feat(hover): peek full URL on mouse hover over links

README.md

@@ -18,7 +18,7 @@ A Markdown rendering engine for Neovim. Transforms raw Markdown into richly high
 - **Video** — local and web video (MP4, WebM, MOV, AVI, MKV, M4V) played as animated frames inline
 - **Mermaid diagrams** — rendered as images inline
 - **CJK-aware word wrapping** — JIS X 4051 kinsoku shori + optional [BudouX](https://github.com/google/budoux) phrase segmentation via [budoux.lua](https://github.com/delphinus/budoux.lua)
-- **Clickable links** — mouse click to open URLs; OSC 8 hyperlink support for compatible terminals
+- **Clickable links** — mouse click to open URLs; hover the mouse over a link to peek the full URL in a subtle floating window; OSC 8 hyperlink support for compatible terminals
 - **`<details>` support** — collapsible sections with click-to-toggle, respecting the `open` attribute
 - **Library API** — use the rendering engine programmatically from your own plugins
 

doc/md-render.jax

@@ -49,7 +49,8 @@ md-render.nvim は Neovim 用の Markdown レンダリングエンジンです
 - Mermaid ダイアグラムを画像としてインライン表示
 - CJK 対応ワードラップ（JIS X 4051 禁則処理 + オプションの BudouX フレーズ分
   割）
-- クリック可能リンク（マウスクリックで URL を開く。OSC 8 ハイパーリンク対応）
+- クリック可能リンク（マウスクリックで URL を開く。マウスをリンクに乗せると
+  完全な URL を控え目なフロートウィンドウに表示。OSC 8 ハイパーリンク対応）
 - `<details>` 対応（クリックで折りたたみ可能なセクション）
 - ライブラリ API（自作プラグインからプログラム的に利用可能）
 
@@ -140,11 +141,15 @@ lazy.nvim の場合: >lua
 	`q` / `<Esc>`	プレビューウィンドウを閉じる
 	`<CR>`		コールアウトの折りたたみ / 省略領域の展開
 	`<LeftMouse>`	リンクのクリック、折りたたみ、領域展開
+	`<MouseMove>`	マウスをリンクに乗せると、エディタ下部の小さな
+			フロートウィンドウに完全な URL を表示。
+			'mousemoveevent' が必要 (md-render はプレビュー
+			ウィンドウが開かれている間、自動で有効化する)。
 
 |:MdRender-toggle| で開かれたレンダーモードのバッファでは `q` / `<Esc>` /
 `<CR>` は閉じる動作に**割り当てられません**。ソースに戻すには再度
 |:MdRender-toggle| を呼びます。`<LeftMouse>` は折りたたみ・展開・リンクを
-引き続き処理します。
+引き続き処理し、`<MouseMove>` の URL 表示も有効なままです。
 
 ==============================================================================
 コマンド						    *md-render-commands*

doc/md-render.txt

@@ -46,7 +46,8 @@ Features: ~
 - Mermaid diagrams rendered as images inline
 - CJK-aware word wrapping (JIS X 4051 kinsoku shori + optional BudouX phrase
   segmentation)
-- Clickable links (mouse click to open URLs; OSC 8 hyperlink support)
+- Clickable links (mouse click to open URLs; mouse hover peeks the full URL
+  in a subtle floating window; OSC 8 hyperlink support)
 - `<details>` support (collapsible sections with click-to-toggle)
 - Library API for programmatic use from other plugins
 
@@ -139,11 +140,15 @@ Inside the preview window, the following keys are available:
 	`q` / `<Esc>`	Close the preview window
 	`<CR>`		Toggle callout fold / expand truncated region
 	`<LeftMouse>`	Click links, toggle folds, expand regions
+	`<MouseMove>`	Hover a link to peek its full URL in a small floating
+			window at the bottom of the editor.  Requires
+			'mousemoveevent' (md-render enables it automatically
+			whenever a preview window is open).
 
 Inside a render-mode buffer opened with |:MdRender-toggle|, `q` / `<Esc>` /
 `<CR>` are NOT bound to close — call |:MdRender-toggle| again to return to
 source mode.  `<LeftMouse>` still toggles folds, expands regions, and
-opens links.
+opens links; `<MouseMove>` hover-peek also stays active.
 
