Added tab expansion preprocessing step.

src/preprocessor.rs

@@ -0,0 +1,35 @@
+use console::AnsiCodeIterator;
+
+/// Expand tabs like an ANSI-enabled expand(1).
+pub fn expand(line: &str, width: usize) -> String {
+    let mut buffer = String::with_capacity(line.len() * 2);
+    let mut cursor = 0;
+
+    for chunk in AnsiCodeIterator::new(line) {
+        match chunk {
+            (text, true) => buffer.push_str(text),
+            (mut text, false) => {
+                while let Some(index) = text.find('\t') {
+                    // Add previous text.
+                    if index > 0 {
+                        cursor += index;
+                        buffer.push_str(&text[0..index]);
+                    }
+
+                    // Add tab.
+                    let spaces = width - (cursor % width);
+                    cursor += spaces;
+                    buffer.push_str(&*" ".repeat(spaces));
+
+                    // Next.
+                    text = &text[index + 1..text.len()];
+                }
+
+                cursor += text.len();
+                buffer.push_str(text);
+            }
+        }
+    }
+
+    buffer
+}