Add unused_macro_rules lint definition

Not fired yet.

Author: est31

compiler/rustc_lint/src/lib.rs

@@ -303,6 +303,7 @@ fn register_builtins(store: &mut LintStore, no_interleave_lints: bool) {
         PATH_STATEMENTS,
         UNUSED_ATTRIBUTES,
         UNUSED_MACROS,
+        UNUSED_MACRO_RULES,
         UNUSED_ALLOCATION,
         UNUSED_DOC_COMMENTS,
         UNUSED_EXTERN_CRATES,

compiler/rustc_lint_defs/src/builtin.rs

@@ -775,6 +775,35 @@ declare_lint! {
     "detects macros that were not used"
 }
 
+declare_lint! {
+    /// The `unused_macro_rules` lint detects macro rules that were not used.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// macro_rules! unused_empty {
+    ///     (hello) => { println!("Hello, world!") };
+    ///     () => { println!("empty") };
+    /// }
+    ///
+    /// fn main() {
+    ///     unused_empty!(hello);
+    /// }
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// Unused macro rules may signal a mistake or unfinished code. Furthermore,
+    /// they slow down compilation. Right now, silencing the warning is not
+    /// supported on a single rule level, so you have to add an allow to the
+    /// entire macro definition.
+    pub UNUSED_MACRO_RULES,
+    Warn,
+    "detects macro rules that were not used"
+}
+
 declare_lint! {
     /// The `warnings` lint allows you to change the level of other
     /// lints which produce warnings.
@@ -3138,6 +3167,7 @@ declare_lint_pass! {
         OVERLAPPING_RANGE_ENDPOINTS,
         BINDINGS_WITH_VARIANT_NAME,
         UNUSED_MACROS,
+        UNUSED_MACRO_RULES,
         WARNINGS,
         UNUSED_FEATURES,
         STABLE_FEATURES,