diff --git a/after/lsp/rust_analyzer.lua b/after/lsp/rust_analyzer.lua
index 85046c9..8adbc6b 100644
--- a/after/lsp/rust_analyzer.lua
+++ b/after/lsp/rust_analyzer.lua
@@ -5,6 +5,11 @@ return {
             check = {
                 command = "clippy",
             },
+            completion = {
+                fullFunctionSignatures = {
+                    enable = true,
+                },
+            },
             diagnostics = {
                 styleLints = {
                     enable = true,
diff --git a/lua/core/options.lua b/lua/core/options.lua
index 2f9c527..821ee68 100644
--- a/lua/core/options.lua
+++ b/lua/core/options.lua
@@ -29,7 +29,6 @@ vim.opt.foldignore = ""
 vim.opt.completeopt = {
     "menu",
     "menuone",
-    "popup",
     "noinsert",
     "noselect",
 }
diff --git a/lua/lsp/completion.lua b/lua/lsp/completion.lua
index 26f3479..2ab0423 100644
--- a/lua/lsp/completion.lua
+++ b/lua/lsp/completion.lua
@@ -1,40 +1,224 @@
 local WORD_CHARS =
     "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_"
 
-local GROUP = vim.api.nvim_create_augroup("ow.lsp.completion", { clear = true })
+local MAX_WIDTH = 80
+local MAX_HEIGHT = 20
 
+local GROUP = vim.api.nvim_create_augroup("ow.lsp.completion", { clear = true })
+local NS = vim.api.nvim_create_namespace("ow.lsp.completion")
+
+---@type table<integer, true>
+local word_chars_extended = {}
+
+---@alias lsp.completion.Pum { row: integer, col: integer, width: integer, height: integer, scrollbar: boolean }
+
+---@param ft string
+---@param text string
+---@return string
 local function fence(ft, text)
     return string.format("```%s\n%s\n```", ft, text)
 end
 
