Stop relying on hashmap iteration for unused macro rules arms

Author: Noratrieb

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -1193,7 +1193,11 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
         if !ident.as_str().starts_with('_') {
             self.r.unused_macros.insert(def_id, (node_id, ident));
             for (rule_i, rule_span) in &self.r.macro_map[&def_id.to_def_id()].rule_spans {
-                self.r.unused_macro_rules.insert((def_id, *rule_i), (ident, *rule_span));
+                self.r
+                    .unused_macro_rules
+                    .entry(def_id)
+                    .or_default()
+                    .insert(*rule_i, (ident, *rule_span));
             }
         }
     }

compiler/rustc_resolve/src/lib.rs

@@ -1122,7 +1122,8 @@ pub struct Resolver<'ra, 'tcx> {
     local_macro_def_scopes: FxHashMap<LocalDefId, Module<'ra>>,
     ast_transform_scopes: FxHashMap<LocalExpnId, Module<'ra>>,
     unused_macros: FxHashMap<LocalDefId, (NodeId, Ident)>,
-    unused_macro_rules: FxHashMap<(LocalDefId, usize), (Ident, Span)>,
+    /// A map from the macro to all its potentially unused arms.
+    unused_macro_rules: FxIndexMap<LocalDefId, FxHashMap<usize, (Ident, Span)>>,
     proc_macro_stubs: FxHashSet<LocalDefId>,
     /// Traces collected during macro resolution and validated when it's complete.
     single_segment_macro_resolutions:

compiler/rustc_resolve/src/macros.rs

@@ -340,7 +340,9 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
 
     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));
+        if let Some(rules) = self.unused_macro_rules.get_mut(&did) {
+            rules.remove(&rule_i);
+        }
     }
 
     fn check_unused_macros(&mut self) {
@@ -352,18 +354,24 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
                 BuiltinLintDiag::UnusedMacroDefinition(ident.name),
             );
         }
-        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;
+
+        for (&def_id, unused_arms) in self.unused_macro_rules.iter() {
+            let mut unused_arms = unused_arms.iter().collect::<Vec<_>>();
+            unused_arms.sort_by_key(|&(&arm_i, _)| arm_i);
+
+            for (&arm_i, &(ident, rule_span)) in unused_arms {
+                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,
+                    BuiltinLintDiag::MacroRuleNeverUsed(arm_i, ident.name),
+                );
             }
-            let node_id = self.def_id_to_node_id[def_id];
-            self.lint_buffer.buffer_lint(
-                UNUSED_MACRO_RULES,
-                node_id,
-                rule_span,
-                BuiltinLintDiag::MacroRuleNeverUsed(arm_i, ident.name),
-            );
         }
     }
 

tests/ui/lint/unused/unused-macro-rules-compile-error.stderr

@@ -10,17 +10,17 @@ note: the lint level is defined here
 LL | #![deny(unused_macro_rules)]
    |         ^^^^^^^^^^^^^^^^^^
 
-error: rule #3 of macro `num2` is never used
-  --> $DIR/unused-macro-rules-compile-error.rs:22:5
-   |
-LL |     (two_) => { compile_error! };
-   |     ^^^^^^
-
 error: rule #2 of macro `num2` is never used
   --> $DIR/unused-macro-rules-compile-error.rs:20:5
    |
 LL |     (two) => { fn compile_error() {} };
    |     ^^^^^
 
+error: rule #3 of macro `num2` is never used
+  --> $DIR/unused-macro-rules-compile-error.rs:22:5
+   |
+LL |     (two_) => { compile_error! };
+   |     ^^^^^^
+
 error: aborting due to 3 previous errors
 

tests/ui/lint/unused/unused-macro-rules-decl.stderr

@@ -1,20 +1,20 @@
-error: rule #4 of macro `num` is never used
-  --> $DIR/unused-macro-rules-decl.rs:11:5
+error: rule #2 of macro `num` is never used
+  --> $DIR/unused-macro-rules-decl.rs:9:5
    |
-LL |     (four) => { 4 },
-   |     ^^^^^^
+LL |     (two) => { 2 },
+   |     ^^^^^
    |
 note: the lint level is defined here
   --> $DIR/unused-macro-rules-decl.rs:2:9
    |
 LL | #![deny(unused_macro_rules)]
    |         ^^^^^^^^^^^^^^^^^^
 
-error: rule #2 of macro `num` is never used
-  --> $DIR/unused-macro-rules-decl.rs:9:5
+error: rule #4 of macro `num` is never used
+  --> $DIR/unused-macro-rules-decl.rs:11:5
    |
-LL |     (two) => { 2 },
-   |     ^^^^^
+LL |     (four) => { 4 },
+   |     ^^^^^^
 
 error: rule #3 of macro `num_rec` is never used
   --> $DIR/unused-macro-rules-decl.rs:31:5

tests/ui/lint/unused/unused-macro-rules.stderr

@@ -1,20 +1,20 @@
-error: rule #4 of macro `num` is never used
-  --> $DIR/unused-macro-rules.rs:10:5
+error: rule #2 of macro `num` is never used
+  --> $DIR/unused-macro-rules.rs:8:5
    |
-LL |     (four) => { 4 };
-   |     ^^^^^^
+LL |     (two) => { 2 };
+   |     ^^^^^
    |
 note: the lint level is defined here
   --> $DIR/unused-macro-rules.rs:1:9
    |
 LL | #![deny(unused_macro_rules)]
    |         ^^^^^^^^^^^^^^^^^^
 
-error: rule #2 of macro `num` is never used
-  --> $DIR/unused-macro-rules.rs:8:5
+error: rule #4 of macro `num` is never used
+  --> $DIR/unused-macro-rules.rs:10:5
    |
-LL |     (two) => { 2 };
-   |     ^^^^^
+LL |     (four) => { 4 };
+   |     ^^^^^^
 
 error: rule #3 of macro `num_rec` is never used
   --> $DIR/unused-macro-rules.rs:30:5