feat(hl): Add plugin local groups for all the diff highlights

Adds new highlight groups shadowing all the default diff highlights:

- `DiffviewDiffAdd` -> `DiffAdd`
- `DiffviewDiffDelete` -> `DiffDelete`
- `DiffviewDiffChange` -> `DiffChange`
- `DiffviewDiffText` -> `DiffText`

These are set as 'winhl' in all the diff buffers created by the plugin.
This way users will be able to change the diff highlighting for Diffview
only, without affecting the use of these groups outside of the plugin.

OTHER CHANGES:

Having `enhanced_diff_hl` enabled will now highlight delete fill-chars
more subtly in *all* layouts. Not only `diff2*` layouts.

(fixes sindrets#340)

Author: sindrets

doc/diffview.txt

@@ -359,12 +359,23 @@ EXAMPLE CONFIGURATION WITH DEFAULT SETTINGS: |diffview.defaults|
 enhanced_diff_hl                                *diffview-config-enhanced_diff_hl*
         Type: `boolean`, Default: `false`
 
-        Enable/disable enhanced diff highlighting. In `diff2*` layouts this
-        will highlight the delete fill-chars more subtly, and show
-        |hl-DiffAdd| in the old state buffer, as |hl-DiffDelete|. This makes
-        the highlighting more inline with how 2-way diffs are displayed in
-        other diff tools. As - in a 2-way diff - an "addition" in the old
-        state actually represents a deletion.
+        Enable/disable enhanced diff highlighting. This option has slightly
+        different effects in different |diffview-layouts|.
+
+        In all layouts: highlight delete fill-chars more subtly. These chars
+            are used as filler in places where other diff buffers have
+            insertions at that postion. Unfortunately many color schemes give
+            it a distracting highlight, such as a bright red. This makes diffs
+            more difficult to visually parse, as your eyes get drawn towards
+            the bright red areas of your display with absolutely no
+            information in them.
+
+        In `diff2*` layouts: show |hl-DiffAdd| as |hl-DiffDelete| in the
+            buffer representing the old state. This makes the highlighting
+            more inline with how 2-way diffs are displayed in other diff
+            tools. As - in a 2-way diff - an "insertion" in the old state
+            actually represents a deletion from the perspective of the new
+            state.
 
 git_cmd                                         *diffview-config-git_cmd*
         Type: `string[]`, Default: `{ "git" }`
@@ -419,6 +430,7 @@ view.x.layout                                   *diffview-config-view.x.layout*
               • C: THEIRS (incoming branch)
               • D: BASE (common ancestor)
 
+                                                *diffview-layouts*
             {diff1_plain}
                 Available for: merge_tool
 
@@ -904,7 +916,7 @@ conflict_choose({version})                      *diffview-actions-conflict_choos
                 See |diffview-conflict-versions| to tell what versions of the
                 file these names correspond with.
 
-conflict_choose_all({version})              *diffview-actions-conflict_choose_all*
+conflict_choose_all({version})                  *diffview-actions-conflict_choose_all*
         Contexts: `merge_tool`, `file_panel`
 
         Replace all merge conflicts in the current file at once. Choosing `'none'`

lua/diffview/hl.lua

@@ -460,6 +460,10 @@ M.hl_links = {
   StatusDeleted = "diffRemoved",
   StatusBroken = "diffRemoved",
   StatusIgnored = "Comment",
+  DiffAdd = "DiffAdd",
+  DiffDelete = "DiffDelete",
+  DiffChange = "DiffChange",
+  DiffText = "DiffText",
 }
 
 function M.update_diff_hl()
@@ -468,12 +472,14 @@ function M.update_diff_hl()
   local style = M.get_style("DiffDelete", true) or "NONE"
 
   M.hi("DiffviewDiffAddAsDelete", { fg = fg, bg = bg, style = style })
-  M.hi_link("DiffviewDiffDelete", "Comment", { default = true })
+  M.hi_link("DiffviewDiffDeleteDim", "Comment", { default = true })
+
+  if config.get_config().enhanced_diff_hl then
+    M.hi_link("DiffviewDiffDelete", "DiffviewDiffDeleteDim")
+  end
 end
 
 function M.setup()
-  M.update_diff_hl()
-
   for name, v in pairs(M.get_hl_groups()) do
     v = vim.tbl_extend("force", v, { default = true })
     M.hi("Diffview" .. name, v)
@@ -482,6 +488,8 @@ function M.setup()
   for from, to in pairs(M.hl_links) do
     M.hi_link("Diffview" .. from, to, { default = true })
   end
+
+  M.update_diff_hl()
 end
 
 return M

lua/diffview/scene/views/standard/standard_view.lua

@@ -78,10 +78,15 @@ function StandardView:post_layout()
   if config.get_config().enhanced_diff_hl then
     self.winopts.diff2.a.winhl = {
       "DiffAdd:DiffviewDiffAddAsDelete",
-      "DiffDelete:DiffviewDiffDelete",
+      "DiffDelete:DiffviewDiffDeleteDim",
+      "DiffChange:DiffviewDiffChange",
+      "DiffText:DiffviewDiffText",
     }
     self.winopts.diff2.b.winhl = {
-      "DiffDelete:DiffviewDiffDelete",
+      "DiffDelete:DiffviewDiffDeleteDim",
+      "DiffAdd:DiffviewDiffAdd",
+      "DiffChange:DiffviewDiffChange",
+      "DiffText:DiffviewDiffText",
     }
   end
 

lua/diffview/vcs/file.lua

@@ -87,6 +87,12 @@ function File:init(opt)
     foldcolumn = "1",
     foldlevel = 0,
     foldenable = true,
+    winhl = {
+      "DiffAdd:DiffviewDiffAdd",
+      "DiffDelete:DiffviewDiffDelete",
+      "DiffChange:DiffviewDiffChange",
+      "DiffText:DiffviewDiffText",
+    },
   }
 
   -- Set winbar info