Auto merge of #96150 - est31:unused_macro_rules, r=petrochenkov

Implement a lint to warn about unused macro rules

This implements a new lint to warn about unused macro rules (arms/matchers), similar to the `unused_macros` lint added by #41907 that warns about entire macros.

```rust
macro_rules! unused_empty {
    (hello) => { println!("Hello, world!") };
    () => { println!("empty") }; //~ ERROR: 1st rule of macro `unused_empty` is never used
}

fn main() {
    unused_empty!(hello);
}
```

Builds upon #96149 and #96156.

Fixes #73576

compiler/rustc_codegen_llvm/src/intrinsic.rs

@@ -816,6 +816,7 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
     span: Span,
 ) -> Result<&'ll Value, ()> {
     // macros for error handling:
+    #[cfg_attr(not(bootstrap), allow(unused_macro_rules))]
     macro_rules! emit_error {
         ($msg: tt) => {
             emit_error!($msg, )
@@ -1144,6 +1145,7 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
         span: Span,
         args: &[OperandRef<'tcx, &'ll Value>],
     ) -> Result<&'ll Value, ()> {
+        #[cfg_attr(not(bootstrap), allow(unused_macro_rules))]
         macro_rules! emit_error {
             ($msg: tt) => {
                 emit_error!($msg, )

compiler/rustc_expand/src/base.rs

@@ -886,6 +886,8 @@ pub trait ResolverExpand {
         force: bool,
     ) -> Result<Lrc<SyntaxExtension>, Indeterminate>;
 
+    fn record_macro_rule_usage(&mut self, mac_id: NodeId, rule_index: usize);
+
     fn check_unused_macros(&mut self);
 
     // Resolver interfaces for specific built-in macros.

compiler/rustc_expand/src/mbe/macro_rules.rs

@@ -156,13 +156,13 @@ impl<'a> ParserAnyMacro<'a> {
 }
 
 struct MacroRulesMacroExpander {
+    node_id: NodeId,
     name: Ident,
     span: Span,
     transparency: Transparency,
     lhses: Vec<Vec<MatcherLoc>>,
     rhses: Vec<mbe::TokenTree>,
     valid: bool,
-    is_local: bool,
 }
 
 impl TTMacroExpander for MacroRulesMacroExpander {
@@ -179,12 +179,12 @@ impl TTMacroExpander for MacroRulesMacroExpander {
             cx,
             sp,
             self.span,
+            self.node_id,
             self.name,
             self.transparency,
             input,
             &self.lhses,
             &self.rhses,
-            self.is_local,
         )
     }
 }
@@ -207,14 +207,17 @@ fn generic_extension<'cx, 'tt>(
     cx: &'cx mut ExtCtxt<'_>,
     sp: Span,
     def_span: Span,
+    node_id: NodeId,
     name: Ident,
     transparency: Transparency,
     arg: TokenStream,
     lhses: &'tt [Vec<MatcherLoc>],
     rhses: &'tt [mbe::TokenTree],
-    is_local: bool,
 ) -> Box<dyn MacResult + 'cx> {
     let sess = &cx.sess.parse_sess;
+    // Macros defined in the current crate have a real node id,
+    // whereas macros from an external crate have a dummy id.
+    let is_local = node_id != DUMMY_NODE_ID;
 
     if cx.trace_macros() {
         let msg = format!("expanding `{}! {{ {} }}`", name, pprust::tts_to_string(&arg));
@@ -296,6 +299,10 @@ fn generic_extension<'cx, 'tt>(
                 let mut p = Parser::new(sess, tts, false, None);
                 p.last_type_ascription = cx.current_expansion.prior_type_ascription;
 
+                if is_local {
+                    cx.resolver.record_macro_rule_usage(node_id, i);
+                }
+
                 // Let the context choose how to interpret the result.
                 // Weird, but useful for X-macros.
                 return Box::new(ParserAnyMacro {
@@ -372,7 +379,7 @@ pub fn compile_declarative_macro(
     features: &Features,
     def: &ast::Item,
     edition: Edition,
-) -> SyntaxExtension {
+) -> (SyntaxExtension, Vec<Span>) {
     debug!("compile_declarative_macro: {:?}", def);
     let mk_syn_ext = |expander| {
         SyntaxExtension::new(
@@ -385,6 +392,7 @@ pub fn compile_declarative_macro(
             &def.attrs,
         )
     };
+    let dummy_syn_ext = || (mk_syn_ext(Box::new(macro_rules_dummy_expander)), Vec::new());
 
