[GitHub] [calcite] wnob commented on a diff in pull request #2973: [CALCITE-5180] Implement some of the overloads for BigQuery's DATE and TIMESTAMP

[GitBox <gi...@apache.org>]

wnob commented on code in PR #2973:
URL: https://github.com/apache/calcite/pull/2973#discussion_r1025778875


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babel/src/main/codegen/includes/parserImpls.ftl:
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@@ -42,6 +42,26 @@ SqlNode DateFunctionCall() :
     }
 }
 
+SqlNode TimestampFunctionCall() :

Review Comment:
   Here's my understanding: Babel is the "universal" parser ¹ that does not understand the semantics of individual dialects (hence the name). Dialect-specific semantic validation is a separate step that occurs after dialect-agnostic parsing.
   
   This is a [FreeMarker template file][1]. It does not contain any interpolation or tags, so running this through FreeMarker would simply remove the license comment at the top of the file. It's processed by [FMPP][2] in `config.fmpp` [here][3], which is in-turn referenced in the [JavaCC][4] grammar [here][5], as well as [here][6] via the `builtinFunctionCallMethods` list where the function name was added above in `config.fmpp`.
   
   Together, these 2 additions to the grammar indicate that there is a *production* called `TimestampFunctionCall` which consists of the [`<TIMESTAMP>` token][7] followed by a [`FunctionParameterList`][8] production, which consists of left-parenthesis, comma-separated arguments, right-parenthesis. The parser does nothing to validate how many arguments there are or what types they are.
   
   So yes, long story short, you're right that we didn't have to modify the `DateFunctionCall` production because it's just a function call either way, and I just added this new production with a different name token but which is otherwise identical to the `DATE` one.
   
   ¹ I've heard Julian make reference to other parsers being potentially usable with Calcite but I don't know of any examples.
   
   [1]: https://freemarker.apache.org/docs/dgui_template_overallstructure.html
   [2]: https://fmpp.sourceforge.net/index.html
   [3]: https://github.com/apache/calcite/blob/a505b25eacc473c6ec0ef8abd40c1ccae86297b6/babel/src/main/codegen/config.fmpp#L566
   [4]: https://javacc.github.io/javacc/
   [5]: https://github.com/apache/calcite/blob/a0e119ea42def418957f214f539469f1aba76c18/core/src/main/codegen/templates/Parser.jj#L1163
   [6]: https://github.com/apache/calcite/blob/a0e119ea42def418957f214f539469f1aba76c18/core/src/main/codegen/templates/Parser.jj#L5992
   [7]: https://github.com/apache/calcite/blob/a0e119ea42def418957f214f539469f1aba76c18/core/src/main/codegen/templates/Parser.jj#L7922
   [8]: https://github.com/apache/calcite/blob/a0e119ea42def418957f214f539469f1aba76c18/core/src/main/codegen/templates/Parser.jj#L948
   



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