fix: prevent flickering in 3-way conflict diff (#317)

lua/codediff/ui/auto_refresh.lua

@@ -114,8 +114,6 @@ local function do_diff_update(bufnr, skip_watcher_check)
     -- Re-sync scrollbind after filler changes
     -- This ensures all windows stay aligned even if fillers were added/removed
     local original_win, modified_win, result_win = nil, nil, nil
-    local lifecycle = require("codediff.ui.lifecycle")
-    local tabpage = vim.api.nvim_get_current_tabpage()
     local _, stored_result_win = lifecycle.get_result(tabpage)
 
     for _, win in ipairs(vim.api.nvim_list_wins()) do

lua/codediff/ui/explorer/render.lua

@@ -327,6 +327,13 @@ function M.create(status_result, git_root, tabpage, width, base_revision, target
       local is_same_file = (session.modified_path == abs_path or session.modified_path == file_path or (session.git_root and session.original_path == file_path))
 
       if is_same_file and not opts.force then
+        -- Conflict mode: skip if already showing the same conflict file
+        -- (revisions :2/:3 are mutable so the staged-base-change logic below
+        --  would incorrectly force a re-render on every refresh cycle)
+        if group == "conflicts" and session.result_win and vim.api.nvim_win_is_valid(session.result_win) then
+          return
+        end
+
         -- Check if it's the same diff comparison
         local is_staged_diff = group == "staged"
         local current_is_staged = session.modified_revision == ":0"

tests/ui/conflict/conflict_dedup_spec.lua

@@ -0,0 +1,109 @@
+-- Test: Conflict file deduplication prevents unnecessary view.update() calls (#317)
+local assert = require("luassert")
+
+describe("Conflict dedup in on_file_select", function()
+  local lifecycle, config
+
+  before_each(function()
+    lifecycle = require("codediff.ui.lifecycle")
+    config = require("codediff.config")
+  end)
+
+  it("should detect conflict mode via result_win on session", function()
+    -- Simulate a conflict session with result_win set
+    local tabpage = vim.api.nvim_get_current_tabpage()
+    local result_win = vim.api.nvim_get_current_win()
+
+    -- Create a mock session with conflict mode indicators
+    local mock_session = {
+      modified_path = "file.txt",
+      original_path = "file.txt",
+      git_root = "/tmp/test",
+      modified_revision = ":2",
+      original_revision = ":3",
+      result_win = result_win,
+      result_bufnr = vim.api.nvim_get_current_buf(),
+    }
+
+    -- The dedup check logic from on_file_select:
+    -- For conflict files (group="conflicts"), if session has valid result_win,
+    -- the same file should be detected as already displayed
+    local group = "conflicts"
+    local file_path = "file.txt"
+    local abs_path = "/tmp/test/file.txt"
+
+    local is_same_file = (mock_session.modified_path == abs_path
+      or mock_session.modified_path == file_path
+      or (mock_session.git_root and mock_session.original_path == file_path))
+
+    assert.is_true(is_same_file, "Should detect same conflict file")
+
+    -- The fix: conflict-specific early return
+    local should_skip = (group == "conflicts"
+      and mock_session.result_win
+      and vim.api.nvim_win_is_valid(mock_session.result_win))
+
+    assert.is_true(should_skip, "Should skip update for same conflict file with active result_win")
+  end)
+
+  it("should NOT skip when result_win is nil (conflict not yet loaded)", function()
+    local mock_session = {
+      modified_path = "file.txt",
+      original_path = "file.txt",
+      git_root = "/tmp/test",
+      modified_revision = nil,
+      original_revision = nil,
+      result_win = nil,
+    }
+
+    local group = "conflicts"
+    local should_skip = (group == "conflicts"
+      and mock_session.result_win
+      and vim.api.nvim_win_is_valid(mock_session.result_win))
+
+    assert.is_falsy(should_skip, "Should NOT skip when result_win is nil")
+  end)
+
+  it("should NOT skip for non-conflict groups even with result_win", function()
+    local result_win = vim.api.nvim_get_current_win()
+
+    local mock_session = {
+      modified_path = "file.txt",
+      original_path = "file.txt",
+      git_root = "/tmp/test",
+      modified_revision = ":0",
+      original_revision = "abc123",
+      result_win = result_win,
+    }
+
+    local group = "staged"
+    local should_skip = (group == "conflicts"
+      and mock_session.result_win
+      and vim.api.nvim_win_is_valid(mock_session.result_win))
+
+    assert.is_false(should_skip, "Should NOT skip for staged group")
+  end)
+
+  it("demonstrates the original bug: mutable revision check fails for conflict revisions", function()
+    -- This is the original buggy check that caused flickering
+    -- Conflict revisions :2/:3 match ^:[0-3]$ causing false positive
+    local mock_session = {
+      original_revision = ":3",  -- conflict THEIRS revision
+    }
+
+    local current_is_mutable = mock_session.original_revision
+      and mock_session.original_revision:match("^:[0-3]$")
+
+    assert.is_truthy(current_is_mutable,
+      "Conflict revision :3 matches mutable pattern (the root cause of the bug)")
+
+    -- And conflict files are NOT in staged list
+    local file_has_staged = false  -- conflict files aren't in status_result.staged
+
+    -- This evaluates to true, meaning "comparison base needs to change" (WRONG for conflicts)
+    local would_skip = not (file_has_staged ~= (current_is_mutable and true or false))
+
+    assert.is_false(would_skip,
+      "Original check incorrectly thinks comparison base needs to change for conflict files")
+  end)
+end)