coverage: Add a coverage field to the MIR builder

Author: Zalathar

compiler/rustc_mir_build/src/build/coverageinfo.rs

@@ -5,15 +5,23 @@ use rustc_middle::ty::TyCtxt;
 use rustc_span::def_id::LocalDefId;
 use rustc_span::{ExpnKind, Span};
 
-/// If the given item is eligible for coverage instrumentation, collect relevant
-/// HIR information that will be needed by the instrumentor pass.
-pub(crate) fn make_coverage_hir_info_if_eligible(
-    tcx: TyCtxt<'_>,
-    def_id: LocalDefId,
-) -> Option<Box<mir::coverage::HirInfo>> {
-    assert!(tcx.sess.instrument_coverage());
+pub(crate) struct HirInfoBuilder {
+    // Currently there is no extra state tracked here.
+}
 
-    is_eligible_for_coverage(tcx, def_id).then(|| Box::new(make_coverage_hir_info(tcx, def_id)))
+impl HirInfoBuilder {
+    pub(crate) fn new_if_enabled_and_eligible(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<Self> {
+        if tcx.sess.instrument_coverage() && is_eligible_for_coverage(tcx, def_id) {
+            Some(Self {})
+        } else {
+            None
+        }
+    }
+
+    pub(crate) fn finish(self, tcx: TyCtxt<'_>, def_id: LocalDefId) -> Box<mir::coverage::HirInfo> {
+        let Self {} = self;
+        Box::new(make_coverage_hir_info(tcx, def_id))
+    }
 }
 
 fn is_eligible_for_coverage(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {

compiler/rustc_mir_build/src/build/mod.rs

@@ -227,6 +227,8 @@ struct Builder<'a, 'tcx> {
     // the root (most of them do) and saves us from retracing many sub-paths
     // many times, and rechecking many nodes.
     lint_level_roots_cache: GrowableBitSet<hir::ItemLocalId>,
+
+    coverage: Option<coverageinfo::HirInfoBuilder>,
 }
 
 type CaptureMap<'tcx> = SortedIndexMultiMap<usize, hir::HirId, Capture<'tcx>>;
@@ -757,6 +759,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             unit_temp: None,
             var_debug_info: vec![],
             lint_level_roots_cache: GrowableBitSet::new_empty(),
+            coverage: coverageinfo::HirInfoBuilder::new_if_enabled_and_eligible(tcx, def),
         };
 
         assert_eq!(builder.cfg.start_new_block(), START_BLOCK);
@@ -776,12 +779,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             }
         }
 
-        let coverage_hir_info = if self.tcx.sess.instrument_coverage() {
-            coverageinfo::make_coverage_hir_info_if_eligible(self.tcx, self.def_id)
-        } else {
-            None
-        };
-
         Body::new(
             MirSource::item(self.def_id.to_def_id()),
             self.cfg.basic_blocks,
@@ -793,7 +790,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             self.fn_span,
             self.coroutine_kind,
             None,
-            coverage_hir_info,
+            self.coverage.map(|coverage| coverage.finish(self.tcx, self.def_id)),
         )
     }