feat(merge)!: honour view.merge_tool.layout / view.default.layout in DiffviewMergeFiles and DiffviewDiffDirs

lua/diffview/scene/views/diff/file_dir_diff_view.lua

@@ -1,14 +1,14 @@
 local lazy = require("diffview.lazy")
 local oop = require("diffview.oop")
 
-local Diff2Hor = lazy.access("diffview.scene.layouts.diff_2_hor", "Diff2Hor") ---@type Diff2Hor|LazyModule
-local Diff3Hor = lazy.access("diffview.scene.layouts.diff_3_hor", "Diff3Hor") ---@type Diff3Hor|LazyModule
+local Diff4Mixed = lazy.access("diffview.scene.layouts.diff_4_mixed", "Diff4Mixed") ---@type Diff4Mixed|LazyModule
 local File = lazy.access("diffview.vcs.file", "File") ---@type vcs.File|LazyModule
 local FileEntry = lazy.access("diffview.scene.file_entry", "FileEntry") ---@type FileEntry|LazyModule
 local NullDiffView = lazy.access("diffview.scene.views.diff.null_diff_view", "NullDiffView") ---@type NullDiffView|LazyModule
 local NullRev = lazy.access("diffview.vcs.adapters.null.rev", "NullRev") ---@type NullRev|LazyModule
 local RevType = lazy.access("diffview.vcs.rev", "RevType") ---@type RevType|LazyModule
 local StandardView = lazy.access("diffview.scene.views.standard.standard_view", "StandardView") ---@type StandardView|LazyModule
+local View = lazy.access("diffview.scene.view", "View") ---@type View|LazyModule
 local utils = lazy.require("diffview.utils") ---@module "diffview.utils"
 
 local fmt = string.format
@@ -214,12 +214,16 @@ function FileDirDiffView:_build_entry(rel, status, a_rev, b_rev, c_rev)
     b_file = make_file(b_abs, b_rev, nil, nil)
   end
 
-  local layout
+  local layout_class
   if three_pane then
-    layout = Diff3Hor.__get()({ a = a_file, b = b_file, c = c_file })
+    layout_class = View.__get().get_default_merge_layout()
+    if layout_class == Diff4Mixed.__get() then
+      layout_class = View.__get().get_default_diff3()
+    end
   else
-    layout = Diff2Hor.__get()({ a = a_file, b = b_file })
+    layout_class = View.__get().get_default_layout()
   end
+  local layout = layout_class({ a = a_file, b = b_file, c = c_file })
 
   return FileEntry({
     adapter = self.adapter,

lua/diffview/scene/views/diff/file_merge_view.lua

@@ -1,13 +1,13 @@
 local lazy = require("diffview.lazy")
 local oop = require("diffview.oop")
 
-local Diff3Hor = lazy.access("diffview.scene.layouts.diff_3_hor", "Diff3Hor") ---@type Diff3Hor|LazyModule
 local Diff4Mixed = lazy.access("diffview.scene.layouts.diff_4_mixed", "Diff4Mixed") ---@type Diff4Mixed|LazyModule
 local File = lazy.access("diffview.vcs.file", "File") ---@type vcs.File|LazyModule
 local FileEntry = lazy.access("diffview.scene.file_entry", "FileEntry") ---@type FileEntry|LazyModule
 local NullDiffView = lazy.access("diffview.scene.views.diff.null_diff_view", "NullDiffView") ---@type NullDiffView|LazyModule
 local NullRev = lazy.access("diffview.vcs.adapters.null.rev", "NullRev") ---@type NullRev|LazyModule
 local RevType = lazy.access("diffview.vcs.rev", "RevType") ---@type RevType|LazyModule
+local View = lazy.access("diffview.scene.view", "View") ---@type View|LazyModule
 local utils = lazy.require("diffview.utils") ---@module "diffview.utils"
 
 local fmt = string.format
@@ -80,14 +80,15 @@ function FileMergeView:init(opt)
   local a_file = make_file(self.left_path, left_rev, "OURS (Current changes)", self.left_path)
   local b_file = make_file(self.output_path, output_rev, "MERGED (Output)", nil)
   local c_file = make_file(self.right_path, right_rev, "THEIRS (Incoming changes)", self.right_path)
+  local d_file = self.base_path
+      and make_file(self.base_path, base_rev, "BASE (Common ancestor)", self.base_path)
+    or nil
 
