cli: extract helpers from show_color_words_context_lines()

This should make the next patch a bit easier to read.

cli/src/diff_util.rs

@@ -583,30 +583,40 @@ fn show_color_words_context_lines(
     num_before: usize,
 ) -> io::Result<DiffLineNumber> {
     const SKIPPED_CONTEXT_LINE: &str = "    ...\n";
+    let extract = || -> (Vec<&[u8]>, Vec<&[u8]>, u32) {
         let mut lines = contents
             .iter()
             .flat_map(|content| content.split_inclusive(|b| *b == b'\n'))
             .fuse();
-    for line in lines.by_ref().take(num_after) {
+        let after_lines = lines.by_ref().take(num_after).collect();
-        show_color_words_line_number(formatter, Some(line_number.left), Some(line_number.right))?;
+        let before_lines = lines.by_ref().rev().take(num_before + 1).collect();
+        let num_skipped: u32 = lines.count().try_into().unwrap();
+        (after_lines, before_lines, num_skipped)
+    };
+    let show = |formatter: &mut dyn Formatter, lines: &[&[u8]], mut line_number: DiffLineNumber| {
+        for line in lines {
+            show_color_words_line_number(
+                formatter,
+                Some(line_number.left),
+                Some(line_number.right),
+            )?;
             show_color_words_inline_hunks(formatter, &[(DiffLineHunkSide::Both, line.as_ref())])?;
             line_number.left += 1;
             line_number.right += 1;
         }
-    let mut before_lines = lines.by_ref().rev().take(num_before + 1).collect_vec();
+        io::Result::Ok(line_number)
-    let num_skipped: u32 = lines.count().try_into().unwrap();
+    };
+
+    let (after_lines, mut before_lines, num_skipped) = extract();
+    line_number = show(formatter, &after_lines, line_number)?;
     if num_skipped > 0 {
         write!(formatter, "{SKIPPED_CONTEXT_LINE}")?;
         before_lines.pop();
         line_number.left += num_skipped + 1;
         line_number.right += num_skipped + 1;
     }
-    for line in before_lines.into_iter().rev() {
+    before_lines.reverse();
-        show_color_words_line_number(formatter, Some(line_number.left), Some(line_number.right))?;
+    line_number = show(formatter, &before_lines, line_number)?;
-        show_color_words_inline_hunks(formatter, &[(DiffLineHunkSide::Both, line.as_ref())])?;
-        line_number.left += 1;
-        line_number.right += 1;
-    }
     Ok(line_number)
 }