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

README.md

@@ -5,7 +5,7 @@
 
 A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
 
-[There are over 700 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
+[There are over 750 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
 
 Lints are divided into categories, each with a default [lint level](https://doc.rust-lang.org/rustc/lints/levels.html).
 You can choose how much Clippy is supposed to ~~annoy~~ help you by changing the lint level by category.

book/src/README.md

@@ -6,7 +6,7 @@
 A collection of lints to catch common mistakes and improve your
 [Rust](https://github.com/rust-lang/rust) code.
 
-[There are over 700 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
+[There are over 750 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
 
 Lints are divided into categories, each with a default [lint
 level](https://doc.rust-lang.org/rustc/lints/levels.html). You can choose how

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 +1,113 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::is_from_proc_macro;
+use clippy_utils::source::snippet;
+use rustc_errors::Applicability;
+use rustc_hir::def_id::LocalDefId;
+use rustc_hir::intravisit::FnKind;
+use rustc_hir::{Body, FnDecl, FnHeader, Item, ItemKind};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::lint::in_external_macro;
+use rustc_session::declare_lint_pass;
+use rustc_span::Span;
+use rustc_target::spec::abi::Abi;
+
+const LINT_MSG: &str = "`extern` missing explicit ABI";
+const LINT_HELP_MSG: &str = "consider using";
+
+const EXTERN: &str = "extern";
+const FN: &str = "fn";
+const OPEN_BRACE: &str = "{";
+const ABI: &str = r#""C""#;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for usage of `extern` without an explicit ABI.
+    ///
+    /// ### Why is this bad?
+    /// Explicitly declaring the ABI is the recommended convention. See:
+    /// [Rust Style Guide - `extern` items](https://doc.rust-lang.org/nightly/style-guide/items.html#extern-items)
+    ///
+    /// It's also enforced by `rustfmt` when the `force_explicit_abi` option is enabled. See:
+    /// [Configuring Rustfmt](https://rust-lang.github.io/rustfmt/?version=master&search=#force_explicit_abi)
+    ///
+    /// ### 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<'tcx> LateLintPass<'tcx> for ExternWithoutAbi {
+    fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
+        if let ItemKind::ForeignMod { abi: Abi::C { .. }, .. } = item.kind
+            && !in_external_macro(cx.sess(), item.span)
+            && let snippet = snippet(cx.sess(), item.span, "").as_ref()
+            && is_extern_followed_by(OPEN_BRACE, snippet)
+            && !is_from_proc_macro(cx, item)
+        {
+            emit_lint(cx, item.span, snippet);
+        }
+    }
+
+    fn check_fn(
+        &mut self,
+        cx: &LateContext<'tcx>,
+        kind: FnKind<'tcx>,
+        _: &'tcx FnDecl<'tcx>,
+        body: &'tcx Body<'tcx>,
+        span: Span,
+        _: LocalDefId,
+    ) {
+        if let FnKind::ItemFn(_, _, header) = kind
+            && let FnHeader { abi: Abi::C { .. }, .. } = header
+            && !in_external_macro(cx.sess(), span)
+            && let snippet = snippet(cx.sess(), span, "").as_ref()
+            && is_extern_followed_by(FN, snippet)
+            && let hir_id = cx.tcx.hir().body_owner(body.id())
+            && !is_from_proc_macro(cx, &(&kind, body, hir_id, span))
+        {
+            emit_lint(cx, span, snippet);
+        }
+    }
+}
+
+fn is_extern_followed_by(item: &str, snippet: &str) -> bool {
+    let mut tokens = snippet.split_whitespace();
+
+    if let (Some(EXTERN), Some(i)) = (tokens.next(), tokens.next())
+        && i.starts_with(item)
+    {
+        return true;
+    }
+    false
+}
+
+fn emit_lint(cx: &LateContext<'_>, span: Span, snippet: &str) {
+    let sugg = snippet.replacen(EXTERN, format!("{EXTERN} {ABI}").as_str(), 1);
+    span_lint_and_sugg(
+        cx,
+        EXTERN_WITHOUT_ABI,
+        span,
+        LINT_MSG,
+        LINT_HELP_MSG,
+        sugg,
+        Applicability::MachineApplicable,
+    );
+}

