Move -Z maximal-hir-to-mir-coverage implementation to new `maybe_new_source_scope` method

2 files changed, 44 insertions, 32 deletions

diff --git a/compiler/rustc_mir_build/src/build/mod.rs b/compiler/rustc_mir_build/src/build/mod.rs
index b456e2aa37a..007f3b55ec8 100644
--- a/compiler/rustc_mir_build/src/build/mod.rs
+++ b/compiler/rustc_mir_build/src/build/mod.rs
@@ -948,20 +948,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         original_source_scope: SourceScope,
         pattern_span: Span,
     ) {
-        let tcx = self.tcx;
-        let current_root = tcx.maybe_lint_level_root_bounded(arg_hir_id, self.hir_id);
-        let parent_root = tcx.maybe_lint_level_root_bounded(
-            self.source_scopes[original_source_scope]
-                .local_data
-                .as_ref()
-                .assert_crate_local()
-                .lint_root,
-            self.hir_id,
-        );
-        if current_root != parent_root {
-            self.source_scope =
-                self.new_source_scope(pattern_span, LintLevel::Explicit(current_root), None);
-        }
+        let parent_id = self.source_scopes[original_source_scope]
+            .local_data
+            .as_ref()
+            .assert_crate_local()
+            .lint_root;
+        self.maybe_new_source_scope(pattern_span, None, arg_hir_id, parent_id);
     }
 
     fn get_unit_temp(&mut self) -> Place<'tcx> {
diff --git a/compiler/rustc_mir_build/src/build/scope.rs b/compiler/rustc_mir_build/src/build/scope.rs
index 5ddae5f5300..33f49ffdaf6 100644
--- a/compiler/rustc_mir_build/src/build/scope.rs
+++ b/compiler/rustc_mir_build/src/build/scope.rs
@@ -85,6 +85,7 @@ use std::mem;
 
 use crate::build::{BlockAnd, BlockAndExtension, BlockFrame, Builder, CFG};
 use rustc_data_structures::fx::FxHashMap;
+use rustc_hir::HirId;
 use rustc_index::vec::IndexVec;
 use rustc_middle::middle::region;
 use rustc_middle::mir::*;
@@ -567,25 +568,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         F: FnOnce(&mut Builder<'a, 'tcx>) -> BlockAnd<R>,
     {
         let source_scope = self.source_scope;
-        let tcx = self.tcx;
         if let LintLevel::Explicit(current_hir_id) = lint_level {
-            // Use `maybe_lint_level_root_bounded` with `root_lint_level` as a bound
-            // to avoid adding Hir dependencies on our parents.
-            // We estimate the true lint roots here to avoid creating a lot of source scopes.
-
-            let parent_root = tcx.maybe_lint_level_root_bounded(
-                self.source_scopes[source_scope].local_data.as_ref().assert_crate_local().lint_root,
-                self.hir_id,
-            );
-            let current_root = tcx.maybe_lint_level_root_bounded(current_hir_id, self.hir_id);
-
-            if parent_root != current_root {
-                self.source_scope = self.new_source_scope(
-                    region_scope.1.span,
-                    LintLevel::Explicit(current_root),
-                    None,
-                );
-            }
+            let parent_id =
+                self.source_scopes[source_scope].local_data.as_ref().assert_crate_local().lint_root;
+            self.maybe_new_source_scope(region_scope.1.span, None, current_hir_id, parent_id);
         }
         self.push_scope(region_scope);
         let mut block;
@@ -758,6 +744,40 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         ))
     }
 
+    /// Possibly creates a new source scope if `current_root` and `parent_root`
+    /// are different, or if -Zmaximal-hir-to-mir-coverage is enabled.
+    pub(crate) fn maybe_new_source_scope(
+        &mut self,
+        span: Span,
+        safety: Option<Safety>,
+        current_id: HirId,
+        parent_id: HirId,
+    ) {
+        let (current_root, parent_root) =
+            if self.tcx.sess.opts.unstable_opts.maximal_hir_to_mir_coverage {
+                // Some consumers of rustc need to map MIR locations back to HIR nodes. Currently the
+                // the only part of rustc that tracks MIR -> HIR is the `SourceScopeLocalData::lint_root`
+                // field that tracks lint levels for MIR locations.  Normally the number of source scopes
+                // is limited to the set of nodes with lint annotations. The -Zmaximal-hir-to-mir-coverage
+                // flag changes this behavior to maximize the number of source scopes, increasing the
+                // granularity of the MIR->HIR mapping.
+                (current_id, parent_id)
+            } else {
+                // Use `maybe_lint_level_root_bounded` with `self.hir_id` as a bound
+                // to avoid adding Hir dependencies on our parents.
+                // We estimate the true lint roots here to avoid creating a lot of source scopes.
+                (
+                    self.tcx.maybe_lint_level_root_bounded(current_id, self.hir_id),
+                    self.tcx.maybe_lint_level_root_bounded(parent_id, self.hir_id),
+                )
+            };
+
+        if current_root != parent_root {
+            let lint_level = LintLevel::Explicit(current_root);
+            self.source_scope = self.new_source_scope(span, lint_level, safety);
+        }
+    }
+
     /// Creates a new source scope, nested in the current one.
     pub(crate) fn new_source_scope(
         &mut self,