Add insert-final-newline config option

This resolves helix-editor#4274 with the implementation largely based off of helix-editor#5435
and also addresses the review from @the-mikedavis on that PR.

The option name is from EditorConfig's `insert_final_newline`, which is
also used by VS Code as `files.insertFinalNewline`.

We match Vim's behavior in that :w will add the newline to unmodified
files but :wa will not; see helix-editor#1760.

Co-authored by: Xalfer <[email protected]>

book/src/configuration.md

@@ -64,6 +64,7 @@ Its settings will be merged with the configuration directory `config.toml` and t
 | `text-width` | Maximum line length. Used for the `:reflow` command and soft-wrapping if `soft-wrap.wrap-at-text-width` is set | `80` |
 | `workspace-lsp-roots` | Directories relative to the workspace root that are treated as LSP roots. Should only be set in `.helix/config.toml` | `[]` |
 | `default-line-ending` | The line ending to use for new documents. Can be `native`, `lf`, `crlf`, `ff`, `cr` or `nel`. `native` uses the platform's native line ending (`crlf` on Windows, otherwise `lf`). | `native` |
+| `insert-final-newline` | Whether to automatically insert a final newline on write if missing | `false` |
 
 ### `[editor.statusline]` Section
 

helix-term/src/commands/typed.rs

@@ -6,7 +6,7 @@ use crate::job::Job;
 use super::*;
 
 use helix_core::fuzzy::fuzzy_match;
-use helix_core::{encoding, shellwords::Shellwords};
+use helix_core::{encoding, line_ending, shellwords::Shellwords};
 use helix_view::document::DEFAULT_LANGUAGE_NAME;
 use helix_view::editor::{Action, CloseError, ConfigEvent};
 use serde_json::Value;
@@ -330,12 +330,12 @@ fn write_impl(
     path: Option<&Cow<str>>,
     force: bool,
 ) -> anyhow::Result<()> {
-    let editor_auto_fmt = cx.editor.config().auto_format;
+    let config = cx.editor.config();
     let jobs = &mut cx.jobs;
     let (view, doc) = current!(cx.editor);
     let path = path.map(AsRef::as_ref);
 
-    let fmt = if editor_auto_fmt {
+    let fmt = if config.auto_format {
         doc.auto_format().map(|fmt| {
             let callback = make_format_callback(
                 doc.id(),
@@ -352,13 +352,26 @@ fn write_impl(
     };
 
     if fmt.is_none() {
+        if config.insert_final_newline {
+            insert_final_newline(doc, view);
+        }
         let id = doc.id();
         cx.editor.save(id, path, force)?;
     }
 
     Ok(())
 }
 
+fn insert_final_newline(doc: &mut Document, view: &mut View) {
+    let text = doc.text();
+    if line_ending::get_line_ending(&text.slice(..)).is_none() {
+        let eof = Selection::point(text.len_chars());
+        let insert = Transaction::insert(text, &eof, doc.line_ending.as_str().into());
+        doc.apply(&insert, view.id);
+        doc.append_changes_to_history(view);
+    }
+}
+
 fn write(
     cx: &mut compositor::Context,
     args: &[Cow<str>],
@@ -658,7 +671,7 @@ pub fn write_all_impl(
     write_scratch: bool,
 ) -> anyhow::Result<()> {
     let mut errors: Vec<&'static str> = Vec::new();
-    let auto_format = cx.editor.config().auto_format;
+    let config = cx.editor.config();
     let jobs = &mut cx.jobs;
     let current_view = view!(cx.editor);
 
@@ -693,7 +706,7 @@ pub fn write_all_impl(
                 current_view.id
             };
 
-            let fmt = if auto_format {
+            let fmt = if config.auto_format {
                 doc.auto_format().map(|fmt| {
                     let callback = make_format_callback(
                         doc.id(),
@@ -709,16 +722,19 @@ pub fn write_all_impl(
             };
 
             if fmt.is_none() {
-                return Some(doc.id());
+                return Some((doc.id(), target_view));
             }
 
             None
         })
         .collect();
 
     // manually call save for the rest of docs that don't have a formatter
-    for id in saves {
-        cx.editor.save::<PathBuf>(id, None, force)?;
+    for (doc_id, view_id) in saves {
+        if config.insert_final_newline {
+            insert_final_newline(doc_mut!(cx.editor, &doc_id), view_mut!(cx.editor, view_id));
+        }
+        cx.editor.save::<PathBuf>(doc_id, None, force)?;
     }
 
     if !errors.is_empty() && !force {

helix-view/src/editor.rs

@@ -287,6 +287,8 @@ pub struct Config {
     pub workspace_lsp_roots: Vec<PathBuf>,
     /// Which line ending to choose for new documents. Defaults to `native`. i.e. `crlf` on Windows, otherwise `lf`.
     pub default_line_ending: LineEndingConfig,
+    /// Whether to automatically insert a final newline on write if missing. Defaults to `false`.
+    pub insert_final_newline: bool,
     /// Enables smart tab
     pub smart_tab: Option<SmartTabConfig>,
 }
@@ -842,6 +844,7 @@ impl Default for Config {
             completion_replace: false,
             workspace_lsp_roots: Vec::new(),
             default_line_ending: LineEndingConfig::default(),
+            insert_final_newline: false,
             smart_tab: Some(SmartTabConfig::default()),
         }
     }