[Expression] Add array return type

[Danieladu]

close: #3615

Add Array return type to make array type errors be discovered during the static check period.

For example, before :

var expr = Expression.Parse("skip(1, 1)"); // it's ok
var result = expr.TryEvaluate(null); // throw runtime exception, skip can not applied on int

After:

var expr = Expression.Parse("skip(1, 1)"); // 1 is not a valid array

remark

why does Expression.Parse("skip(1, 1)") not throw exception before.
If the method accepts Object type, e.g. count method accepts one parameter, which could be string or array. If the param is a string, return string length, and if the param is an array, return the array size.
So, we can only mark the param object, any return type here is ok during the static checker period.
Same logic with skip(1, 1), skip accepts an object as the first parameters, and all the input types here are treated as valid types in the static checker.

The root cause is that we treat Object as the base type (or any type). So, extract Array type may help us get array related errors in advance.

Additional feature:

Support mixed return type in the static check.
Before, if the expression needs one param that maybe a string or a number. we can only mark it as Object return type, but now, we can use ReturnType.Number | ReturnType.String to mark it.
This can make type matching more precise.

[boydc2014]

Looks good to me, but i can't tell all cases are covered, can you add test cases in both "Good" and "Bad" expression tests, to make things clear.

[chrimc62]

ValidateBinary [](start = 20, length = 14)

Do we need more precision than this, i.e. string | array and object? #Resolved

[Danieladu]

Hi chris, I have modified the ReturnType enum to make it has the ability to combine choices or intersect combinations of choices.
So the above code has been changed to

expr => ValidateOrder(expr, null, ReturnType.Array | ReturnType.String, ReturnType.Object)

Looking forward the comments. #Resolved

[chrimc62]

ValidateBinary [](start = 20, length = 14)

Same here. #Resolved

[chrimc62]

🕐

[chrimc62]

public enum ReturnType

Should tag with flags, i.e. https://docs.microsoft.com/en-us/dotnet/api/system.flagsattribute?view=netframework-4.8

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Refers to: libraries/AdaptiveExpressions/Expression.cs:21 in 66e3e1e. [](commit_id = 66e3e1e, deletion_comment = False)

[chrimc62]

Indentation.

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Refers to: libraries/AdaptiveExpressions/ExpressionFunctions.cs:3049 in 66e3e1e. [](commit_id = 66e3e1e, deletion_comment = False)

[chrimc62]

String [](start = 31, length = 6)

Good catch. #Resolved

[chrimc62]