-local function style_popup(winid, bufnr, width)
-    if
-        not winid
-        or winid <= 0
-        or not vim.api.nvim_win_is_valid(winid)
-        or vim.api.nvim_win_get_config(winid).relative == ""
-    then
+---@param item lsp.CompletionItem
+---@return string
+local function signature_of(item)
+    return item.detail or vim.tbl_get(item, "labelDetails", "description") or ""
+end
+
+---@type { winid: integer?, bufnr: integer?, pending: { client: vim.lsp.Client, id: integer }? }
+local popup = {
+    winid = nil,
+    bufnr = nil,
+    pending = nil,
+}
+
+local function cancel_pending()
+    if popup.pending then
+        pcall(
+            popup.pending.client.cancel_request,
+            popup.pending.client,
+            popup.pending.id
+        )
+        popup.pending = nil
+    end
+end
+
+---@return integer bufnr
+local function ensure_buffer()
+    if not popup.bufnr or not vim.api.nvim_buf_is_valid(popup.bufnr) then
+        popup.bufnr = vim.api.nvim_create_buf(false, true)
+        vim.bo[popup.bufnr].buftype = "nofile"
+        vim.bo[popup.bufnr].bufhidden = "hide"
+        vim.bo[popup.bufnr].swapfile = false
+        pcall(vim.treesitter.start, popup.bufnr, "markdown")
+    end
+    return popup.bufnr
+end
+
+local function update_indicators()
+    if not popup.winid or not vim.api.nvim_win_is_valid(popup.winid) then
         return
     end
-    local cfg = { border = "rounded" }
-    if width then
-        cfg.width = math.min(width, 80)
+    local visible = vim.api.nvim_win_get_height(popup.winid)
+    local topline, botline = unpack(vim.api.nvim_win_call(popup.winid, function()
+        return { vim.fn.line("w0"), vim.fn.line("w$") }
+    end))
+    local ok_total, info_total =
+        pcall(vim.api.nvim_win_text_height, popup.winid, {})
+    local total = ok_total and info_total.all or visible
+
+    local display_topline = 1
+    if topline > 1 then
+        local ok, info = pcall(vim.api.nvim_win_text_height, popup.winid, {
+            end_row = topline - 2,
+        })
+        if ok then
+            display_topline = (info.all or 0) + 1
+        end
     end
-    if bufnr and vim.api.nvim_buf_is_valid(bufnr) then
-        vim.wo[winid].wrap = true
-        vim.wo[winid].linebreak = true
-        vim.wo[winid].conceallevel = 2
-        pcall(vim.treesitter.start, bufnr, "markdown")
+    local display_bot = display_topline + visible - 1
+
+    local has_above = display_topline > 1
+    local has_below = display_bot < total and botline < vim.api.nvim_buf_line_count(
+        vim.api.nvim_win_get_buf(popup.winid)
+    )
+    pcall(vim.api.nvim_win_set_config, popup.winid, {
+        title = has_above and { { "▲ ", "FloatBorder" } } or "",
+        title_pos = has_above and "right" or nil,
+        footer = has_below and { { "▼ ", "FloatBorder" } } or "",
+        footer_pos = has_below and "right" or nil,
+    })
+end
+
+local function close()
+    cancel_pending()
+    if popup.winid and vim.api.nvim_win_is_valid(popup.winid) then
+        pcall(vim.api.nvim_win_close, popup.winid, true)
     end
-    pcall(vim.api.nvim_win_set_config, winid, cfg)
+    popup.winid = nil
+end
+
+---@param content string
+---@param pum lsp.completion.Pum
+---@param width integer
+local function show(content, pum, width)
+    local bufnr = ensure_buffer()
+    local lines = vim.split(content, "\n", { plain = true })
+    vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, lines)
+
+    vim.api.nvim_buf_clear_namespace(bufnr, NS, 0, -1)
+    for i, line in ipairs(lines) do
+        if line ~= "" and line:gsub("─", "") == "" then
+            vim.api.nvim_buf_set_extmark(bufnr, NS, i - 1, 0, {
+                end_row = i - 1,
+                end_col = #line,
+                hl_group = "FloatBorder",
+                priority = 200,
+            })
+        end
+    end
+
+    width = math.min(width, MAX_WIDTH)
+    local height = math.min(#lines, MAX_HEIGHT)
+
+    local right_edge = pum.col + pum.width + (pum.scrollbar and 1 or 0)
+    local right_space = vim.o.columns - right_edge
+    local col
+    if right_space >= width + 2 then
+        col = right_edge
+    else
+        col = math.max(pum.col - width - 2, 0)
+    end
+
+    local cfg = {
+        relative = "editor",
+        row = pum.row,
+        col = col,
+        width = width,
+        height = height,
+        border = "rounded",
+        focusable = false,
+        style = "minimal",
+    }
+
+    if popup.winid and vim.api.nvim_win_is_valid(popup.winid) then
+        pcall(vim.api.nvim_win_set_config, popup.winid, cfg)
+    else
+        cfg.noautocmd = true
+        popup.winid = vim.api.nvim_open_win(bufnr, false, cfg)
+        vim.wo[popup.winid].wrap = true
+        vim.wo[popup.winid].linebreak = true
+        vim.wo[popup.winid].conceallevel = 2
+    end
+    pcall(vim.api.nvim_win_set_cursor, popup.winid, { 1, 0 })
+
+    local ok, info = pcall(vim.api.nvim_win_text_height, popup.winid, {})
+    if ok and info.all and info.all ~= height then
+        pcall(
+            vim.api.nvim_win_set_height,
+            popup.winid,
+            math.min(info.all, MAX_HEIGHT)
+        )
+    end
+
+    update_indicators()
+end
+
+---@param item lsp.CompletionItem
+---@param ft string
+---@return string? content
+---@return integer? width
+local function build_content(item, ft)
+    local signature = signature_of(item)
+    local doc = item.documentation
+    if type(doc) == "table" then
+        doc = doc.value
+    end
+    doc = doc or ""
+
+    local code_parts = {}
+    if item.additionalTextEdits then
+        for _, edit in ipairs(item.additionalTextEdits) do
+            local text = (edit.newText or ""):gsub("%s+$", "")
+            if text ~= "" then
+                table.insert(code_parts, fence(ft, text))
+            end
+        end
+    end
+    if signature ~= "" then
+        table.insert(code_parts, fence(ft, signature))
+    end
+
+    local sections = {}
+    if #code_parts > 0 then
+        table.insert(sections, table.concat(code_parts, "\n\n"))
+    end
+    if doc ~= "" then
+        table.insert(sections, doc)
+    end
+    if #sections == 0 then
+        return nil, nil
+    end
+
+    local max_w = 0
+    for _, s in ipairs(sections) do
+        for _, line in ipairs(vim.split(s, "\n", { plain = true })) do
+            max_w = math.max(max_w, vim.fn.strdisplaywidth(line))
+        end
+    end
+    local sep = "\n" .. string.rep("─", math.min(max_w, MAX_WIDTH)) .. "\n"
+    return table.concat(sections, sep), max_w
 end
 