 ==============================================================================
 COMMANDS						    *md-render-commands*

lua/md-render/display_utils.lua

@@ -1,4 +1,5 @@
 local FloatWin = require "md-render.float_win"
+local UrlHover = require "md-render.url_hover"
 
 local M = {}
 
@@ -284,6 +285,8 @@ function M.setup_float_keymaps(buf, ns, win, content, close_handle, opts)
     vim.api.nvim_buf_set_keymap(buf, "n", key, ":close<CR>", { noremap = true, silent = true })
   end
 
+  UrlHover.attach(buf, ns, win)
+
   vim.keymap.set("n", "<LeftRelease>", function()
     local mouse = vim.fn.getmousepos()
     if mouse.winid == win then

lua/md-render/url_hover.lua

@@ -0,0 +1,253 @@
+--- Show the full URL in a small floating window at the bottom-right of the
+--- editor while the mouse hovers over a link in a md-render preview.
+
+local M = {}
+
+local DEBOUNCE_MS = 100
+local WINBLEND = 15
+local AUGROUP = "md_render_url_hover"
+
+---@type table<integer, { buf: integer, ns: integer }>
+local registered = {}
+
+local state = {
+  ---@type integer?
+  hover_win = nil,
+  ---@type integer?
+  hover_buf = nil,
+  ---@type string?
+  current_url = nil,
+  ---@type integer?
+  current_win = nil,
+  ---@type string?
+  pending_url = nil,
+  ---@type table?
+  pending_token = nil,
+}
+
+local augroup_initialized = false
+
+local function ensure_hover_buf()
+  if state.hover_buf and vim.api.nvim_buf_is_valid(state.hover_buf) then
+    return state.hover_buf
+  end
+  state.hover_buf = vim.api.nvim_create_buf(false, true)
+  vim.bo[state.hover_buf].bufhidden = "hide"
+  return state.hover_buf
+end
+
+---@param url string
+---@param max_width integer
+---@return string
+local function truncate_url(url, max_width)
+  if max_width <= 0 then return "" end
+  if vim.api.nvim_strwidth(url) <= max_width then return url end
+  if max_width == 1 then return "…" end
+
+  local result_width = 0
+  local pieces = {}
+  local len = vim.fn.strchars(url)
+  for i = 0, len - 1 do
+    local ch = vim.fn.strcharpart(url, i, 1)
+    local w = vim.api.nvim_strwidth(ch)
+    if result_width + w + 1 > max_width then break end
+    pieces[#pieces + 1] = ch
+    result_width = result_width + w
+  end
+  return table.concat(pieces) .. "…"
+end
+
+local function cancel_pending()
+  state.pending_token = nil
+  state.pending_url = nil
+end
+
+local function close_hover()
+  if state.hover_win and vim.api.nvim_win_is_valid(state.hover_win) then
+    pcall(vim.api.nvim_win_close, state.hover_win, true)
+  end
+  state.hover_win = nil
+  state.current_url = nil
+  state.current_win = nil
+end
+
+--- How many rows at the bottom of the editor are occupied by cmdline +
+--- statusline. The hover is placed just above this band so it doesn't
+--- overlap either.
+---@return integer
+local function bottom_reserved_rows()
+  local rows = vim.o.cmdheight
+  local ls = vim.o.laststatus
+  if ls == 2 or ls == 3 then
+    rows = rows + 1
+  elseif ls == 1 and #vim.api.nvim_tabpage_list_wins(0) > 1 then
+    rows = rows + 1
+  end
+  return rows
+end
+
+---@param url string
+---@param source_win integer
+local function show_hover(url, source_win)
+  if state.current_url == url and state.current_win == source_win then
+    return
+  end
+
+  local max_width = math.max(1, math.floor(vim.o.columns / 2))
+  local display = truncate_url(url, max_width)
+  local width = math.max(1, vim.api.nvim_strwidth(display))
+  local row = math.max(0, vim.o.lines - bottom_reserved_rows() - 1)
+  local col = math.max(0, vim.o.columns - width)
+
+  if state.hover_win and vim.api.nvim_win_is_valid(state.hover_win) then
+    local buf = vim.api.nvim_win_get_buf(state.hover_win)
+    vim.api.nvim_buf_set_lines(buf, 0, -1, false, { display })
+    vim.api.nvim_win_set_config(state.hover_win, {
+      relative = "editor",
+      width = width,
+      height = 1,
+      row = row,
+      col = col,
+    })
