inject language based on file extension

Nodes can now be captured with "injection.extension". If this capture
contains a valid file extension known to Helix, then the content will
be highlighted as that language.

helix-core/src/syntax.rs

@@ -1163,6 +1163,7 @@ pub struct HighlightConfiguration {
     non_local_variable_patterns: Vec<bool>,
     injection_content_capture_index: Option<u32>,
     injection_language_capture_index: Option<u32>,
+    injection_filename_capture_index: Option<u32>,
     local_scope_capture_index: Option<u32>,
     local_def_capture_index: Option<u32>,
     local_def_value_capture_index: Option<u32>,
@@ -1307,6 +1308,7 @@ impl HighlightConfiguration {
         // Store the numeric ids for all of the special captures.
         let mut injection_content_capture_index = None;
         let mut injection_language_capture_index = None;
+        let mut injection_filename_capture_index = None;
         let mut local_def_capture_index = None;
         let mut local_def_value_capture_index = None;
         let mut local_ref_capture_index = None;
@@ -1327,6 +1329,7 @@ impl HighlightConfiguration {
             match name.as_str() {
                 "injection.content" => injection_content_capture_index = i,
                 "injection.language" => injection_language_capture_index = i,
+                "injection.filename" => injection_filename_capture_index = i,
                 _ => {}
             }
         }
@@ -1342,6 +1345,7 @@ impl HighlightConfiguration {
             non_local_variable_patterns,
             injection_content_capture_index,
             injection_language_capture_index,
+            injection_filename_capture_index,
             local_scope_capture_index,
             local_def_capture_index,
             local_def_value_capture_index,
@@ -1817,6 +1821,7 @@ fn injection_for_match<'a>(
 ) -> (Option<Cow<'a, str>>, Option<Node<'a>>, IncludedChildren) {
     let content_capture_index = config.injection_content_capture_index;
     let language_capture_index = config.injection_language_capture_index;
+    let language_filename_index = config.injection_filename_capture_index;
 
     let mut language_name = None;
     let mut content_node = None;
@@ -1827,6 +1832,21 @@ fn injection_for_match<'a>(
             language_name = Some(name);
         } else if index == content_capture_index {
             content_node = Some(capture.node);
+        } else if index == language_filename_index {
+            let languages = super::config::default_syntax_loader().language;
+            let file = byte_range_to_str(capture.node.byte_range(), source);
+            let extension = Path::new(file.as_ref()).extension();
+            if let Some(extension) = extension {
+                let language = languages.iter().find(|language| {
+                    language
+                        .file_types
+                        .iter()
+                        .any(|e| extension.to_str() == Some(e))
+                });
+                if let Some(language) = language {
+                    language_name = Some(Cow::from(language.language_id.clone()));
+                }
+            }
         }
     }
 

runtime/queries/nix/injections.scm

@@ -37,3 +37,10 @@
   (#match? @_path "^text$")
   (#set! injection.language "bash")
   (#set! injection.combined))
+
+((apply_expression
+   function: (apply_expression function: (_) @_func
+     argument: (string_expression (string_fragment) @injection.filename))
+   argument: (indented_string_expression (string_fragment) @injection.content))
+ (#match? @_func "(^|\\.)write(Text|Script(Bin)?)$")
+ (#set! injection.combined))