     let diag = &sess.parse_sess.span_diagnostic;
     let lhs_nm = Ident::new(sym::lhs, def.span);
@@ -445,17 +453,17 @@ pub fn compile_declarative_macro(
             let s = parse_failure_msg(&token);
             let sp = token.span.substitute_dummy(def.span);
             sess.parse_sess.span_diagnostic.struct_span_err(sp, &s).span_label(sp, msg).emit();
-            return mk_syn_ext(Box::new(macro_rules_dummy_expander));
+            return dummy_syn_ext();
         }
         Error(sp, msg) => {
             sess.parse_sess
                 .span_diagnostic
                 .struct_span_err(sp.substitute_dummy(def.span), &msg)
                 .emit();
-            return mk_syn_ext(Box::new(macro_rules_dummy_expander));
+            return dummy_syn_ext();
         }
         ErrorReported => {
-            return mk_syn_ext(Box::new(macro_rules_dummy_expander));
+            return dummy_syn_ext();
         }
     };
 
@@ -530,6 +538,15 @@ pub fn compile_declarative_macro(
         None => {}
     }
 
+    // Compute the spans of the macro rules
+    // We only take the span of the lhs here,
+    // so that the spans of created warnings are smaller.
+    let rule_spans = if def.id != DUMMY_NODE_ID {
+        lhses.iter().map(|lhs| lhs.span()).collect::<Vec<_>>()
+    } else {
+        Vec::new()
+    };
+
     // Convert the lhses into `MatcherLoc` form, which is better for doing the
     // actual matching. Unless the matcher is invalid.
     let lhses = if valid {
@@ -549,17 +566,16 @@ pub fn compile_declarative_macro(
         vec![]
     };
 
-    mk_syn_ext(Box::new(MacroRulesMacroExpander {
+    let expander = Box::new(MacroRulesMacroExpander {
         name: def.ident,
         span: def.span,
+        node_id: def.id,
         transparency,
         lhses,
         rhses,
         valid,
-        // Macros defined in the current crate have a real node id,
-        // whereas macros from an external crate have a dummy id.
-        is_local: def.id != DUMMY_NODE_ID,
-    }))
+    });
+    (mk_syn_ext(expander), rule_spans)
 }
 
 fn check_lhs_nt_follows(sess: &ParseSess, def: &ast::Item, lhs: &mbe::TokenTree) -> bool {

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

@@ -749,6 +749,10 @@ declare_lint! {
 declare_lint! {
     /// The `unused_macros` lint detects macros that were not used.
     ///
+    /// Note that this lint is distinct from the `unused_macro_rules` lint,
+    /// which checks for single rules that never match of an otherwise used
+    /// macro, and thus never expand.
+    ///
     /// ### Example
     ///
     /// ```rust
@@ -775,6 +779,45 @@ declare_lint! {
     "detects macros that were not used"
 }
 
+declare_lint! {
+    /// The `unused_macro_rules` lint detects macro rules that were not used.
+    ///
+    /// Note that the lint is distinct from the `unused_macros` lint, which
+    /// fires if the entire macro is never called, while this lint fires for
+    /// single unused rules of the macro that is otherwise used.
+    /// `unused_macro_rules` fires only if `unused_macros` wouldn't fire.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// macro_rules! unused_empty {
+    ///     (hello) => { println!("Hello, world!") }; // This rule is unused
+    ///     () => { println!("empty") }; // This rule is used
+    /// }
+    ///
+    /// 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.
+    ///
+    /// If you intended to export the macro to make it
+    /// available outside of the crate, use the [`macro_export` attribute].
+    ///
+    /// [`macro_export` attribute]: https://doc.rust-lang.org/reference/macros-by-example.html#path-based-scope
+    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.
@@ -3104,6 +3147,7 @@ declare_lint_pass! {
         OVERLAPPING_RANGE_ENDPOINTS,
         BINDINGS_WITH_VARIANT_NAME,
         UNUSED_MACROS,
+        UNUSED_MACRO_RULES,
         WARNINGS,
         UNUSED_FEATURES,
         STABLE_FEATURES,

compiler/rustc_middle/src/mir/visit.rs

@@ -258,6 +258,7 @@ macro_rules! make_mir_visitor {
                 // for best performance, we want to use an iterator rather
                 // than a for-loop, to avoid calling `body::Body::invalidate` for
                 // each basic block.
+                #[cfg_attr(not(bootstrap), allow(unused_macro_rules))]
                 macro_rules! basic_blocks {
                     (mut) => (body.basic_blocks_mut().iter_enumerated_mut());
                     () => (body.basic_blocks().iter_enumerated());
@@ -279,6 +280,7 @@ macro_rules! make_mir_visitor {
                     self.visit_local_decl(local, & $($mutability)? body.local_decls[local]);
                 }
 
