allow whitespace to be rendered

Co-authored-by: Michael Davis <mcarsondavis@gmail.com>

8 files changed, 166 insertions, 9 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 22c128d9..0835d107 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -457,6 +457,7 @@ dependencies = [
  "once_cell",
  "pulldown-cmark",
  "retain_mut",
+ "ropey",
  "serde",
  "serde_json",
  "signal-hook",
diff --git a/book/src/configuration.md b/book/src/configuration.md
index 153ebb80..fea60d2f 100644
--- a/book/src/configuration.md
+++ b/book/src/configuration.md
@@ -137,3 +137,29 @@ Search specific options.
 |--|--|---------|
 | `smart-case` | Enable smart case regex searching (case insensitive unless pattern contains upper case characters) | `true` |
 | `wrap-around`| Whether the search should wrap after depleting the matches | `true` |
+
+### `[editor.whitespace]` Section
+
+Options for rendering whitespace with visible characters. Use `:set whitespace.render all` to temporarily enable visible whitespace.
+
+| Key | Description | Default |
+|-----|-------------|---------|
+| `render` | Whether to render whitespace. May either be `"all"` or `"none"`, or a table with sub-keys `space`, `tab`, and `newline`. | `"none"` |
+| `characters` | Literal characters to use when rendering whitespace. Sub-keys may be any of `tab`, `space` or `newline` | See example below |
+
+Example
+
+```toml
+[editor.whitespace]
+render = "all"
+# or control each character
+[editor.whitespace.render]
+space = "all"
+tab = "all"
+newline = "none"
+
+[editor.whitespace.characters]
+space = "·"
+tab = "→"
+newline = "⏎"
+```
diff --git a/book/src/themes.md b/book/src/themes.md
index e23dbb69..9009e2ca 100644
--- a/book/src/themes.md
+++ b/book/src/themes.md
@@ -224,6 +224,7 @@ These scopes are used for theming the editor interface.
 | `ui.text`                | Command prompts, popup text, etc.              |
 | `ui.text.focus`          |                                                |
 | `ui.text.info`           | The key: command text in `ui.popup.info` boxes |
+| `ui.virtual.whitespace`  | Visible white-space characters                 |
 | `ui.menu`                | Code and command completion menus              |
 | `ui.menu.selected`       | Selected autocomplete item                     |
 | `ui.selection`           | For selections in the editing area             |
@@ -233,4 +234,3 @@ These scopes are used for theming the editor interface.
 | `info`                   | Diagnostics info (gutter)                      |
 | `hint`                   | Diagnostics hint (gutter)                      |
 | `diagnostic`             | For text in editing area                       |
-
diff --git a/helix-term/Cargo.toml b/helix-term/Cargo.toml
index 2e0b774b..4b2611ed 100644
--- a/helix-term/Cargo.toml
+++ b/helix-term/Cargo.toml
@@ -33,6 +33,7 @@ anyhow = "1"
 once_cell = "1.10"
 
 which = "4.2"
+ropey = { version = "1.4", default-features = false }
 
 tokio = { version = "1", features = ["rt", "rt-multi-thread", "io-util", "io-std", "time", "process", "macros", "fs", "parking_lot"] }
 num_cpus = "1"
diff --git a/helix-term/src/application.rs b/helix-term/src/application.rs
index 7733c2c6..91caade7 100644
--- a/helix-term/src/application.rs
+++ b/helix-term/src/application.rs
@@ -283,7 +283,7 @@ impl Application {
             // the Application can apply it.
             ConfigEvent::Update(editor_config) => {
                 let mut app_config = (*self.config.load().clone()).clone();
-                app_config.editor = editor_config;
+                app_config.editor = *editor_config;
                 self.config.store(Arc::new(app_config));
             }
         }
diff --git a/helix-term/src/ui/editor.rs b/helix-term/src/ui/editor.rs
index 318180d7..798b8ac8 100644
--- a/helix-term/src/ui/editor.rs
+++ b/helix-term/src/ui/editor.rs
@@ -124,7 +124,15 @@ impl EditorView {
             Box::new(highlights)
         };
 
