Implement `hx --tutor` and `:tutor` to load `tutor.txt` (#898)

* Implement `hx --tutor` and `:tutor` to load `tutor.txt`

* Document `hx --tutor` and `:tutor`

* Change `Document::set_path` to take an `Option`

* `Document::set_path` accepts an `Option<&Path>` instead of `&Path`.
* Remove `Editor::open_tutor` and make tutor-open functionality use
  `Editor::open` and `Document::set_path`.

* Use `PathBuf::join`

Co-authored-by: Ivan Tham <pickfire@riseup.net>

* Add comments explaining unsetting tutor path

Co-authored-by: Ivan Tham <pickfire@riseup.net>

5 files changed, 39 insertions, 8 deletions

diff --git a/book/src/usage.md b/book/src/usage.md
index d31e03a1..71730fa8 100644
--- a/book/src/usage.md
+++ b/book/src/usage.md
@@ -2,7 +2,7 @@
 
 (Currently not fully documented, see the [keymappings](./keymap.md) list for more.)
 
-See [tutor.txt](https://github.com/helix-editor/helix/blob/master/runtime/tutor.txt) for a vimtutor-like introduction.
+See [tutor.txt](https://github.com/helix-editor/helix/blob/master/runtime/tutor.txt) (accessible via `hx --tutor` or `:tutor`) for a vimtutor-like introduction.
 
 ## Registers
 
diff --git a/helix-term/src/application.rs b/helix-term/src/application.rs
index 662573c6..55b12c5a 100644
--- a/helix-term/src/application.rs
+++ b/helix-term/src/application.rs
@@ -97,7 +97,12 @@ impl Application {
         let editor_view = Box::new(ui::EditorView::new(std::mem::take(&mut config.keys)));
         compositor.push(editor_view);
 
-        if !args.files.is_empty() {
+        if args.load_tutor {
+            let path = helix_core::runtime_dir().join("tutor.txt");
+            editor.open(path, Action::VerticalSplit)?;
+            // Unset path to prevent accidentally saving to the original tutor file.
+            doc_mut!(editor).set_path(None)?;
+        } else if !args.files.is_empty() {
             let first = &args.files[0]; // we know it's not empty
             if first.is_dir() {
                 std::env::set_current_dir(&first)?;
diff --git a/helix-term/src/args.rs b/helix-term/src/args.rs
index f0ef09eb..40113db9 100644
--- a/helix-term/src/args.rs
+++ b/helix-term/src/args.rs
@@ -5,6 +5,7 @@ use std::path::PathBuf;
 pub struct Args {
     pub display_help: bool,
     pub display_version: bool,
+    pub load_tutor: bool,
     pub verbosity: u64,
     pub files: Vec<PathBuf>,
 }
@@ -22,6 +23,7 @@ impl Args {
                 "--" => break, // stop parsing at this point treat the remaining as files
                 "--version" => args.display_version = true,
                 "--help" => args.display_help = true,
+                "--tutor" => args.load_tutor = true,
                 arg if arg.starts_with("--") => {
                     return Err(Error::msg(format!(
                         "unexpected double dash argument: {}",
diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index d6e5bfe7..b3be6d5b 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -1557,7 +1557,8 @@ mod cmd {
         let (_, doc) = current!(cx.editor);
 
         if let Some(path) = path {
-            doc.set_path(path.as_ref()).context("invalid filepath")?;
+            doc.set_path(Some(path.as_ref()))
+                .context("invalid filepath")?;
         }
         if doc.path().is_none() {
             bail!("cannot write a buffer without a filename");
@@ -2099,6 +2100,18 @@ mod cmd {
         Ok(())
     }
 
+    fn tutor(
+        cx: &mut compositor::Context,
+        _args: &[&str],
+        _event: PromptEvent,
+    ) -> anyhow::Result<()> {
+        let path = helix_core::runtime_dir().join("tutor.txt");
+        cx.editor.open(path, Action::Replace)?;
+        // Unset path to prevent accidentally saving to the original tutor file.
+        doc_mut!(cx.editor).set_path(None)?;
+        Ok(())
+    }
+
     pub const TYPABLE_COMMAND_LIST: &[TypableCommand] = &[
         TypableCommand {
             name: "quit",
@@ -2351,7 +2364,14 @@ mod cmd {
             doc: "Open the file in a horizontal split.",
             fun: hsplit,
             completer: Some(completers::filename),
-        }
+        },
+        TypableCommand {
+            name: "tutor",
+            aliases: &[],
+            doc: "Open the tutorial.",
+            fun: tutor,
+            completer: None,
+        },
     ];
 
     pub static COMMANDS: Lazy<HashMap<&'static str, &'static TypableCommand>> = Lazy::new(|| {
diff --git a/helix-view/src/document.rs b/helix-view/src/document.rs
index b0257f03..4d779656 100644
--- a/helix-view/src/document.rs
+++ b/helix-view/src/document.rs
@@ -368,7 +368,7 @@ impl Document {
         let mut doc = Self::from(rope, Some(encoding));
 
         // set the path and try detecting the language
-        doc.set_path(path)?;
+        doc.set_path(Some(path))?;
         if let Some(loader) = config_loader {
             doc.detect_language(theme, loader);
         }
@@ -553,12 +553,16 @@ impl Document {
         self.encoding
     }
 
-    pub fn set_path(&mut self, path: &Path) -> Result<(), std::io::Error> {
-        let path = helix_core::path::get_canonicalized_path(path)?;
+    pub fn set_path(&mut self, path: Option<&Path>) -> Result<(), std::io::Error> {
+        let path = if let Some(p) = path {
+            Some(helix_core::path::get_canonicalized_path(p)?)
+        } else {
+            path.map(|p| p.into())
+        };
 
         // if parent doesn't exist we still want to open the document
         // and error out when document is saved
-        self.path = Some(path);
+        self.path = path;
 
         Ok(())
     }