formatter: add support for reversing colors

CHANGELOG.md

@@ -85,6 +85,10 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   now show up in `git diff` (as if you had run `git add --intent-to-add` on
   them).
 
+* Reversing colors is now supported. For example, to highlight words by
+  reversing colors rather than underlining, you can set
+  `colors."diff token"={ underline = false, reverse = true }` in your config.
+
 ### Fixed bugs
 
 * `jj log -p --stat` now shows diff stats as well as the default color-words/git

cli/src/config-schema.json

@@ -342,6 +342,9 @@
                             },
                             "underline": {
                                 "type": "boolean"
+                            },
+                            "reverse": {
+                                "type": "boolean"
                             }
                         }
                     }

cli/src/formatter.rs

@@ -266,6 +266,7 @@ pub struct Style {
     pub bold: Option<bool>,
     pub italic: Option<bool>,
     pub underline: Option<bool>,
+    pub reverse: Option<bool>,
 }
 
 impl Style {
@@ -275,6 +276,7 @@ impl Style {
         self.bold = other.bold.or(self.bold);
         self.italic = other.italic.or(self.italic);
         self.underline = other.underline.or(self.underline);
+        self.reverse = other.reverse.or(self.reverse);
     }
 }
 
@@ -396,6 +398,13 @@ impl<W: Write> ColorFormatter<W> {
                     queue!(self.output, SetAttribute(Attribute::NoUnderline))?;
                 }
             }
+            if new_style.reverse != self.current_style.reverse {
+                if new_style.reverse.unwrap_or_default() {
+                    queue!(self.output, SetAttribute(Attribute::Reverse))?;
+                } else {
+                    queue!(self.output, SetAttribute(Attribute::NoReverse))?;
+                }
+            }
             if new_style.fg != self.current_style.fg {
                 queue!(
                     self.output,
@@ -436,6 +445,7 @@ fn rules_from_config(config: &StackedConfig) -> Result<Rules, ConfigGetError> {
                         bold: None,
                         italic: None,
                         underline: None,
+                        reverse: None,
                     })
                 } else if value.is_inline_table() {
                     Style::deserialize(value.into_deserializer())
@@ -884,7 +894,8 @@ mod tests {
         colors.bold_font = { bold = true }
         colors.italic_text = { italic = true }
         colors.underlined_text = { underline = true }
-        colors.multiple = { fg = "green", bg = "yellow", bold = true, italic = true, underline = true }
+        colors.reversed_colors = { reverse = true }
+        colors.multiple = { fg = "green", bg = "yellow", bold = true, italic = true, underline = true, reverse = true }
         "#,
         );
         let mut output: Vec<u8> = vec![];
@@ -909,6 +920,10 @@ mod tests {
         write!(formatter, " underlined only ").unwrap();
         formatter.pop_label().unwrap();
         writeln!(formatter).unwrap();
+        formatter.push_label("reversed_colors").unwrap();
+        write!(formatter, " reverse only ").unwrap();
+        formatter.pop_label().unwrap();
+        writeln!(formatter).unwrap();
         formatter.push_label("multiple").unwrap();
         write!(formatter, " single rule ").unwrap();
         formatter.pop_label().unwrap();
@@ -926,7 +941,8 @@ mod tests {
          bold only 
          italic only 
          underlined only 
-         single rule 
+         reverse only 
+         single rule 
          two rules 
         [EOF]
         ");

docs/config.md

@@ -129,12 +129,14 @@ change_id = "#ff1525"
 ```
 
 If you use a string value for a color, as in the examples above, it will be used
-for the foreground color. You can also set the background color, or make the
-text bold, italic, or underlined. For that, you need to use a table:
+for the foreground color. You can also set the background color, reverse colors
+(swap foreground and background), or make the text bold, italic, or underlined.
+For that, you need to use a table:
 
 ```toml
 [colors]
-commit_id = { fg = "green", bg = "#ff1525", bold = true, italic = true, underline = true }
+commit_id = { fg = "green", bg = "#ff1525", bold = true, underline = true }
+change_id = { reverse = true, italic = true }
 ```
 
 The key names are called "labels". The above used `commit_id` as label. You can
@@ -205,6 +207,8 @@ can override the default style with the following keys:
 # Highlight hunks with background
 "diff removed token" = { bg = "#221111", underline = false }
 "diff added token" = { bg = "#002200", underline = false }
+# Alternatively, swap colors
+"diff token" = { reverse = true, underline = false }
 ```
 
 ### Diff format