add option to specify syntax

src/main.rs

@@ -1,12 +1,13 @@
 use std::{
-    io::{BufRead, Cursor},
+    fs::File,
+    io::{BufRead, BufReader, Cursor},
     path::PathBuf,
 };
 
 use clap::{crate_authors, crate_version, Parser};
-use miette::{bail, IntoDiagnostic, WrapErr};
+use miette::{bail, miette, IntoDiagnostic, WrapErr};
 use syntect::{
-    easy::HighlightFile,
+    easy::HighlightLines,
     highlighting::{Color, Style, ThemeSet},
     parsing::SyntaxSet,
 };
@@ -26,6 +27,9 @@ enum Cmd {
     #[clap(about = "Print available themes and exit")]
     ListThemes,
 
+    #[clap(about = "Print available syntaxes and exit")]
+    ListSyntaxes,
+
     #[clap(about = "Highlight a file", alias = "hl")]
     Highlight {
         #[clap(about = "The file to highlight")]
@@ -38,6 +42,13 @@ enum Cmd {
             about = "The color scheme to use"
         )]
         theme: String,
+
+        #[clap(
+            long,
+            short,
+            about = "The syntax to use. Uses file extension if not provided."
+        )]
+        syntax: Option<String>,
     },
 }
 
@@ -54,6 +65,7 @@ fn main() -> miette::Result<()> {
         .into_diagnostic()
         .wrap_err("Failed to load static dracula theme")?,
     );
+    let ss = SyntaxSet::load_defaults_newlines();
 
     match opt.cmd {
         Cmd::ListThemes => {
@@ -63,22 +75,52 @@ fn main() -> miette::Result<()> {
 
             Ok(())
         },
-        Cmd::Highlight { file, theme } => {
-            let ss = SyntaxSet::load_defaults_newlines();
+
+        Cmd::ListSyntaxes => {
+            let mut syntaxes = ss.syntaxes().to_vec();
+            syntaxes.sort_by(|a, b| a.name.cmp(&b.name));
+            for syn in syntaxes {
+                println!("{}\t[{}]", syn.name, syn.file_extensions.join(", "))
+            }
+
+            Ok(())
+        },
+
+        Cmd::Highlight {
+            file,
+            theme,
+            syntax,
+        } => {
             let theme = if let Some(t) = ts.themes.get(&theme) {
                 t
             } else {
                 bail!("No such theme! Use list-themes to list themes.");
             };
 
-            let mut h = HighlightFile::new(file, &ss, theme)
-                .into_diagnostic()
-                .wrap_err("Failed to open file")?;
+            let syntax = if let Some(syn) = syntax {
+                ss.find_syntax_by_name(&syn)
+            } else {
+                ss.find_syntax_for_file(&file)
+                    .into_diagnostic()
+                    .wrap_err("Failed to open file for finding syntax.")?
+            };
+
+            let reader = BufReader::new(
+                File::open(file)
+                    .into_diagnostic()
+                    .wrap_err("Failed to open file")?,
+            );
+
+            let syntax = syntax.ok_or_else(|| {
+                miette!("Couldn't find syntax. Set one that exists.\nList with list-syntaxes.")
+            })?;
+
+            let mut hl = HighlightLines::new(syntax, theme);
 
             print!("<pre>");
-            for line in h.reader.lines() {
+            for line in reader.lines() {
                 let line = line.into_diagnostic().wrap_err("Failed to read file")?;
-                let regions = h.highlight_lines.highlight(&line, &ss);
+                let regions = hl.highlight(&line, &ss);
 
                 for (
                     Style {