Re: [PATCH v2 3/6] lua: add luaT_newtuple()

[Alexander Turenko <alexander.turenko@tarantool.org>]

Comments are below, diff is at the bottom of the email.

> Let's just call this function luaT_tuple_new ;-)

Ok.

> 
> > 
> > > 
> > > > +{
> > > > +	struct tuple *tuple;
> > > > +
> > > > +	if (idx == 0 || lua_istable(L, idx)) {
> > > > +		struct ibuf *buf = tarantool_lua_ibuf;
> > > > +		ibuf_reset(buf);
> > > > +		struct mpstream stream;
> > > > +		mpstream_init(&stream, buf, ibuf_reserve_cb, ibuf_alloc_cb,
> > > > +		      luamp_error, L);
> > > > +		if (idx == 0) {
> > > > +			/*
> > > > +			 * Create the tuple from lua stack
> > > > +			 * objects.
> > > > +			 */
> > > > +			int argc = lua_gettop(L);
> > > > +			mpstream_encode_array(&stream, argc);
> > > > +			for (int k = 1; k <= argc; ++k) {
> > > > +				luamp_encode(L, luaL_msgpack_default, &stream,
> > > > +					     k);
> > > > +			}
> > > > +		} else {
> > > > +			/* Create the tuple from a Lua table. */
> > > > +			luamp_encode_tuple(L, luaL_msgpack_default, &stream,
> > > > +					   idx);
> > > > +		}
> > > > +		mpstream_flush(&stream);
> > > > +		tuple = box_tuple_new(format, buf->buf,
> > > > +				      buf->buf + ibuf_used(buf));
> > > > +		if (tuple == NULL) {
> > > > +			luaT_pusherror(L, diag_last_error(diag_get()));
> > > 
> > > Why not simply throw the error with luaT_error()? Other similar
> > > functions throw an error, not just push it to the stack.
> > 
> > Because in a caller I need to perform clean up before reraise it.
> > lua_pcall() would be expensive.
> > 
> > luaT_tuple_new() is used in a table and an iterator source in next().
> > next() is used in two places: merger_next() where I just pop and raise
> > the error and in merger_source_new() to acquire a first tuple. If an
> 
> Why do you need to acquire the first tuple in merger_source_new()?
> Can't you do that in next()?

It is possible, but we need to call next() (and, then, luaT_tuple_new())
from C part of merger, so API of those functions should not use a lua
stack for errors. So I'll leave diag_set() for errors in
luaT_tuple_new().

BTW, we'll need to introduce a flag in merger_state (states that sources
was not initialized yet) to roll a loop with inserts into the heap.

> 
> > error occurs here I need to free the newly created source, then in
> > merger_state_new() free newly created merger_state with all successfully
> > created sources (it also perform needed unref's). I cannot allow any
> > function called on this path to raise an error.
> > 
> > I can implement reference counting of all that objects and free them in
> > the next call to merger (some kind of simple gc), but this way looks as
> > overengineered.
> > 
> > Mine errors are strings and it is convenient to create them with
> > lua_pushfstring() or push memory errors with luaT_pusherror().
> > 
> > There are two variants how to avoid raising an error:
> > 
> > * lua_pushfstring();
> > * diag_set().
> > 
> > Latter seems to be more native for tarantool. I would use something like
> > XlogError: printf-style format string + vararg. But I doubt how should I
> > name such class? ContractError (most of them are about bad args)? There
> > is also unexpected buffer end, it is more RuntimeError.
> 
> Use IllegalParams (already exists)?

Looks okay. Thanks!

> 
> > 
> > I dislike the idea to copy XlogError code under another name. Maybe we
> > can implement a general class for such errors and inherit it in
> > XlogError, ContractError and RuntimeError?
> > 
> > I choose pushing to stack, because it is the most simple solution, and
> > forget to discuss it with you. My bad.
> > 
> > Please, give me some pointer here.
> 
> I'd prefer to either throw an error (if the merger can handle it) or set
> diag to IllegalParams.

I'll use diag_set().

