tarantool.debug.getsources() used to provide
lua sources only for libserver lua modules,
and was not providing sources for src/box/lua/*
modules.

Now this code works:
```lua
local tnt = require 'tarantool'
local code1 = tnt.debug.getsources('box/session')
local code1 = tnt.debug.getsources('@builtin/box/session..lua')
```

Closes #7839

NO_DOC=bugfix
NO_CHANGELOG=later

See [1] for some details on why the code for log configuration needs
some care. In short log config validity checks are spread thru many
places, on some code paths we use one checks and on other code paths
other checks. And we make repetitive validity checks many times in
runtime on single configure call.

We can also reuse code for setting default values, checking options
type and resetting values to default.

- As a side effect of refactoring one can now reset values to default thru
  `log.cfg()` so now `log.cfg()` is on par with `box.cfg` in this respect.

- This patch also drops conversion `log_level` from string to number.

  Before (shorten):

    tarantool> box.cfg{log_level='warn'}
    tarantool> box.cfg.log_level
    - info
    tarantool> log.cfg.level
    - 5

  Also:
    tarantool> log.cfg{level='info'}
    tarantool> log.cfg.level
    - 5
    tarantool> box.cfg{}
    tarantool> box.cfg.log_level
    - 5

  After patch if `log_level`/`level` is given as string than it is saved
  and returned as string too. I guess it should not affect users but looks
  more handy.

- Also fixed issue with inconsistent setting `log_nonblock` thru
  `box.cfg()` and `log.cfg()`. In former case `nil` means setting default
  depending on logger type. In the latter case `nil` meant setting
  `nonblock` to `false`.

- Also patch fixes #7447.

Closes #7447.

[1] PR for this refactoring
https://github.com/tarantool/tarantool/pull/7454

NO_DOC=refactoring/tiny API improvemnent

If a complex (tuple) foreign key is added along with a new field name
that participates in that foreign key, the foreign key does not work
correctly. This happens because the new name of a local field is added
to new_space->def->dict only in ModifySpace::alter, while before that,
new_space->def->dict points to the old dictionary with old names (see
ModifySpace::alter_def). So when local_field_no is initialized earlier
in alter_space_do -> space_create -> tuple_constraint_fkey_init, it's
unable to find the new field number in the old dictionary.

Fix this by moving `new_def->dict = alter->old_space->def->dict;` from
ModifySpace::alter_def() to ModifySpace::alter(). Note that, as before,
we refer to the old dictionary from the new space (just put new names
into it), because that dict is referenced by existing tuple formats.

Closes #7652

NO_DOC=bugfix

It was disabled in the commit ccfef5fd ("memtx: ignore
slab_alloc_granularity < machine word size") to postpone addressing
unaligned objects issues.

Add PACKED attribute to inform compiler of unaligned objects. We also
need to introduce `struct stailq_entry_ptr` to be able to inform compiler
that `last` pointer unaligned too.

Closes #7422

NO_DOC=internal
NO_CHANGELOG=internal

This commit fixes BEGIN, COMMIT, and ROLLBACK counters in the box.stat()
output. Before this commit, they always showed 0. Now, they report
the number of started, committed, and rolled back transactions,
respectively.

Closes #7583

NO_DOC=bug fix

Currently, if a snapshot contains some correct entries, but doesn't
include system spaces, Tarantool crashes with segmentation fault, or
for Debug build: void diag_raise(): Assertion `e != NULL' failed.
This happens because memtx_engine_recover_snapshot returns -1, while
diag is not set. Let's panic instead of a crash.

Closes #7800

NO_DOC=bugfix

We need this option to implement a basic MT-safe read view C API
in the EE repository.

Closes #7815

NO_DOC=internal
NO_CHANGELOG=internal
NO_TEST=will be added to the EE repository

We need the options to optionally disable tuple decompression in memtx.

