coverage: Don't refer to the body span when enlarging empty spans

Given that we now only enlarge empty spans to "{" or "}", there shouldn't be
any danger of enlarging beyond a function body.

Author: Zalathar

compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/covfun.rs

@@ -118,9 +118,8 @@ fn fill_region_tables<'tcx>(
     let ffi::Regions { code_regions, branch_regions, mcdc_branch_regions, mcdc_decision_regions } =
         &mut covfun.regions;
 
-    let make_cov_span = |span: Span| {
-        spans::make_coverage_span(local_file_id, source_map, fn_cov_info, &source_file, span)
-    };
+    let make_cov_span =
+        |span: Span| spans::make_coverage_span(local_file_id, source_map, &source_file, span);
     let discard_all = tcx.sess.coverage_discard_all_spans_in_codegen();
 
     // For each counter/region pair in this function+file, convert it to a

compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/spans.rs

@@ -1,4 +1,3 @@
-use rustc_middle::mir::coverage::FunctionCoverageInfo;
 use rustc_span::source_map::SourceMap;
 use rustc_span::{BytePos, Pos, SourceFile, Span};
 use tracing::debug;
@@ -19,11 +18,10 @@ use crate::coverageinfo::mapgen::LocalFileId;
 pub(crate) fn make_coverage_span(
     file_id: LocalFileId,
     source_map: &SourceMap,
-    fn_cov_info: &FunctionCoverageInfo,
     file: &SourceFile,
     span: Span,
 ) -> Option<ffi::CoverageSpan> {
-    let span = ensure_non_empty_span(source_map, fn_cov_info, span)?;
+    let span = ensure_non_empty_span(source_map, span)?;
 
     let lo = span.lo();
     let hi = span.hi();
@@ -55,36 +53,22 @@ pub(crate) fn make_coverage_span(
     })
 }
 
-fn ensure_non_empty_span(
-    source_map: &SourceMap,
-    fn_cov_info: &FunctionCoverageInfo,
-    span: Span,
-) -> Option<Span> {
+fn ensure_non_empty_span(source_map: &SourceMap, span: Span) -> Option<Span> {
     if !span.is_empty() {
         return Some(span);
     }
 
-    let lo = span.lo();
-    let hi = span.hi();
-
-    // The span is empty, so try to expand it to cover an adjacent '{' or '}',
-    // but only within the bounds of the body span.
-    let try_next = hi < fn_cov_info.body_span.hi();
-    let try_prev = fn_cov_info.body_span.lo() < lo;
-    if !(try_next || try_prev) {
-        return None;
-    }
-
+    // The span is empty, so try to enlarge it to cover an adjacent '{' or '}'.
     source_map
         .span_to_source(span, |src, start, end| try {
             // Adjusting span endpoints by `BytePos(1)` is normally a bug,
             // but in this case we have specifically checked that the character
             // we're skipping over is one of two specific ASCII characters, so
             // adjusting by exactly 1 byte is correct.
-            if try_next && src.as_bytes()[end] == b'{' {
-                Some(span.with_hi(hi + BytePos(1)))
-            } else if try_prev && src.as_bytes()[start - 1] == b'}' {
-                Some(span.with_lo(lo - BytePos(1)))
+            if src.as_bytes().get(end).copied() == Some(b'{') {
+                Some(span.with_hi(span.hi() + BytePos(1)))
+            } else if start > 0 && src.as_bytes()[start - 1] == b'}' {
+                Some(span.with_lo(span.lo() - BytePos(1)))
             } else {
                 None
             }