test: add nonstandard_style lint test

Adds a test to make sure that no excess warnings are emitted by
`#[pin_data]`, `init!` or `pin_init!` when dealing with non-standard
field names.

Signed-off-by: Mirko Adzic <adzicmirko97@gmail.com>

Author: Mirko-A

tests/nonstandard_style.rs

@@ -0,0 +1,62 @@
+//! Tests that no extra warnings are emitted for non-snake-case fields when using
+//! `#[pin_data]`, `init!` or `pin_init!`.
+//!
+//! See: https://github.com/Rust-for-Linux/pin-init/issues/125
+
+#![deny(nonstandard_style)]
+#![allow(dead_code)]
+#![cfg_attr(USE_RUSTC_FEATURES, feature(lint_reasons))]
+#![cfg_attr(USE_RUSTC_FEATURES, feature(raw_ref_op))]
+
+use pin_init::*;
+
+#[allow(non_snake_case)]
+struct Foo {
+    NON_STANDARD_A: usize,
+    nonStandardB: Bar,
+}
+
+#[allow(non_snake_case)]
+struct Bar {
+    Non_Standard_C: usize,
+}
+
+impl Foo {
+    fn new() -> impl Init<Self> {
+        init!(Self {
+            NON_STANDARD_A: {
+                #[expect(
+                    nonstandard_style,
+                    reason = "User code warnings should not be suppressed"
+                )]
+                (0..2).map(|NonStandardInUserCode| NonStandardInUserCode + 1).sum()
+            },
+            nonStandardB <- init!(Bar { Non_Standard_C: 42 }),
+        })
+    }
+}
+
+// Non-camel-case struct name should not produce warnings.
+#[allow(nonstandard_style)]
+#[pin_data]
+struct non_standard_baz {
+    NON_STANDARD: usize,
+    #[pin]
+    nonStandardPin: usize,
+}
+
+impl non_standard_baz {
+    fn new(a: impl PinInit<usize>) -> impl PinInit<Self> {
+        pin_init!(Self {
+            NON_STANDARD: {
+                #[expect(
+                    nonstandard_style,
+                    reason = "User code warnings should not be suppressed"
+                )]
+                let NON_STANDARD_IN_USER_CODE = 41;
+                NON_STANDARD_IN_USER_CODE + 1
+            },
+            nonStandardPin <- a,
+        })
+    }
+}