tarantool / tarantool / 11891

83%

master: 87%

push

travis-ci

lua: implement json path access to tuple fields

Until this moment in Lua a tuple data could be accessed in 3 ways:
- get field by field number, decode into Lua,
- get field by field name, decode into Lua
- decode entire tuple into Lua.

It was impossible to decode into Lua only a part of the field to
avoid Lua garbage creating. For example, consider the tuple:
`{1, 2, {key1 = value1,
         key2 = {key21 = {key211 = {key2111, key2112}}}}}`
with field names `field1`, `field2`, `field3`.

To get `key2112` it is necessary to decode into Lua the entire
3-th field, including `key1`, `value1`, `key2`, `key21`,
`key211`, `key2111` using the syntax
`key2112 = tuple.field3.key2.key21.key211[2]`.

Now the one can use the following syntax:
`key2112 = tuple["field3.key2.key21.key211[2]"]`. The difference
is in placing all the path into quotes and brackets `["..."]`.
The Tarantool goes through this path and MessagePack tuple body,
gets the needed tuple part and decodes into Lua only it.

The path must be valid JSON path with one exception - in
Tarantool a path can start with `.`. For example:
`tuple[".field3..."]` - it is done to lay emphasis that the JSON
path here is just a suffix for the tuple.

At the same time tuple field names still work: `tuple["field1"]`,
`tuple.field2`.

If the field name looks like JSON path, for example:
`my.field.name`, then it works too. The path at first is checked
to be a real JSON path, and if nothing is found, then the entire
path is considered as a field name. To combine such names and
path elements the one can use `["..."]`. For example:
`tuple["['my.field.name'].key1.key2.['another.key.in.map']"]`.

Closes #1285

94 of 94 new or added lines in 3 files covered. (100.0%)

38395 of 47073 relevant lines covered (81.56%)

880194.73 hits per line