+  else
+    local buf = ensure_hover_buf()
+    vim.api.nvim_buf_set_lines(buf, 0, -1, false, { display })
+    state.hover_win = vim.api.nvim_open_win(buf, false, {
+      relative = "editor",
+      width = width,
+      height = 1,
+      row = row,
+      col = col,
+      style = "minimal",
+      border = "none",
+      focusable = false,
+      zindex = 250,
+      noautocmd = true,
+    })
+    vim.wo[state.hover_win].winblend = WINBLEND
+    vim.wo[state.hover_win].winhighlight = "Normal:Comment,NormalFloat:Comment"
+  end
+
+  state.current_url = url
+  state.current_win = source_win
+end
+
+---@param mouse { winid: integer, line: integer, column: integer }
+---@param buf integer
+---@param ns integer
+---@return string?
+local function url_at_mouse(mouse, buf, ns)
+  if mouse.line < 1 or mouse.column < 1 then return nil end
+  local line = mouse.line - 1
+  local col = mouse.column - 1
+
+  if not vim.api.nvim_buf_is_valid(buf) then return nil end
+  local line_count = vim.api.nvim_buf_line_count(buf)
+  if line >= line_count then return nil end
+
+  local ok, marks = pcall(
+    vim.api.nvim_buf_get_extmarks,
+    buf, ns, { line, 0 }, { line + 1, 0 }, { details = true }
+  )
+  if not ok then return nil end
+
+  for _, mark in ipairs(marks) do
+    local _, _, start_col, details = unpack(mark)
+    if details and details.url then
+      local end_col = details.end_col or (start_col + 1)
+      if col >= start_col and col < end_col then
+        return details.url
+      end
+    end
+  end
+  return nil
+end
+
+local function handle_mouse_move()
+  local mouse = vim.fn.getmousepos()
+  local entry = registered[mouse.winid]
+
+  if not entry then
+    cancel_pending()
+    close_hover()
+    return
+  end
+
+  local url = url_at_mouse(mouse, entry.buf, entry.ns)
+
+  if not url then
+    cancel_pending()
+    close_hover()
+    return
+  end
+
+  if state.current_url == url and state.current_win == mouse.winid then
+    cancel_pending()
+    return
+  end
+
+  if state.pending_url == url then return end
+
+  local token = {}
+  state.pending_token = token
+  state.pending_url = url
+  local source_win = mouse.winid
+
+  vim.defer_fn(function()
+    if state.pending_token ~= token then return end
+    state.pending_token = nil
+    state.pending_url = nil
+    if not registered[source_win] then return end
+    show_hover(url, source_win)
+  end, DEBOUNCE_MS)
+end
+
+local function ensure_initialized()
+  if augroup_initialized then return end
+  augroup_initialized = true
+  vim.o.mousemoveevent = true
+  -- <MouseMove> is a keycode, not an autocmd event. The mapping below fires
+  -- whenever 'mousemoveevent' is on and the mouse moves; the global handler
+  -- checks the current mouse position against the registered windows.
+  vim.keymap.set({ "n", "i", "v" }, "<MouseMove>", function()
+    handle_mouse_move()
+  end, { silent = true, desc = "md-render: URL hover" })
+end
+
+--- Start showing URL hovers for the given preview window.
+---@param buf integer
+---@param ns integer
+---@param win integer
+function M.attach(buf, ns, win)
+  ensure_initialized()
+  registered[win] = { buf = buf, ns = ns }
+  vim.api.nvim_create_autocmd("WinClosed", {
+    group = vim.api.nvim_create_augroup(AUGROUP, { clear = false }),
+    pattern = tostring(win),
+    once = true,
+    callback = function()
+      registered[win] = nil
+      cancel_pending()
+      if state.current_win == win then
+        close_hover()
+      end
+    end,
+  })
+end
+
+--- Exposed for tests.
+function M._internal()
+  return {
+    state = state,
+    registered = registered,
+    truncate_url = truncate_url,
+    url_at_mouse = url_at_mouse,
+    handle_mouse_move = handle_mouse_move,
+    show_hover = show_hover,
+    close_hover = close_hover,
+    bottom_reserved_rows = bottom_reserved_rows,
+    DEBOUNCE_MS = DEBOUNCE_MS,
+  }
+end
+
+return M