coverage: Avoid getting extra unexpansion info when we don't need it

compiler/rustc_mir_transform/src/coverage/mappings.rs

@@ -9,9 +9,8 @@ use rustc_middle::ty::TyCtxt;
 use rustc_span::Span;
 
 use crate::coverage::graph::{BasicCoverageBlock, CoverageGraph, START_BCB};
-use crate::coverage::spans::{
-    extract_refined_covspans, unexpand_into_body_span_with_visible_macro,
-};
+use crate::coverage::spans::extract_refined_covspans;
+use crate::coverage::unexpand::unexpand_into_body_span;
 use crate::coverage::ExtractedHirInfo;
 
 /// Associates an ordinary executable code span with its corresponding BCB.
@@ -202,8 +201,7 @@ pub(super) fn extract_branch_pairs(
             if !raw_span.ctxt().outer_expn_data().is_root() {
                 return None;
             }
-            let (span, _) =
-                unexpand_into_body_span_with_visible_macro(raw_span, hir_info.body_span)?;
+            let span = unexpand_into_body_span(raw_span, hir_info.body_span)?;
 
             let bcb_from_marker =
                 |marker: BlockMarkerId| basic_coverage_blocks.bcb_from_bb(block_markers[marker]?);
@@ -238,7 +236,7 @@ pub(super) fn extract_mcdc_mappings(
             if !raw_span.ctxt().outer_expn_data().is_root() {
                 return None;
             }
-            let (span, _) = unexpand_into_body_span_with_visible_macro(raw_span, body_span)?;
+            let span = unexpand_into_body_span(raw_span, body_span)?;
 
             let true_bcb = bcb_from_marker(true_marker)?;
             let false_bcb = bcb_from_marker(false_marker)?;
@@ -261,7 +259,7 @@ pub(super) fn extract_mcdc_mappings(
 
     mcdc_decisions.extend(branch_info.mcdc_decision_spans.iter().filter_map(
         |decision: &mir::coverage::MCDCDecisionSpan| {
-            let (span, _) = unexpand_into_body_span_with_visible_macro(decision.span, body_span)?;
+            let span = unexpand_into_body_span(decision.span, body_span)?;
 
             let end_bcbs = decision
                 .end_markers

compiler/rustc_mir_transform/src/coverage/mod.rs

@@ -6,6 +6,7 @@ mod mappings;
 mod spans;
 #[cfg(test)]
 mod tests;
+mod unexpand;
 
 use rustc_middle::mir::coverage::{
     CodeRegion, CoverageKind, DecisionInfo, FunctionCoverageInfo, Mapping, MappingKind,

compiler/rustc_mir_transform/src/coverage/spans.rs

@@ -14,11 +14,6 @@ use crate::coverage::ExtractedHirInfo;
 
 mod from_mir;
 
-// FIXME(#124545) It's awkward that we have to re-export this, because it's an
-// internal detail of `from_mir` that is also needed when handling branch and
-// MC/DC spans. Ideally we would find a more natural home for it.
-pub(super) use from_mir::unexpand_into_body_span_with_visible_macro;
-
 pub(super) fn extract_refined_covspans(
     mir_body: &mir::Body<'_>,
     hir_info: &ExtractedHirInfo,

compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs

@@ -4,12 +4,13 @@ use rustc_middle::mir::{
     self, AggregateKind, FakeReadCause, Rvalue, Statement, StatementKind, Terminator,
     TerminatorKind,
 };
-use rustc_span::{ExpnKind, MacroKind, Span, Symbol};
+use rustc_span::{Span, Symbol};
 
 use crate::coverage::graph::{
     BasicCoverageBlock, BasicCoverageBlockData, CoverageGraph, START_BCB,
 };
 use crate::coverage::spans::Covspan;
+use crate::coverage::unexpand::unexpand_into_body_span_with_visible_macro;
 use crate::coverage::ExtractedHirInfo;
 
 pub(crate) struct ExtractedCovspans {
@@ -215,59 +216,6 @@ fn filtered_terminator_span(terminator: &Terminator<'_>) -> Option<Span> {
     }
 }
 