Needed for #7815

NO_DOC=refactoring
NO_TEST=refactoring
NO_CHANGELOG=refactoring

memtx_read_view_opts contains the only flag include_temporary_tuples,
which is set to read_view_opts.enable_temporary_spaces. Let's drop this
intermediary structure and pass read_view_opts to the allocator instead.

NO_DOC=refactoring
NO_CHANGELOG=refactoring

needs_FOO looks awkward for a flag name. Let's rename the flags to
enable_FOO. The new names will also look better in conjunction with the
disable_decompression flag that will be added in the scope of #7815.

NO_DOC=internal
NO_TEST=internal
NO_CHANGELOG=internal

So one can easily check current box status.

NO_DOC=minor change

Closes #7255

getenv() return values cannot be trusted, because an attacker might set
them. For instance, we shouldn't expect, that getenv() returns a value
of some sane size.

Another problem is that getenv() returns a pointer to one of
`char **environ` members, which might change upon next setenv().

Introduce a wrapper, getenv_safe(), which returns the value only when
it fits in a buffer of a specified size, and copies the value onto the
buffer. Use this wrapper everywhere in our code.

Below's a slightly decorated output of `grep -rwn getenv ./src --include
*.c --include *.h --include *.cc --include *.cpp --include *.hpp
--exclude *.lua.c` as of 2022-10-14.
`-` marks invalid occurences (comments, for example),
`*` marks the places that are already guarded before this patch,
`X` mars the places guarded in this patch, and
`^` marks places fixed in the next commit:

NO_WRAP
```
* ./src/lib/core/coio_file.c:509:	const char *tmpdir = getenv("TMPDIR");
X ./src/lib/core/errinj.c:75: const char *env_value = getenv(inj->name);
- ./src/proc_title.c:202: * that might try to hang onto a getenv() result.)
- ./src/proc_title.c:241:	* is mandatory to flush internal libc caches on getenv/setenv
X ./src/systemd.c:54: sd_unix_path = getenv("NOTIFY_SOCKET");
* ./src/box/module_cache.c:300: const char *tmpdir = getenv("TMPDIR");
X ./src/box/sql/os_unix.c:1441: azDirs[0] = getenv("SQL_TMPDIR");
X ./src/box/sql/os_unix.c:1446: azDirs[1] = getenv("TMPDIR");
* ./src/box/lua/console.c:394: const char *envvar = getenv("TT_CONSOLE_HIDE_SHOW_PROMPT");
^ ./src/box/lua/console.lua:771: local home_dir = os.getenv('HOME')
^ ./src/box/lua/load_cfg.lua:1007: local raw_value = os.getenv(env_var_name)
X ./src/lua/init.c:575: const char *path = getenv(envname);
X ./src/lua/init.c:592: const char *home = getenv("HOME");
* ./src/find_path.c:77: snprintf(buf, sizeof(buf) - 1, "%s", getenv("_"));
```
NO_WRAP

Part-of #7797

NO_DOC=security

This patch fixes the issue described in issue #5310 when the tuple
format has more fields than the space format. This solution is more
general than the solution in 89057a21.

Follow-up #5310
Closes #4666

NO_DOC=bugfix

If we raise different errors in case of entering an invalid password and
entering the login of a non-existent user during authorization, it will
open the door for an unauthorized person to enumerate users.
So let's unify raised errors in the cases described above.

Closes #tarantool/security#16

NO_DOC=security fix

This is a straightforward patch that makes the read view iterator struct
fixed-size so that it can be allocated on stack. This is a pre-requisite
for the raw C API for read views: the function that creates an iterator
should allocate no memory.

Closes #7813

NO_DOC=refactoring
NO_TEST=refactoring
NO_CHANGELOG=refactoring

The _vfunc system space is the sysview for the _func system space.
However, the _vfunc format is different from the _func format. This
patch makes the _vfunc format the same as the _func format.

