test: include stderr in EOF failure message

3 files changed, 20 insertions, 14 deletions

diff --git a/test/client/session.lua b/test/client/session.lua
index 5b7f1a7caa..a5839e012a 100644
--- a/test/client/session.lua
+++ b/test/client/session.lua
@@ -12,10 +12,8 @@ local RpcStream = require('test.client.rpc_stream')
 --- @field private _rpc_stream test.RpcStream
 --- @field private _prepare uv.uv_prepare_t
 --- @field private _timer uv.uv_timer_t
---- @field exec_lua_setup boolean
 --- @field private _is_running boolean true during `Session:run()` scope.
---- @field private _stdout_buffer string[] Stores stdout chunks
---- @field public stdout string Full stdout after the process exits
+--- @field exec_lua_setup boolean
 local Session = {}
 Session.__index = Session
 if package.loaded['jit'] then
@@ -231,7 +229,13 @@ function Session:_run(request_cb, notification_cb, timeout)
   end
   self._rpc_stream:read_start(request_cb, notification_cb, function()
     uv.stop()
-    self.eof_err = { 1, 'EOF was received from Nvim. Likely the Nvim process crashed.' }
+
+    --- @diagnostic disable-next-line: invisible
+    local stderr = self._rpc_stream._stream.stderr --[[@as string?]]
+    -- See if `ProcStream.stderr` has anything useful.
+    stderr = '' ~= ((stderr or ''):match('^%s*(.*%S)') or '') and ' stderr:\n' .. stderr or ''
+
+    self.eof_err = { 1, 'EOF was received from Nvim. Likely the Nvim process crashed.' .. stderr }
   end)
   uv.run()
   self._prepare:stop()
diff --git a/test/client/uv_stream.lua b/test/client/uv_stream.lua
index ac84cbf9bc..a9ef2db115 100644
--- a/test/client/uv_stream.lua
+++ b/test/client/uv_stream.lua
@@ -127,9 +127,11 @@ end
 --- @field private _child_stdout uv.uv_pipe_t
 --- @field private _child_stderr uv.uv_pipe_t
 --- @field stdout string
+--- stderr is always collected in this field, regardless of `collect_output`.
 --- @field stderr string
 --- @field stdout_eof boolean
 --- @field stderr_eof boolean
+--- Collects stdout in the `stdout` field, and stdout+stderr in `output` field.
 --- @field private collect_output boolean
 --- Exit code
 --- @field status integer
@@ -149,8 +151,6 @@ function ProcStream.spawn(argv, env, io_extra)
     output = '',
     stdout = '',
     stderr = '',
-    stdout_error = nil, -- TODO: not used, remove
-    stderr_error = nil, -- TODO: not used, remove
     stdout_eof = false,
     stderr_eof = false,
     _child_stdin = assert(uv.new_pipe(false)),
@@ -189,14 +189,16 @@ end
 
 function ProcStream:on_read(stream, cb, err, chunk)
   if err then
-    -- stderr_error/stdout_error
-    self[stream .. '_error'] = err ---@type string
-    -- error(err)
+    error(err) -- stream read failed?
   elseif chunk then
-    -- 'stderr' or 'stdout'
+    -- Always collect stderr, in case it gives useful info on failure.
+    if stream == 'stderr' then
+      self.stderr = self.stderr .. chunk ---@type string
+    end
+    -- Collect stdout if `collect_output` is enabled.
     if self.collect_output then
-      self[stream] = self[stream] .. chunk ---@type string
-      --- Collects both stdout + stderr.
+      self.stdout = self.stdout .. chunk ---@type string
+      --- Collect both stdout + stderr in the `output` field.
       self.output = self[stream] .. chunk ---@type string
     end
   else
diff --git a/test/functional/testnvim.lua b/test/functional/testnvim.lua
index d65cbf685e..c8f1c35555 100644
--- a/test/functional/testnvim.lua
+++ b/test/functional/testnvim.lua
@@ -333,9 +333,9 @@ end
 function M.expect_exit(fn_or_timeout, ...)
   local eof_err_msg = 'EOF was received from Nvim. Likely the Nvim process crashed.'
   if type(fn_or_timeout) == 'function' then
-    eq(eof_err_msg, t.pcall_err(fn_or_timeout, ...))
+    t.matches(eof_err_msg, t.pcall_err(fn_or_timeout, ...))
   else
-    eq(
+    t.matches(
       eof_err_msg,
       t.pcall_err(function(timeout, fn, ...)
         fn(...)