fix(embed): handle stdio in server properly

Rename stdin/stdout in the server, so that RPC data won't get corrupted.
This also restores the use of stderr to write directly to the terminal.

3 files changed, 9 insertions, 2 deletions

diff --git a/src/nvim/event/libuv_process.c b/src/nvim/event/libuv_process.c
index 811d96ff93..10a09275d9 100644
--- a/src/nvim/event/libuv_process.c
+++ b/src/nvim/event/libuv_process.c
@@ -85,6 +85,9 @@ int libuv_process_spawn(LibuvProcess *uvproc)
     uvproc->uvstdio[2].flags = UV_CREATE_PIPE | UV_WRITABLE_PIPE;
     uvproc->uvstdio[2].data.stream = STRUCT_CAST(uv_stream_t,
                                                  &proc->err.uv.pipe);
+  } else if (proc->fwd_err) {
+    uvproc->uvstdio[2].flags = UV_INHERIT_FD;
+    uvproc->uvstdio[2].data.fd = STDERR_FILENO;
   }
 
   int status;
diff --git a/src/nvim/event/process.c b/src/nvim/event/process.c
index 2fa789ac9a..9dfd6f329a 100644
--- a/src/nvim/event/process.c
+++ b/src/nvim/event/process.c
@@ -43,6 +43,9 @@ static int exit_need_delay = 0;
 int process_spawn(Process *proc, bool in, bool out, bool err)
   FUNC_ATTR_NONNULL_ALL
 {
+  // forwarding stderr contradicts with processing it internally
+  assert(!(err && proc->fwd_err));
+
   if (in) {
     uv_pipe_init(&proc->loop->uv, &proc->in.uv.pipe, 0);
   } else {
diff --git a/src/nvim/event/process.h b/src/nvim/event/process.h
index 26e03ff4f3..e0057faffb 100644
--- a/src/nvim/event/process.h
+++ b/src/nvim/event/process.h
@@ -38,7 +38,7 @@ struct process {
   /// Exit handler. If set, user must call process_free().
   process_exit_cb cb;
   internal_process_cb internal_exit_cb, internal_close_cb;
-  bool closed, detach, overlapped;
+  bool closed, detach, overlapped, fwd_err;
   MultiQueue *events;
 };
 
@@ -62,7 +62,8 @@ static inline Process process_init(Loop *loop, ProcessType type, void *data)
     .closed = false,
     .internal_close_cb = NULL,
     .internal_exit_cb = NULL,
-    .detach = false
+    .detach = false,
+    .fwd_err = false,
   };
 }