Closes #7822

NO_DOC=bugfix

Currently, in case of recovery from an old snapshot, Tarantool allows to
perform DDL operations on an instance with non-upgraded schema.
It leads to various unpredictable errors (because the DDL code assumes
that the schema is already upgraded). This patch forbids the following
operations unless the user has the most recent schema version:
- box.schema.space.create
- box.schema.space.drop
- box.schema.space.alter
- box.schema.index.create
- box.schema.index.drop
- box.schema.index.alter
- box.schema.sequence.create
- box.schema.sequence.drop
- box.schema.sequence.alter
- box.schema.func.create
- box.schema.func.drop

Closes #7149

NO_DOC=bugfix

By default a user might not have privileges to access the _schema space,
that will cause an error during schema_needs_upgrade(), which calls
get_version(). Fix this by using C variable dd_version_id, which is
updated in the _schema.version replace trigger.

There's a special case for upgrade() during bootstrap() - triggers are
disabled during bootstrap, that's why dd_version_id is not being updated.
Handle this by passing _initial_version=1.7.5 to the upgrade function.

Part of #7149

NO_DOC=internal
NO_CHANGELOG=internal

This patch fixed the assertion when JOIN uses index of unsupported type.

Closes #5678

NO_DOC=bugfix

This commit adds support of transaction isolation levels introduced
earlier for memtx mvcc by commit ec750af6 ("txm: introduce
transaction isolation levels"). The isolation levels work exactly in
the same way as in memtx:

 - Unless a transaction explicitly specifies the 'read-committed'
   isolation level, it'll skip prepared statements, even if they are
   visible from its read view. The background for this was implemented
   in the previous patches, which added the is_prepared_ok flag to
   cache and mem iterators.

 - If a transaction skips a prepared statement, which would otherwise be
   visible from its read view, it's sent to the most recent read view
   preceding the prepared statement LSN. Note, older prepared statements
   are still visible from this read view and can actually be selected if
   committed later.

 - A transaction using the 'best-effort' isolation level (default) is
   switched to 'read-committed' when it executes the first write
   statement.

The implementation is tested by the existing memtx mvcc tests that were
made multi-engine in the scope of this commit. However, we add one more
test case - the one that checks that a 'best-effort' read view is
properly updated in case there is more than one prepared transaction.
Also, there are few tests that relied upon the old implementation and
assumed that select from Vinyl may return unconfirmed tuples. We update
those tests here as well.

Closes #5522

NO_DOC=already documented

To implement read-confirmed and best-effort isolation levels, we need
to skip unconfirmed (aka prepared) statements in the cache iterator. To
achieve that, we add a new flag is_prepared_ok. Unless the flag is set,
the iterator will skip prepared statements even if they are visible from
the iterator read view. Note, in contrast to the mem iterator, we don't
need to keep track of the min skipped statement LSN, because the cache
is just a view of the underlying levels so we'll find it out when we
descend to the mem level.

Needed for #5522

NO_DOC=internal
NO_CHANGELOG=internal

To implement read-confirmed and best-effort isolation levels, we need
to skip unconfirmed (aka prepared) statements in the mem iterator. To
achieve that, we add a new flag is_prepared_ok. Unless the flag is set,
the iterator will skip prepared statements even if they are visible from
the iterator read view. Upon skipping a statement, the iterator updates
min_skipped_plsn if the LSN of the skipped statement is less. We'll use
this LSN to update the transaction read view accordingly.

Needed for #5522

NO_DOC=internal
NO_CHANGELOG=internal

This commit replaces vy_tx_manager::last_prepared_tx with a list of all
prepared transactions sorted by PSN. We need this list to find the
newest prepared transaction that is older than a given PSN, which is
required to switch to the most recent read view in the 'best-effort'
isolation level when an unconfirmed (prepared) statement is skipped.

Needed for #5522

NO_DOC=internal
NO_TEST=internal
NO_CHANGELOG=internal

Unconfirmed statements have lsn >= MAX_LEN. Let's add a helper function
that would check this.

