small cleanups in rustc_errors / emitter

compiler/rustc_errors/src/emitter.rs

@@ -434,34 +434,31 @@ pub trait Emitter {
         span: &mut MultiSpan,
         children: &mut Vec<SubDiagnostic>,
     ) {
+        let source_map = if let Some(ref sm) = source_map {
+            sm
+        } else {
+            return;
+        };
         debug!("fix_multispans_in_extern_macros: before: span={:?} children={:?}", span, children);
-        for span in iter::once(&mut *span).chain(children.iter_mut().map(|child| &mut child.span)) {
-            self.fix_multispan_in_extern_macros(source_map, span);
+        self.fix_multispan_in_extern_macros(source_map, span);
+        for child in children.iter_mut() {
+            self.fix_multispan_in_extern_macros(source_map, &mut child.span);
         }
         debug!("fix_multispans_in_extern_macros: after: span={:?} children={:?}", span, children);
     }
 
     // This "fixes" MultiSpans that contain `Span`s pointing to locations inside of external macros.
     // Since these locations are often difficult to read,
     // we move these spans from the external macros to their corresponding use site.
-    fn fix_multispan_in_extern_macros(
-        &self,
-        source_map: &Option<Lrc<SourceMap>>,
-        span: &mut MultiSpan,
-    ) {
-        let sm = match source_map {
-            Some(ref sm) => sm,
-            None => return,
-        };
-
+    fn fix_multispan_in_extern_macros(&self, source_map: &Lrc<SourceMap>, span: &mut MultiSpan) {
         // First, find all the spans in external macros and point instead at their use site.
         let replacements: Vec<(Span, Span)> = span
             .primary_spans()
             .iter()
             .copied()
             .chain(span.span_labels().iter().map(|sp_label| sp_label.span))
             .filter_map(|sp| {
-                if !sp.is_dummy() && sm.is_imported(sp) {
+                if !sp.is_dummy() && source_map.is_imported(sp) {
                     let maybe_callsite = sp.source_callsite();
                     if sp != maybe_callsite {
                         return Some((sp, maybe_callsite));
@@ -1232,7 +1229,6 @@ impl EmitterWriter {
         is_secondary: bool,
     ) -> io::Result<()> {
         let mut buffer = StyledBuffer::new();
-        let header_style = if is_secondary { Style::HeaderMsg } else { Style::MainHeaderMsg };
 
         if !msp.has_primary_spans() && !msp.has_span_labels() && is_secondary && !self.short_message
         {
@@ -1257,6 +1253,7 @@ impl EmitterWriter {
                 buffer.append(0, &code, Style::Level(*level));
                 buffer.append(0, "]", Style::Level(*level));
             }
+            let header_style = if is_secondary { Style::HeaderMsg } else { Style::MainHeaderMsg };
             if *level != Level::FailureNote {
                 buffer.append(0, ": ", header_style);
             }
@@ -1470,9 +1467,7 @@ impl EmitterWriter {
                     let mut to_add = FxHashMap::default();
 
                     for (depth, style) in depths {
-                        if multilines.get(&depth).is_some() {
-                            multilines.remove(&depth);
-                        } else {
+                        if multilines.remove(&depth).is_none() {
                             to_add.insert(depth, style);
                         }
                     }
@@ -1726,14 +1721,13 @@ impl EmitterWriter {
                     if !self.short_message {
                         draw_col_separator_no_space(&mut buffer, 0, max_line_num_len + 1);
                     }
-                    match emit_to_destination(
+                    if let Err(e) = emit_to_destination(
                         &buffer.render(),
                         level,
                         &mut self.dst,
                         self.short_message,
                     ) {
-                        Ok(()) => (),
-                        Err(e) => panic!("failed to emit error: {}", e),
+                        panic!("failed to emit error: {}", e)
                     }
                 }
                 if !self.short_message {