Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/18749#discussion_r129929153
--- Diff:
sql/catalyst/src/main/java/org/apache/spark/sql/catalyst/expressions/ExpressionDescription.java
---
@@ -29,15 +29,40 @@
* show the usage of the function in human language.
*
* `usage()` will be used for the function usage in brief way.
- * `extended()` will be used for the function usage in verbose way, suppose
- * an example will be provided.
*
- * And we can refer the function name by `_FUNC_`, in `usage` and
`extended`, as it's
+ * These below are concatenated and used for the function usage in verbose
way, suppose arguments,
+ * examples, note and since will be provided.
+ *
+ * `arguments()` describes arguments for the expression. This should
follow the format as below:
+ *
+ * Arguments:
+ * * arg0 - ...
+ * ....
+ * * arg1 - ...
+ * ....
+ *
+ * `examples()` describes examples for the expression. This should follow
the format as below:
+ *
+ * Examples:
+ * > SELECT ...;
+ * ...
+ * > SELECT ...;
+ * ...
+ *
+ * `note()` contains some notes for the expression optionally.
+ *
+ * `since()` contains version information for the expression. Version is
specified by,
+ * for example, "2.2.0".
+ *
+ * We can refer the function name by `_FUNC_`, in `usage`, `arguments`
and `examples`, as it's
* registered in `FunctionRegistry`.
*/
@DeveloperApi
--- End diff --
Agree, that's my only question, whether this change matters, because it's a
developer API. You provide default implementations, though `extended()` gets
removed. Hm. I am wondering if it's possible to keep `extended()` but, well,
ignore it? it would at least be compatible even if it meant someone's
implementation out there would have to update to provide information to
`ExpressionInfo` correctly. That's not really a functional problem though.
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