Expose max-buffered-lines as a new option

Fixes #427

src/cli.rs

@@ -509,6 +509,15 @@ pub struct Opt {
     #[structopt(long = "whitespace-error-style", default_value = "auto auto")]
     pub whitespace_error_style: String,
 
+    #[structopt(long = "line-buffer-size", default_value = "32")]
+    /// Size of internal line buffer. Delta compares the added and removed versions of nearby lines
+    /// in order to detect and highlight changes at the level of individual words/tokens.
+    /// Therefore, nearby lines must be buffered internally before they are painted and emitted.
+    /// Increasing this value might improve highlighting of some large diff hunks. However, setting
+    /// this to a high value will adversely affect delta's performance when entire files are
+    /// added/removed.
+    pub line_buffer_size: usize,
+
     #[structopt(long = "minus-color")]
     /// Deprecated: use --minus-style='normal my_background_color'.
     pub deprecated_minus_background_color: Option<String>,

src/config.rs

@@ -43,7 +43,7 @@ pub struct Config {
     pub line_numbers_right_style: Style,
     pub line_numbers_show_first_line_number: bool,
     pub line_numbers_zero_style: Style,
-    pub max_buffered_lines: usize,
+    pub line_buffer_size: usize,
     pub max_line_distance: f64,
     pub max_line_distance_for_naively_paired_lines: f64,
     pub max_line_length: usize,
@@ -173,7 +173,7 @@ impl From<cli::Opt> for Config {
             line_numbers_show_first_line_number: (opt.computed.line_numbers_mode
                 == cli::LineNumbersMode::First),
             line_numbers_zero_style,
-            max_buffered_lines: 32,
+            line_buffer_size: opt.line_buffer_size,
             max_line_distance: opt.max_line_distance,
             max_line_distance_for_naively_paired_lines,
             max_line_length: opt.max_line_length,

src/delta.rs

@@ -518,8 +518,8 @@ fn handle_hunk_line(
     // Don't let the line buffers become arbitrarily large -- if we
     // were to allow that, then for a large deleted/added file we
     // would process the entire file before painting anything.
-    if painter.minus_lines.len() > config.max_buffered_lines
-        || painter.plus_lines.len() > config.max_buffered_lines
+    if painter.minus_lines.len() > config.line_buffer_size
+        || painter.plus_lines.len() > config.line_buffer_size
     {
         painter.paint_buffered_minus_and_plus_lines();
     }

src/options/set.rs

@@ -141,6 +141,7 @@ pub fn set_options(
             hyperlinks_file_link_format,
             inspect_raw_lines,
             keep_plus_minus_markers,
+            line_buffer_size,
             max_line_distance,
             max_line_length,
             // Hack: minus-style must come before minus-*emph-style because the latter default