-        Self::render_text_highlights(doc, view.offset, inner, surface, theme, highlights);
+        Self::render_text_highlights(
+            doc,
+            view.offset,
+            inner,
+            surface,
+            theme,
+            highlights,
+            &editor.config().whitespace,
+        );
         Self::render_gutter(editor, doc, view, view.area, surface, theme, is_focused);
         Self::render_rulers(editor, doc, view, inner, surface, theme);
 
@@ -344,7 +352,10 @@ impl EditorView {
         surface: &mut Surface,
         theme: &Theme,
         highlights: H,
+        whitespace: &helix_view::editor::WhitespaceConfig,
     ) {
+        use helix_view::editor::WhitespaceRenderValue;
+
         // It's slightly more efficient to produce a full RopeSlice from the Rope, then slice that a bunch
         // of times than it is to always call Rope::slice/get_slice (it will internally always hit RSEnum::Light).
         let text = doc.text().slice(..);
@@ -353,9 +364,20 @@ impl EditorView {
         let mut visual_x = 0u16;
         let mut line = 0u16;
         let tab_width = doc.tab_width();
-        let tab = " ".repeat(tab_width);
+        let tab = if whitespace.render.tab() == WhitespaceRenderValue::All {
+            (1..tab_width).fold(whitespace.characters.tab.to_string(), |s, _| s + " ")
+        } else {
+            " ".repeat(tab_width)
+        };
+        let space = whitespace.characters.space.to_string();
+        let newline = if whitespace.render.newline() == WhitespaceRenderValue::All {
+            whitespace.characters.newline.to_string()
+        } else {
+            " ".to_string()
+        };
 
         let text_style = theme.get("ui.text");
+        let whitespace_style = theme.get("ui.virtual.whitespace");
 
         'outer: for event in highlights {
             match event {
@@ -374,6 +396,14 @@ impl EditorView {
                         .iter()
                         .fold(text_style, |acc, span| acc.patch(theme.highlight(span.0)));
 
+                    let space = if whitespace.render.space() == WhitespaceRenderValue::All
+                        && text.len_chars() < end
+                    {
+                        &space
+                    } else {
+                        " "
+                    };
+
                     use helix_core::graphemes::{grapheme_width, RopeGraphemes};
 
                     for grapheme in RopeGraphemes::new(text) {
@@ -386,8 +416,8 @@ impl EditorView {
                                 surface.set_string(
                                     viewport.x + visual_x - offset.col as u16,
                                     viewport.y + line,
-                                    " ",
-                                    style,
+                                    &newline,
+                                    style.patch(whitespace_style),
                                 );
                             }
 
@@ -400,12 +430,21 @@ impl EditorView {
                             }
                         } else {
                             let grapheme = Cow::from(grapheme);
+                            let is_whitespace;
 
                             let (grapheme, width) = if grapheme == "\t" {
+                                is_whitespace = true;
                                 // make sure we display tab as appropriate amount of spaces
                                 let visual_tab_width = tab_width - (visual_x as usize % tab_width);
-                                (&tab[..visual_tab_width], visual_tab_width)
+                                let grapheme_tab_width =
+                                    ropey::str_utils::char_to_byte_idx(&tab, visual_tab_width);
+
+                                (&tab[..grapheme_tab_width], visual_tab_width)
+                            } else if grapheme == " " {
+                                is_whitespace = true;
+                                (space, 1)
                             } else {
+                                is_whitespace = false;
                                 // Cow will prevent allocations if span contained in a single slice
                                 // which should really be the majority case
                                 let width = grapheme_width(&grapheme);
@@ -418,7 +457,11 @@ impl EditorView {
                                     viewport.x + visual_x - offset.col as u16,
                                     viewport.y + line,
                                     grapheme,
-                                    style,
+                                    if is_whitespace {
+                                        style.patch(whitespace_style)
+                                    } else {
+                                        style
+                                    },
                                 );
                             }
 
diff --git a/helix-term/src/ui/picker.rs b/helix-term/src/ui/picker.rs
index dec59c89..3ca6965c 100644
--- a/helix-term/src/ui/picker.rs
+++ b/helix-term/src/ui/picker.rs
@@ -240,6 +240,7 @@ impl<T: 'static> Component for FilePicker<T> {
                 surface,
                 &cx.editor.theme,
                 highlights,
+                &cx.editor.config().whitespace,
             );
 