 local M = {}
 
+---@param capabilities lsp.ClientCapabilities
 function M.apply_capabilities(capabilities)
     capabilities.textDocument.completion.completionItem.snippetSupport = false
 end
 
+---@param client vim.lsp.Client
+---@param buf integer
 function M.on_attach(client, buf)
     if
         not client:supports_method(
@@ -45,9 +229,12 @@ function M.on_attach(client, buf)
     end
 
     local provider = client.server_capabilities.completionProvider
+    if not provider then
+        return
+    end
     provider.triggerCharacters = provider.triggerCharacters or {}
-    if not provider._word_chars_added then
-        provider._word_chars_added = true
+    if not word_chars_extended[client.id] then
+        word_chars_extended[client.id] = true
         for c in WORD_CHARS:gmatch(".") do
             table.insert(provider.triggerCharacters, c)
         end
@@ -75,18 +262,13 @@ function M.on_attach(client, buf)
     vim.lsp.completion.enable(true, client.id, buf, {
         autotrigger = true,
         convert = function(item)
-            local signature = vim.tbl_get(
-                item,
-                "labelDetails",
-                "description"
-            ) or item.detail or ""
             return {
                 abbr = item.label:match("[^(]+") or item.label,
                 menu = "",
                 kind = "",
-                info = signature ~= ""
-                        and fence(vim.bo[buf].filetype, signature)
-                    or " ",
+                -- non-empty info blocks vim.lsp.completion's built-in
+                -- resolve so our own CompleteChanged handler can run it
+                info = " ",
             }
         end,
     })
@@ -96,12 +278,6 @@ function M.setup()
     vim.api.nvim_create_autocmd("CompleteChanged", {
         group = GROUP,
         callback = function(ev)
-            local cinfo = vim.fn.complete_info({
-                "selected",
-                "preview_winid",
-                "preview_bufnr",
-            })
-
             local completed = vim.v.event.completed_item or {}
             local lsp_item = vim.tbl_get(
                 completed,
@@ -113,111 +289,104 @@ function M.setup()
             local client_id =
                 vim.tbl_get(completed, "user_data", "nvim", "lsp", "client_id")
             local client = client_id and vim.lsp.get_client_by_id(client_id)
-            if
-                not lsp_item
-                or not client
-                or not client:supports_method(
-                    vim.lsp.protocol.Methods.completionItem_resolve
-                )
-            then
-                style_popup(cinfo.preview_winid, cinfo.preview_bufnr)
+
+            if not lsp_item or not client then
+                vim.schedule(close)
                 return
             end
 
