With new macro ERROR_INJECT_COUNTDOWN it is possible to delay error
injection by iparam value: injection will be set only after iparam
times the path is executed. For instance:

void
foo(int i)
{
	/* 2 is delay counter. */
	ERROR_INJECT_COUNTDOWN(ERRINJ_FOO, {
		 printf("Error injection on %d cycle!\n", i);
		});
}

void
boo(void)
{
	for (int i = 0; i < 10; ++i)
		foo(i);
}

box.error.injection.set('ERRINJ_FOO', 2)

The result is "Error injection on 2 cycle!". This type of error
injection can turn out to be useful to set injection in the middle of
query processing. Imagine following scenario:

void
foo(void)
{
	int *fds[10];
	for (int i = 0; i < 10; ++i) {
		fds[i] = malloc(sizeof(int));
		if (fds[i] == NULL)
			goto cleanup;
	}
cleanup:
	free(fds[0]);
}

"cleanup" section obviously contains error and leads to memory leak.
But using means of casual error injection without delay such situation
can't be detected: OOM can be set only for first cycle iteration and in
this particular case no leaks take place.

Reviewed-by: Vladislav Shpilevoy <vshpilevoi@mail.ru>

vy_task_write_run() is executed in auxiliary thread (dump or
compaction). Write iterator is created and used inside this function.
Meanwhile, creating/destroying tuples in these threads does not change
reference counter of corresponding  tuple formats (see vy_tuple_delete()
and vy_stmt_alloc()). Without cleaning up write iterator right in
write_iterator_start() after fail, this procedure takes place in
vy_task_compaction_abort() or vy_task_dump_abort().  These *_abort()
functions in turn are executed in the main thread.  Taking this into
consideration, tuple might be allocated in aux. thread and deleted in
the main thread. As a result, format reference counter might decrease,
whereas it shouldn't change (otherwise tuple format will be destroyed
before all tuples of this format are gone).

Fortunately, clean-up of write iterator in another thread was found only
on 1.10 branch, master branch already contains fix but lacks test
(2f17c929). So let's introduce test with following scenario:

1. run compaction process;
2. add one or more slice sources in vy_write_iterator_start():
corresponding slice_stream structures obtain newly created tuples
in vy_slice_stream_next();
3. the next call of vy_write_iterator_add_src() fails due to OOM,
invalid run file or whatever;
4. if write_iterator_start() didn't provide clean-up of sources, it
would take place in vy_task_dump_abort() which would be executed in
the main thread;
5. now format reference counter would be less than it was before
compaction.

Closes #4864

vy_write_iterator->read_views[i].history objects are allocated on
region (see vy_write_iterator_push_rv()) during building history of the
given key. However, in case of fail of vy_write_iterator_build_history()
region is truncated but pointers to vy_write_history objects are not
nullified. As a result, they may be accessed (for instance while
finalizing write_iterator object in  vy_write_iterator_stop) which in
turn may lead to crash, segfaul or disk formatting. The same may happen
if vy_read_view_merge() fails during processing of read view array.
Let's clean-up those objects in case of error takes place.

Part of #4864

According to dockerfile reference, there are two forms of specifying
entrypoint: exec and shell. Exec form is preferrable and  allows use
this image in scripts.

Close #4960

Added Catalina OSX 10.15 to gitlab-ci testing and removed OSX 10.13,
due to decided to have only 2 last major releases, for now it is
10.14 and 10.15 OSX versions. Also changed the commit job for branches
from 10.14 to 10.15 OSX version.

Additional cleanup for 'box_return_mp' and 'box_session_push',
added API_EXPORT which defines nothrow, compiler warns or errors
depending on the build options.

Part of #4885
Close #4873

Fragiled flaky tests from parallel runs to avoid
of flaky fails in regular testing:

  box-py/snapshot.test.py                ; gh-4514
  replication/misc.test.lua              ; gh-4940
  replication/skip_conflict_row.test.lua ; gh-4958
  replication-py/init_storage.test.py    ; gh-4949
  vinyl/stat.test.lua                    ; gh-4951
  xlog/checkpoint_daemon.test.lua        ; gh-4952

Part of #4953

Gitlab-ci pipeline modified in order to keep
performance results into gitlab-ci artifacts.

Closes #4920

Here is a summary on how and when rollback works in WAL.

Disk write failure can cause rollback. In that case the failed and
all next transactions, sent to WAL, should be rolled back.
Together. Following transactions should be rolled back too,
because they could make their statements based on what they saw in
the failed transaction. Also rollback of the failed transaction
without rollback of the next ones can actually rewrite what they
committed.