+                #[cfg_attr(not(bootstrap), allow(unused_macro_rules))]
                 macro_rules! type_annotations {
                     (mut) => (body.user_type_annotations.iter_enumerated_mut());
                     () => (body.user_type_annotations.iter_enumerated());
@@ -932,6 +934,7 @@ macro_rules! make_mir_visitor {
                 body: &$($mutability)? Body<'tcx>,
                 location: Location
             ) {
+                #[cfg_attr(not(bootstrap), allow(unused_macro_rules))]
                 macro_rules! basic_blocks {
                     (mut) => (body.basic_blocks_mut());
                     () => (body.basic_blocks());

compiler/rustc_resolve/Cargo.toml

@@ -4,7 +4,6 @@ version = "0.0.0"
 edition = "2021"
 
 [lib]
-test = false
 doctest = false
 
 [dependencies]

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -194,7 +194,7 @@ impl<'a> Resolver<'a> {
         }
 
         let ext = Lrc::new(match self.cstore().load_macro_untracked(def_id, &self.session) {
-            LoadedMacro::MacroDef(item, edition) => self.compile_macro(&item, edition),
+            LoadedMacro::MacroDef(item, edition) => self.compile_macro(&item, edition).0,
             LoadedMacro::ProcMacro(ext) => ext,
         });
 
@@ -1218,9 +1218,18 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
     // Mark the given macro as unused unless its name starts with `_`.
     // Macro uses will remove items from this set, and the remaining
     // items will be reported as `unused_macros`.
-    fn insert_unused_macro(&mut self, ident: Ident, def_id: LocalDefId, node_id: NodeId) {
+    fn insert_unused_macro(
+        &mut self,
+        ident: Ident,
+        def_id: LocalDefId,
+        node_id: NodeId,
+        rule_spans: &[Span],
+    ) {
         if !ident.as_str().starts_with('_') {
             self.r.unused_macros.insert(def_id, (node_id, ident));
+            for (rule_i, rule_span) in rule_spans.iter().enumerate() {
+                self.r.unused_macro_rules.insert((def_id, rule_i), (ident, *rule_span));
+            }
         }
     }
 
@@ -1228,15 +1237,16 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
         let parent_scope = self.parent_scope;
         let expansion = parent_scope.expansion;
         let def_id = self.r.local_def_id(item.id);
-        let (ext, ident, span, macro_rules) = match &item.kind {
+        let (ext, ident, span, macro_rules, rule_spans) = match &item.kind {
             ItemKind::MacroDef(def) => {
-                let ext = Lrc::new(self.r.compile_macro(item, self.r.session.edition()));
-                (ext, item.ident, item.span, def.macro_rules)
+                let (ext, rule_spans) = self.r.compile_macro(item, self.r.session.edition());
+                let ext = Lrc::new(ext);
+                (ext, item.ident, item.span, def.macro_rules, rule_spans)
             }
             ItemKind::Fn(..) => match self.proc_macro_stub(item) {
                 Some((macro_kind, ident, span)) => {
                     self.r.proc_macro_stubs.insert(def_id);
-                    (self.r.dummy_ext(macro_kind), ident, span, false)
+                    (self.r.dummy_ext(macro_kind), ident, span, false, Vec::new())
                 }
                 None => return parent_scope.macro_rules,
             },
@@ -1264,7 +1274,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                 self.r.define(module, ident, MacroNS, (res, vis, span, expansion, IsMacroExport));
             } else {
                 self.r.check_reserved_macro_name(ident, res);
-                self.insert_unused_macro(ident, def_id, item.id);
+                self.insert_unused_macro(ident, def_id, item.id, &rule_spans);
             }
             self.r.visibilities.insert(def_id, vis);
             let scope = self.r.arenas.alloc_macro_rules_scope(MacroRulesScope::Binding(
@@ -1287,7 +1297,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                 _ => self.resolve_visibility(&item.vis),
             };
             if vis != ty::Visibility::Public {
-                self.insert_unused_macro(ident, def_id, item.id);
+                self.insert_unused_macro(ident, def_id, item.id, &rule_spans);
             }
             self.r.define(module, ident, MacroNS, (res, vis, span, expansion));
             self.r.visibilities.insert(def_id, vis);

compiler/rustc_resolve/src/diagnostics.rs

@@ -35,6 +35,9 @@ use crate::{LexicalScopeBinding, NameBinding, NameBindingKind, PrivacyError, Vis
 use crate::{ParentScope, PathResult, ResolutionError, Resolver, Scope, ScopeSet};
 use crate::{Segment, UseError};
 
