lints: add improper_ctypes_definitions

This commit adds a new lint - `improper_ctypes_definitions` - which
functions identically to `improper_ctypes`, but on `extern "C" fn`
definitions (as opposed to `improper_ctypes`'s `extern "C" {}`
declarations).

Signed-off-by: David Wood <david@davidtw.co>

Author: davidtwco

src/liballoc/boxed.rs

@@ -92,11 +92,13 @@
 //! pub struct Foo;
 //!
 //! #[no_mangle]
+//! #[allow(improper_ctypes_definitions)]
 //! pub extern "C" fn foo_new() -> Box<Foo> {
 //!     Box::new(Foo)
 //! }
 //!
 //! #[no_mangle]
+//! #[allow(improper_ctypes_definitions)]
 //! pub extern "C" fn foo_delete(_: Option<Box<Foo>>) {}
 //! ```
 //!

src/libpanic_abort/lib.rs

@@ -21,6 +21,7 @@
 use core::any::Any;
 
 #[rustc_std_internal_symbol]
+#[cfg_attr(not(bootstrap), allow(improper_ctypes_definitions))]
 pub unsafe extern "C" fn __rust_panic_cleanup(_: *mut u8) -> *mut (dyn Any + Send + 'static) {
     unreachable!()
 }

src/libpanic_unwind/lib.rs

@@ -81,6 +81,7 @@ extern "C" {
 mod dwarf;
 
 #[rustc_std_internal_symbol]
+#[cfg_attr(not(bootstrap), allow(improper_ctypes_definitions))]
 pub unsafe extern "C" fn __rust_panic_cleanup(payload: *mut u8) -> *mut (dyn Any + Send + 'static) {
     Box::into_raw(imp::cleanup(payload))
 }

src/librustc_lint/lib.rs

@@ -165,7 +165,8 @@ macro_rules! late_lint_mod_passes {
             $args,
             [
                 HardwiredLints: HardwiredLints,
-                ImproperCTypes: ImproperCTypes,
+                ImproperCTypesDeclarations: ImproperCTypesDeclarations,
+                ImproperCTypesDefinitions: ImproperCTypesDefinitions,
                 VariantSizeDifferences: VariantSizeDifferences,
                 BoxPointers: BoxPointers,
                 PathStatements: PathStatements,

src/librustc_lint/types.rs

@@ -498,10 +498,24 @@ declare_lint! {
     "proper use of libc types in foreign modules"
 }
 
-declare_lint_pass!(ImproperCTypes => [IMPROPER_CTYPES]);
+declare_lint_pass!(ImproperCTypesDeclarations => [IMPROPER_CTYPES]);
+
+declare_lint! {
+    IMPROPER_CTYPES_DEFINITIONS,
+    Warn,
+    "proper use of libc types in foreign item definitions"
+}
+
+declare_lint_pass!(ImproperCTypesDefinitions => [IMPROPER_CTYPES_DEFINITIONS]);
+
+enum ImproperCTypesMode {
+    Declarations,
+    Definitions,
+}
 
 struct ImproperCTypesVisitor<'a, 'tcx> {
     cx: &'a LateContext<'a, 'tcx>,
+    mode: ImproperCTypesMode,
 }
 
 enum FfiResult<'tcx> {
@@ -811,20 +825,16 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
             ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
 
             ty::FnPtr(sig) => {
-                match sig.abi() {
-                    Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic | Abi::RustCall => {
-                        return FfiUnsafe {
-                            ty,
-                            reason: "this function pointer has Rust-specific calling convention"
+                if self.is_internal_abi(sig.abi()) {
+                    return FfiUnsafe {
+                        ty,
+                        reason: "this function pointer has Rust-specific calling convention".into(),
+                        help: Some(
+                            "consider using an `extern fn(...) -> ...` \
+                                    function pointer instead"
                                 .into(),
-                            help: Some(
-                                "consider using an `extern fn(...) -> ...` \
-                                        function pointer instead"
-                                    .into(),
-                            ),
-                        };
-                    }
-                    _ => {}
+                        ),
+                    };
                 }
 
                 let sig = cx.erase_late_bound_regions(&sig);
@@ -857,15 +867,17 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
                 FfiUnsafe { ty, reason: "opaque types have no C equivalent".into(), help: None }
             }
 
