Support --let

[dveeden]

Issue: ref #110

• Support setting variables based on a constant --let $a=5
• Support setting variables based on a query: --let $b=`SELECT VERSION()`
• Support echoing back variables --echo $a and $b

See also: https://dev.mysql.com/doc/dev/mysql-server/latest/PAGE_MYSQL_TEST_COMMANDS.html

$ cat t/let.test 
--echo $SHELL
--let $a= 5
--echo a is $a
--let $b=`SELECT VERSION()`
--echo b is $b
$ ./mysql-tester --record let
INFO[0000] recording tests: [let]                       
WARN[0000] Create new db&{0 0xc000126000 0 {0 0} [0xc000290000] map[] 0 1 0xc00012a000 false map[0xc000290000:map[0xc000290000:true]] map[] 0 0 0 0 <nil> 0 0 0 0 0x49d880} 
./t/let.test: ok! 0 test cases passed, take time 0.000539828 s
INFO[0000] run test [let] ok                            

Great, All tests passed
$ cat r/let.result 
/bin/bash
a is 5
b is 5.7.25-TiDB-v5.5.0-alpha-79-g1d20bbfeb-dirty

[dveeden]

cc @morgo @mjonss

[mjonss]

LGTM + some suggestions.

Also should we start to add more tests? Like in t/*.test and r/*.result files?

[dveeden]

/cc @bb7133

[dveeden]

let.test:

--echo $SHELL
--let $a= 5
--echo a is $a
--let $b=`SELECT "foobar"`
--echo b is $b
--let $abc123= "foo bar baz"
--echo abc123 is $abc123
--let $def_456= "aaa bbb ccc"
--echo $def_456

let.result:

/bin/bash
a is 5
b is foobar
abc123 is "foo bar baz"
"aaa bbb ccc"

[dveeden]

PTAL @mjonss

[mjonss]

LGTM, but please also add some tests.

I'm approving it, but I think we can extend this a bit further to be more compatible with the let command of mysqltest client. Like handling backtick quoting the same.

Should we also make a feature request for --expr?

[dveeden]

LGTM, but please also add some tests.

I've added a test for Q_LET in 4ab1f13

We could add tests like #49 (comment) in this repo or rely on this being used in other repos.

I'm approving it, but I think we can extend this a bit further to be more compatible with the let command of mysqltest client. Like handling backtick quoting the same.

Yes, we could do that, but this does most of what most tests need. I think we can extend this in another PR later when needed.

Should we also make a feature request for --expr?

I'm not sure if there is any demand for that. Maybe add a note about this in #110 ?

[dveeden]

PTAL @bb7133

[bb7133]

LGTM