Customizable/configurable status line (#2434)

* feat(statusline): add the file type (language id) to the status line

* refactor(statusline): move the statusline implementation into an own struct

* refactor(statusline): split the statusline implementation into different functions

* refactor(statusline): Append elements using a consistent API

This is a preparation for the configurability which is about to be
implemented.

* refactor(statusline): implement render_diagnostics()

This avoid cluttering the render() function and will simplify
configurability.

* feat(statusline): make the status line configurable

* refactor(statusline): make clippy happy

* refactor(statusline): avoid intermediate StatusLineObject

Use a more functional approach to obtain render functions and write to
the buffers, and avoid an intermediate StatusLineElement object.

* fix(statusline): avoid rendering the left elements twice

* refactor(statusline): make clippy happy again

* refactor(statusline): rename `buffer` into `parts`

* refactor(statusline): ensure the match is exhaustive

* fix(statusline): avoid an overflow when calculating the maximal center width

* chore(statusline): Describe the statusline configurability in the book

* chore(statusline): Correct and add documentation

* refactor(statusline): refactor some code following the code review

Avoid very small helper functions for the diagnositcs and inline them
instead.
Rename the config field `status_line` to `statusline` to remain
consistent with `bufferline`.

* chore(statusline): adjust documentation following the config field refactoring

* revert(statusline): revert regression introduced by c0a1870

* chore(statusline): slight adjustment in the configuration documentation

* feat(statusline): integrate changes from #2676 after rebasing

* refactor(statusline): remove the StatusLine struct

Because none of the functions need `Self` and all of them are in an own
file, there is no explicit need for the struct.

* fix(statusline): restore the configurability of color modes

The configuration was ignored after reintegrating the changes of #2676
in 8d28f95.

* fix(statusline): remove the spinner padding

* refactor(statusline): remove unnecessary format!()

1 files changed, 51 insertions, 0 deletions

diff --git a/helix-view/src/editor.rs b/helix-view/src/editor.rs
index a2943af9..51c0eee0 100644
--- a/helix-view/src/editor.rs
+++ b/helix-view/src/editor.rs
@@ -147,6 +147,8 @@ pub struct Config {
     /// Whether to display infoboxes. Defaults to true.
     pub auto_info: bool,
     pub file_picker: FilePickerConfig,
+    /// Configuration of the statusline elements
+    pub statusline: StatusLineConfig,
     /// Shape for cursor in each mode
     pub cursor_shape: CursorShapeConfig,
     /// Set to `true` to override automatic detection of terminal truecolor support in the event of a false negative. Defaults to `false`.
@@ -180,6 +182,54 @@ pub struct SearchConfig {
     pub wrap_around: bool,
 }
 
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[serde(rename_all = "kebab-case", default, deny_unknown_fields)]
+pub struct StatusLineConfig {
+    pub left: Vec<StatusLineElement>,
+    pub center: Vec<StatusLineElement>,
+    pub right: Vec<StatusLineElement>,
+}
+
+impl Default for StatusLineConfig {
+    fn default() -> Self {
+        use StatusLineElement as E;
+
+        Self {
+            left: vec![E::Mode, E::Spinner, E::FileName],
+            center: vec![],
+            right: vec![E::Diagnostics, E::Selections, E::Position, E::FileEncoding],
+        }
+    }
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "kebab-case")]
+pub enum StatusLineElement {
+    /// The editor mode (Normal, Insert, Visual/Selection)
+    Mode,
+
+    /// The LSP activity spinner
+    Spinner,
+
+    /// The file nane/path, including a dirty flag if it's unsaved
+    FileName,
+
+    /// The file encoding
+    FileEncoding,
+
+    /// The file type (language ID or "text")
+    FileType,
+
+    /// A summary of the number of errors and warnings
+    Diagnostics,
+
+    /// The number of selections (cursors)
+    Selections,
+
+    /// The cursor position
+    Position,
+}
+
 // Cursor shape is read and used on every rendered frame and so needs
 // to be fast. Therefore we avoid a hashmap and use an enum indexed array.
 #[derive(Debug, Clone, PartialEq)]
@@ -409,6 +459,7 @@ impl Default for Config {
             completion_trigger_len: 2,
             auto_info: true,
             file_picker: FilePickerConfig::default(),
+            statusline: StatusLineConfig::default(),
             cursor_shape: CursorShapeConfig::default(),
             true_color: false,
             search: SearchConfig::default(),