Avoid another &Lrc<..> in a return value.

compiler/rustc_span/src/lib.rs

@@ -1380,7 +1380,7 @@ pub enum ExternalSourceKind {
 }
 
 impl ExternalSource {
-    pub fn get_source(&self) -> Option<&Lrc<String>> {
+    pub fn get_source(&self) -> Option<&str> {
         match self {
             ExternalSource::Foreign { kind: ExternalSourceKind::Present(ref src), .. } => Some(src),
             _ => None,

compiler/rustc_span/src/source_map/tests.rs

@@ -257,7 +257,7 @@ fn t10() {
     );
     imported_src_file.add_external_src(|| Some(unnormalized.to_string()));
     assert_eq!(
-        imported_src_file.external_src.borrow().get_source().unwrap().as_ref(),
+        imported_src_file.external_src.borrow().get_source().unwrap(),
         normalized,
         "imported source file should be normalized"
     );

src/tools/clippy/clippy_utils/src/source.rs

@@ -287,6 +287,7 @@ pub fn as_str(&self) -> Option<&str> {
         self.sf
             .src
             .as_ref()
+            .map(|src| src.as_str())
             .or_else(|| self.sf.external_src.get().and_then(|src| src.get_source()))
             .and_then(|x| x.get(self.range.clone()))
     }