             // highlight the line
diff --git a/helix-view/src/editor.rs b/helix-view/src/editor.rs
index 0c2fad2b..79775c89 100644
--- a/helix-view/src/editor.rs
+++ b/helix-view/src/editor.rs
@@ -148,6 +148,8 @@ pub struct Config {
     pub lsp: LspConfig,
     /// Column numbers at which to draw the rulers. Default to `[]`, meaning no rulers.
     pub rulers: Vec<u16>,
+    #[serde(default)]
+    pub whitespace: WhitespaceConfig,
 }
 
 #[derive(Debug, Default, Clone, PartialEq, Serialize, Deserialize)]
@@ -263,6 +265,88 @@ impl std::str::FromStr for GutterType {
     }
 }
 
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[serde(default)]
+pub struct WhitespaceConfig {
+    pub render: WhitespaceRender,
+    pub characters: WhitespaceCharacters,
+}
+
+impl Default for WhitespaceConfig {
+    fn default() -> Self {
+        Self {
+            render: WhitespaceRender::Basic(WhitespaceRenderValue::None),
+            characters: WhitespaceCharacters::default(),
+        }
+    }
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(untagged, rename_all = "kebab-case")]
+pub enum WhitespaceRender {
+    Basic(WhitespaceRenderValue),
+    Specific {
+        default: Option<WhitespaceRenderValue>,
+        space: Option<WhitespaceRenderValue>,
+        tab: Option<WhitespaceRenderValue>,
+        newline: Option<WhitespaceRenderValue>,
+    },
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "kebab-case")]
+pub enum WhitespaceRenderValue {
+    None,
+    // TODO
+    // Selection,
+    All,
+}
+
+impl WhitespaceRender {
+    pub fn space(&self) -> WhitespaceRenderValue {
+        match *self {
+            Self::Basic(val) => val,
+            Self::Specific { default, space, .. } => {
+                space.or(default).unwrap_or(WhitespaceRenderValue::None)
+            }
+        }
+    }
+    pub fn tab(&self) -> WhitespaceRenderValue {
+        match *self {
+            Self::Basic(val) => val,
+            Self::Specific { default, tab, .. } => {
+                tab.or(default).unwrap_or(WhitespaceRenderValue::None)
+            }
+        }
+    }
+    pub fn newline(&self) -> WhitespaceRenderValue {
+        match *self {
+            Self::Basic(val) => val,
+            Self::Specific {
+                default, newline, ..
+            } => newline.or(default).unwrap_or(WhitespaceRenderValue::None),
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(default)]
+pub struct WhitespaceCharacters {
+    pub space: char,
+    pub tab: char,
+    pub newline: char,
+}
+
+impl Default for WhitespaceCharacters {
+    fn default() -> Self {
+        Self {
+            space: '·',    // U+00B7
+            tab: '→',     // U+2192
+            newline: '⏎', // U+23CE
+        }
+    }
+}
+
 impl Default for Config {
     fn default() -> Self {
         Self {
@@ -288,6 +372,7 @@ impl Default for Config {
             search: SearchConfig::default(),
             lsp: LspConfig::default(),
             rulers: Vec::new(),
+            whitespace: WhitespaceConfig::default(),
         }
     }
 }
@@ -366,7 +451,7 @@ pub struct Editor {
 #[derive(Debug, Clone)]
 pub enum ConfigEvent {
     Refresh,
-    Update(Config),
+    Update(Box<Config>),
 }
 
 #[derive(Debug, Clone)]