So when rollback is started, *all* pending transactions should be
rolled back. However if they would keep coming, the rollback would
be infinite. This means to complete a rollback it is necessary to
stop sending new transactions to WAL, then rollback all already
sent. In the end allow new transactions again.

Step-by-step:

1) stop accepting all new transactions in WAL thread, where
rollback is started. All new transactions don't even try to go to
disk. They added to rollback queue immediately after arriving to
WAL thread.

2) tell TX thread to stop sending new transactions to WAL. So as
the rollback queue would stop growing.

3) rollback all transactions in reverse order.

4) allow transactions again in WAL thread and TX thread.

The algorithm is long, but simple and understandable. However
implementation wasn't so easy. It was done using a 4-hop cbus
route. 2 hops of which were supposed to clear cbus channel from
all other cbus messages. Next two hops implemented steps 3 and 4.
Rollback state of the WAL was signaled by checking internals of a
preallocated cbus message.

The patch makes it simpler and more straightforward. Rollback
state is now signaled by a simple flag, and there is no a hack
about clearing cbus channel, no touching attributes of a cbus
message. The moment when all transactions are stopped and the last
one has returned from WAL is visible explicitly, because the last
sent to WAL journal entry is saved.

Also there is a single route for commit and rollback cbus
messages now, called tx_complete_batch(). This change will come
in hand in scope of synchronous replication, when WAL write won't
be enough for commit. And therefore 'commit' as a concept should
be washed away from WAL's code gradually. Migrate to solely txn
module.

Add check that on_shutdown() triggers were called before exit,
because in case of EOF or Ctrl+D (no signals) they were ignored.

Closes #4703

If vy_key_from_msgpack() fails in vy_lsm_split_range(), clean-up
procedure is called. However, at this moment struct vy_range *parts[2]
is not initialized ergo contains garbage and access to this structure
may result in crash, segfault or disk formatting. Let's move
initialization of mentioned variables before call of
vy_lsm_split_range().

Part of #4864

Found that in commit 'travis-ci/gitlab-ci: add Ubuntu Focal 20.04'
forgot to add Ubuntu Focal to the list of the available Ubuntu
distributions in the script for saving built packages at S3.

Follow up #4863

Closes #4863

API_EXPORT defines nothrow, so compiler warns or errors depending on the
build options.

Closes #4885

Fixed flaky upstream checks at replication/skip_conflict_row test,
also check on lsn set in test-run wait condition routine.

Errors fixed:

[024] @@ -66,11 +66,11 @@
[024]  ...
[024]  box.info.replication[1].upstream.message
[024]  ---
[024] -- null
[024] +- timed out
[024]  ...
[024]  box.info.replication[1].upstream.status
[024]  ---
[024] -- follow
[024] +- disconnected
[024]  ...
[024]  box.space.test:select()
[024]  ---
[024]

[004] @@ -125,11 +125,11 @@
[004]  ...
[004]  box.info.replication[1].upstream.message
[004]  ---
[004] -- Duplicate key exists in unique index 'primary' in space 'test'
[004] -...
[004] -box.info.replication[1].upstream.status
[004] ----
[004] -- stopped
[004] +- null
[004] +...
[004] +box.info.replication[1].upstream.status
[004] +---
[004] +- follow
[004]  ...
[004]  test_run:cmd("switch default")
[004]  ---
[004]

[038] @@ -174,7 +174,7 @@
[038]  ...
[038]  box.info.replication[1].upstream.status
[038]  ---
[038] -- follow
[038] +- disconnected
[038]  ...
[038]  -- write some conflicting records on slave
[038]  for i = 1, 10 do box.space.test:insert({i, 'r'}) end
Line 201 (often):

[039] @@ -201,7 +201,7 @@
[039]  -- lsn should be incremented
[039]  v1 == box.info.vclock[1] - 10
[039]  ---
[039] -- true
[039] +- false
[039]  ...
[039]  -- and state is follow
[039]  box.info.replication[1].upstream.status
[039]

[030] @@ -201,12 +201,12 @@
[030]  -- lsn should be incremented
[030]  v1 == box.info.vclock[1] - 10
[030]  ---
[030] -- true
[030] +- false
[030]  ...
[030]  -- and state is follow
[030]  box.info.replication[1].upstream.status
[030]  ---
[030] -- follow
[030] +- disconnected
[030]  ...
[030]  -- restart server and check replication continues from nop-ed vclock
[030]  test_run:cmd("switch default")
Line 230 (OSX):

[022] --- replication/skip_conflict_row.result	Thu Apr 16 21:54:28 2020
[022] +++ replication/skip_conflict_row.reject	Mon Apr 27 00:52:56 2020
[022] @@ -230,7 +230,7 @@
[022]  ...
[022]  box.info.replication[1].upstream.status
[022]  ---
[022] -- follow
[022] +- disconnected
[022]  ...
[022]  box.space.test:select({11}, {iterator = "GE"})
[022]  ---
[022]

Close #4457

Now we have S3 based infrastructure for RPM / Deb packages and GitLab CI
pipelines, which deploys packages to it.

