feat(ivy): reuse focused win for blines/git_blame preview

Can be used for a single picker with:
```lua
:FzfLua blines profile=ivy
-- combined with "hide" profile
:FzfLua blines profile={"ivy","hide"}
-- lua version:
:lua FzfLua.git_blame({ profile={"ivy","hide"} })
```

Closes #1754

Author: ibhagwan

lua/fzf-lua/profiles/ivy.lua

@@ -1,4 +1,4 @@
-local M       = {
+local M              = {
   { "default-title" }, -- base profile
   desc = "UI at the bottom of the screen",
   winopts = {
@@ -40,7 +40,7 @@ local M       = {
   },
 }
 
-local up      = {
+local up             = {
   row = 1,
   col = 0,
   width = 1,
@@ -52,10 +52,114 @@ local up      = {
   },
 }
 
-M.blines      = { winopts = up, previewer = { toggle_behavior = "extend" } }
-M.lines       = M.blines
-M.grep        = M.blines
-M.grep_curbuf = M.blines
-M.git         = { blame = { winopts = up } }
+---Extract lnum, col from blines/git_blame entries
+---@param sel string[]
+---@param opts table
+---@return integer?, integer?
+local parse_lnum_col = function(sel, opts)
+  if not sel[1] then return end
+  local lnum = sel[1]:match("^%w+ %(.-(%d+)%)") -- git_blame
+  if tonumber(lnum) then return tonumber(lnum), 1 end
+  local entry = FzfLua.path.entry_to_file(sel[1], opts)
+  return entry.line, entry.col
+end
+
+-- Credit to phanen@GitHub:
+-- https://github.com/ibhagwan/fzf-lua/issues/1754#issuecomment-2944053022
+local focused_win    = {
+  -- _treesitter = function(line) return "foo.lua", nil, line:sub(2) end,
+  -- fzf_opts = { ["--nth"] = "1.." },
+  fzf_args = "--pointer=",
+  winopts = function()
+    local off = vim.o.cmdheight + (vim.o.laststatus and 1 or 0)
+    local height = math.ceil(vim.o.lines / 4)
+    local ns = vim.api.nvim_create_namespace("fzf-lua.preview.swiper")
+    local buf = vim.api.nvim_get_current_buf()
+    local hl = function(start_row, start_col, end_row, end_col)
+      assert(start_col >= 0 and end_col >= 0, "start_col and end_col must be non-negative")
+      vim.hl.range(buf, ns, "IncSearch", { start_row, start_col }, { end_row, end_col }, {})
+    end
+    local on_buf_change = function()
+      vim.api.nvim_buf_clear_namespace(buf, ns, 0, -1)
+      local lines = vim.o.lines
+      local l_s = lines - height - off + 1
+      local l_e = lines - off - 1
+      local max_columns = vim.o.columns
+      for r = l_s, l_e do
+        local state = {}
+        for c = 1, max_columns do
+          local ok, ret = pcall(vim.api.nvim__inspect_cell, 1, r, c)
+          if not ok or not ret[1] then break end
+          (function()
+            if not state.lnum then -- parsing lnum
+              local d = tonumber(ret[1])
+              if not state.parsing_lnum and not d then return end
+              if not state.parsing_lnum then
+                state.parsing_lnum = d
+                return
+              end
+              if d then
+                state.parsing_lnum = state.parsing_lnum * 10 + d
+                return
+              end
+              state.lnum, state.parsing_lnum = assert(state.parsing_lnum), nil
+              return
+            end
+            local in_matched = ret[2] and ret[2].reverse
+            if in_matched and not state.in_matched then
+              state.start_col = math.max(c - 8, 0)
+              state.text = { ret[1] }
+              state.in_matched = in_matched
+              return
+            end
+            if in_matched then
+              state.text[#state.text + 1] = ret[1]
+              return
+            end
+            if state.in_matched then
+              hl(state.lnum - 1, state.start_col, state.lnum - 1, c - 8)
+              state.in_matched = nil
+            end
+          end)()
+        end
+      end
+    end
+    return {
+      preview = { hidden = true },
+      split = ("botright %snew +set\\ nobl"):format(height),
+      on_create = function(e)
+        vim.api.nvim_create_autocmd("TextChangedT", { buffer = e.bufnr, callback = on_buf_change })
+      end,
+      on_close = function()
+        vim.api.nvim_buf_clear_namespace(buf, ns, 0, -1)
+        vim.api.nvim_win_set_cursor(0, FzfLua.utils.__CTX().cursor)
+        FzfLua.utils.zz()
+      end,
+    }
+  end,
+  actions = {
+    enter = function(sel, opts)
+      local lnum, col = parse_lnum_col(sel, opts)
+      pcall(vim.api.nvim_win_set_cursor, 0, { lnum, col })
+    end,
+    focus = {
+      fn = function(sel, opts)
+        local lnum, col = parse_lnum_col(sel, opts)
+        if not lnum then return end
+        local ctx = FzfLua.utils.CTX()
+        vim.wo[ctx.winid].cursorline = true
+        pcall(vim.api.nvim_win_set_cursor, ctx.winid, { lnum, col })
+      end,
+      field_index = "{}",
+      exec_silent = true,
+    },
+  },
+}
+
+M.blines             = focused_win
+M.git                = { blame = focused_win }
+M.lines              = { winopts = up, previewer = { toggle_behavior = "extend" } }
+M.grep               = { winopts = up, previewer = { toggle_behavior = "extend" } }
+M.grep_curbuf        = { winopts = up, previewer = { toggle_behavior = "extend" } }
 
 return M

lua/fzf-lua/providers/git.lua

@@ -62,7 +62,7 @@ local function git_cmd(opts)
 end
 
 local function git_preview(opts, file)
-  if not type(opts.preview) == "string" then return end
+  if type(opts.preview) ~= "string" then return end
   if file then
     opts.preview = opts.preview:gsub("[<{]file[}>]", file)
   end