Add --[no-]unindent for removing leading indentation

src/main.rs

@@ -9,10 +9,16 @@ struct Args {
     /// The input path. If unset, stdin is used.
     input: Option<PathBuf>,
 
-    /// Whether the input should be formatted to be Discord-compatible.
-    #[clap(short, long)]
+    /// Wrap the output in a Discord-flavoured-markdown–style ANSI codeblock.
+    #[clap(short, long, overrides_with = "_no_discord")]
     discord: bool,
 
+    /// Don't wrap the output in a markdown-style codeblock. [default]
+    #[clap(short = 'D', long = "no-discord")]
+    #[clap(hide_short_help = true)]
+    #[doc(hidden)]
+    _no_discord: bool,
+
     // Logically this comes after `Args::strip_ansi`, but in clap it makes more sense before.
     // Also see https://jwodder.github.io/kbits/posts/clap-bool-negate/
     /// Strip all ANSI escape sequences from the input before processing. [default]
@@ -39,6 +45,16 @@ struct Args {
     #[doc(hidden)]
     _no_unwrap_codeblock: bool,
 
+    /// Strip any top-level indentation in the input prior to highlighting it.
+    #[clap(short = 'u', long, overrides_with = "_no_unindent")]
+    unindent: bool,
+
+    /// Keep indents as-is. [default]
+    #[clap(short = 'U', long = "no-unindent")]
+    #[clap(hide_short_help = true)]
+    #[doc(hidden)]
+    _no_unindent: bool,
+
     /// Softly enforce a byte size limit.
     ///
     /// This means that if the size limit is exceeded, less colors are used
@@ -92,11 +108,18 @@ fn main() -> Result<()> {
         &input
     };
 
-    if args.strip_ansi {
+    // If the input doesn't contain escape sequences, avoid processing it because strip-ansi-escapes
+    // also strips tabs unfortunately. (https://github.com/luser/strip-ansi-escapes/issues/20)
+    if args.strip_ansi && stripped.contains('\x1B') {
         input = strip_ansi_escapes::strip_str(stripped);
         stripped = &input;
     }
 
+    if args.unindent {
+        input = dedent(stripped);
+        stripped = &input;
+    }
+
     let out = termcolor::Ansi::new(std::io::stdout().lock());
     let mut highlighter = Highlighter::default();
     if args.discord {
@@ -123,3 +146,27 @@ fn unwrap_codeblock(input: &str) -> &str {
     };
     rest
 }
+
+fn dedent(input: &str) -> String {
+    let shared_indent = input
+        .lines()
+        .filter(|l| !l.trim().is_empty())
+        .map(|l| {
+            let nonspace = l.find(|c: char| !c.is_whitespace()).unwrap();
+            &l[..nonspace]
+        })
+        .min_by_key(|s| s.len() + s.matches('\t').count()) // Assume tabs are 2-wide
+        .unwrap_or("");
+
+    input
+        .split_inclusive('\n')
+        .map(|l| {
+            if shared_indent.starts_with(l) {
+                // Trim partial indents
+                ""
+            } else {
+                l.strip_prefix(shared_indent).unwrap_or(l)
+            }
+        })
+        .collect()
+}