We don't plan to add 2.5+ repositories on packagecloud.io, so instead of
usual change of target bucket from 2_N to 2_(N+1), the deploy stage is
removed.

Since all distro specific jobs are duplicated in GitLab CI pipelines and
those Travis-CI jobs are needed just for deployment, it worth to remove
them too.

Follows up #3380.
Part of #4947.

A couple of functions were mistakenly declared as 'function'
instead of 'local function' in schema.lua. That led to their
presence in the global namespace.

Closes #4812

When index:alter() was called on a non-functional index with
specified 'func', it led to accessing a not declared variable in
schema.lua.

Port_tuple is exactly the same as port_c, but is not able to store
raw MessagePack. In theory it sounds like port_tuple should be a
bit simpler and therefore faster, but in fact it is not.
Microbenchmarks didn't reveal any difference. So port_tuple is no
longer needed, all its functionality is covered by port_c.

Follow up #4641

Closes #4641

@TarantoolBot document
Title: box_return_mp() public C function

Stored C functions could return a result only via
`box_return_tuple()` function. That made users create a tuple
every time they wanted to return something from a C function.

Now public C API offers another way to return - `box_return_mp()`.
It allows to return arbitrary MessagePack, not wrapped into a
tuple object. This is simpler to use for small results like a
number, boolean, or a short string. Besides, `box_return_mp()` is
much faster than `box_return_tuple()`, especially for small
MessagePack.

Note, that it is faster only if an alternative is to create a
tuple by yourself. If an already existing tuple was obtained from
an iterator, and you want to return it, then of course it is
faster to return via `box_return_tuple()`, than via extraction of
tuple data, and calling `box_return_mp()`.

Here is the function declaration from module.h:
```C
/**
 * Return MessagePack from a stored C procedure. The MessagePack
 * is copied, so it is safe to free/reuse the passed arguments
 * after the call.
 * MessagePack is not validated, for the sake of speed. It is
 * expected to be a single encoded object. An attempt to encode
 * and return multiple objects without wrapping them into an
 * MP_ARRAY or MP_MAP is undefined behaviour.
 *
 * \param ctx An opaque structure passed to the stored C procedure
 *        by Tarantool.
 * \param mp Begin of MessagePack.
 * \param mp_end End of MessagePack.
 * \retval -1 Error.
 * \retval 0 Success.
 */
API_EXPORT int
box_return_mp(box_function_ctx_t *ctx, const char *mp, const char *mp_end);
```

Port_c is a new descendant of struct port. It is used now for
public C functions to store their result. Currently they can
return only a tuple, but it will change soon, they will be able to
return arbitrary MessagePack.

Port_tuple is not removed, because still is used for box_select(),
for functional indexes, and in SQL as a base for port_sql.
Although that may be changed later. Functional indexes really need
only a single MessagePack object from their function. While
box_select() working via port_tuple or port_c didn't show any
significant difference during micro benchmarks.

Part of #4641

Since the introduction of transaction boundaries in replication
protocol, appliers follow replicaset.applier.vclock to the lsn of the
first row in an arrived batch. This is enough and doesn't lead to errors
when replicating from other instances, respecting transaction boundaries
(instances with version 2.1.2 and up).

However, if there's a 1.10 instance in 2.1.2+ cluster, it sends every
single tx row as a separate transaction, breaking the comparison with
replicaset.applier.vclock and making the applier apply part of the
changes, it has already applied when processing a full transaction
coming from another 2.x instance. Such behaviour leads to
ER_TUPLE_FOUND errors in the scenario described above.

In order to guard from such cases, follow replicaset.applier.vclock to
the lsn of the last row in tx.

Closes #4924

Reviewed-by: Cyrill Gorcunov <gorcunov@gmail.com>

Function implementing comparison during VDBE sorting routine
(sqlVdbeCompareMsgpack) did not account values of boolean type in some
cases. Let's fix it so that booleans always precede numbers if they are
sorted in ascending order.

Closes #4697

The notification of wait variable shall be done under
a bound mutex locked. Otherwise the results are not
guaranteed (see pthread manuals).

