Don't add extra newlines to REPL on output events

Closes #845 and #854

Author: mfussenegger

lua/dap.lua

@@ -850,7 +850,7 @@ function M.run_to_cursor()
 end
 
 
----@param opts table<string, any>
+---@param opts? table<string, any>
 function M.continue(opts)
   if not session then
     session = first_stopped_session()

lua/dap/repl.lua

@@ -351,7 +351,9 @@ end
 
 ---@param line string
 ---@param lnum (integer|string)?
-function M.append(line, lnum)
+---@param opts? {newline: boolean}
+function M.append(line, lnum, opts)
+  opts = opts or {}
   local buf = repl._init_buf()
   if api.nvim_get_current_win() == repl.win and lnum == '$' then
     lnum = nil
@@ -360,12 +362,17 @@ function M.append(line, lnum)
     line = line:gsub('\r\n', '\n')
   end
   local lines = vim.split(line, '\n')
-  if #lines > 1 and lines[#lines] == '' then
-    table.remove(lines)
-  end
   if lnum == '$' or not lnum then
     lnum = api.nvim_buf_line_count(buf) - 1
-    api.nvim_buf_set_lines(buf, -1, -1, true, lines)
+    if opts.newline == false then
+      local last_line = api.nvim_buf_get_lines(buf, -2, -1, true)[1]
+      if vim.startswith(last_line, 'dap> ') then
+        table.insert(lines, 1, '')
+      end
+      api.nvim_buf_set_text(buf, lnum, #last_line, lnum, #last_line, lines)
+    else
+      api.nvim_buf_set_lines(buf, -1, -1, true, lines)
+    end
   else
     api.nvim_buf_set_lines(buf, lnum, lnum, true, lines)
   end
@@ -438,6 +445,7 @@ do
         return {}
       end
     end
+    assert(session, 'Session must exist if supportsCompletionsRequest is true')
     session:request('completions', {
       frameId = (session.current_frame or {}).id;
       text = line_to_cursor;

lua/dap/session.lua

@@ -710,7 +710,7 @@ function Session.event_output(_, body)
   if body.category == 'telemetry' then
     log.info('Telemetry', body.output)
   else
-    repl.append(body.output, '$')
+    repl.append(body.output, '$', { newline = false })
   end
 end
 

lua/dap/ui.lua

@@ -455,7 +455,7 @@ function M.layer(buf)
     ---
     ---@generic T
     ---@param xs T[]
-    ---@param render_fn fun(T):string
+    ---@param render_fn? fun(T):string
     ---@param context table|nil
     ---@param start nil|number 0-indexed
     ---@param end_ nil|number 0-indexed exclusive

tests/repl_spec.lua

@@ -0,0 +1,14 @@
+local api = vim.api
+
+describe('dap.repl', function()
+  it("append doesn't add newline with newline = false", function()
+    local repl = require('dap.repl')
+    local buf = repl.open()
+    repl.append('foo', nil, { newline = false })
+    repl.append('bar', nil, { newline = false })
+    repl.append('\nbaz\n', nil, { newline = false })
+
+    local lines = api.nvim_buf_get_lines(buf, 0, -1, true)
+    assert.are.same({'foobar', 'baz', ''}, lines)
+  end)
+end)