+#[cfg(test)]
+mod tests;
+
 type Res = def::Res<ast::NodeId>;
 
 /// A vector of spans and replacements, a message and applicability.
@@ -2675,3 +2678,14 @@ fn is_span_suitable_for_use_injection(s: Span) -> bool {
     // import or other generated ones
     !s.from_expansion()
 }
+
+/// Convert the given number into the corresponding ordinal
+crate fn ordinalize(v: usize) -> String {
+    let suffix = match ((11..=13).contains(&(v % 100)), v % 10) {
+        (false, 1) => "st",
+        (false, 2) => "nd",
+        (false, 3) => "rd",
+        _ => "th",
+    };
+    format!("{v}{suffix}")
+}

compiler/rustc_resolve/src/diagnostics/tests.rs

@@ -0,0 +1,40 @@
+use super::ordinalize;
+
+#[test]
+fn test_ordinalize() {
+    assert_eq!(ordinalize(1), "1st");
+    assert_eq!(ordinalize(2), "2nd");
+    assert_eq!(ordinalize(3), "3rd");
+    assert_eq!(ordinalize(4), "4th");
+    assert_eq!(ordinalize(5), "5th");
+    // ...
+    assert_eq!(ordinalize(10), "10th");
+    assert_eq!(ordinalize(11), "11th");
+    assert_eq!(ordinalize(12), "12th");
+    assert_eq!(ordinalize(13), "13th");
+    assert_eq!(ordinalize(14), "14th");
+    // ...
+    assert_eq!(ordinalize(20), "20th");
+    assert_eq!(ordinalize(21), "21st");
+    assert_eq!(ordinalize(22), "22nd");
+    assert_eq!(ordinalize(23), "23rd");
+    assert_eq!(ordinalize(24), "24th");
+    // ...
+    assert_eq!(ordinalize(30), "30th");
+    assert_eq!(ordinalize(31), "31st");
+    assert_eq!(ordinalize(32), "32nd");
+    assert_eq!(ordinalize(33), "33rd");
+    assert_eq!(ordinalize(34), "34th");
+    // ...
+    assert_eq!(ordinalize(7010), "7010th");
+    assert_eq!(ordinalize(7011), "7011th");
+    assert_eq!(ordinalize(7012), "7012th");
+    assert_eq!(ordinalize(7013), "7013th");
+    assert_eq!(ordinalize(7014), "7014th");
+    // ...
+    assert_eq!(ordinalize(7020), "7020th");
+    assert_eq!(ordinalize(7021), "7021st");
+    assert_eq!(ordinalize(7022), "7022nd");
+    assert_eq!(ordinalize(7023), "7023rd");
+    assert_eq!(ordinalize(7024), "7024th");
+}

compiler/rustc_resolve/src/lib.rs

@@ -975,6 +975,7 @@ pub struct Resolver<'a> {
     local_macro_def_scopes: FxHashMap<LocalDefId, Module<'a>>,
     ast_transform_scopes: FxHashMap<LocalExpnId, Module<'a>>,
     unused_macros: FxHashMap<LocalDefId, (NodeId, Ident)>,
+    unused_macro_rules: FxHashMap<(LocalDefId, usize), (Ident, Span)>,
     proc_macro_stubs: FxHashSet<LocalDefId>,
     /// Traces collected during macro resolution and validated when it's complete.
     single_segment_macro_resolutions:
@@ -1374,6 +1375,7 @@ impl<'a> Resolver<'a> {
             potentially_unused_imports: Vec::new(),
             struct_constructors: Default::default(),
             unused_macros: Default::default(),
+            unused_macro_rules: Default::default(),
             proc_macro_stubs: Default::default(),
             single_segment_macro_resolutions: Default::default(),
             multi_segment_macro_resolutions: Default::default(),

