fix(git): stop the blame statuscolumn leaking into new windows

lua/git/blame.lua

@@ -521,9 +521,21 @@ end
 ---@type table<integer, string>
 local saved_statuscolumn = {}
 
----Reconcile every window's `'statuscolumn'` with the overlay state: a
----window showing an overlay buffer gets the blame statuscolumn, and its
----previous value is saved so it can be restored on toggle-off.
+---Set a window's `'statuscolumn'` with `scope = "local"`, so the global
+---value stays clean and splits and new windows do not inherit the gutter.
+---@param win integer
+---@param value string
+local function set_statuscolumn(win, value)
+    vim.api.nvim_set_option_value(
+        "statuscolumn",
+        value,
+        { win = win, scope = "local" }
+    )
+end
+
+---Reconcile every window's `'statuscolumn'` with the overlay state.
+---Overlay windows get the blame statuscolumn, and a window that has it
+---but should not (a split inherits window options) is restored.
 local function refresh_overlay_columns()
     for win in pairs(saved_statuscolumn) do
         if not vim.api.nvim_win_is_valid(win) then
@@ -533,11 +545,16 @@ local function refresh_overlay_columns()
     for _, win in ipairs(vim.api.nvim_list_wins()) do
         local state = states[vim.api.nvim_win_get_buf(win)]
         local on = state ~= nil and state.overlay
-        if on and saved_statuscolumn[win] == nil then
-            saved_statuscolumn[win] = vim.wo[win].statuscolumn
-            vim.wo[win].statuscolumn = BLAME_EXPR .. native_items(win)
-        elseif not on and saved_statuscolumn[win] ~= nil then
-            vim.wo[win].statuscolumn = saved_statuscolumn[win]
+        local has_blame = vim.startswith(vim.wo[win].statuscolumn, BLAME_EXPR)
+        if on and not has_blame then
+            saved_statuscolumn[win] = saved_statuscolumn[win]
+                or vim.wo[win].statuscolumn
+            set_statuscolumn(win, BLAME_EXPR .. native_items(win))
+        elseif not on and has_blame then
+            set_statuscolumn(
+                win,
+                saved_statuscolumn[win] or vim.go.statuscolumn
+            )
             saved_statuscolumn[win] = nil
         end
     end
@@ -560,7 +577,7 @@ local function render(buf)
                 build_blame_text(state, win)
                 built = true
             end
-            vim.wo[win].statuscolumn = BLAME_EXPR .. native_items(win)
+            set_statuscolumn(win, BLAME_EXPR .. native_items(win))
         end
     end
 end

test/git/blame_test.lua

@@ -450,6 +450,32 @@ t.test("overlay re-budgets when a gutter option changes", function()
     end, "the blame to re-budget for the widened signcolumn")
 end)
 
+t.test("the overlay statuscolumn does not leak into other windows", function()
+    local _, buf = setup("a\nb\nc\n")
+    vim.api.nvim_set_current_buf(buf)
+    blame.toggle_overlay(buf)
+    t.wait_for(function()
+        local s = blame.state(buf)
+        return s ~= nil and s.blame_width ~= nil
+    end, "the overlay to render")
+    t.falsy(
+        vim.go.statuscolumn:find("git.blame", 1, true),
+        "the overlay leaves the global statuscolumn untouched"
+    )
+
+    vim.cmd("new")
+    local plain = vim.api.nvim_get_current_win()
+    t.defer(function()
+        if vim.api.nvim_win_is_valid(plain) then
+            vim.api.nvim_win_close(plain, true)
+        end
+    end)
+    t.falsy(
+        vim.wo[plain].statuscolumn:find("git.blame", 1, true),
+        "a new window does not inherit the blame gutter"
+    )
+end)
+
 t.test("overlay gutter shows sha, author and an absolute date", function()
     local _, buf = setup("a\nb\nc\n")
     vim.api.nvim_set_current_buf(buf)