Add [extern_without_abi] lint

CHANGELOG.md

@@ -5456,6 +5456,7 @@ Released 2018-09-13
 [`explicit_write`]: https://rust-lang.github.io/rust-clippy/master/index.html#explicit_write
 [`extend_from_slice`]: https://rust-lang.github.io/rust-clippy/master/index.html#extend_from_slice
 [`extend_with_drain`]: https://rust-lang.github.io/rust-clippy/master/index.html#extend_with_drain
+[`extern_without_abi`]: https://rust-lang.github.io/rust-clippy/master/index.html#extern_without_abi
 [`extra_unused_lifetimes`]: https://rust-lang.github.io/rust-clippy/master/index.html#extra_unused_lifetimes
 [`extra_unused_type_parameters`]: https://rust-lang.github.io/rust-clippy/master/index.html#extra_unused_type_parameters
 [`fallible_impl_from`]: https://rust-lang.github.io/rust-clippy/master/index.html#fallible_impl_from

clippy_lints/src/declared_lints.rs

@@ -173,6 +173,7 @@ pub static LINTS: &[&crate::LintInfo] = &[
     crate::exhaustive_items::EXHAUSTIVE_STRUCTS_INFO,
     crate::exit::EXIT_INFO,
     crate::explicit_write::EXPLICIT_WRITE_INFO,
+    crate::extern_without_abi::EXTERN_WITHOUT_ABI_INFO,
     crate::extra_unused_type_parameters::EXTRA_UNUSED_TYPE_PARAMETERS_INFO,
     crate::fallible_impl_from::FALLIBLE_IMPL_FROM_INFO,
     crate::field_scoped_visibility_modifiers::FIELD_SCOPED_VISIBILITY_MODIFIERS_INFO,

clippy_lints/src/extern_without_abi.rs

@@ -0,0 +1,61 @@
+use clippy_utils::diagnostics::span_lint;
+use rustc_ast::visit::FnKind;
+use rustc_ast::{Extern, FnHeader, FnSig, ForeignMod, Item, ItemKind, NodeId};
+use rustc_lint::{EarlyContext, EarlyLintPass};
+use rustc_session::declare_lint_pass;
+use rustc_span::Span;
+
+const LINT_MSG: &str = "`extern` missing explicit ABI";
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for usage of `extern` without an explicit ABI.
+    ///
+    /// ### Why is this bad?
+    /// Explicitly declaring the ABI improves readability.
+    //
+    /// ### Example
+    /// ```no_run
+    /// extern fn foo() {}
+    ///
+    /// extern {
+    ///     fn bar();
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// extern "C" fn foo() {}
+    ///
+    /// extern "C" {
+    ///     fn bar();
+    /// }
+    /// ```
+    #[clippy::version = "1.83.0"]
+    pub EXTERN_WITHOUT_ABI,
+    style,
+    "`extern` missing explicit ABI"
+}
+
+declare_lint_pass!(ExternWithoutAbi => [EXTERN_WITHOUT_ABI]);
+
+impl EarlyLintPass for ExternWithoutAbi {
+    fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
+        if let ItemKind::ForeignMod(ref foreign_mod) = item.kind
+            && let ForeignMod { abi: None, .. } = foreign_mod
+        {
+            span_lint(cx, EXTERN_WITHOUT_ABI, item.span, LINT_MSG);
+        }
+    }
+
+    fn check_fn(&mut self, cx: &EarlyContext<'_>, kind: FnKind<'_>, _: Span, _: NodeId) {
+        if let FnKind::Fn(_, _, sig, ..) = kind
+            && let FnSig { header, .. } = sig
+            && let FnHeader {
+                ext: Extern::Implicit(span),
+                ..
+            } = header
+        {
+            span_lint(cx, EXTERN_WITHOUT_ABI, *span, LINT_MSG);
+        }
+    }
+}

clippy_lints/src/lib.rs

@@ -135,6 +135,7 @@ mod excessive_nesting;
 mod exhaustive_items;
 mod exit;
 mod explicit_write;
+mod extern_without_abi;
 mod extra_unused_type_parameters;
 mod fallible_impl_from;
 mod field_scoped_visibility_modifiers;
@@ -942,5 +943,6 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     store.register_late_pass(move |_| Box::new(manual_div_ceil::ManualDivCeil::new(conf)));
     store.register_late_pass(|_| Box::new(manual_is_power_of_two::ManualIsPowerOfTwo));
     store.register_late_pass(|_| Box::new(non_zero_suggestions::NonZeroSuggestions));
+    store.register_early_pass(|| Box::new(extern_without_abi::ExternWithoutAbi));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }

tests/ui/boxed_local.rs

@@ -1,5 +1,6 @@
 #![allow(
     clippy::borrowed_box,
+    clippy::extern_without_abi,
     clippy::needless_pass_by_value,
     clippy::unused_unit,
     clippy::redundant_clone,

