Highlight merge conflicts and provide for resolving them (#28065)

TODO:

- [x] Make it work in the project diff:
  - [x] Support non-singleton buffers
  - [x] Adjust excerpt boundaries to show full conflicts
- [x] Write tests for conflict-related events and state management
- [x] Prevent hunk buttons from appearing inside conflicts
- [x] Make sure it works over SSH, collab
- [x] Allow separate theming of markers

Bonus:

- [ ] Count of conflicts in toolbar
- [ ] Keyboard-driven navigation and resolution
- [ ] ~~Inlay hints to contextualize "ours"/"theirs"~~

Release Notes:

- Implemented initial support for resolving merge conflicts.

---------

Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>

crates/theme/src/default_colors.rs

@@ -143,6 +143,11 @@ impl ThemeColors {
             version_control_renamed: MODIFIED_COLOR,
             version_control_conflict: orange().light().step_12(),
             version_control_ignored: gray().light().step_12(),
+            version_control_conflict_ours_background: green().light().step_10().alpha(0.5),
+            version_control_conflict_theirs_background: blue().light().step_10().alpha(0.5),
+            version_control_conflict_ours_marker_background: green().light().step_10().alpha(0.7),
+            version_control_conflict_theirs_marker_background: blue().light().step_10().alpha(0.7),
+            version_control_conflict_divider_background: Hsla::default(),
         }
     }
 
@@ -258,6 +263,11 @@ impl ThemeColors {
             version_control_renamed: MODIFIED_COLOR,
             version_control_conflict: orange().dark().step_12(),
             version_control_ignored: gray().dark().step_12(),
+            version_control_conflict_ours_background: green().dark().step_10().alpha(0.5),
+            version_control_conflict_theirs_background: blue().dark().step_10().alpha(0.5),
+            version_control_conflict_ours_marker_background: green().dark().step_10().alpha(0.7),
+            version_control_conflict_theirs_marker_background: blue().dark().step_10().alpha(0.7),
+            version_control_conflict_divider_background: Hsla::default(),
         }
     }
 }

crates/theme/src/fallback_themes.rs

@@ -201,6 +201,23 @@ pub(crate) fn zed_default_dark() -> Theme {
                 version_control_renamed: MODIFIED_COLOR,
                 version_control_conflict: crate::orange().light().step_12(),
                 version_control_ignored: crate::gray().light().step_12(),
+                version_control_conflict_ours_background: crate::green()
+                    .light()
+                    .step_12()
+                    .alpha(0.5),
+                version_control_conflict_theirs_background: crate::blue()
+                    .light()
+                    .step_12()
+                    .alpha(0.5),
+                version_control_conflict_ours_marker_background: crate::green()
+                    .light()
+                    .step_12()
+                    .alpha(0.7),
+                version_control_conflict_theirs_marker_background: crate::blue()
+                    .light()
+                    .step_12()
+                    .alpha(0.7),
+                version_control_conflict_divider_background: Hsla::default(),
             },
             status: StatusColors {
                 conflict: yellow,

crates/theme/src/schema.rs

@@ -586,6 +586,26 @@ pub struct ThemeColorsContent {
     /// Ignored version control color.
     #[serde(rename = "version_control.ignored")]
     pub version_control_ignored: Option<String>,
+
+    /// Background color for row highlights of "ours" regions in merge conflicts.
+    #[serde(rename = "version_control.conflict.ours_background")]
+    pub version_control_conflict_ours_background: Option<String>,
+
+    /// Background color for row highlights of "theirs" regions in merge conflicts.
+    #[serde(rename = "version_control.conflict.theirs_background")]
+    pub version_control_conflict_theirs_background: Option<String>,
+
+    /// Background color for row highlights of "ours" conflict markers in merge conflicts.
+    #[serde(rename = "version_control.conflict.ours_marker_background")]
+    pub version_control_conflict_ours_marker_background: Option<String>,
+
+    /// Background color for row highlights of "theirs" conflict markers in merge conflicts.
+    #[serde(rename = "version_control.conflict.theirs_marker_background")]
+    pub version_control_conflict_theirs_marker_background: Option<String>,
+
+    /// Background color for row highlights of the "ours"/"theirs" divider in merge conflicts.
+    #[serde(rename = "version_control.conflict.divider_background")]
+    pub version_control_conflict_divider_background: Option<String>,
 }
 
 impl ThemeColorsContent {
@@ -1037,6 +1057,26 @@ impl ThemeColorsContent {
                 .and_then(|color| try_parse_color(color).ok())
                 // Fall back to `conflict`, for backwards compatibility.
                 .or(status_colors.ignored),
+            version_control_conflict_ours_background: self
+                .version_control_conflict_ours_background
+                .as_ref()
+                .and_then(|color| try_parse_color(color).ok()),
+            version_control_conflict_theirs_background: self
+                .version_control_conflict_theirs_background
+                .as_ref()
+                .and_then(|color| try_parse_color(color).ok()),
+            version_control_conflict_ours_marker_background: self
+                .version_control_conflict_ours_marker_background
+                .as_ref()
+                .and_then(|color| try_parse_color(color).ok()),
+            version_control_conflict_theirs_marker_background: self
+                .version_control_conflict_theirs_marker_background
+                .as_ref()
+                .and_then(|color| try_parse_color(color).ok()),
+            version_control_conflict_divider_background: self
+                .version_control_conflict_divider_background
+                .as_ref()
+                .and_then(|color| try_parse_color(color).ok()),
         }
     }
 }

crates/theme/src/styles/colors.rs

@@ -261,6 +261,14 @@ pub struct ThemeColors {
     pub version_control_conflict: Hsla,
     /// Represents an ignored entry in version control systems.
     pub version_control_ignored: Hsla,
+
+    /// Represents the "ours" region of a merge conflict.
+    pub version_control_conflict_ours_background: Hsla,
+    /// Represents the "theirs" region of a merge conflict.
+    pub version_control_conflict_theirs_background: Hsla,
+    pub version_control_conflict_ours_marker_background: Hsla,
+    pub version_control_conflict_theirs_marker_background: Hsla,
+    pub version_control_conflict_divider_background: Hsla,
 }
 
 #[derive(EnumIter, Debug, Clone, Copy, AsRefStr)]