compiler/rustc_resolve/src/macros.rs

@@ -22,7 +22,8 @@ use rustc_hir::def::{self, DefKind, NonMacroAttrKind};
 use rustc_hir::def_id::{CrateNum, LocalDefId};
 use rustc_middle::middle::stability;
 use rustc_middle::ty::RegisteredTools;
-use rustc_session::lint::builtin::{LEGACY_DERIVE_HELPERS, SOFT_UNSTABLE, UNUSED_MACROS};
+use rustc_session::lint::builtin::{LEGACY_DERIVE_HELPERS, SOFT_UNSTABLE};
+use rustc_session::lint::builtin::{UNUSED_MACROS, UNUSED_MACRO_RULES};
 use rustc_session::lint::BuiltinLintDiagnostics;
 use rustc_session::parse::feature_err;
 use rustc_session::Session;
@@ -311,6 +312,11 @@ impl<'a> ResolverExpand for Resolver<'a> {
         Ok(ext)
     }
 
+    fn record_macro_rule_usage(&mut self, id: NodeId, rule_i: usize) {
+        let did = self.local_def_id(id);
+        self.unused_macro_rules.remove(&(did, rule_i));
+    }
+
     fn check_unused_macros(&mut self) {
         for (_, &(node_id, ident)) in self.unused_macros.iter() {
             self.lint_buffer.buffer_lint(
@@ -320,6 +326,23 @@ impl<'a> ResolverExpand for Resolver<'a> {
                 &format!("unused macro definition: `{}`", ident.as_str()),
             );
         }
+        for (&(def_id, arm_i), &(ident, rule_span)) in self.unused_macro_rules.iter() {
+            if self.unused_macros.contains_key(&def_id) {
+                // We already lint the entire macro as unused
+                continue;
+            }
+            let node_id = self.def_id_to_node_id[def_id];
+            self.lint_buffer.buffer_lint(
+                UNUSED_MACRO_RULES,
+                node_id,
+                rule_span,
+                &format!(
+                    "{} rule of macro `{}` is never used",
+                    crate::diagnostics::ordinalize(arm_i + 1),
+                    ident.as_str()
+                ),
+            );
+        }
     }
 
     fn has_derive_copy(&self, expn_id: LocalExpnId) -> bool {
@@ -830,10 +853,15 @@ impl<'a> Resolver<'a> {
         }
     }
 
-    /// Compile the macro into a `SyntaxExtension` and possibly replace
-    /// its expander to a pre-defined one for built-in macros.
-    crate fn compile_macro(&mut self, item: &ast::Item, edition: Edition) -> SyntaxExtension {
-        let mut result = compile_declarative_macro(
+    /// Compile the macro into a `SyntaxExtension` and its rule spans.
+    ///
+    /// Possibly replace its expander to a pre-defined one for built-in macros.
+    crate fn compile_macro(
+        &mut self,
+        item: &ast::Item,
+        edition: Edition,
+    ) -> (SyntaxExtension, Vec<Span>) {
+        let (mut result, mut rule_spans) = compile_declarative_macro(
             &self.session,
             self.session.features_untracked(),
             item,
@@ -849,6 +877,7 @@ impl<'a> Resolver<'a> {
                 match mem::replace(builtin_macro, BuiltinMacroState::AlreadySeen(item.span)) {
                     BuiltinMacroState::NotYetSeen(ext) => {
                         result.kind = ext;
+                        rule_spans = Vec::new();
                         if item.id != ast::DUMMY_NODE_ID {
                             self.builtin_macro_kinds
                                 .insert(self.local_def_id(item.id), result.macro_kind());
@@ -871,6 +900,6 @@ impl<'a> Resolver<'a> {
             }
         }
 
-        result
+        (result, rule_spans)
     }
 }

library/alloc/src/macros.rs

@@ -56,6 +56,7 @@ macro_rules! vec {
 // `slice::into_vec`  function which is only available with cfg(test)
 // NB see the slice::hack module in slice.rs for more information
 #[cfg(all(not(no_global_oom_handling), test))]
+#[cfg_attr(not(bootstrap), allow(unused_macro_rules))]
 macro_rules! vec {
     () => (
         $crate::vec::Vec::new()

library/stdarch

@@ -1 +1 @@
-Subproject commit d215afe9d1cf79c5edb0dfd3cdf4c50aca1f1760
+Subproject commit 28335054b1f417175ab5005cf1d9cf7937737930

src/test/ui/consts/const-float-bits-conv.rs

@@ -3,6 +3,7 @@
 
 #![feature(const_float_bits_conv)]
 #![feature(const_float_classify)]
+#![allow(unused_macro_rules)]
 
