Fix a bug where the result of a function that returns an array is not able to be accessed by array index.

[brianpursley]

Fix a bug where the result of a function that returns an array is not able to be accessed by array index.

This allows array indexing to be used on the result of an expression, not just a column. For example:

var count = context.Customers
            .Select(c => EF.Functions.StringToArray(c.ContactName, " ")[0])
            .Distinct()
            .Count(c => c == "Maria");

There were two problems that needed to be fixed:

1. NpgsqlArrayTypeMapping was not being translated into an array index expression.
2. The inner expression was not being wrapped in parentheses.

Fixes #3383

[Copilot]

Pull request overview

This PR fixes a bug where array indexing could not be applied to the result of a function that returns an array. The issue occurred because the Npgsql EF Core provider did not properly translate array indexing operations on expressions (like function results) and did not wrap function expressions in parentheses when applying array indexing.

Changes:

• Added support for translating array indexing on any expression with NpgsqlArrayTypeMapping
• Added logic to wrap function expressions in parentheses when used with array indexing
• Added test to verify array indexing on function results works correctly

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
test/EFCore.PG.FunctionalTests/Query/NorthwindDbFunctionsQueryNpgsqlTest.cs	Adds test case StringToArray_with_index() to verify array indexing on function results produces correct SQL with parentheses
src/EFCore.PG/Query/Internal/NpgsqlQuerySqlGenerator.cs	Adds requirement for parentheses around SqlFunctionExpression when used as inner expression of array indexing
src/EFCore.PG/Query/ExpressionTranslators/Internal/NpgsqlArrayMethodTranslator.cs	Adds translation of ElementAt on expressions with NpgsqlArrayTypeMapping to PostgreSQL array index syntax

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[roji]

Thanks! Pushed some tweaks and will merge and backport for 10.0.

[roji]

Backported to 10.0.1 via 253d4ae