----

(Below are resulting changes, but I amended them into 'lua: add
luaT_tuple_new()' and 'lua: optimize creation of a tuple from a tuple'
commits as approariate.)

diff --git a/src/box/lua/tuple.c b/src/box/lua/tuple.c
index ab861c6d2..c4f323717 100644
--- a/src/box/lua/tuple.c
+++ b/src/box/lua/tuple.c
@@ -122,18 +122,16 @@ luaT_tuple_new(struct lua_State *L, int idx, box_tuple_format_t *format)
 		mpstream_flush(&stream);
 		tuple = box_tuple_new(format, buf->buf,
 				      buf->buf + ibuf_used(buf));
-		if (tuple == NULL) {
-			luaT_pusherror(L, diag_last_error(diag_get()));
+		if (tuple == NULL)
 			return NULL;
-		}
 		ibuf_reinit(tarantool_lua_ibuf);
 		return tuple;
 	}
 
 	tuple = luaT_istuple(L, idx);
 	if (tuple == NULL) {
-		lua_pushfstring(L, "A tuple or a table expected, got %s",
-				lua_typename(L, lua_type(L, idx)));
+		diag_set(IllegalParams, "A tuple or a table expected, got %s",
+			 lua_typename(L, lua_type(L, idx)));
 		return NULL;
 	}
 
@@ -144,10 +142,8 @@ luaT_tuple_new(struct lua_State *L, int idx, box_tuple_format_t *format)
 	const char *tuple_beg = tuple_data(tuple);
 	const char *tuple_end = tuple_beg + tuple->bsize;
 	tuple = box_tuple_new(format, tuple_beg, tuple_end);
-	if (tuple == NULL) {
-		luaT_pusherror(L, diag_last_error(diag_get()));
+	if (tuple == NULL)
 		return NULL;
-	}
 	return tuple;
 }
 
@@ -169,7 +165,7 @@ lbox_tuple_new(lua_State *L)
 	box_tuple_format_t *fmt = box_tuple_format_default();
 	struct tuple *tuple = luaT_tuple_new(L, idx, fmt);
 	if (tuple == NULL)
-		return lua_error(L);
+		return luaT_error(L);
 	/* box_tuple_new() doesn't leak on exception, see public API doc */
 	luaT_pushtuple(L, tuple);
 	return 1;
diff --git a/src/box/lua/tuple.h b/src/box/lua/tuple.h
index f8c8ccf1c..06efa277a 100644
--- a/src/box/lua/tuple.h
+++ b/src/box/lua/tuple.h
@@ -75,8 +75,7 @@ luaT_istuple(struct lua_State *L, int idx);
  * Set idx to zero to create the new tuple from objects on the lua
  * stack.
  *
- * In case of an error push the error message to the Lua stack and
- * return NULL.
+ * In case of an error set diag and return NULL.
  */
 struct tuple *
 luaT_tuple_new(struct lua_State *L, int idx, box_tuple_format_t *format);
diff --git a/test/unit/luaT_tuple_new.c b/test/unit/luaT_tuple_new.c
index 07fa1a792..582d6c616 100644
--- a/test/unit/luaT_tuple_new.c
+++ b/test/unit/luaT_tuple_new.c
@@ -10,6 +10,8 @@
 #include "box/tuple.h"        /* box_tuple_format_default() */
 #include "lua/msgpack.h"      /* luaopen_msgpack() */
 #include "box/lua/tuple.h"    /* luaL_iterator_*() */
+#include "diag.h"             /* struct error, diag_*() */
+#include "exception.h"        /* type_IllegalParams */
 
 /*
  * This test checks all usage cases of luaT_tuple_new():
@@ -52,10 +54,10 @@ void check_error(struct lua_State *L, const struct tuple *tuple, int retvals,
 {
 	const char *exp_err = "A tuple or a table expected, got number";
 	is(tuple, NULL, "%s: tuple == NULL", case_name);
-	is(retvals, 1, "%s: check retvals count", case_name);
-	is(lua_type(L, -1), LUA_TSTRING, "%s: check error type", case_name);
-	ok(!strcmp(lua_tostring(L, -1), exp_err), "%s: check error message",
-	   case_name);
+	is(retvals, 0, "%s: check retvals count", case_name);
+	struct error *e = diag_last_error(diag_get());
+	is(e->type, &type_IllegalParams, "%s: check error type", case_name);
+	ok(!strcmp(e->errmsg, exp_err), "%s: check error message", case_name);
 }
 
 int
@@ -147,7 +149,7 @@ test_basic(struct lua_State *L)
 	check_error(L, tuple, lua_gettop(L) - top, "unexpected type");
 
 	/* Clean up. */
-	lua_pop(L, 2);
+	lua_pop(L, 1);
 	assert(lua_gettop(L) == 0);
 
 	footer();