Detect filetype from shebang line (#1001)

helix-core/src/syntax.rs

@@ -14,6 +14,8 @@ use std::{
     cell::RefCell,
     collections::{HashMap, HashSet},
     fmt,
+    fs::File,
+    io::Read,
     path::Path,
     sync::Arc,
 };
@@ -52,6 +54,7 @@ pub struct LanguageConfiguration {
     pub language_id: String,
     pub scope: String,           // source.rust
     pub file_types: Vec<String>, // filename ends_with? <Gemfile, rb, etc>
+    pub shebangs: Vec<String>,   // interpreter(s) associated with language
     pub roots: Vec<String>,      // these indicate project roots <.git, Cargo.toml>
     pub comment_token: Option<String>,
 
@@ -254,6 +257,7 @@ pub struct Loader {
     // highlight_names ?
     language_configs: Vec<Arc<LanguageConfiguration>>,
     language_config_ids_by_file_type: HashMap<String, usize>, // Vec<usize>
+    language_config_ids_by_shebang: HashMap<String, usize>,
 }
 
 impl Loader {
@@ -261,6 +265,7 @@ impl Loader {
         let mut loader = Self {
             language_configs: Vec::new(),
             language_config_ids_by_file_type: HashMap::new(),
+            language_config_ids_by_shebang: HashMap::new(),
         };
 
         for config in config.language {
@@ -273,6 +278,11 @@ impl Loader {
                     .language_config_ids_by_file_type
                     .insert(file_type.clone(), language_id);
             }
+            for shebang in &config.shebangs {
+                loader
+                    .language_config_ids_by_shebang
+                    .insert(shebang.clone(), language_id);
+            }
 
             loader.language_configs.push(Arc::new(config));
         }
@@ -298,6 +308,20 @@ impl Loader {
         // TODO: content_regex handling conflict resolution
     }
 
+    pub fn language_config_for_shebang(&self, path: &Path) -> Option<Arc<LanguageConfiguration>> {
+        // Read the first 128 bytes of the file. If its a shebang line, try to find the language
+        let file = File::open(path).ok()?;
+        let mut buf = String::with_capacity(128);
+        file.take(128).read_to_string(&mut buf).ok()?;
+        static SHEBANG_REGEX: Lazy<Regex> =
+            Lazy::new(|| Regex::new(r"^#!\s*(?:\S*[/\\](?:env\s+)?)?([^\s\.\d]+)").unwrap());
+        let configuration_id = SHEBANG_REGEX
+            .captures(&buf)
+            .and_then(|cap| self.language_config_ids_by_shebang.get(&cap[1]));
+
+        configuration_id.and_then(|&id| self.language_configs.get(id).cloned())
+    }
+
     pub fn language_config_for_scope(&self, scope: &str) -> Option<Arc<LanguageConfiguration>> {
         self.language_configs
             .iter()