1 files changed, 8 insertions, 4 deletions
diff --git a/compiler/rustc_span/src/source_map.rs b/compiler/rustc_span/src/source_map.rs
index e9b4eb6e4ab..6635d44496c 100644
--- a/compiler/rustc_span/src/source_map.rs
+++ b/compiler/rustc_span/src/source_map.rs
@@ -1,9 +1,11 @@
-//! The `SourceMap` tracks all the source code used within a single crate, mapping
+//! Types for tracking pieces of source code within a crate.
+//!
+//! The [`SourceMap`] tracks all the source code used within a single crate, mapping
 //! from integer byte positions to the original source code location. Each bit
 //! of source parsed during crate parsing (typically files, in-memory strings,
 //! or various bits of macro expansion) cover a continuous range of bytes in the
-//! `SourceMap` and are represented by `SourceFile`s. Byte positions are stored in
-//! `Span` and used pervasively in the compiler. They are absolute positions
+//! `SourceMap` and are represented by [`SourceFile`]s. Byte positions are stored in
+//! [`Span`] and used pervasively in the compiler. They are absolute positions
 //! within the `SourceMap`, which upon request can be converted to line and column
 //! information, source code snippets, etc.
 
@@ -669,7 +671,9 @@ impl SourceMap {
             let pat = pat.to_owned() + ws;
             if let Ok(prev_source) = self.span_to_prev_source(sp) {
                 let prev_source = prev_source.rsplit(&pat).next().unwrap_or("").trim_start();
-                if !prev_source.is_empty() && (!prev_source.contains('\n') || accept_newlines) {
+                if prev_source.is_empty() && sp.lo().0 != 0 {
+                    return sp.with_lo(BytePos(sp.lo().0 - 1));
+                } else if !prev_source.contains('\n') || accept_newlines {
                     return sp.with_lo(BytePos(sp.lo().0 - prev_source.len() as u32));
                 }
             }