Adds coverage graphviz

compiler/rustc_mir/src/transform/coverage/counters.rs

@@ -1,3 +1,7 @@
+use super::debug;
+
+use debug::DebugCounters;
+
 use rustc_middle::mir::coverage::*;
 
 /// Manages the counter and expression indexes/IDs to generate `CoverageKind` components for MIR
@@ -6,6 +10,7 @@ pub(crate) struct CoverageCounters {
     function_source_hash: u64,
     next_counter_id: u32,
     num_expressions: u32,
+    pub debug_counters: DebugCounters,
 }
 
 impl CoverageCounters {
@@ -14,24 +19,46 @@ impl CoverageCounters {
             function_source_hash,
             next_counter_id: CounterValueReference::START.as_u32(),
             num_expressions: 0,
+            debug_counters: DebugCounters::new(),
         }
     }
 
-    pub fn make_counter(&mut self) -> CoverageKind {
-        CoverageKind::Counter {
+    /// Activate the `DebugCounters` data structures, to provide additional debug formatting
+    /// features when formating `CoverageKind` (counter) values.
+    pub fn enable_debug(&mut self) {
+        self.debug_counters.enable();
+    }
+
+    pub fn make_counter<F>(&mut self, debug_block_label_fn: F) -> CoverageKind
+    where
+        F: Fn() -> Option<String>,
+    {
+        let counter = CoverageKind::Counter {
             function_source_hash: self.function_source_hash,
             id: self.next_counter(),
+        };
+        if self.debug_counters.is_enabled() {
+            self.debug_counters.add_counter(&counter, (debug_block_label_fn)());
         }
+        counter
     }
 
-    pub fn make_expression(
+    pub fn make_expression<F>(
         &mut self,
         lhs: ExpressionOperandId,
         op: Op,
         rhs: ExpressionOperandId,
-    ) -> CoverageKind {
+        debug_block_label_fn: F,
+    ) -> CoverageKind
+    where
+        F: Fn() -> Option<String>,
+    {
         let id = self.next_expression();
-        CoverageKind::Expression { id, lhs, op, rhs }
+        let expression = CoverageKind::Expression { id, lhs, op, rhs };
+        if self.debug_counters.is_enabled() {
+            self.debug_counters.add_counter(&expression, (debug_block_label_fn)());
+        }
+        expression
     }
 
     /// Counter IDs start from one and go up.