Color palettes (#393)

* Enable using color palettes in theme files.

* Add an example theme defined using a gruvbox color palette.

* Fix clippy error.

* Small style improvement.

* Add documentation for the features to themes.md.

* Update runtime/themes/gruvbox.toml

Fix the value of purple0.

Co-authored-by: DrZingo <DrZingo@users.noreply.github.com>

Co-authored-by: DrZingo <DrZingo@users.noreply.github.com>

3 files changed, 143 insertions, 10 deletions

diff --git a/book/src/themes.md b/book/src/themes.md
index 2ece2491..d6ed78ba 100644
--- a/book/src/themes.md
+++ b/book/src/themes.md
@@ -99,3 +99,21 @@ Possible keys:
 These keys match [tree-sitter scopes](https://tree-sitter.github.io/tree-sitter/syntax-highlighting#theme). We half-follow the common scopes from [macromates language grammars](https://macromates.com/manual/en/language_grammars) with some differences.
 
 For a given highlight produced, styling will be determined based on the longest matching theme key. So it's enough to provide function to highlight `function.macro` and `function.builtin` as well, but you can use more specific scopes to highlight specific cases differently.
+
+## Color palettes
+
+You can define a palette of named colors, and refer to them from the
+configuration values in your theme. To do this, add a table called
+`palette` to your theme file:
+
+```toml
+ui.background = "white"
+ui.text = "black"
+
+[palette]
+white = "#ffffff"
+black = "#000000"
+```
+
+Remember that the `[palette]` table includes all keys after its header,
+so you should define the palette after normal theme options.
diff --git a/helix-view/src/theme.rs b/helix-view/src/theme.rs
index ece4fe9a..756e34f6 100644
--- a/helix-view/src/theme.rs
+++ b/helix-view/src/theme.rs
@@ -102,12 +102,13 @@ impl<'de> Deserialize<'de> for Theme {
     {
         let mut styles = HashMap::new();
 
-        if let Ok(colors) = HashMap::<String, Value>::deserialize(deserializer) {
+        if let Ok(mut colors) = HashMap::<String, Value>::deserialize(deserializer) {
+            let palette = parse_palette(colors.remove("palette"));
             // scopes.reserve(colors.len());
             styles.reserve(colors.len());
             for (name, style_value) in colors {
                 let mut style = Style::default();
-                parse_style(&mut style, style_value);
+                parse_style(&mut style, style_value, &palette);
                 // scopes.push(name);
                 styles.insert(name, style);
             }
@@ -118,18 +119,31 @@ impl<'de> Deserialize<'de> for Theme {
     }
 }
 
-fn parse_style(style: &mut Style, value: Value) {
+fn parse_palette(value: Option<Value>) -> HashMap<String, Color> {
+    match value {
+        Some(Value::Table(entries)) => entries,
+        _ => return HashMap::default(),
+    }
+    .into_iter()
+    .filter_map(|(name, value)| {
+        let color = parse_color(value, &HashMap::default())?;
+        Some((name, color))
+    })
+    .collect()
+}
+
+fn parse_style(style: &mut Style, value: Value, palette: &HashMap<String, Color>) {
     //TODO: alert user of parsing failures
     if let Value::Table(entries) = value {
         for (name, value) in entries {
             match name.as_str() {
                 "fg" => {
-                    if let Some(color) = parse_color(value) {
+                    if let Some(color) = parse_color(value, palette) {
                         *style = style.fg(color);
                     }
                 }
                 "bg" => {
-                    if let Some(color) = parse_color(value) {
+                    if let Some(color) = parse_color(value, palette) {
                         *style = style.bg(color);
                     }
                 }
@@ -143,7 +157,7 @@ fn parse_style(style: &mut Style, value: Value) {
                 _ => (),
             }
         }
-    } else if let Some(color) = parse_color(value) {
+    } else if let Some(color) = parse_color(value, palette) {
         *style = style.fg(color);
     }
 }
@@ -164,9 +178,11 @@ fn hex_string_to_rgb(s: &str) -> Option<(u8, u8, u8)> {
     }
 }
 
