[DRAFT] Make the return type of lambda functions inferrable

[yuancu]

Description

Status: blocked by #4892 , diff can be viewed from 42a7386

Lambda function is used in transform function:

sql/docs/user/ppl/functions/collection.md

Lines 157 to 171 in 1192376

	## TRANSFORM
	### Description
	Usage: `transform(array, function)` transform the element of array one by one using lambda. The lambda function can accept one single input or two input. If the lambda accepts two argument, the second one is the index of element in array.
	Argument type: array:ARRAY, function:LAMBDA
	Return type: ARRAY
	Example
	```ppl
	source=people
	| eval array = array(1, -2, 3), result = transform(array, x -> x + 2)
	| fields result
	| head 1
	```

Normally, the operand type of a function can be automatically inferred. Therefore, we did not need to define an SqlOperandTypeInference for most functions.However, it's different for lambda functions -- the system does not automatically know the parameter types of a lambda function. When defining a lambda function, its parameter type needs to be explicitly specified. Otherwise, the parameters will be deemed of type ANY per the constructor of SqlLambdaScope, blocking the subsequent type inference.

public SqlLambdaScope(
    SqlValidatorScope parent, SqlLambda lambdaExpr) {
  super(parent);
  this.lambdaExpr = lambdaExpr;

  // default parameter type is ANY
  final RelDataType any =
      validator.typeFactory.createTypeWithNullability(
          validator.typeFactory.createSqlType(SqlTypeName.ANY), true);
  parameterTypes = new HashMap<>();
  lambdaExpr.getParameters().forEach(param -> parameterTypes.put(param.toString(), any));
}

For the expressiontransform(array, (x, i) -> x + i) , x should be of array's element type, while i should be of integer type (it represents index). This PR passes on this semantic via a SqlOperandTypeInference definition.

TODOs:

• Make lambda return type inferrable
• Yaml test, Explain IT, integration test

Related Issues

Resolves #4972

Check List

• New functionality includes testing.
• New functionality has been documented.
• New functionality has javadoc added.
• New functionality has a user manual doc added.
• New PPL command checklist all confirmed.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff or -s.
• Public documentation issue/PR created.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[coderabbitai]

Important

Review skipped

Ignore keyword(s) in the title.

⛔ Ignored keywords (3)

• WIP
• DO NOT MERGE
• DRAFT

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}