-            ty::Param(..)
-            | ty::Infer(..)
+            // `extern "C" fn` functions can have type parameters, which may or may not be FFI-safe,
+            //  so they are currently ignored for the purposes of this lint.
+            ty::Param(..) | ty::Projection(..) => FfiSafe,
+
+            ty::Infer(..)
             | ty::Bound(..)
             | ty::Error(_)
             | ty::Closure(..)
             | ty::Generator(..)
             | ty::GeneratorWitness(..)
             | ty::Placeholder(..)
-            | ty::Projection(..)
             | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
         }
     }
@@ -877,9 +889,20 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
         note: &str,
         help: Option<&str>,
     ) {
-        self.cx.struct_span_lint(IMPROPER_CTYPES, sp, |lint| {
-            let mut diag =
-                lint.build(&format!("`extern` block uses type `{}`, which is not FFI-safe", ty));
+        let lint = match self.mode {
+            ImproperCTypesMode::Declarations => IMPROPER_CTYPES,
+            ImproperCTypesMode::Definitions => IMPROPER_CTYPES_DEFINITIONS,
+        };
+
+        self.cx.struct_span_lint(lint, sp, |lint| {
+            let item_description = match self.mode {
+                ImproperCTypesMode::Declarations => "block",
+                ImproperCTypesMode::Definitions => "fn",
+            };
+            let mut diag = lint.build(&format!(
+                "`extern` {} uses type `{}`, which is not FFI-safe",
+                item_description, ty
+            ));
             diag.span_label(sp, "not FFI-safe");
             if let Some(help) = help {
                 diag.help(help);
@@ -936,7 +959,7 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 
         // it is only OK to use this function because extern fns cannot have
         // any generic types right now:
-        let ty = self.cx.tcx.normalize_erasing_regions(ParamEnv::reveal_all(), ty);
+        let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
 
         // C doesn't really support passing arrays by value - the only way to pass an array by value
         // is through a struct. So, first test that the top level isn't an array, and then
@@ -986,15 +1009,22 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
         let ty = self.cx.tcx.type_of(def_id);
         self.check_type_for_ffi_and_report_errors(span, ty, true, false);
     }
+
+    fn is_internal_abi(&self, abi: Abi) -> bool {
+        if let Abi::Rust | Abi::RustCall | Abi::RustIntrinsic | Abi::PlatformIntrinsic = abi {
+            true
+        } else {
+            false
+        }
+    }
 }
 
-impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
+impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypesDeclarations {
     fn check_foreign_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::ForeignItem<'_>) {
-        let mut vis = ImproperCTypesVisitor { cx };
+        let mut vis = ImproperCTypesVisitor { cx, mode: ImproperCTypesMode::Declarations };
         let abi = cx.tcx.hir().get_foreign_abi(it.hir_id);
-        if let Abi::Rust | Abi::RustCall | Abi::RustIntrinsic | Abi::PlatformIntrinsic = abi {
-            // Don't worry about types in internal ABIs.
-        } else {
+
+        if !vis.is_internal_abi(abi) {
             match it.kind {
                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
                     vis.check_foreign_fn(it.hir_id, decl);
@@ -1008,6 +1038,31 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
     }
 }
 
+impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypesDefinitions {
+    fn check_fn(
+        &mut self,
+        cx: &LateContext<'a, 'tcx>,
+        kind: hir::intravisit::FnKind<'tcx>,
+        decl: &'tcx hir::FnDecl<'_>,
+        _: &'tcx hir::Body<'_>,
+        _: Span,
+        hir_id: hir::HirId,
+    ) {
+        use hir::intravisit::FnKind;
+
+        let abi = match kind {
+            FnKind::ItemFn(_, _, header, ..) => header.abi,
+            FnKind::Method(_, sig, ..) => sig.header.abi,
+            _ => return,
+        };
+
+        let mut vis = ImproperCTypesVisitor { cx, mode: ImproperCTypesMode::Definitions };
+        if !vis.is_internal_abi(abi) {
+            vis.check_foreign_fn(hir_id, decl);
+        }
+    }
+}
+
 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
 
 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {

src/librustc_llvm/lib.rs

@@ -15,6 +15,7 @@ pub struct RustString {
 
 /// Appending to a Rust string -- used by RawRustStringOstream.
 #[no_mangle]
+#[cfg_attr(not(bootstrap), allow(improper_ctypes_definitions))]
 pub unsafe extern "C" fn LLVMRustStringWriteImpl(
     sr: &RustString,
     ptr: *const c_char,

src/test/ui/abi/abi-sysv64-register-usage.rs

@@ -38,6 +38,7 @@ pub struct LargeStruct(i64, i64, i64, i64, i64, i64, i64, i64);
 
 #[cfg(target_arch = "x86_64")]
 #[inline(never)]
+#[allow(improper_ctypes_definitions)]
 pub extern "sysv64" fn large_struct_by_val(mut foo: LargeStruct) -> LargeStruct {
     foo.0 *= 1;
     foo.1 *= 2;

src/test/ui/align-with-extern-c-fn.rs

@@ -10,6 +10,7 @@
 #[repr(align(16))]
 pub struct A(i64);
 
+#[allow(improper_ctypes_definitions)]
 pub extern "C" fn foo(x: A) {}
 
 fn main() {

src/test/ui/issues/issue-16441.rs

@@ -5,6 +5,7 @@
 struct Empty;
 
 // This used to cause an ICE
+#[allow(improper_ctypes_definitions)]
 extern "C" fn ice(_a: Empty) {}
 
 fn main() {

src/test/ui/issues/issue-26997.rs

@@ -6,6 +6,7 @@ pub struct Foo {
 }
 
 impl Foo {
+    #[allow(improper_ctypes_definitions)]
     pub extern fn foo_new() -> Foo {
         Foo { x: 21, y: 33 }
     }