clippy_lints/src/lib.rs

@@ -137,6 +137,7 @@ 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;
@@ -951,5 +952,6 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     store.register_late_pass(move |_| Box::new(unused_trait_names::UnusedTraitNames::new(conf)));
     store.register_late_pass(|_| Box::new(manual_ignore_case_cmp::ManualIgnoreCaseCmp));
     store.register_late_pass(|_| Box::new(unnecessary_literal_bound::UnnecessaryLiteralBound));
+    store.register_late_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:40:13
+  --> tests/ui/boxed_local.rs:41:13
    |
 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:123:12
+  --> tests/ui/boxed_local.rs:124:12
    |
 LL | pub fn new(_needs_name: Box<PeekableSeekable<&()>>) -> () {}
    |            ^^^^^^^^^^^
 
 error: local variable doesn't need to be boxed here
-  --> tests/ui/boxed_local.rs:188:44
+  --> tests/ui/boxed_local.rs:189:44
    |
 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:196:16
+  --> tests/ui/boxed_local.rs:197:16
    |
 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.fixed

@@ -0,0 +1,60 @@
+//@aux-build:proc_macros.rs
+
+#![warn(clippy::extern_without_abi)]
+
+extern crate proc_macros;
+use proc_macros::{external, with_span};
+
+#[rustfmt::skip]
+extern "C" fn foo() {}
+//~^ ERROR: `extern` missing explicit ABI
+
+#[rustfmt::skip]
+extern "C" 	
+fn foo_two() {}
+//~^^ ERROR: `extern` missing explicit ABI
+
+extern "C" fn bar() {}
+
+#[rustfmt::skip]
+extern 	
+"C" 
+fn bar_two() {}
+
+extern "system" fn baz() {}
+
+#[rustfmt::skip]
+extern "C" {
+//~^ ERROR: `extern` missing explicit ABI
+    fn qux();
+}
+
+#[rustfmt::skip]
+extern "C" 	
+{
+//~^^ ERROR: `extern` missing explicit ABI
+    fn qux_two();
+}
+
+#[rustfmt::skip]
+extern "C" {fn qux_three();}
+//~^ ERROR: `extern` missing explicit ABI
+
+extern "C" {
+    fn grault();
+}
+
+extern "system" {
+    fn grault_two();
+}
+
+external! {
+    extern fn waldo() {}
+}
+
+with_span! {
+    span
+    extern fn waldo_two() {}
+}
+
+fn main() {}

tests/ui/extern_without_abi.rs

@@ -0,0 +1,60 @@
+//@aux-build:proc_macros.rs
+
+#![warn(clippy::extern_without_abi)]
+
+extern crate proc_macros;
+use proc_macros::{external, with_span};
+
+#[rustfmt::skip]
+extern fn foo() {}
+//~^ ERROR: `extern` missing explicit ABI
+
+#[rustfmt::skip]
+extern 	
+fn foo_two() {}
+//~^^ ERROR: `extern` missing explicit ABI
+
+extern "C" fn bar() {}
+
+#[rustfmt::skip]
+extern 	
+"C" 
+fn bar_two() {}
+
+extern "system" fn baz() {}
+
+#[rustfmt::skip]
+extern {
+//~^ ERROR: `extern` missing explicit ABI
+    fn qux();
+}
+
+#[rustfmt::skip]
+extern 	
+{
+//~^^ ERROR: `extern` missing explicit ABI
+    fn qux_two();
+}
+
+#[rustfmt::skip]
+extern {fn qux_three();}
+//~^ ERROR: `extern` missing explicit ABI
+
+extern "C" {
+    fn grault();
+}
+
+extern "system" {
+    fn grault_two();
+}
+
+external! {
+    extern fn waldo() {}
+}
+
+with_span! {
+    span
+    extern fn waldo_two() {}
+}
+
+fn main() {}