 // Don't promote
 const fn nop<T>(x: T) -> T { x }

src/test/ui/lint/unused/unused-macro-rules-decl.rs

@@ -0,0 +1,49 @@
+#![feature(decl_macro)]
+#![deny(unused_macro_rules)]
+// To make sure we are not hitting this
+#![deny(unused_macros)]
+
+// Most simple case
+macro num {
+    (one) => { 1 },
+    (two) => { 2 }, //~ ERROR: 2nd rule of macro
+    (three) => { 3 },
+    (four) => { 4 }, //~ ERROR: 4th rule of macro
+}
+const _NUM: u8 = num!(one) + num!(three);
+
+// Check that allowing the lint works
+#[allow(unused_macro_rules)]
+macro num_allowed {
+    (one) => { 1 },
+    (two) => { 2 },
+    (three) => { 3 },
+    (four) => { 4 },
+}
+const _NUM_ALLOWED: u8 = num_allowed!(one) + num_allowed!(three);
+
+// Check that macro calls inside the macro trigger as usage
+macro num_rec {
+    (one) => { 1 },
+    (two) => {
+        num_rec!(one) + num_rec!(one)
+    },
+    (three) => { //~ ERROR: 3rd rule of macro
+        num_rec!(one) + num_rec!(two)
+    },
+    (four) => {
+        num_rec!(two) + num_rec!(two)
+    },
+}
+const _NUM_RECURSIVE: u8 = num_rec!(four);
+
+// No error if the macro is public
+pub macro num_public {
+    (one) => { 1 },
+    (two) => { 2 },
+    (three) => { 3 },
+    (four) => { 4 },
+}
+const _NUM_PUBLIC: u8 = num_public!(one) + num_public!(three);
+
+fn main() {}

src/test/ui/lint/unused/unused-macro-rules-decl.stderr

@@ -0,0 +1,26 @@
+error: 4th rule of macro `num` is never used
+  --> $DIR/unused-macro-rules-decl.rs:11:5
+   |
+LL |     (four) => { 4 },
+   |     ^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/unused-macro-rules-decl.rs:2:9
+   |
+LL | #![deny(unused_macro_rules)]
+   |         ^^^^^^^^^^^^^^^^^^
+
+error: 2nd rule of macro `num` is never used
+  --> $DIR/unused-macro-rules-decl.rs:9:5
+   |
+LL |     (two) => { 2 },
+   |     ^^^^^
+
+error: 3rd rule of macro `num_rec` is never used
+  --> $DIR/unused-macro-rules-decl.rs:31:5
+   |
+LL |     (three) => {
+   |     ^^^^^^^
+
+error: aborting due to 3 previous errors
+

src/test/ui/lint/unused/unused-macro-rules.rs

@@ -1,29 +1,47 @@
+#![deny(unused_macro_rules)]
+// To make sure we are not hitting this
 #![deny(unused_macros)]
 
 // Most simple case
-macro_rules! unused { //~ ERROR: unused macro definition
-    () => {};
+macro_rules! num {
+    (one) => { 1 };
+    (two) => { 2 }; //~ ERROR: 2nd rule of macro
+    (three) => { 3 };
+    (four) => { 4 }; //~ ERROR: 4th rule of macro
 }
+const _NUM: u8 = num!(one) + num!(three);
 
-// Test macros created by macros
-macro_rules! create_macro {
-    () => {
-        macro_rules! m { //~ ERROR: unused macro definition
-            () => {};
-        }
+// Check that allowing the lint works
+#[allow(unused_macro_rules)]
+macro_rules! num_allowed {
+    (one) => { 1 };
+    (two) => { 2 };
+    (three) => { 3 };
+    (four) => { 4 };
+}
+const _NUM_ALLOWED: u8 = num_allowed!(one) + num_allowed!(three);
+
+// Check that macro calls inside the macro trigger as usage
+macro_rules! num_rec {
+    (one) => { 1 };
+    (two) => {
+        num_rec!(one) + num_rec!(one)
     };
+    (three) => { //~ ERROR: 3rd rule of macro
+        num_rec!(one) + num_rec!(two)
+    };
+    (four) => { num_rec!(two) + num_rec!(two) };
 }
-create_macro!();
+const _NUM_RECURSIVE: u8 = num_rec!(four);
 