-  local layout
-  if self.base_path then
-    local d_file = make_file(self.base_path, base_rev, "BASE (Common ancestor)", self.base_path)
-    layout = Diff4Mixed.__get()({ a = a_file, b = b_file, c = c_file, d = d_file })
-  else
-    layout = Diff3Hor.__get()({ a = a_file, b = b_file, c = c_file })
+  local layout_class = View.__get().get_default_merge_layout()
+  if not d_file and layout_class == Diff4Mixed.__get() then
+    layout_class = View.__get().get_default_diff3()
   end
+  local layout = layout_class({ a = a_file, b = b_file, c = c_file, d = d_file })
 
   local entry = FileEntry({
     adapter = self.adapter,

lua/diffview/tests/functional/file_merge_view_spec.lua

@@ -1,4 +1,5 @@
 local actions = require("diffview.actions")
+local config = require("diffview.config")
 local helpers = require("diffview.tests.helpers")
 local lib = require("diffview.lib")
 local Diff3Hor = require("diffview.scene.layouts.diff_3_hor").Diff3Hor
@@ -65,7 +66,8 @@ describe("diffview.scene.views.diff.file_merge_view", function()
       assert.True(view.files.conflicting[1].layout:instanceof(Diff3Hor))
     end)
 
-    it("uses Diff4Mixed when base is provided", function()
+    it("uses Diff4Mixed when base is provided and config selects Diff4Mixed", function()
+      config.setup({ view = { merge_tool = { layout = "diff4_mixed" } } })
       local adapter = NullAdapter.create({ toplevel = "/tmp" })
       local view = FileMergeView({
         adapter = adapter,
@@ -76,6 +78,39 @@ describe("diffview.scene.views.diff.file_merge_view", function()
       })
 
       assert.True(view.files.conflicting[1].layout:instanceof(Diff4Mixed))
+      config.setup({})
+    end)
+
+    it("downgrades a configured Diff4Mixed to Diff3 default when no base is provided", function()
+      config.setup({ view = { merge_tool = { layout = "diff4_mixed" } } })
+      local Diff3 = require("diffview.scene.layouts.diff_3").Diff3
+      local adapter = NullAdapter.create({ toplevel = "/tmp" })
+      local view = FileMergeView({
+        adapter = adapter,
+        output_path = output_path,
+        left_path = left_path,
+        right_path = right_path,
+      })
+
+      assert.False(view.files.conflicting[1].layout:instanceof(Diff4Mixed))
+      assert.True(view.files.conflicting[1].layout:instanceof(Diff3))
+      config.setup({})
+    end)
+
+    it("honours a Diff3 config even when base is provided (base is dropped)", function()
+      config.setup({ view = { merge_tool = { layout = "diff3_mixed" } } })
+      local Diff3Mixed = require("diffview.scene.layouts.diff_3_mixed").Diff3Mixed
+      local adapter = NullAdapter.create({ toplevel = "/tmp" })
+      local view = FileMergeView({
+        adapter = adapter,
+        output_path = output_path,
+        base_path = base_path,
+        left_path = left_path,
+        right_path = right_path,
+      })
+
+      assert.True(view.files.conflicting[1].layout:instanceof(Diff3Mixed))
+      config.setup({})
     end)
 
     it("populates conflicting (not working) with a single entry", function()
@@ -126,6 +161,7 @@ describe("diffview.scene.views.diff.file_merge_view", function()
     end)
 
     it("binds each window's file to the matching on-disk path", function()
+      config.setup({ view = { merge_tool = { layout = "diff4_mixed" } } })
       local adapter = NullAdapter.create({ toplevel = "/tmp" })
       local view = FileMergeView({
         adapter = adapter,
@@ -140,6 +176,7 @@ describe("diffview.scene.views.diff.file_merge_view", function()
       eq(output_path, layout.b.file.path) -- OUTPUT (editable)
       eq(right_path, layout.c.file.path) -- THEIRS
       eq(base_path, layout.d.file.path) -- BASE
+      config.setup({})
     end)
 
     it("populates `merge_ctx` so `merge_only` keymaps show in the help panel", function()