feat(buffer_updates): allow ignoring when previewing

Also adds a test that we actually subscribe to buffer events when in
CMDPREVIEW.

3 files changed, 12 insertions, 3 deletions

diff --git a/src/nvim/api/buffer.c b/src/nvim/api/buffer.c
index db37e2100d..45545d24d9 100644
--- a/src/nvim/api/buffer.c
+++ b/src/nvim/api/buffer.c
@@ -121,6 +121,8 @@ Integer nvim_buf_line_count(Buffer buffer, Error *err)
 ///               - buffer handle
 ///             - utf_sizes: include UTF-32 and UTF-16 size of the replaced
 ///               region, as args to `on_lines`.
+///             - preview: also attach to command preview (i.e. 'inccommand')
+///               events.
 /// @param[out] err Error details, if any
 /// @return False if attach failed (invalid parameter, or buffer isn't loaded);
 ///         otherwise True. TODO: LUA_API_NO_EVAL
@@ -176,6 +178,12 @@ Boolean nvim_buf_attach(uint64_t channel_id,
         goto error;
       }
       cb.utf_sizes = v->data.boolean;
+    } else if (is_lua && strequal("preview", k.data)) {
+      if (v->type != kObjectTypeBoolean) {
+        api_set_error(err, kErrorTypeValidation, "preview must be boolean");
+        goto error;
+      }
+      cb.preview = v->data.boolean;
     } else {
       api_set_error(err, kErrorTypeValidation, "unexpected key: %s", k.data);
       goto error;
diff --git a/src/nvim/buffer_defs.h b/src/nvim/buffer_defs.h
index dba02a67e8..44a9b39939 100644
--- a/src/nvim/buffer_defs.h
+++ b/src/nvim/buffer_defs.h
@@ -491,9 +491,10 @@ typedef struct {
   LuaRef on_changedtick;
   LuaRef on_detach;
   bool utf_sizes;
+  bool preview;
 } BufUpdateCallbacks;
 #define BUF_UPDATE_CALLBACKS_INIT { LUA_NOREF, LUA_NOREF, LUA_NOREF, \
-                                    LUA_NOREF, false }
+                                    LUA_NOREF, false, false }
 
 EXTERN int curbuf_splice_pending INIT(= 0);
 
diff --git a/src/nvim/buffer_updates.c b/src/nvim/buffer_updates.c
index fc671ad9e2..68e123896b 100644
--- a/src/nvim/buffer_updates.c
+++ b/src/nvim/buffer_updates.c
@@ -237,7 +237,7 @@ void buf_updates_send_changes(buf_T *buf,
   for (size_t i = 0; i < kv_size(buf->update_callbacks); i++) {
     BufUpdateCallbacks cb = kv_A(buf->update_callbacks, i);
     bool keep = true;
-    if (cb.on_lines != LUA_NOREF) {
+    if (cb.on_lines != LUA_NOREF && (cb.preview || !(State & CMDPREVIEW))) {
       Array args = ARRAY_DICT_INIT;
       Object items[8];
       args.size = 6;  // may be increased to 8 below
@@ -298,7 +298,7 @@ void buf_updates_send_splice(
   for (size_t i = 0; i < kv_size(buf->update_callbacks); i++) {
     BufUpdateCallbacks cb = kv_A(buf->update_callbacks, i);
     bool keep = true;
-    if (cb.on_bytes != LUA_NOREF) {
+    if (cb.on_bytes != LUA_NOREF && (cb.preview || !(State & CMDPREVIEW))) {
       FIXED_TEMP_ARRAY(args, 11);
 
       // the first argument is always the buffer handle