-#[allow(unused_macros)]
-mod bar {
-    // Test that putting the #[deny] close to the macro's definition
-    // works.
-
-    #[deny(unused_macros)]
-    macro_rules! unused { //~ ERROR: unused macro definition
-        () => {};
-    }
+// No error if the macro is being exported
+#[macro_export]
+macro_rules! num_exported {
+    (one) => { 1 };
+    (two) => { 2 };
+    (three) => { 3 };
+    (four) => { 4 };
 }
+const _NUM_EXPORTED: u8 = num_exported!(one) + num_exported!(three);
 
 fn main() {}

src/test/ui/lint/unused/unused-macro-rules.stderr

@@ -1,32 +1,26 @@
-error: unused macro definition: `unused`
-  --> $DIR/unused-macro-rules.rs:4:14
+error: 4th rule of macro `num` is never used
+  --> $DIR/unused-macro-rules.rs:10:5
    |
-LL | macro_rules! unused {
-   |              ^^^^^^
+LL |     (four) => { 4 };
+   |     ^^^^^^
    |
 note: the lint level is defined here
   --> $DIR/unused-macro-rules.rs:1:9
    |
-LL | #![deny(unused_macros)]
-   |         ^^^^^^^^^^^^^
+LL | #![deny(unused_macro_rules)]
+   |         ^^^^^^^^^^^^^^^^^^
 
-error: unused macro definition: `m`
-  --> $DIR/unused-macro-rules.rs:11:22
+error: 2nd rule of macro `num` is never used
+  --> $DIR/unused-macro-rules.rs:8:5
    |
-LL |         macro_rules! m {
-   |                      ^
+LL |     (two) => { 2 };
+   |     ^^^^^
 
-error: unused macro definition: `unused`
-  --> $DIR/unused-macro-rules.rs:24:18
+error: 3rd rule of macro `num_rec` is never used
+  --> $DIR/unused-macro-rules.rs:30:5
    |
-LL |     macro_rules! unused {
-   |                  ^^^^^^
-   |
-note: the lint level is defined here
-  --> $DIR/unused-macro-rules.rs:23:12
-   |
-LL |     #[deny(unused_macros)]
-   |            ^^^^^^^^^^^^^
+LL |     (three) => {
+   |     ^^^^^^^
 
 error: aborting due to 3 previous errors
 

src/test/ui/lint/unused/unused-macros-decl.rs

@@ -1,5 +1,7 @@
 #![feature(decl_macro)]
 #![deny(unused_macros)]
+// To make sure we are not hitting this
+#![deny(unused_macro_rules)]
 
 // Most simple case
 macro unused { //~ ERROR: unused macro definition

src/test/ui/lint/unused/unused-macros-decl.stderr

@@ -1,29 +1,29 @@
 error: unused macro definition: `unused`
-  --> $DIR/unused-macro.rs:5:7
+  --> $DIR/unused-macros-decl.rs:7:7
    |
 LL | macro unused {
    |       ^^^^^^
    |
 note: the lint level is defined here
-  --> $DIR/unused-macro.rs:2:9
+  --> $DIR/unused-macros-decl.rs:2:9
    |
 LL | #![deny(unused_macros)]
    |         ^^^^^^^^^^^^^
 
 error: unused macro definition: `unused`
-  --> $DIR/unused-macro.rs:15:11
+  --> $DIR/unused-macros-decl.rs:17:11
    |
 LL |     macro unused {
    |           ^^^^^^
    |
 note: the lint level is defined here
-  --> $DIR/unused-macro.rs:14:12
+  --> $DIR/unused-macros-decl.rs:16:12
    |
 LL |     #[deny(unused_macros)]
    |            ^^^^^^^^^^^^^
 
 error: unused macro definition: `unused`
-  --> $DIR/unused-macro.rs:21:22
+  --> $DIR/unused-macros-decl.rs:23:22
    |
 LL |     pub(crate) macro unused {
    |                      ^^^^^^

src/test/ui/lint/unused/unused-macros.rs

@@ -0,0 +1,31 @@
+#![deny(unused_macros)]
+// To make sure we are not hitting this
+#![deny(unused_macro_rules)]
+
+// Most simple case
+macro_rules! unused { //~ ERROR: unused macro definition
+    () => {};
+}
+
+// Test macros created by macros
+macro_rules! create_macro {
+    () => {
+        macro_rules! m { //~ ERROR: unused macro definition
+            () => {};
+        }
+    };
+}
+create_macro!();
+
+#[allow(unused_macros)]
+mod bar {
+    // Test that putting the #[deny] close to the macro's definition
+    // works.
+
+    #[deny(unused_macros)]
+    macro_rules! unused { //~ ERROR: unused macro definition
+        () => {};
+    }
+}
+
+fn main() {}