Thus when we create a new endpoint via cbus_endpoint_create
and there is an other thread which sleeps inside cpipe_create
we should notify the sleeper under cbus.mutex.

Fixes #4806

Reported-by: Alexander Turenko <alexander.turenko@tarantool.org>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

The cbus hang test uses glibc pthread mutex implementation details.
The reason why mutex implementation details is used:
"For the bug reproducing the canceled thread must be canceled
during processing cpipe_flush_cb. We need to synchronize
the main thread and the canceled worker thread for that.
So, thread synchronization has been realized by means of
endpoint's mutex internal field(__data.__lock)."
Therefore, it should not compile in case of using another library.

While refactoring of say module in commit
5db765a7 (say: fix non-informative error
messages for log cfg) format of syslog was broken.

Closes #4785

In case accessing previous error doesn't come alongside with
incrementing its reference counter, it may lead to use-after-free bug.
Consider following scenario:

_, err = foo() -- foo() returns diagnostic error stack
preve = err.prev -- err.prev ref. counter == 1
err:set_prev(nil) -- err.prev ref. counter == 0 so err.prev is destroyed
preve -- accessing already freed memory

To avoid that let's increment reference counter of .prev member while
calling error.prev and set corresponding gc finalizer (error_unref()).

Closes #4887

There's no overflow check while incrementing error's reference counter
in error_ref(). Meanwhile, stubborn users still may achieve overflow:
each call of box.error.last() increments reference counter of error
residing in diagnostic area. As a result, 2^32 calls of box.error.last()
in a row will lead to counter overflow ergo - to unpredictable results.
Let's fix it and introduce dummy check in error_ref().

Fixa clash in struct names detected by LTO.

Make older compiler happy w.r.t.
initialization of locals.

Fixes the regression from 335f80a0
('test: adjust luajit-tap testing machinery').

Fix possible overlap of IPROTO_ERROR by IPROTO_ERROR_24.
This was possible because messages are transmitted in a map and
an order is not defined. IPROTO_ERROR_24 could be parsed after
the IPROTO_ERROR, and could throw it away.

IPROTO_ERROR in fact is not an error. It is an error message.
Secondly, this key is deprecated in favor of IPROTO_ERROR_STACK,
which contains all attributes of the whole error stack. It uses
MP_ERROR MessagePack extenstion for that.

So IPROTO_ERROR is renamed to IPROTO_ERROR_24 (similar to how old
call was renamed to IPROTO_CALL_16). IPROTO_ERROR_STACK becomes
new IPROTO_ERROR.

Follow up #4398

After error objects marshaling was implemented in #4398, there
were essentially 2 versions of the marshaling - when an error is
sent inside response body, and when it is thrown and is encoded
in iproto fields IPROTO_ERROR and IPROTO_ERROR_STACK. That is not
really useful to have 2 implementation of the same feature. This
commit drops the old iproto error encoding (its IPROTO_ERROR_STACK
part), and makes it reuse the common error encoder.

Note, the encoder skips MP_EXT header. This is because

* The header is not needed - error is encoded as a value of
  IPROTO_ERROR_STACK key, so it is known this is an error. MP_EXT
  is needed only when type is unknown on decoding side in advance;

* Old clients may not expect MP_EXT in iproto fields. That is the
  case of netbox connector, at least.

Follow up #4398

@TarantoolBot document
Title: Stacked diagnostics binary protocol
Stacked diagnostics is described in details in
https://github.com/tarantool/doc/issues/1224. This commit
changes nothing except binary protocol. The old protocol should
not be documented anywhere.

`IPROTO_ERROR_STACK` is still 0x52, but format of its value is
different now. It looks exactly like `MP_ERROR` object, without
`MP_EXT` header.

```
IPROTO_ERROR_STACK: <MP_MAP> {
    MP_ERROR_STACK: <MP_ARRAY> [
        <MP_MAP> {
            ... <all the other fields of MP_ERROR> ...
        },
        ...
    ]
}
```

It is easy to see, that key `IPROTO_ERROR_STACK` is called
'stack', and `MP_ERROR_STACK` is also 'stack'. So it may be good
to rename the former key in the documentation. For example, the
old `IPROTO_ERROR` can be renamed to `IPROTO_ERROR_24` and
`IPROTO_ERROR_STACK` can be renamed to just `IPROTO_ERROR`.

C struct error objects can be created directly only in C.
C-side increments their reference counter when pushes to the Lua
stack.

It is not going to be so convenient soon. error_unpack() function
will be used in netbox to decode error object via Lua FFI.

Such error object will have 0 refs and no Lua GC callback
established. Because it won't be pushed on Lua stack natually,
from Lua C. To make such errors alive their reference counter
will be incremented and error_unref() will be set as GC callback.

