## What changes were proposed in this pull request?
This PR proposes to separate `extended` into `examples` and `arguments` internally so that both can be separately documented and add `since` and `note` for additional information.
For `since`, it looks users sometimes get confused by, up to my knowledge, missing version information. For example, see https://www.mail-archive.com/userspark.apache.org/msg64798.html
For few good examples to check the built documentation, please see both:
`from_json` - https://spark-test.github.io/sparksqldoc/#from_json
`like` - https://spark-test.github.io/sparksqldoc/#like
For `DESCRIBE FUNCTION`, `note` and `since` are added as below:
```
> DESCRIBE FUNCTION EXTENDED rlike;
...
Extended Usage:
Arguments:
...
Examples:
...
Note:
Use LIKE to match with simple string pattern
```
```
> DESCRIBE FUNCTION EXTENDED to_json;
...
Examples:
...
Since: 2.2.0
```
For the complete documentation, see https://spark-test.github.io/sparksqldoc/
## How was this patch tested?
Manual tests and existing tests. Please see https://spark-test.github.io/sparksqldoc
Jenkins tests are needed to double check
Author: hyukjinkwon <gurwls223@gmail.com>
Closes#18749 from HyukjinKwon/followup-sql-doc-gen.
## What changes were proposed in this pull request?
This generates a documentation for Spark SQL built-in functions.
One drawback is, this requires a proper build to generate built-in function list.
Once it is built, it only takes few seconds by `sql/create-docs.sh`.
Please see https://spark-test.github.io/sparksqldoc/ that I hosted to show the output documentation.
There are few more works to be done in order to make the documentation pretty, for example, separating `Arguments:` and `Examples:` but I guess this should be done within `ExpressionDescription` and `ExpressionInfo` rather than manually parsing it. I will fix these in a follow up.
This requires `pip install mkdocs` to generate HTMLs from markdown files.
## How was this patch tested?
Manually tested:
```
cd docs
jekyll build
```
,
```
cd docs
jekyll serve
```
and
```
cd sql
create-docs.sh
```
Author: hyukjinkwon <gurwls223@gmail.com>
Closes#18702 from HyukjinKwon/SPARK-21485.