Needed for #5522

NO_DOC=refactoring
NO_TEST=refactoring
NO_CHANGELOG=refactoring

If index.get is called outside a transaction, we use the global read
view for it and set tx to NULL. This works fine for now, but may result
in dirty reads in a single statement, because prepared but not yet
committed to WAL statements are visible in the global read view. We are
planning to fix it in the tx manager. Let's make index.get create a
dummy transaction so once we fix it, index.get will always return
committed statements.

Note, index.pairs already creates a dummy transaction if called
outside a transaction (see vinyl_index_create_iterator) so this patch
makes behavior consistent across both read paths.

Needed for #5522

NO_DOC=refactoring
NO_TEST=refactoring
NO_CHANGELOG=refactoring

There was a bug that an instance could ack a transaction from an
old Raft term thus allowing the old leader to CONFIRM it, even if
that first instance knew there is a newer Raft term going on.

As a result, the old leader could write CONFIRM even if there is
already a new leader elected and the synchro quorum was > half.
That led to split-brain, when bad txn reached the new leader, and
PROMOTE reached the old leader.

Split-brain here is totally unnecessary. If the quorum is correct,
synchro timeout is infinite, and there is no async transactions,
then split-brain shouldn't ever happen.

The fix is as simple as attach the current Raft term number to
applier heartbeats.

In the testcase above if terms are attached, the old leader gets
ACK + new term. That causes the old leader freeze even if the
pending txn got quorum. The old leader can't CONFIRM nor ROLLBACK
its pending txns until a new leader is elected.

Freeze is guaranteed, because if a new leader was elected, then it
had got votes from > half cluster. It means > half nodes have the
new term. That in turn means the old leader during collecting ACKs
for its "new" txn will get the new term number from at least one
replica.

When the new leader finished writing PROMOTE, it either confirms
or rolls back the txn of the old leader (depending on whether it
has reached the new leader before promotion). Neither result
causes split brain. The rollback only causes a non-critical error
on the old leader raised by the bad txn's commit attempt.

There were some alternatives considered. One of the most promising
ones was to make instances reject txns if they see these txns
coming from an instance having an old Raft term. It would help in
the test provided above. But wouldn't do in a more complicated
test, when there is a third node which gets the bad transaction,
then gets local term bumped, and then replicates to any other
instance. Others would accept that bad txn, because the sender has
a newer Raft term, even though the txn author is still in the old
term. Tracking terms of txn author is not possible in too many
cases so as to rely on that.

Closes #7253

@TarantoolBot document
Title: New iproto field in applier -> relay ACKs
The applier->relay channel (from replica back to master) is used
only for sending ACKs. Replication data goes the other way
(relay->applier).

These ACKs had 2 fields: `IPROTO_VCLOCK (0x26)` and
`IPROTO_VCLOCK_SYNC (0x5a)`.

Now they have a new field: `IPROTO_TERM (0x53)`. It is a unsigned
number containing `box.info.election.term` of the sender node
(applier, replica).

The patch adds structs applier_heartbeat and relay_heartbeat.

It is similar to the previous commit, which does the same for all
the other replication requests, but these work not via struct
replication_request.

The heartbeats have their own codecs. The goal is to avoid the big
expensive replication_request usage with a lot of optional fields.
It makes sense, because the HBs are sent somewhat frequently.

They also store members by values. But copying before encoding and
decoding is avoided by storing the HB structs by values right
inside applier and relay.

The motivation is to simplify addition of a new field to
applier_heartbeat in a next commit.

Needed for #7253

NO_DOC=refactoring
NO_CHANGELOG=refactoring
NO_TEST=refactoring

There were 3 comments which mentioned relay stream restart. It
could happen when replicas ignored data from non-leaders. A newly
elected leader had to re-send data, which others ignored, while
the source wasn't a leader.

Was removed in the commit 6336ea26
("refactoring: remove relay_restart_recovery as unneeded").