Follow up for #4398

Co-authored-by: Vladislav <Shpilevoy&lt;v.shpilevoy@tarantool.org>

Closes #4398

@TarantoolBot document
Title: Error objects encoding in MessagePack

Until now an error sent over IProto, or serialized into
MessagePack was turned into a string consisting of the error
message. As a result, all other error object attributes were lost,
including type of the object. On client side seeing a string it
was not possible to tell whether the string is a real string, or
it is a serialized error.

To deal with that the error objects encoding is reworked from the
scratch. Now, when session setting `error_marshaling_enabled` is
true, all fibers of that session will encode error objects as a
new MP_EXT type - MP_ERROR (0x03).

```
    +--------+----------+========+
    | MP_EXT | MP_ERROR | MP_MAP |
    +--------+----------+========+

    MP_ERROR: <MP_MAP> {
        MP_ERROR_STACK: <MP_ARRAY> [
            <MP_MAP> {
                MP_ERROR_TYPE: <MP_STR>,
                MP_ERROR_FILE: <MP_STR>,
                MP_ERROR_LINE: <MP_UINT>,
                MP_ERROR_MESSAGE: <MP_STR>,
                MP_ERROR_ERRNO: <MP_UINT>,
                MP_ERROR_CODE: <MP_UINT>,
                MP_ERROR_FIELDS: <MP_MAP> {
                    <MP_STR>: ...,
                    <MP_STR>: ...,
                    ...
                },
                ...
            },
            ...
        ]
    }
```

On the top level there is a single key: `MP_ERROR_STACK = 0x00`.
More keys can be added in future, and a client should ignore all
unknown keys to keep compatibility with new versions.

Every error in the stack is a map with the following keys:
* `MP_ERROR_TYPE = 0x00` - error type. This is what is visible in
  `<error_object>.base_type` field;
* `MP_ERROR_FILE = 0x01` - file name from `<error_object>.trace`;
* `MP_ERROR_LINE = 0x02` - line from `<error_object>.trace`;
* `MP_ERROR_MESSAGE = 0x03` - error message from
  `<error_object>.message`;
* `MP_ERROR_ERRNO = 0x04` - errno saved at the moment of the error
  creation. Visible in `<error_object>.errno`;
* `MP_ERROR_CODE = 0x05` - error code. Visible in
  `<error_object>.code` and in C function `box_error_code()`.
* `MP_ERROR_FIELDS = 0x06` - additional fields depending on error
  type. For example, AccessDenied error type stores here fields
  `access_type`, `object_type`, `object_name`. Connector's code
  should ignore unknown keys met here, and be ready, that for some
  existing errors new fields can be added, old can be dropped.

Lua C module 'msgpack' supports registration of custom extension
decoders for MP_EXT values. That is needed to make 'msgpack' not
depending on any modules which use it.

So far the only box-related extension were tuples - struct tuple
cdata needed to be encoded as an array.

That is going to change in next commits, where struct error cdata
appears, also depending on box. So the decoder can't be located
in src/box/lua/tuple.c. It is moved to a more common place -
src/box/lua/init.c.

Needed for #4398

We want to have a transparent marshalling through net.box
for errors. To do this, we need to recreate the error
on the client side with the same parameters as on the server.
For convenience, we update AccessDeniedError constructor
which has pointers to static strings and add the XlogGapError
constructor that does not require vclock.

Needed for #4398

Errors are encoded as a string when serialized to MessagePack to
be sent over IProto or when just saved into a buffer via Lua
modules msgpackffi and msgpack.

That is not very useful on client-side, because most of the error
metadata is lost: code, type, trace - everything except the
message.

Next commits are going to dedicate a new MP_EXT type to error
objects so as everything could be encoded, and on client side it
would be possible to restore types.

But this is a breaking change in case some users use old
connectors when work with newer Tarantool instances. So to smooth
the upgrade there is a new session setting -
'error_marshaling_enabled'.

By default it is false. When it is true, all fibers of the given
session will serialize error objects as MP_EXT.

Co-authored-by: Vladislav <Shpilevoy&lt;v.shpilevoy@tarantool.org>

Needed for #4398

Session settings are stored in a monolithic array. Submodules
can define a range of settings in there. For example, SQL. It
occupies settings from 0 to 8. There is a second array of only
SQL settings in build.c, of the same size, and it uses the same
indexes.

But if something will be added before SQL settings, so as they
won't start from 0, it will break the equal indexes assumption.
SQL should normalize all setting identifiers by
SESSION_SETTING_SQL_BEGIN.