Auto merge of #43270 - petrochenkov:fixstab, r=alexcrichton

[rust.git] / src / librustc_errors / emitter.rs

diff --git a/src/librustc_errors/emitter.rs b/src/librustc_errors/emitter.rs
index 3e8bd093f4f93f0a19ba063ae30d8179bb7c7c8c..ad2562e28fa4f5b001d88200144f0de85e01d455 100644 (file)
--- a/src/librustc_errors/emitter.rs
+++ b/src/librustc_errors/emitter.rs
@@ -346,9 +346,20 @@ fn render_source_line(&self,
         // and "annotations lines", where the highlight lines have the `^`.
 
         // Sort the annotations by (start, end col)
+        // The labels are reversed, sort and then reversed again.
+        // Consider a list of annotations (A1, A2, C1, C2, B1, B2) where
+        // the letter signifies the span. Here we are only sorting by the
+        // span and hence, the order of the elements with the same span will
+        // not change. On reversing the ordering (|a, b| but b.cmp(a)), you get
+        // (C1, C2, B1, B2, A1, A2). All the elements with the same span are
+        // still ordered first to last, but all the elements with different
+        // spans are ordered by their spans in last to first order. Last to
+        // first order is important, because the jiggly lines and | are on
+        // the left, so the rightmost span needs to be rendered first,
+        // otherwise the lines would end up needing to go over a message.
+
         let mut annotations = line.annotations.clone();
-        annotations.sort();
-        annotations.reverse();
+        annotations.sort_by(|a,b| b.start_col.cmp(&a.start_col));
 
         // First, figure out where each label will be positioned.
         //