Bug fix: fix spurious application of non-emph styles

2 files changed, 24 insertions, 4 deletions

diff --git a/src/edits.rs b/src/edits.rs
index f19d25b0..7b6e4674 100644
--- a/src/edits.rs
+++ b/src/edits.rs
@@ -100,9 +100,11 @@ fn tokenize(line: &str) -> Vec<&str> {
 }
 
 /// Use alignment to "annotate" minus and plus lines. An "annotated" line is a sequence of
-/// (s: &str, a: Annotation) pairs, where the &strs reference the memory
+/// (a: Annotation, s: &str) pairs, where the &strs reference the memory
 /// of the original line and their concatenation equals the line.
-// TODO: Coalesce runs of the same operation.
+// This function doesn't return "coalesced" annotations: i.e. they're often are runs of consecutive
+// occurrences of the same operation. Since it is returning &strs pointing into the memory of the
+// original line, it's not possible to coalesce them in this function.
 fn annotate<'a, Annotation>(
     alignment: align::Alignment<'a>,
     noop_deletion: Annotation,
diff --git a/src/paint.rs b/src/paint.rs
index 85939890..60f72519 100644
--- a/src/paint.rs
+++ b/src/paint.rs
@@ -123,7 +123,7 @@ impl<'a> Painter<'a> {
         for (syntax_sections, diff_sections) in
             syntax_style_sections.iter().zip(diff_style_sections.iter())
         {
-            let right_fill_style = if diff_sections.len() > 1 {
+            let right_fill_style = if style_sections_contain_more_than_one_style(diff_sections) {
                 non_emph_style // line contains an emph section
             } else {
                 base_style
@@ -258,7 +258,10 @@ impl<'a> Painter<'a> {
         non_emph_style: Style,
     ) {
         for line_sections in style_sections {
-            if line_sections.len() > 1 {
+            // If there multiple diff styles in the line, then the line must have some inferred
+            // edit operations and so the non-emph color style should be used for the non-emph
+            // style sections.
+            if style_sections_contain_more_than_one_style(line_sections) {
                 for section in line_sections.iter_mut() {
                     if section.0 != emph_style {
                         *section = (non_emph_style, section.1);
@@ -269,6 +272,21 @@ impl<'a> Painter<'a> {
     }
 }
 
+// edits::annotate doesn't return "coalesced" annotations (see comment there), so we can't assume
+// that `sections.len() > 1 <=> (multiple styles)`.
+fn style_sections_contain_more_than_one_style(sections: &Vec<(Style, &str)>) -> bool {
+    if sections.len() > 1 {
+        let (first_style, _) = sections[0];
+        sections
+            .iter()
+            .filter(|(style, _)| *style != first_style)
+            .next()
+            .is_some()
+    } else {
+        false
+    }
+}
+
 mod superimpose_style_sections {
     use syntect::highlighting::Style as SyntectStyle;