From 893f79270f3ef7a7e3fea895f3b96b64e3b6fa85 Mon Sep 17 00:00:00 2001
From: valadaptive <valadaptive@protonmail.com>
Date: Wed, 18 Sep 2024 01:51:13 -0400
Subject: [PATCH] Don't lint names of #[no_mangle] extern fns

---
 crates/hir-ty/src/diagnostics/decl_check.rs   | 21 +++++--
 .../src/handlers/incorrect_case.rs            | 58 +++++++++++++++++++
 2 files changed, 73 insertions(+), 6 deletions(-)

diff --git a/crates/hir-ty/src/diagnostics/decl_check.rs b/crates/hir-ty/src/diagnostics/decl_check.rs
index 0249f3ba25..82517e6991 100644
--- a/crates/hir-ty/src/diagnostics/decl_check.rs
+++ b/crates/hir-ty/src/diagnostics/decl_check.rs
@@ -24,6 +24,7 @@ use hir_expand::{
     name::{AsName, Name},
     HirFileId, HirFileIdExt,
 };
+use intern::sym;
 use stdx::{always, never};
 use syntax::{
     ast::{self, HasName},
@@ -197,12 +198,20 @@ impl<'a> DeclValidator<'a> {
         // Skipped if function is an associated item of a trait implementation.
         if !self.is_trait_impl_container(container) {
             let data = self.db.function_data(func);
-            self.create_incorrect_case_diagnostic_for_item_name(
-                func,
-                &data.name,
-                CaseType::LowerSnakeCase,
-                IdentType::Function,
-            );
+
+            // Don't run the lint on extern "[not Rust]" fn items with the
+            // #[no_mangle] attribute.
+            let no_mangle = data.attrs.by_key(&sym::no_mangle).exists();
+            if no_mangle && data.abi.as_ref().is_some_and(|abi| *abi != sym::Rust) {
+                cov_mark::hit!(extern_func_no_mangle_ignored);
+            } else {
+                self.create_incorrect_case_diagnostic_for_item_name(
+                    func,
+                    &data.name,
+                    CaseType::LowerSnakeCase,
+                    IdentType::Function,
+                );
+            }
         } else {
             cov_mark::hit!(trait_impl_assoc_func_name_incorrect_case_ignored);
         }
diff --git a/crates/ide-diagnostics/src/handlers/incorrect_case.rs b/crates/ide-diagnostics/src/handlers/incorrect_case.rs
index ddc19a0121..ec25c3d52b 100644
--- a/crates/ide-diagnostics/src/handlers/incorrect_case.rs
+++ b/crates/ide-diagnostics/src/handlers/incorrect_case.rs
@@ -418,6 +418,64 @@ fn f((_O): u8) {}
         )
     }
 
+    #[test]
+    fn ignores_no_mangle_items() {
+        cov_mark::check!(extern_func_no_mangle_ignored);
+        check_diagnostics(
+            r#"
+#[no_mangle]
+extern "C" fn NonSnakeCaseName(some_var: u8) -> u8;
+            "#,
+        );
+    }
+
+    #[test]
+    fn ignores_no_mangle_items_with_no_abi() {
+        cov_mark::check!(extern_func_no_mangle_ignored);
+        check_diagnostics(
+            r#"
+#[no_mangle]
+extern fn NonSnakeCaseName(some_var: u8) -> u8;
+            "#,
+        );
+    }
+
+    #[test]
+    fn no_mangle_items_with_rust_abi() {
+        check_diagnostics(
+            r#"
+#[no_mangle]
+extern "Rust" fn NonSnakeCaseName(some_var: u8) -> u8;
+              // ^^^^^^^^^^^^^^^^ 💡 warn: Function `NonSnakeCaseName` should have snake_case name, e.g. `non_snake_case_name`
+            "#,
+        );
+    }
+
+    #[test]
+    fn no_mangle_items_non_extern() {
+        check_diagnostics(
+            r#"
+#[no_mangle]
+fn NonSnakeCaseName(some_var: u8) -> u8;
+// ^^^^^^^^^^^^^^^^ 💡 warn: Function `NonSnakeCaseName` should have snake_case name, e.g. `non_snake_case_name`
+            "#,
+        );
+    }
+
+    #[test]
+    fn extern_fn_name() {
+        check_diagnostics(
+            r#"
+extern "C" fn NonSnakeCaseName(some_var: u8) -> u8;
+           // ^^^^^^^^^^^^^^^^ 💡 warn: Function `NonSnakeCaseName` should have snake_case name, e.g. `non_snake_case_name`
+extern "Rust" fn NonSnakeCaseName(some_var: u8) -> u8;
+              // ^^^^^^^^^^^^^^^^ 💡 warn: Function `NonSnakeCaseName` should have snake_case name, e.g. `non_snake_case_name`
+extern fn NonSnakeCaseName(some_var: u8) -> u8;
+       // ^^^^^^^^^^^^^^^^ 💡 warn: Function `NonSnakeCaseName` should have snake_case name, e.g. `non_snake_case_name`
+            "#,
+        );
+    }
+
     #[test]
     fn ignores_extern_items() {
         cov_mark::check!(extern_func_incorrect_case_ignored);