This is fixed now, because otherwise some of these comments would
need to be updated by a next commit in this series.

In scope of #7253

NO_DOC=refactoring
NO_CHANGELOG=refactoring
NO_TEST=refactoring

The patch adds `struct <name>_request` types for replication
requests: join, subscribe, register. Only not for ack/heartbeat
requests. They are covered separately in a next commit.

The motivation is to make them independent. Previously a lot of
codecs were calling xrow_encode/decode_subscribe() under the hood
with tons of optional params.

Now inside they all fallback to internal
`struct replication_request`. The code duplication is reduced,
because all encoding/decoding is handled by replication_request.
Also alteration of any of the requests only requires to update
that request itself and replication_request codec.

Additionally, this is consistent with other requests having their
own structs like synchro_request, raft_request, call_request, etc.

Alongside the commit fixes xrow_decode_register(), which used to
try to decode version_id, but the result wasn't used and the
version_id wasn't encoded in xrow_encode_register() anyway.

This work is done now, because soon replication acks will get a
new field and it wouldn't be good to update all this codecs mess
again just for that field.

The downside is that the requests store their members by values.
That requires to copy them before encoding. Not good for big
fields like vclocks. OTOH the requests affected by this commit are
sent very rarely, perf is not important at all.

Needed for #7253

NO_DOC=refactoring
NO_CHANGELOG=refactoring
NO_TEST=refactoring

Currently if a non-string type is passed to luaT_key_def_set_part,
lua_tolstring returns null-pointer type_name, which is passed to
a string formatting function in diag_set.

Closes #5222

NO_DOC=bugfix

Don't accept an empty string or leading part of "str" or "num" as a
valid field type.

Closes #5940

NO_DOC=Partial field types weren't documented

Co-authored-by: Alexander Turenko <alexander.turenko@tarantool.org>

Since the function is actually an eval, by default there should
be no execute access right in public role.

Closes tarantool/security#14

NO_DOC=bugfix

Prior to this patch, it was possible to call box.execute() before box
was initialized, i.e. before calling box.cfg(). This, however, caused
box.cfg() to be called automatically, which could be problematic as some
parameters could not be changed after box.cfg() was called. After this
patch, box.execute() will only be available when the box has been
initialized.

Closes #4726

@TarantoolBot document
Title: box.execute() now available only after initialization of box

Previously, it was possible to call box.execute() before the box was
configured, in which case the box was configured automatically, which
could lead to problems with box parameters. Now box.execute() can only
be called after the box has been properly configured.

It is also forbidden to set language to SQL in a console with an
unconfigured box.

Fix a simple typo that caused the problem.

Closes #7645

NO_DOC=bugfix

This patch introduces new rules to determine type of NULLIF() built-in
function.

Closes #6990

@TarantoolBot document
Title: New rules to determine type of result of NULLIF

The type of the result of NULLIF() function now matches the type of the
first argument.

This patch introduces new rules to determine type of CASE operation.

Part of #6990

@TarantoolBot document
Title: New rules to determine type of result of CASE

New rules are applied to determine the type of the CASE operation. If
all values are NULL with no type, or if a bind variable exists among
the possible results, then the type of CASE is ANY. Otherwise, all NULL
values with no type are ignored, and the type of CASE is determined
using the following rules:
1) if all values of the same type, then type of CASE is this type;
2) otherwise, if any of the possible results is of one of the
incomparable types, then the type of CASE is ANY;
3) otherwise, if any of the possible results is of one of the
non-numeric types, then the type of CASE is SCALAR;
4) otherwise, if any of the possible results is of type NUMBER, then the
type of CASE is NUMBER;
5) otherwise, if any of the possible results is of type DECIMAL, then
the type of CASE is DECIMAL;
6) otherwise, if any of the possible results is of type DOUBLE, then the
type of CASE is DOUBLE;
7) otherwise the type of CASE is INTEGER.

