Add --test-panic

To test the debug handler

src/cli.rs

@@ -984,6 +984,13 @@ pub struct Opt {
     /// Second file to be compared when delta is being used to diff two files.
     pub plus_file: Option<PathBuf>,
 
+    /*
+    Panic on purpose. When a `diff -u a b` (without a `git diff` header) is encountered
+    then panic early, otherwise panic after processing all input.
+     */
+    #[arg(hide = true, long = "test-panic")]
+    pub test_panic: bool,
+
     #[arg(skip)]
     pub computed: ComputedValues,
 

src/config.rs

@@ -131,6 +131,7 @@ pub struct Config {
     pub syntax_set: SyntaxSet,
     pub syntax_theme: Option<SyntaxTheme>,
     pub tab_cfg: utils::tabs::TabCfg,
+    pub test_panic: bool,
     pub tokenization_regex: Regex,
     pub true_color: bool,
     pub truncation_symbol: String,
@@ -419,6 +420,7 @@ impl From<cli::Opt> for Config {
             plus_file: opt.plus_file,
             plus_non_emph_style: styles["plus-non-emph-style"],
             plus_style: styles["plus-style"],
+            test_panic: opt.test_panic,
             git_minus_style: styles["git-minus-style"],
             git_plus_style: styles["git-plus-style"],
             relative_paths: opt.relative_paths,

src/delta.rs

@@ -161,6 +161,9 @@ impl<'a> StateMachine<'a> {
                 // to introduce and handle a Source::DiffUnifiedAmbiguous variant everywhere.
                 if self.line.starts_with("--- ") {
                     self.minus_line_counter = AmbiguousDiffMinusCounter::prepare_to_count();
+                    if self.config.test_panic {
+                        panic!("An early panic as requested by --test-panic");
+                    }
                 }
             }
 

src/main.rs

@@ -195,6 +195,10 @@ pub fn run_app(
 
         let res = delta(io::stdin().lock().byte_lines(), &mut writer, &config);
 
+        if config.test_panic {
+            panic!("A panic before the exit as requested by --test-panic");
+        }
+
         if let Err(error) = res {
             match error.kind() {
                 ErrorKind::BrokenPipe => return Ok(0),