-/// Returns an extrapolated span (pre-expansion[^1]) corresponding to a range
-/// within the function's body source. This span is guaranteed to be contained
-/// within, or equal to, the `body_span`. If the extrapolated span is not
-/// contained within the `body_span`, `None` is returned.
-///
-/// [^1]Expansions result from Rust syntax including macros, syntactic sugar,
-/// etc.).
-pub(crate) fn unexpand_into_body_span_with_visible_macro(
-    original_span: Span,
-    body_span: Span,
-) -> Option<(Span, Option<Symbol>)> {
-    let (span, prev) = unexpand_into_body_span_with_prev(original_span, body_span)?;
-
-    let visible_macro = prev
-        .map(|prev| match prev.ctxt().outer_expn_data().kind {
-            ExpnKind::Macro(MacroKind::Bang, name) => Some(name),
-            _ => None,
-        })
-        .flatten();
-
-    Some((span, visible_macro))
-}
-
-/// Walks through the expansion ancestors of `original_span` to find a span that
-/// is contained in `body_span` and has the same [`SyntaxContext`] as `body_span`.
-/// The ancestor that was traversed just before the matching span (if any) is
-/// also returned.
-///
-/// For example, a return value of `Some((ancestor, Some(prev))` means that:
-/// - `ancestor == original_span.find_ancestor_inside_same_ctxt(body_span)`
-/// - `ancestor == prev.parent_callsite()`
-///
-/// [`SyntaxContext`]: rustc_span::SyntaxContext
-fn unexpand_into_body_span_with_prev(
-    original_span: Span,
-    body_span: Span,
-) -> Option<(Span, Option<Span>)> {
-    let mut prev = None;
-    let mut curr = original_span;
-
-    while !body_span.contains(curr) || !curr.eq_ctxt(body_span) {
-        prev = Some(curr);
-        curr = curr.parent_callsite()?;
-    }
-
-    debug_assert_eq!(Some(curr), original_span.find_ancestor_in_same_ctxt(body_span));
-    if let Some(prev) = prev {
-        debug_assert_eq!(Some(curr), prev.parent_callsite());
-    }
-
-    Some((curr, prev))
-}
-
 #[derive(Debug)]
 pub(crate) struct Hole {
     pub(crate) span: Span,

compiler/rustc_mir_transform/src/coverage/unexpand.rs

@@ -0,0 +1,60 @@
+use rustc_span::{ExpnKind, MacroKind, Span, Symbol};
+
+/// Walks through the expansion ancestors of `original_span` to find a span that
+/// is contained in `body_span` and has the same [syntax context] as `body_span`.
+pub(crate) fn unexpand_into_body_span(original_span: Span, body_span: Span) -> Option<Span> {
+    // Because we don't need to return any extra ancestor information,
+    // we can just delegate directly to `find_ancestor_inside_same_ctxt`.
+    original_span.find_ancestor_inside_same_ctxt(body_span)
+}
+
+/// Walks through the expansion ancestors of `original_span` to find a span that
+/// is contained in `body_span` and has the same [syntax context] as `body_span`.
+///
+/// If the returned span represents a bang-macro invocation (e.g. `foo!(..)`),
+/// the returned symbol will be the name of that macro (e.g. `foo`).
+pub(crate) fn unexpand_into_body_span_with_visible_macro(
+    original_span: Span,
+    body_span: Span,
+) -> Option<(Span, Option<Symbol>)> {
+    let (span, prev) = unexpand_into_body_span_with_prev(original_span, body_span)?;
+
+    let visible_macro = prev
+        .map(|prev| match prev.ctxt().outer_expn_data().kind {
+            ExpnKind::Macro(MacroKind::Bang, name) => Some(name),
+            _ => None,
+        })
+        .flatten();
+
+    Some((span, visible_macro))
+}
+
+/// Walks through the expansion ancestors of `original_span` to find a span that
+/// is contained in `body_span` and has the same [syntax context] as `body_span`.
+/// The ancestor that was traversed just before the matching span (if any) is
+/// also returned.
+///
+/// For example, a return value of `Some((ancestor, Some(prev)))` means that:
+/// - `ancestor == original_span.find_ancestor_inside_same_ctxt(body_span)`
+/// - `prev.parent_callsite() == ancestor`
+///
+/// [syntax context]: rustc_span::SyntaxContext
+fn unexpand_into_body_span_with_prev(
+    original_span: Span,
+    body_span: Span,
+) -> Option<(Span, Option<Span>)> {
+    let mut prev = None;
+    let mut curr = original_span;
+
+    while !body_span.contains(curr) || !curr.eq_ctxt(body_span) {
+        prev = Some(curr);
+        curr = curr.parent_callsite()?;
+    }
+
+    debug_assert_eq!(Some(curr), original_span.find_ancestor_inside_same_ctxt(body_span));
+    if let Some(prev) = prev {
+        debug_assert_eq!(Some(curr), prev.parent_callsite());
+    }
+
+    Some((curr, prev))
+}