CSHARP-5655: Support regular expressions in $replaceAll search string and $split delimiter

[sanych-sun]

No description provided.

[Copilot]

Pull request overview

Adds LINQ3 translation support for using regular expressions as the $replaceAll.find argument and as the $split delimiter, along with accompanying serializer deduction and test coverage.

Changes:

• Implemented $replaceAll translation for string.Replace(...) and Regex.Replace(...) (including regex literals and regex values stored as BSON regular expressions).
• Extended $split translation to support regex delimiters via Regex.Split(...) and regex instance .Split(...) when stored as BSON regular expressions, plus additional string.Split overload handling.
• Added/updated unit + integration tests and updated expression preprocessing in test helpers.

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/MongoDB.Driver.Tests/Linq/TestHelpers.cs	Preprocesses test expressions using LinqExpressionPreprocessor before serializer finding/translation.
tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Translators/…/SplitMethodToAggregationExpressionTranslatorTests.cs	New unit tests for $split translation across many string.Split overloads and regex delimiters.
tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Translators/…/ReplaceMethodToAggregationExpressionTranslatorTests.cs	New unit tests for $replaceAll translation including regex-based replace.
tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/SerializerFinders/StringTests.cs	Expands serializer-finder coverage for Replace/Split and adds unsupported-case assertions.
tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/SerializerFinders/RegexTests.cs	Expands serializer-finder coverage for regex Replace/Split and adds unsupported-case assertions.
tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Jira/CSharp5928Tests.cs	Updates a non-translatable-expression regression to use unsupported Regex.Replace overload and asserts message content.
tests/MongoDB.Driver.Tests/Linq/Integration/StringSplitTests.cs	New integration tests validating $split output for supported string.Split shapes.
tests/MongoDB.Driver.Tests/Linq/Integration/StringReplaceTests.cs	New integration tests validating $replaceAll for string.Replace (feature-gated).
tests/MongoDB.Driver.Tests/Linq/Integration/RegexSplitTests.cs	New integration tests validating regex delimiter support in $split (feature-gated).
tests/MongoDB.Driver.Tests/Linq/Integration/RegexReplaceTests.cs	New integration tests validating regex find support in $replaceAll (feature-gated).
src/MongoDB.Driver/Linq/Linq3Implementation/Translators/…/SplitMethodToAggregationExpressionTranslator.cs	Adds regex delimiter support and extends handling of additional string.Split overloads.
src/MongoDB.Driver/Linq/Linq3Implementation/Translators/…/ReplaceMethodToAggregationExpressionTranslator.cs	New translator implementing $replaceAll for string/regex replace operations.
src/MongoDB.Driver/Linq/Linq3Implementation/Translators/…/MethodCallExpressionToAggregationExpressionTranslator.cs	Routes method calls named Replace to the new replace translator.
src/MongoDB.Driver/Linq/Linq3Implementation/SerializerFinders/SerializerFinderVisitMethodCall.cs	Deduces serializers for Replace and extends Split deduction to regex splits.
src/MongoDB.Driver/Linq/Linq3Implementation/Reflection/StringMethod.cs	Adds Replace reflection metadata and expands split overload sets (char + string separator overloads).
src/MongoDB.Driver/Linq/Linq3Implementation/Reflection/RegexMethod.cs	Adds Replace/Split reflection metadata and overload sets for serializer finding/translation.
src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstExpression.cs	Adds AstExpression.ReplaceAll(...) factory method.
src/MongoDB.Driver/Core/Misc/Feature.cs	Fixes lookup feature typos and introduces ReplaceAll, ReplaceAllWithRegex, and SplitWithRegex feature flags.

Comments suppressed due to low confidence (1)

src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/MethodTranslators/SplitMethodToAggregationExpressionTranslator.cs:73

• For the string separator overloads, a null or empty separator has special meaning in .NET (and MongoDB $split also rejects empty delimiters). Currently separatorString/separatorStrings[0] are used without validating null/empty, which can generate an invalid $split delimiter or change semantics. Please add explicit validation (e.g., reject null/empty with ExpressionNotSupportedException, or implement equivalent semantics if intended).

                else if (method.IsOneOf(StringMethod.SplitWithStringOverloads))
                {
                    var separatorsExpression = arguments[0];
                    var separatorString = separatorsExpression.GetConstantValue<string>(containingExpression: expression);
                    delimiter = separatorString;
                }
                else if (method.IsOneOf(StringMethod.SplitWithStringsOverloads))
                {
                    var separatorsExpression = arguments[0];
                    var separatorStrings = separatorsExpression.GetConstantValue<string[]>(containingExpression: expression);
                    if (separatorStrings.Length != 1)
                    {
                        goto notSupported;
                    }
                    delimiter = separatorStrings[0];
                }

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[Copilot]

The comment has several grammar issues (e.g., “passing them”, “both of them are expecting”, “subset of Expressions functionality”). Please rewrite for clarity/grammar so it’s easy to understand why preprocessing is required here.

Suggested change

	// We must run LinqExpressionPreprocessor on the expression before passing them into SerializerFinder or Translators,
	// both of them are expecting to work with subset of Expressions functionality based on PartialEvaluator and ClrCompatExpressionRewriter output.
	// We must run LinqExpressionPreprocessor on the expression before passing it to SerializerFinder or the translators.
	// They expect to work with only the subset of expression functionality produced by PartialEvaluator and ClrCompatExpressionRewriter.

[Copilot]

Test method name contains a grammatical error and an extra underscore ("should_unknowable_serializer__for..."). Please rename it to something like "SerializerFinder_should_set_unknowable_serializer_for_unsupported_regex_methods" for readability and consistency with the StringTests naming.

Suggested change

	public void SerializerFinder_should_unknowable_serializer__for_unsupported_regex_methods(LambdaExpression expression)
	public void SerializerFinder_should_set_unknowable_serializer_for_unsupported_regex_methods(LambdaExpression expression)

[Copilot]

For string.Replace(string oldValue, string newValue), .NET treats newValue == null as string.Empty. Translating a null replacement via ExpressionToAggregationExpressionTranslator will emit BSON null, which diverges from .NET semantics and is likely invalid for $replaceAll. Consider normalizing a constant null replacement to "" (or explicitly rejecting null with a clear ExpressionNotSupportedException).