new lint: clippy::ref_pattern

Author: NotAPenguin0

CHANGELOG.md

@@ -4978,6 +4978,7 @@ Released 2018-09-13
 [`ref_binding_to_reference`]: https://rust-lang.github.io/rust-clippy/master/index.html#ref_binding_to_reference
 [`ref_in_deref`]: https://rust-lang.github.io/rust-clippy/master/index.html#ref_in_deref
 [`ref_option_ref`]: https://rust-lang.github.io/rust-clippy/master/index.html#ref_option_ref
+[`ref_pattern`]: https://rust-lang.github.io/rust-clippy/master/index.html#ref_pattern
 [`regex_macro`]: https://rust-lang.github.io/rust-clippy/master/index.html#regex_macro
 [`repeat_once`]: https://rust-lang.github.io/rust-clippy/master/index.html#repeat_once
 [`replace_consts`]: https://rust-lang.github.io/rust-clippy/master/index.html#replace_consts

clippy_lints/src/declared_lints.rs

@@ -539,6 +539,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::redundant_slicing::REDUNDANT_SLICING_INFO,
     crate::redundant_static_lifetimes::REDUNDANT_STATIC_LIFETIMES_INFO,
     crate::ref_option_ref::REF_OPTION_REF_INFO,
+    crate::ref_pattern::REF_PATTERN_INFO,
     crate::reference::DEREF_ADDROF_INFO,
     crate::regex::INVALID_REGEX_INFO,
     crate::regex::TRIVIAL_REGEX_INFO,

clippy_lints/src/lib.rs

@@ -266,6 +266,7 @@ mod redundant_pub_crate;
 mod redundant_slicing;
 mod redundant_static_lifetimes;
 mod ref_option_ref;
+mod ref_pattern;
 mod reference;
 mod regex;
 mod return_self_not_must_use;
@@ -972,6 +973,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_early_pass(|| Box::new(suspicious_doc_comments::SuspiciousDocComments));
     store.register_late_pass(|_| Box::new(items_after_test_module::ItemsAfterTestModule));
     store.register_late_pass(|_| Box::new(default_constructed_unit_structs::DefaultConstructedUnitStructs));
+    store.register_early_pass(|| Box::new(ref_pattern::RefPattern));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
 

clippy_lints/src/ref_pattern.rs

@@ -0,0 +1,45 @@
+use clippy_utils::diagnostics::span_lint_and_help;
+use rustc_ast::ast::*;
+use rustc_lint::{EarlyContext, EarlyLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for usages of the `ref` keyword.
+    /// ### Why is this bad?
+    /// The `ref` keyword can be confusing for people unfamiliar with it, and often
+    /// it is more concise to use `&` instead.
+    /// ### Example
+    /// ```rust
+    /// let opt = Some(5);
+    /// if let Some(ref foo) = opt {}
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// let opt = Some(5);
+    /// if let Some(foo) = &opt {}
+    /// ```
+    #[clippy::version = "1.71.0"]
+    pub REF_PATTERN,
+    restriction,
+    "use of a ref pattern, e.g. Some(ref value)"
+}
+declare_lint_pass!(RefPattern => [REF_PATTERN]);
+
+impl EarlyLintPass for RefPattern {
+    fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &Pat) {
+        match pat.kind {
+            PatKind::Ident(BindingAnnotation::REF, _, _) => {
+                span_lint_and_help(
+                    cx,
+                    REF_PATTERN,
+                    pat.span,
+                    "usage of ref pattern",
+                    None,
+                    "consider using `&` for clarity instead.",
+                );
+            },
+            _ => {},
+        }
+    }
+}

tests/ui/ref_pattern.rs

@@ -0,0 +1,18 @@
+#![allow(unused)]
+#![allow(clippy::toplevel_ref_arg)]
+#![warn(clippy::ref_pattern)]
+
+fn use_in_pattern() {
+    let opt = Some(5);
+    match opt {
+        None => {},
+        Some(ref opt) => {},
+    }
+}
+
+fn use_in_binding() {
+    let x = 5;
+    let ref y = x;
+}
+
+fn main() {}

tests/ui/ref_pattern.stderr

@@ -0,0 +1,19 @@
+error: usage of ref pattern
+  --> $DIR/ref_pattern.rs:9:14
+   |
+LL |         Some(ref opt) => {},
+   |              ^^^^^^^
+   |
+   = help: consider using `&` for clarity instead.
+   = note: `-D clippy::ref-pattern` implied by `-D warnings`
+
+error: usage of ref pattern
+  --> $DIR/ref_pattern.rs:15:9
+   |
+LL |     let ref y = x;
+   |         ^^^^^
+   |
+   = help: consider using `&` for clarity instead.
+
+error: aborting due to 2 previous errors
+