Allow adding prefix to version-control statusline element

Adds `config.toml` option `editor.statusline.version-control-prefix`,
to allow adding a user-defined prefix to the branch name.
This can be used to add an icon to the element.

As an additional fix, if the HEAD name is empty
the version-control element won't get drawn.

book/src/editor.md

@@ -72,6 +72,7 @@ ### `[editor.statusline]` Section
 mode.normal = "NORMAL"
 mode.insert = "INSERT"
 mode.select = "SELECT"
+version-control-prefix = "vcs: "
 ```
 The `[editor.statusline]` key takes the following sub-keys:
 
@@ -84,6 +85,7 @@ ### `[editor.statusline]` Section
 | `mode.normal` | The text shown in the `mode` element for normal mode | `"NOR"` |
 | `mode.insert` | The text shown in the `mode` element for insert mode | `"INS"` |
 | `mode.select` | The text shown in the `mode` element for select mode | `"SEL"` |
+| `version-control-prefix` | A prefix for the `version-control` element | `"vcs: "` |
 
 The following statusline elements can be configured:
 

helix-term/src/ui/statusline.rs

@@ -519,8 +519,13 @@ fn render_version_control<F>(context: &mut RenderContext, write: F)
         .version_control_head()
         .unwrap_or_default()
         .to_string();
+    if head.is_empty() {
+        return;
+    }
 
-    write(context, head, None);
+    let config = context.editor.config.load();
+    let prefix = &config.statusline.version_control_prefix;
+    write(context, format!("{prefix}{head}"), None);
 }
 
 fn render_register<F>(context: &mut RenderContext, write: F)

helix-view/src/editor.rs

@@ -468,6 +468,7 @@ pub struct StatusLineConfig {
     pub right: Vec<StatusLineElement>,
     pub separator: String,
     pub mode: ModeConfig,
+    pub version_control_prefix: String,
 }
 
 impl Default for StatusLineConfig {
@@ -492,6 +493,7 @@ fn default() -> Self {
             ],
             separator: String::from("│"),
             mode: ModeConfig::default(),
+            version_control_prefix: String::from("vcs: "),
         }
     }
 }