-            local selected = cinfo.selected
+            local ft = vim.bo[ev.buf].filetype
+            ---@type lsp.completion.Pum
+            local pum = {
+                row = vim.v.event.row,
+                col = vim.v.event.col,
+                width = vim.v.event.width,
+                height = vim.v.event.height,
+                scrollbar = vim.v.event.scrollbar,
+            }
+
+            local will_resolve = client:supports_method(
+                vim.lsp.protocol.Methods.completionItem_resolve
+            )
+
+            if not will_resolve then
+                local initial, width = build_content(lsp_item, ft)
+                vim.schedule(function()
+                    if initial and width then
+                        show(initial, pum, width)
+                    else
+                        close()
+                    end
+                end)
+                return
+            end
+
+            cancel_pending()
             local word = completed.word
-            client:request(
+            local _, request_id = client:request(
                 vim.lsp.protocol.Methods.completionItem_resolve,
                 lsp_item,
                 function(err, result)
+                    popup.pending = nil
                     if err or not result then
                         return
                     end
-
-                    local cur = vim.fn.complete_info({
-                        "selected",
-                        "completed",
-                        "preview_winid",
-                    })
+                    local cur = vim.fn.complete_info({ "completed" })
                     if
-                        cur.selected ~= selected
-                        or (vim.tbl_get(cur, "completed", "word") or "")
-                            ~= word
+                        (vim.tbl_get(cur, "completed", "word") or "") ~= word
                     then
                         return
                     end
-
-                    local signature = vim.tbl_get(
-                        result,
-                        "labelDetails",
-                        "description"
-                    ) or result.detail or ""
-                    local doc = result.documentation
-                    if type(doc) == "table" then
-                        doc = doc.value
-                    end
-                    doc = doc or ""
-
-                    local ft = vim.bo[ev.buf].filetype
-                    local code_parts = {}
-                    if result.additionalTextEdits then
-                        for _, edit in ipairs(result.additionalTextEdits) do
-                            local text = (edit.newText or ""):gsub("%s+$", "")
-                            if text ~= "" then
-                                table.insert(code_parts, fence(ft, text))
-                            end
-                        end
-                    end
-                    if signature ~= "" then
-                        table.insert(code_parts, fence(ft, signature))
-                    end
-                    local sections = {}
-                    if #code_parts > 0 then
-                        table.insert(sections, table.concat(code_parts, "\n\n"))
-                    end
-                    if doc ~= "" then
-                        table.insert(sections, doc)
-                    end
-                    if #sections == 0 then
-                        if
-                            cur.preview_winid
-                            and cur.preview_winid > 0
-                            and vim.api.nvim_win_is_valid(cur.preview_winid)
-                        then
-                            pcall(
-                                vim.api.nvim_win_close,
-                                cur.preview_winid,
-                                true
-                            )
-                        end
-                        return
-                    end
-
-                    local max_w = 0
-                    for _, s in ipairs(sections) do
-                        for _, line in
-                            ipairs(vim.split(s, "\n", { plain = true }))
-                        do
-                            max_w =
-                                math.max(max_w, vim.fn.strdisplaywidth(line))
-                        end
-                    end
-                    local sep = "\n"
-                        .. string.rep("─", math.min(max_w, 80))
-                        .. "\n"
-                    local combined = table.concat(sections, sep)
-
-                    local windata = vim.api.nvim__complete_set(selected, {
-                        info = combined,
-                    })
-                    if windata then
-                        style_popup(windata.winid, windata.bufnr, max_w)
+                    local content, width = build_content(result, ft)
+                    if content and width then
+                        show(content, pum, width)
+                    else
+                        close()
                     end
                 end,
                 ev.buf
             )
+            if request_id then
+                popup.pending = { client = client, id = request_id }
+            end
         end,
     })
+
+    vim.api.nvim_create_autocmd({ "CompleteDonePre", "InsertLeave" }, {
+        group = GROUP,
+        callback = close,
+    })
+
+    ---@param key string
+    ---@param direction string  single-line scroll keycode (<C-e> or <C-y>)
+    ---@param count integer
+    local function scroll_map(key, direction, count)
+        vim.keymap.set("i", key, function()
+            if popup.winid and vim.api.nvim_win_is_valid(popup.winid) then
+                vim.schedule(function()
+                    if
+                        popup.winid
+                        and vim.api.nvim_win_is_valid(popup.winid)
+                    then
+                        vim.api.nvim_win_call(popup.winid, function()
+                            vim.cmd.normal({
+                                args = { count .. direction },
+                                bang = true,
+                            })
+                        end)
+                        update_indicators()
+                    end
+                end)
+                return ""
+            end
+            return key
+        end, { expr = true, replace_keycodes = true })
+    end
+    local half = math.floor(MAX_HEIGHT / 2)
+    scroll_map("<C-d>", vim.keycode("<C-e>"), half)
+    scroll_map("<C-u>", vim.keycode("<C-y>"), half)
+    scroll_map("<C-j>", vim.keycode("<C-e>"), 1)
+    scroll_map("<C-k>", vim.keycode("<C-y>"), 1)
 end
 
 return M