fix(messages): truncate warning messages only in display (#38901)

For now, add a private "_truncate" flag to nvim_echo, using a truncation
method similar to showmode().

test/functional/ex_cmds/swapfile_preserve_recover_spec.lua

@@ -360,9 +360,36 @@ pcall(vim.cmd.edit, 'Xtest_swapredraw.lua')
     set_session(nvim1)
     local screen = Screen.new(75, 18)
     exec(init)
-    feed(':edit Xfile1\n')
 
-    screen:expect({ any = ('W325: Ignoring swapfile from Nvim process %d'):format(nvimpid) })
+    feed(':edit Xfile1\n')
+    local msg_expected = ('W325: Ignoring swapfile from Nvim process %d'):format(nvimpid)
+    screen:expect({ any = vim.pesc(msg_expected) })
+    eq(msg_expected, n.exec_capture('messages'))
+    command('bwipe!')
+
+    -- With smaller screen, the message should be truncated, but only in display.
+    screen:try_resize(40, 18)
+    feed(':edit Xfile1\n')
+    screen:expect([[
+      ^                                        |
+      {1:~                                       }|*16
+      {19:W325: Ignoring swapfile from Nvim proces}|
+    ]])
+    eq(('\n' .. msg_expected):rep(2):sub(2), n.exec_capture('messages'))
+    command('bwipe!')
+
+    -- Also test with 'ruler'.
+    screen:try_resize(60, 18)
+    command('set ruler')
+    feed(':edit Xfile1\n')
+    screen:expect([[
+      ^                                                            |
+      {1:~                                                           }|*16
+      {19:W325: Ignoring swapfile from Nvim process }0,0-1         All |
+    ]])
+    eq(('\n' .. msg_expected):rep(3):sub(2), n.exec_capture('messages'))
+    command('bwipe!')
+
     nvim1:close()
   end)
 

test/functional/lua/vim_spec.lua

@@ -134,18 +134,20 @@ describe('lua stdlib', function()
 
     describe(('vim.deprecate prerel=%s,'):format(prerel or 'nil'), function()
       local curver --- @type {major:number, minor:number}
+      local curstr --- @type string
+      local nextver --- @type string
 
       before_each(function()
         curver = exec_lua('return vim.version()')
+        -- "0.10" or "0.10-dev+xxx"
+        curstr = ('%s.%s%s'):format(curver.major, curver.minor, prerel or '')
+        -- "0.10" or "0.11"
+        nextver = ('%s.%s'):format(curver.major, curver.minor + (prerel and 0 or 1))
       end)
 
       it('plugin=nil, same message skipped', function()
-        -- "0.10" or "0.10-dev+xxx"
-        local curstr = ('%s.%s%s'):format(curver.major, curver.minor, prerel or '')
         eq(
-          ([[foo.bar() is deprecated. Run ":checkhealth vim.deprecated" for more information]]):format(
-            curstr
-          ),
+          [[foo.bar() is deprecated. Run ":checkhealth vim.deprecated" for more information]],
           exec_lua('return vim.deprecate(...)', 'foo.bar()', 'zub.wooo{ok=yay}', curstr)
         )
         -- Same message as above; skipped this time.
@@ -160,19 +162,26 @@ describe('lua stdlib', function()
       end)
 
       it('plugin=nil, show error if hard-deprecated', function()
-        -- "0.10" or "0.11"
-        local nextver = ('%s.%s'):format(curver.major, curver.minor + (prerel and 0 or 1))
-
-        local was_removed = prerel and 'was removed' or 'will be removed'
         eq(
-          dedent(
-            [[
-            foo.hard_dep() is deprecated. Run ":checkhealth vim.deprecated" for more information]]
-          ):format(was_removed, nextver),
+          [[foo.hard_dep() is deprecated. Run ":checkhealth vim.deprecated" for more information]],
           exec_lua('return vim.deprecate(...)', 'foo.hard_dep()', 'vim.new_api()', nextver)
         )
       end)
 
+      it('plugin=nil, message is only truncated in display #38841', function()
+        local screen = Screen.new(50, 10)
+        exec_lua('vim.deprecate(...)', 'foo.bar()', 'zub.wooo{ok=yay}', curstr)
+        screen:expect([[
+          ^                                                  |
+          {1:~                                                 }|*8
+          {19:foo.bar() is deprecated. Run ":checkhealth vim.dep}|
+        ]])
+        eq(
+          [[foo.bar() is deprecated. Run ":checkhealth vim.deprecated" for more information]],
+          n.exec_capture('messages')
+        )
+      end)
+
       it('plugin specified', function()
         -- When `plugin` is specified, don't show ":help deprecated". #22235
         eq(

test/functional/terminal/tui_spec.lua

@@ -3213,6 +3213,42 @@ describe('TUI', function()
     feed_data(':set columns=99|set stl=redrawn%m\n')
     screen:expect({ any = 'redrawn%[%+%]' })
   end)
+
+  it('missing DSR response does not lead to hit-enter prompt #38877', function()
+    local child_server = n.new_pipename()
+    exec_lua('vim.uv.os_unsetenv("NVIM_TEST")')
+    local job = fn.jobstart({ nvim_prog, '--clean', '--listen', child_server }, {
+      -- Use pty = true for a PTY without a terminal, so that there is no DSR response.
+      pty = true,
+      env = {
+        VIMRUNTIME = os.getenv('VIMRUNTIME'),
+        COLORTERM = 'xterm-256color',
+        NVIM_LOG_FILE = testlog,
+      },
+    })
+    finally(function()
+      exec_lua(function()
+        vim.fn.jobstop(job)
+        vim.fn.jobwait({ job }, 5000)
+      end)
+      os.remove(testlog)
+    end)
+    retry(nil, nil, function()
+      t.neq(nil, vim.uv.fs_stat(child_server))
+    end)
+    local child_session = n.connect(child_server)
+    local expected_msg =
+      'defaults.lua: Did not detect DSR response from terminal. This results in a slower startup time.'
+    retry(nil, 4000, function()
+      eq({ true, { mode = 'n', blocking = false } }, { child_session:request('nvim_get_mode') })
+      if not is_os('win') then -- ConPTY provides DSR response on Windows?
+        eq(
+          { true, { output = expected_msg } },
+          { child_session:request('nvim_exec2', 'messages', { output = true }) }
+        )
+      end
+    end)
+  end)
 end)
 
 describe('TUI UIEnter/UILeave', function()