tests/ui/boxed_local.stderr

@@ -1,5 +1,5 @@
 error: local variable doesn't need to be boxed here
-  --> tests/ui/boxed_local.rs:39:13
+  --> tests/ui/boxed_local.rs:40:13
    |
 LL | fn warn_arg(x: Box<A>) {
    |             ^
@@ -8,19 +8,19 @@ LL | fn warn_arg(x: Box<A>) {
    = help: to override `-D warnings` add `#[allow(clippy::boxed_local)]`
 
 error: local variable doesn't need to be boxed here
-  --> tests/ui/boxed_local.rs:122:12
+  --> tests/ui/boxed_local.rs:123:12
    |
 LL | pub fn new(_needs_name: Box<PeekableSeekable<&()>>) -> () {}
    |            ^^^^^^^^^^^
 
 error: local variable doesn't need to be boxed here
-  --> tests/ui/boxed_local.rs:187:44
+  --> tests/ui/boxed_local.rs:188:44
    |
 LL |         fn default_impl_x(self: Box<Self>, x: Box<u32>) -> u32 {
    |                                            ^
 
 error: local variable doesn't need to be boxed here
-  --> tests/ui/boxed_local.rs:195:16
+  --> tests/ui/boxed_local.rs:196:16
    |
 LL |         fn foo(x: Box<u32>) {}
    |                ^

tests/ui/doc/doc-fixable.fixed

@@ -1,7 +1,7 @@
 
 //! This file tests for the `DOC_MARKDOWN` lint.
 
-#![allow(dead_code, incomplete_features)]
+#![allow(dead_code, incomplete_features, clippy::extern_without_abi)]
 #![warn(clippy::doc_markdown)]
 #![feature(custom_inner_attributes, generic_const_exprs, const_option)]
 #![rustfmt::skip]

tests/ui/doc/doc-fixable.rs

@@ -1,7 +1,7 @@
 
 //! This file tests for the `DOC_MARKDOWN` lint.
 
-#![allow(dead_code, incomplete_features)]
+#![allow(dead_code, incomplete_features, clippy::extern_without_abi)]
 #![warn(clippy::doc_markdown)]
 #![feature(custom_inner_attributes, generic_const_exprs, const_option)]
 #![rustfmt::skip]

tests/ui/extern_without_abi.rs

@@ -0,0 +1,31 @@
+#![warn(clippy::extern_without_abi)]
+
+fn main() {}
+
+#[rustfmt::skip]
+extern fn foo() {}
+//~^ ERROR: `extern` missing explicit ABI
+
+extern "C" fn bar() {}
+
+extern "system" fn baz() {}
+
+#[rustfmt::skip]
+extern {
+//~^ ERROR: `extern` missing explicit ABI
+    static QUX: std::ffi::c_int;
+
+    fn quux();
+}
+
+extern "C" {
+    static CORGE: std::ffi::c_int;
+
+    fn grault();
+}
+
+extern "system" {
+    static GARPLY: std::ffi::c_int;
+
+    fn waldo();
+}

tests/ui/extern_without_abi.stderr

@@ -0,0 +1,21 @@
+error: `extern` missing explicit ABI
+  --> tests/ui/extern_without_abi.rs:6:1
+   |
+LL | extern fn foo() {}
+   | ^^^^^^
+   |
+   = note: `-D clippy::extern-without-abi` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::extern_without_abi)]`
+
+error: `extern` missing explicit ABI
+  --> tests/ui/extern_without_abi.rs:14:1
+   |
+LL | / extern {
+LL | |
+LL | |     static QUX: std::ffi::c_int;
+...  |
+LL | | }
+   | |_^
+
+error: aborting due to 2 previous errors
+

tests/ui/missing_const_for_fn/could_be_const.fixed

@@ -1,5 +1,10 @@
 #![warn(clippy::missing_const_for_fn)]
-#![allow(incomplete_features, clippy::let_and_return, clippy::missing_transmute_annotations)]
+#![allow(
+    incomplete_features,
+    clippy::extern_without_abi,
+    clippy::let_and_return,
+    clippy::missing_transmute_annotations
+)]
 #![feature(const_mut_refs)]
 #![feature(const_trait_impl)]
 

tests/ui/missing_const_for_fn/could_be_const.rs

@@ -1,5 +1,10 @@
 #![warn(clippy::missing_const_for_fn)]
-#![allow(incomplete_features, clippy::let_and_return, clippy::missing_transmute_annotations)]
+#![allow(
+    incomplete_features,
+    clippy::extern_without_abi,
+    clippy::let_and_return,
+    clippy::missing_transmute_annotations
+)]
 #![feature(const_mut_refs)]
 #![feature(const_trait_impl)]