Syntax-highlight regex prompts

We can use tree-sitter-regex highlighting in prompts for entering
regexes, like `search` or `global_search`. The `highlighted_code_block`
function from the markdown component makes this a very small change.

This could be improved in the future by leaving the parsed syntax tree
on the prompt, allowing incremental updates. Prompt lines are usually so
short though and tree-sitter-regex is rather small and uncomplicated,
so that improvement probably wouldn't make a big difference.

2 files changed, 28 insertions, 20 deletions

diff --git a/helix-term/src/ui/mod.rs b/helix-term/src/ui/mod.rs
index 3359155d..8ca1b131 100644
--- a/helix-term/src/ui/mod.rs
+++ b/helix-term/src/ui/mod.rs
@@ -151,7 +151,8 @@ pub fn regex_prompt(
                 }
             }
         },
-    );
+    )
+    .with_language("regex", std::sync::Arc::clone(&cx.editor.syn_loader));
     // Calculate initial completion
     prompt.recalculate_completion(cx.editor);
     // prompt
diff --git a/helix-term/src/ui/prompt.rs b/helix-term/src/ui/prompt.rs
index 4f383bf5..f376b9c9 100644
--- a/helix-term/src/ui/prompt.rs
+++ b/helix-term/src/ui/prompt.rs
@@ -1,7 +1,9 @@
 use crate::compositor::{Component, Compositor, Context, Event, EventResult};
 use crate::{alt, ctrl, key, shift, ui};
+use helix_core::syntax;
 use helix_view::input::KeyEvent;
 use helix_view::keyboard::KeyCode;
+use std::sync::Arc;
 use std::{borrow::Cow, ops::RangeFrom};
 use tui::buffer::Buffer as Surface;
 use tui::widgets::{Block, Borders, Widget};
@@ -32,6 +34,7 @@ pub struct Prompt {
     callback_fn: CallbackFn,
     pub doc_fn: DocFn,
     next_char_handler: Option<PromptCharHandler>,
+    language: Option<(&'static str, Arc<syntax::Loader>)>,
 }
 
 #[derive(Clone, Copy, PartialEq, Eq)]
@@ -83,6 +86,7 @@ impl Prompt {
             callback_fn: Box::new(callback_fn),
             doc_fn: Box::new(|_| None),
             next_char_handler: None,
+            language: None,
         }
     }
 
@@ -94,6 +98,11 @@ impl Prompt {
         self
     }
 
+    pub fn with_language(mut self, language: &'static str, loader: Arc<syntax::Loader>) -> Self {
+        self.language = Some((language, loader));
+        self
+    }
+
     pub fn line(&self) -> &String {
         &self.line
     }
@@ -456,30 +465,28 @@ impl Prompt {
         // render buffer text
         surface.set_string(area.x, area.y + line, &self.prompt, prompt_color);
 
-        let (input, is_suggestion): (Cow<str>, bool) = if self.line.is_empty() {
-            // latest value in the register list
-            match self
+        let line_area = area.clip_left(self.prompt.len() as u16).clip_top(line);
+        if self.line.is_empty() {
+            // Show the most recently entered value as a suggestion.
+            if let Some(suggestion) = self
                 .history_register
                 .and_then(|reg| cx.editor.registers.last(reg))
-                .map(|entry| entry.into())
             {
-                Some(value) => (value, true),
-                None => (Cow::from(""), false),
+                surface.set_string(line_area.x, line_area.y, suggestion, suggestion_color);
             }
+        } else if let Some((language, loader)) = self.language.as_ref() {
+            let mut text: ui::text::Text = crate::ui::markdown::highlighted_code_block(
+                self.line.clone(),
+                language,
+                Some(&cx.editor.theme),
+                loader.clone(),
+                None,
+            )
+            .into();
+            text.render(line_area, surface, cx);
         } else {
-            (self.line.as_str().into(), false)
-        };
-
-        surface.set_string(
-            area.x + self.prompt.len() as u16,
-            area.y + line,
-            &input,
-            if is_suggestion {
-                suggestion_color
-            } else {
-                prompt_color
-            },
-        );
+            surface.set_string(line_area.x, line_area.y, self.line.clone(), prompt_color);
+        }
     }
 }