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.

3 files changed, 41 insertions, 7 deletions

diff --git a/src/librustc_errors/emitter.rs b/src/librustc_errors/emitter.rs
index ffb5efd93ed..a59f68a6442 100644
--- a/src/librustc_errors/emitter.rs
+++ b/src/librustc_errors/emitter.rs
@@ -106,6 +106,7 @@ pub struct EmitterWriter {
     dst: Destination,
     cm: Option<Rc<CodeMapper>>,
     short_message: bool,
+    teach: bool,
 }
 
 struct FileWithAnnotatedLines {
@@ -117,32 +118,37 @@ struct FileWithAnnotatedLines {
 impl EmitterWriter {
     pub fn stderr(color_config: ColorConfig,
                   code_map: Option<Rc<CodeMapper>>,
-                  short_message: bool)
+                  short_message: bool,
+                  teach: bool)
                   -> EmitterWriter {
         if color_config.use_color() {
             let dst = Destination::from_stderr();
             EmitterWriter {
                 dst,
                 cm: code_map,
-                short_message: short_message,
+                short_message,
+                teach,
             }
         } else {
             EmitterWriter {
                 dst: Raw(Box::new(io::stderr())),
                 cm: code_map,
-                short_message: short_message,
+                short_message,
+                teach,
             }
         }
     }
 
     pub fn new(dst: Box<Write + Send>,
                code_map: Option<Rc<CodeMapper>>,
-               short_message: bool)
+               short_message: bool,
+               teach: bool)
                -> EmitterWriter {
         EmitterWriter {
             dst: Raw(dst),
             cm: code_map,
-            short_message: short_message,
+            short_message,
+            teach,
         }
     }
 
@@ -551,7 +557,14 @@ impl EmitterWriter {
                                code_offset + annotation.start_col,
                                style);
                 }
-                _ => (),
+                _ if self.teach => {
+                    buffer.set_style_range(line_offset,
+                                           code_offset + annotation.start_col,
+                                           code_offset + annotation.end_col,
+                                           style,
+                                           annotation.is_primary);
+                }
+                _ => {}
             }
         }
 
diff --git a/src/librustc_errors/lib.rs b/src/librustc_errors/lib.rs
index 3d50c95d3f4..47eb04621a1 100644
--- a/src/librustc_errors/lib.rs
+++ b/src/librustc_errors/lib.rs
@@ -297,7 +297,7 @@ impl Handler {
                                       cm: Option<Rc<CodeMapper>>,
                                       flags: HandlerFlags)
                                       -> Handler {
-        let emitter = Box::new(EmitterWriter::stderr(color_config, cm, false));
+        let emitter = Box::new(EmitterWriter::stderr(color_config, cm, false, false));
         Handler::with_emitter_and_flags(emitter, flags)
     }
 
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;
+                }
+            }
+        }
+    }
 }