-fn parse_color(value: Value) -> Option<Color> {
+fn parse_color(value: Value, palette: &HashMap<String, Color>) -> Option<Color> {
     if let Value::String(s) = value {
-        if let Some((red, green, blue)) = hex_string_to_rgb(&s) {
+        if let Some(color) = palette.get(&s) {
+            Some(*color)
+        } else if let Some((red, green, blue)) = hex_string_to_rgb(&s) {
             Some(Color::Rgb(red, green, blue))
         } else {
             warn!("malformed hexcode in theme: {}", s);
@@ -226,7 +242,23 @@ fn test_parse_style_string() {
     let fg = Value::String("#ffffff".to_string());
 
     let mut style = Style::default();
-    parse_style(&mut style, fg);
+    parse_style(&mut style, fg, &HashMap::default());
+
+    assert_eq!(style, Style::default().fg(Color::Rgb(255, 255, 255)));
+}
+
+#[test]
+fn test_palette() {
+    let fg = Value::String("my_color".to_string());
+
+    let mut style = Style::default();
+    parse_style(
+        &mut style,
+        fg,
+        &vec![("my_color".to_string(), Color::Rgb(255, 255, 255))]
+            .into_iter()
+            .collect(),
+    );
 
     assert_eq!(style, Style::default().fg(Color::Rgb(255, 255, 255)));
 }
@@ -244,7 +276,7 @@ fn test_parse_style_table() {
     let mut style = Style::default();
     if let Value::Table(entries) = table {
         for (_name, value) in entries {
-            parse_style(&mut style, value);
+            parse_style(&mut style, value, &HashMap::default());
         }
     }
 
diff --git a/runtime/themes/gruvbox.toml b/runtime/themes/gruvbox.toml
new file mode 100644
index 00000000..b606568d
--- /dev/null
+++ b/runtime/themes/gruvbox.toml
@@ -0,0 +1,83 @@
+# Author : Jakub Bartodziej <kubabartodziej@gmail.com>
+# The theme uses the gruvbox dark palette with standard contrast: github.com/morhetz/gruvbox
+
+"attribute" = "fg2"
+"keyword" = { fg = "red1" }
+"keyword.directive" = "red0"
+"namespace" = "yellow0"
+"punctuation" = "fg4"
+"punctuation.delimiter" = "fg4"
+"operator" = "orange0"
+"special" = "purple0"
+"property" = "fg2"
+"variable" = "fg2"
+"variable.builtin" = "fg3"
+"variable.parameter" = "fg2"
+"type" = "orange1"
+"type.builtin" = "orange0"
+"constructor" = "fg2"
+"function" = "green0"
+"function.macro" = "aqua1"
+"function.builtin" = "yellow1"
+"comment" = "gray1"
+"constant" = { fg = "fg2", modifiers = ["bold"] }
+"constant.builtin" = { fg = "fg1", modifiers = ["bold"] }
+"string" = "green1"
+"number" = "purple1"
+"escape" = { fg = "fg2", modifiers = ["bold"] }
+"label" = "aqua1"
+"module" = "yellow1"
+
+"warning" = "orange0"
+"error" = "red0"
+"info" = "purple0"
+"hint" = "blue0"
+
+"ui.background" = { bg = "bg0" }
+"ui.linenr" = { fg = "fg3" }
+"ui.linenr.selected" = { fg = "fg1", modifiers = ["bold"] }
+"ui.statusline" = { fg = "fg2", bg = "bg2" }
+"ui.statusline.inactive" = { fg = "fg3", bg = "bg4" }
+"ui.popup" = { bg = "bg1" }
+"ui.window" = { bg = "bg1" }
+"ui.help" = { bg = "bg1", fg = "fg1" }
+"ui.text" = { fg = "fg1" }
+"ui.text.focus" = { fg = "fg1", modifiers = ["bold"] }
+"ui.selection" = { bg = "bg3" }
+"ui.cursor.primary" = { bg = "bg3" }
+"ui.cursor.match" = { bg = "bg4" }
+"ui.menu" = { fg = "fg1" }
+"ui.menu.selected" = { fg = "fg3", bg = "bg3" }
+
+"diagnostic" = { modifiers = ["underlined"] }
+
+[palette]
+bg0 = "#282828" # main background
+bg1 = "#3c3836"
+bg2 = "#504945"
+bg3 = "#665c54"
+bg4 = "#7c6f64"
+
+fg0 = "#fbf1c7"
+fg1 = "#ebdbb2" # main foreground
+fg2 = "#d5c4a1"
+fg3 = "#bdae93"
+fg4 = "#a89984" # gray0
+
+gray0 = "#a89984"
+gray1 = "#928374"
+
+red0 = "#cc241d" # neutral
+red1 = "#fb4934" # bright
+green0 = "#98971a"
+green1 = "#b8bb26"
+yellow0 = "#d79921"
+yellow1 = "#fabd2f"
+blue0 = "#458588"
+blue1 = "#83a598"
+purple0 = "#b16286"
+purple1 = "#d3869b"
+aqua0 = "#689d6a"
+aqua1 = "#8ec07c"
+orange0 = "#d65d0e"
+orange1 = "#fe8019"