Do not insert duplicate SourceFile

compiler/rustc_span/src/source_map.rs

@@ -12,6 +12,7 @@
 use std::io::{self, BorrowedBuf, Read};
 use std::{fs, path};
 
+use rustc_data_structures::fx::StdEntry;
 use rustc_data_structures::sync::{IntoDynSyncSend, MappedReadGuard, ReadGuard, RwLock};
 use rustc_data_structures::unhash::UnhashMap;
 use rustc_macros::{Decodable, Encodable};
@@ -282,20 +283,24 @@ impl SourceMap {
  mut file: SourceFile,
  ) -> Result<Arc<SourceFile>, OffsetOverflowError> {
  let mut files = self.files.borrow_mut();
+ let SourceMapFiles { source_files, stable_id_to_source_file } = &mut *files;
+ let file = match stable_id_to_source_file.entry(file_id) {
+ StdEntry::Occupied(o) => o.into_mut(),
+ StdEntry::Vacant(v) => {
+ file.start_pos = BytePos(if let Some(last_file) = source_files.last() {
+ // Add one so there is some space between files. This lets us distinguish
+ // positions in the `SourceMap`, even in the presence of zero-length files.
+ last_file.end_position().0.checked_add(1).ok_or(OffsetOverflowError)?
+ } else {
+ 0
+ });
 
- file.start_pos = BytePos(if let Some(last_file) = files.source_files.last() {
- // Add one so there is some space between files. This lets us distinguish
- // positions in the `SourceMap`, even in the presence of zero-length files.
- last_file.end_position().0.checked_add(1).ok_or(OffsetOverflowError)?
- } else {
- 0
- });
-
- let file = Arc::new(file);
- files.source_files.push(Arc::clone(&file));
- files.stable_id_to_source_file.insert(file_id, Arc::clone(&file));
-
- Ok(file)
+ let file = Arc::new(file);
+ source_files.push(Arc::clone(&file));
+ v.insert(file)
+ }
+ };
+ Ok(Arc::clone(file))
  }
 
  /// Creates a new `SourceFile`.

compiler/rustc_span/src/source_map/tests.rs

@@ -234,15 +234,17 @@ fn t10() {
  lines,
  multibyte_chars,
  normalized_pos,
- stable_id,
+ stable_id: _,
  ..
  } = (*src_file).clone();
 
  let imported_src_file = sm.new_imported_source_file(
  name,
  src_hash,
  checksum_hash,
- stable_id,
+ StableSourceFileId::from_filename_in_current_crate(
+ &PathBuf::from("imported-blork.rs").into(),
+ ),
  source_len.to_u32(),
  CrateNum::ZERO,
  FreezeLock::new(lines.read().clone()),