Use u8 for tab

src/cli.rs

@@ -36,7 +36,7 @@ pub struct Cli {
         help = "Number of spaces to use as tab size",
         default_value_t = 2
     )]
-    pub tab: i8,
+    pub tab: u8,
     #[arg(long, help = "Use tabs instead of spaces for indentation")]
     pub usetabs: bool,
     #[arg(long, help = "Line length for wrapping", default_value_t = 80)]

src/format.rs

@@ -74,7 +74,7 @@ pub fn format_file(
                     &pattern,
                 );
 
-                let indent_length = usize::try_from(indent.visual * args.tab)
+                let indent_length = usize::try_from(indent.visual * args.tab as i8)
                     .expect("Visual indent is non-negative.");
 
                 // Wrap the line before applying the indent, and loop back

src/indent.rs

@@ -184,7 +184,7 @@ pub fn apply_indent(
     // Otherwise, allocate enough memory to fit line with the added
     // indentation and insert the appropriate string slices
     } else {
-        let n_indent_chars = usize::try_from(indent.visual * args.tab).unwrap();
+        let n_indent_chars = usize::try_from(indent.visual * args.tab as i8).unwrap();
         let mut new_line =
             String::with_capacity(trimmed_line.len() + n_indent_chars);
         for idx in 0..n_indent_chars {