, instead of skipping functions with internal ABIs, check that the signature doesn't contain any fn-ptr types with external ABIs that aren't FFI-safe.
- When computing the ABI for fn-ptr types, remove an `unwrap` that assumed FFI-safe types in foreign fn-ptr types.
  - I'm not certain that this is the correct approach.

tests/ui/abi/foreign/foreign-fn-with-byval.rs

@@ -1,5 +1,5 @@
 // run-pass
-#![allow(improper_ctypes)]
+#![allow(improper_ctypes, improper_ctypes_definitions)]
 
 // ignore-wasm32-bare no libc to test ffi with
 

tests/ui/abi/issue-94223.rs

@@ -0,0 +1,8 @@
+// check-pass
+#![allow(improper_ctypes_definitions)]
+#![crate_type = "lib"]
+
+// Check that computing the fn abi for `bad`, with a external ABI fn ptr that is not FFI-safe, does
+// not ICE.
+
+pub fn bad(f: extern "C" fn([u8])) {}

tests/ui/hashmap/hashmap-memory.rs

@@ -1,5 +1,6 @@
 // run-pass
 
+#![allow(improper_ctypes_definitions)]
 #![allow(non_camel_case_types)]
 #![allow(dead_code)]
 #![allow(unused_mut)]

tests/ui/lint/lint-ctypes-94223.rs

@@ -0,0 +1,42 @@
+#![crate_type = "lib"]
+#![deny(improper_ctypes_definitions)]
+
+pub fn bad(f: extern "C" fn([u8])) {}
+//~^ ERROR `extern` fn uses type `[u8]`, which is not FFI-safe
+
+pub fn bad_twice(f: Result<extern "C" fn([u8]), extern "C" fn([u8])>) {}
+//~^ ERROR `extern` fn uses type `[u8]`, which is not FFI-safe
+//~^^ ERROR `extern` fn uses type `[u8]`, which is not FFI-safe
+
+struct BadStruct(extern "C" fn([u8]));
+//~^ ERROR `extern` fn uses type `[u8]`, which is not FFI-safe
+
+enum BadEnum {
+    A(extern "C" fn([u8])),
+    //~^ ERROR `extern` fn uses type `[u8]`, which is not FFI-safe
+}
+
+enum BadUnion {
+    A(extern "C" fn([u8])),
+    //~^ ERROR `extern` fn uses type `[u8]`, which is not FFI-safe
+}
+
+type Foo = extern "C" fn([u8]);
+//~^ ERROR `extern` fn uses type `[u8]`, which is not FFI-safe
+
+pub struct FfiUnsafe;
+
+#[allow(improper_ctypes_definitions)]
+extern "C" fn f(_: FfiUnsafe) {
+    unimplemented!()
+}
+
+pub static BAD: extern "C" fn(FfiUnsafe) = f;
+//~^ ERROR `extern` fn uses type `FfiUnsafe`, which is not FFI-safe
+
+pub static BAD_TWICE: Result<extern "C" fn(FfiUnsafe), extern "C" fn(FfiUnsafe)> = Ok(f);
+//~^ ERROR `extern` fn uses type `FfiUnsafe`, which is not FFI-safe
+//~^^ ERROR `extern` fn uses type `FfiUnsafe`, which is not FFI-safe
+
+pub const BAD_CONST: extern "C" fn(FfiUnsafe) = f;
+//~^ ERROR `extern` fn uses type `FfiUnsafe`, which is not FFI-safe

tests/ui/lint/lint-ctypes-94223.stderr

@@ -0,0 +1,126 @@
+error: `extern` fn uses type `[u8]`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:4:15
+   |
+LL | pub fn bad(f: extern "C" fn([u8])) {}
+   |               ^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider using a raw pointer instead
+   = note: slices have no C equivalent
+note: the lint level is defined here
+  --> $DIR/lint-ctypes-94223.rs:2:9
+   |
+LL | #![deny(improper_ctypes_definitions)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: `extern` fn uses type `[u8]`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:7:28
+   |
+LL | pub fn bad_twice(f: Result<extern "C" fn([u8]), extern "C" fn([u8])>) {}
+   |                            ^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider using a raw pointer instead
+   = note: slices have no C equivalent
+
+error: `extern` fn uses type `[u8]`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:7:49
+   |
+LL | pub fn bad_twice(f: Result<extern "C" fn([u8]), extern "C" fn([u8])>) {}
+   |                                                 ^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider using a raw pointer instead
+   = note: slices have no C equivalent
+
+error: `extern` fn uses type `[u8]`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:11:18
+   |
+LL | struct BadStruct(extern "C" fn([u8]));
+   |                  ^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider using a raw pointer instead
+   = note: slices have no C equivalent
+
+error: `extern` fn uses type `[u8]`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:15:7
+   |
+LL |     A(extern "C" fn([u8])),
+   |       ^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider using a raw pointer instead
+   = note: slices have no C equivalent
+
+error: `extern` fn uses type `[u8]`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:20:7
+   |
+LL |     A(extern "C" fn([u8])),
+   |       ^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider using a raw pointer instead
+   = note: slices have no C equivalent
+
+error: `extern` fn uses type `[u8]`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:24:12
+   |
+LL | type Foo = extern "C" fn([u8]);
+   |            ^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider using a raw pointer instead
+   = note: slices have no C equivalent
+
+error: `extern` fn uses type `FfiUnsafe`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:34:17
+   |
+LL | pub static BAD: extern "C" fn(FfiUnsafe) = f;
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = 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
+  --> $DIR/lint-ctypes-94223.rs:27:1
+   |
+LL | pub struct FfiUnsafe;
+   | ^^^^^^^^^^^^^^^^^^^^
+
+error: `extern` fn uses type `FfiUnsafe`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:37:30
+   |
+LL | pub static BAD_TWICE: Result<extern "C" fn(FfiUnsafe), extern "C" fn(FfiUnsafe)> = Ok(f);
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = 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
+  --> $DIR/lint-ctypes-94223.rs:27:1
+   |
+LL | pub struct FfiUnsafe;
+   | ^^^^^^^^^^^^^^^^^^^^
+
+error: `extern` fn uses type `FfiUnsafe`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:37:56
+   |
+LL | pub static BAD_TWICE: Result<extern "C" fn(FfiUnsafe), extern "C" fn(FfiUnsafe)> = Ok(f);
+   |                                                        ^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = 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
+  --> $DIR/lint-ctypes-94223.rs:27:1
+   |
+LL | pub struct FfiUnsafe;
+   | ^^^^^^^^^^^^^^^^^^^^
+
+error: `extern` fn uses type `FfiUnsafe`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:41:22
+   |
+LL | pub const BAD_CONST: extern "C" fn(FfiUnsafe) = f;
+   |                      ^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = 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
+  --> $DIR/lint-ctypes-94223.rs:27:1
+   |
+LL | pub struct FfiUnsafe;
+   | ^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 11 previous errors
+