src/test/ui/lint/unused/unused-macros.stderr

@@ -0,0 +1,32 @@
+error: unused macro definition: `unused`
+  --> $DIR/unused-macros.rs:6:14
+   |
+LL | macro_rules! unused {
+   |              ^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/unused-macros.rs:1:9
+   |
+LL | #![deny(unused_macros)]
+   |         ^^^^^^^^^^^^^
+
+error: unused macro definition: `m`
+  --> $DIR/unused-macros.rs:13:22
+   |
+LL |         macro_rules! m {
+   |                      ^
+
+error: unused macro definition: `unused`
+  --> $DIR/unused-macros.rs:26:18
+   |
+LL |     macro_rules! unused {
+   |                  ^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/unused-macros.rs:25:12
+   |
+LL |     #[deny(unused_macros)]
+   |            ^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+

src/test/ui/macros/issue-41803.rs

@@ -1,4 +1,6 @@
 // run-pass
+#![allow(unused_macro_rules)]
+
 /// A compile-time map from identifiers to arbitrary (heterogeneous) expressions
 macro_rules! ident_map {
     ( $name:ident = { $($key:ident => $e:expr,)* } ) => {

src/test/ui/macros/issue-52169.rs

@@ -1,5 +1,6 @@
 // run-pass
 
+#[allow(unused_macro_rules)]
 macro_rules! a {
     ($i:literal) => { "right" };
     ($i:tt) => { "wrong" };

src/test/ui/macros/macro-first-set.rs

@@ -1,4 +1,5 @@
 // run-pass
+#![allow(unused_macro_rules)]
 
 //{{{ issue 40569 ==============================================================
 

src/test/ui/macros/macro-literal.rs

@@ -21,6 +21,7 @@ macro_rules! only_expr {
     };
 }
 
+#[allow(unused_macro_rules)]
 macro_rules! mtester_dbg {
     ($l:literal) => {
         &format!("macro caught literal: {:?}", $l)

src/test/ui/macros/macro-pub-matcher.rs

@@ -1,5 +1,5 @@
 // run-pass
-#![allow(dead_code, unused_imports)]
+#![allow(dead_code, unused_imports, unused_macro_rules)]
 #![feature(crate_visibility_modifier)]
 
 /**

src/test/ui/macros/stmt_expr_attr_macro_parse.rs

@@ -1,4 +1,6 @@
 // run-pass
+#![allow(unused_macro_rules)]
+
 macro_rules! m {
     ($e:expr) => {
         "expr includes attr"

src/test/ui/macros/type-macros-hlist.rs

@@ -1,4 +1,6 @@
 // run-pass
+#![allow(unused_macro_rules)]
+
 use std::ops::*;
 
 #[derive(Copy, Clone, Debug, Eq, Ord, PartialEq, PartialOrd)]

src/test/ui/parser/issues/issue-65846-rollback-gating-failing-matcher.rs

@@ -3,6 +3,7 @@
 // Test that failing macro matchers will not cause pre-expansion errors
 // even though they use a feature that is pre-expansion gated.
 
+#[allow(unused_macro_rules)]
 macro_rules! m {
     ($e:expr) => { 0 }; // This fails on the input below due to `, foo`.
     ($e:expr,) => { 1 }; // This also fails to match due to `foo`.

src/test/ui/rust-2018/async-ident.fixed

@@ -1,4 +1,4 @@
-#![allow(dead_code, unused_variables, non_camel_case_types, non_upper_case_globals)]
+#![allow(dead_code, unused_variables, unused_macro_rules, bad_style)]
 #![deny(keyword_idents)]
 
 // edition:2015

src/test/ui/rust-2018/async-ident.rs

@@ -1,4 +1,4 @@
-#![allow(dead_code, unused_variables, non_camel_case_types, non_upper_case_globals)]
+#![allow(dead_code, unused_variables, unused_macro_rules, bad_style)]
 #![deny(keyword_idents)]
 
 // edition:2015

src/tools/error_index_generator/main.rs

@@ -280,10 +280,6 @@ fn main() {
 fn register_all() -> Vec<(&'static str, Option<&'static str>)> {
     let mut long_codes: Vec<(&'static str, Option<&'static str>)> = Vec::new();
     macro_rules! register_diagnostics {
-        ($($ecode:ident: $message:expr,)*) => (
-            register_diagnostics!{$($ecode:$message,)* ;}
-        );
-
         ($($ecode:ident: $message:expr,)* ; $($code:ident,)*) => (
             $(
                 {long_codes.extend([