Auto merge of #45752 - estebank:highlight-primary, r=nikomatsakis

Highlight code on diagnostics when underlined

Highlight the label's span with the respective color:

<img width="692" alt="" src="https://user-images.githubusercontent.com/1606434/32411026-a1842482-c18d-11e7-9933-6510eefbad19.png">

Fix #42112.

1 files changed, 21 insertions, 0 deletions

diff --git a/src/librustc_errors/styled_buffer.rs b/src/librustc_errors/styled_buffer.rs
index 2c33f805203..2c736ec22c3 100644
--- a/src/librustc_errors/styled_buffer.rs
+++ b/src/librustc_errors/styled_buffer.rs
@@ -144,4 +144,25 @@ impl StyledBuffer {
     pub fn num_lines(&self) -> usize {
         self.text.len()
     }
+
+    pub fn set_style_range(&mut self,
+                           line: usize,
+                           col_start: usize,
+                           col_end: usize,
+                           style: Style,
+                           overwrite: bool) {
+        for col in col_start..col_end {
+            self.set_style(line, col, style, overwrite);
+        }
+    }
+
+    pub fn set_style(&mut self, line: usize, col: usize, style: Style, overwrite: bool) {
+        if let Some(ref mut line) = self.styles.get_mut(line) {
+            if let Some(s) = line.get_mut(col) {
+                if *s == Style::NoStyle || *s == Style::Quotation || overwrite {
+                    *s = style;
+                }
+            }
+        }
+    }
 }