The commit c1c77782 ("replication: fix bootstrap failing with
ER_READONLY") made applier retry connection infinitely upon receiving a
ER_READONLY error on join. At the time of writing that commit, this was
the only way to make join retriable. Because there were no retries in
scope of bootstrap_from_master. The join either succeeded or failed.

Later on, bootstrap_from_master was made retriable in commit
f2ad1dee ("replication: retry join automatically"). Now when
bootstrap_from_master fails, replica reconnects to all the remote nodes,
thus updating their ballots, chooses a new (probably different from the
previous approach) bootstrap leader, and retries booting from it.

The second approach is more preferable, and here's why. Imagine
bootstrapping a cluster of 3 nodes, A, B and C in a full-mesh topology.
B and C connect to all the remote peers almost instantly, and both
independently decide that B will be the bootstrap leader (it means it
has the smallest uuid among A, B, C).

At the same time, A can't connect to C. B bootstraps the cluster, and
joins C. After C is joined, A finally connects to C. Now A can choose a
bootstrap leader. It has an old B's ballot (smallest uuid, but not yet
booted) and C's ballot (already booted). This is because C's ballot is
received after cluster bootstrap, and B's ballot was received earlier
than that. So A believes C is a better bootstrap leader, and tries to
boot from it.

A will fail joining to C, because at the same time C tries to sync with
everyone, including A, and thus stays read-only. Since A retries joining
to the same instance over and over again, this situation makes the A and
C stuck forever.

Let's retry ER_READONLY on another level: instead of trying to join to
the same bootstrap leader over and over, try to choose a new bootstrap
leader and boot from it.

In the situation described above, this means that A would try to join to
C once, fail due to ER_READONLY, re-fetch new ballots from everyone and
choose B as a join master (now it has smallest uuid and is booted).

The issue was discovered due to linearizable_test.lua hanging
occasionally with the following output:
NO_WRAP
 No output during 40 seconds. Will abort after 320 seconds without output. List of workers not reporting the status:
- 059_replication-luatest [replication-luatest/linearizable_test.lua, None] at /tmp/t/059_replication-luatest/linearizable.result:0
[059] replication-luatest/linearizable_test.lua                       [ fail ]
[059] Test failed! Output from reject file /tmp/t/rejects/replication-luatest/linearizable.reject:
[059] TAP version 13
[059] 1..6
[059] # Started on Thu Sep 29 10:30:45 2022
[059] # Starting group: linearizable-read
[059] not ok 1	linearizable-read.test_wait_others
[059] #   ....11.0~entrypoint.531.dev/test/luatest_helpers/server.lua:104: Waiting for "readiness" on server server_1-q7berSRY4Q_E (PID 53608) timed out
[059] #   stack traceback:
[059] #   	....11.0~entrypoint.531.dev/test/luatest_helpers/server.lua:104: in function 'wait_for_readiness'
[059] #   	...11.0~entrypoint.531.dev/test/luatest_helpers/cluster.lua:92: in function 'start'
[059] #   	...t.531.dev/test/replication-luatest/linearizable_test.lua:50: in function <...t.531.dev/test/replication-luatest/linearizable_test.lua:20>
[059] #   	...
[059] #   	[C]: in function 'xpcall'
NO_WRAP

Part-of #7737

NO_DOC=bugfix

This patch fixed the assertion when using INDEXED BY with an index that
is at least the third in space.

Closes #5976

NO_DOC=bugfix

If the length of the tuple is greater than the number of fields in the
format, it is possible that the cursor in the VDBE will be overridden
with zeros.

Closes #5310

NO_DOC=bugfix

For reasons described in #7231 HASH index 'GT' iterator type is deprecated:
print a warning exactly once about the deprecation.

Closes #7231

@TarantoolBot document
Title: memtx HASH index 'GT' iterator deprecation

memtx HASH index 'GT' iterator is deprecated since Tarantool 2.11
(tarantool/tarantool#7231) and will removed in a future release of
Tarantool: the user will get a warning when using it.