public static IEnumerable<ReplaceAction> GetSimplifications(ForEachStatementSyntax forLoop, ISemanticModel model, Assumptions assumptions, CancellationToken cancellationToken = default(CancellationToken))
{
if (forLoop.IsAnyIterationSufficient(model, assumptions) == true)
yield break; // a more appropriate code issue handles this case
// can the loop be replaced by its first or last iteration?
var isFirstSufficient = forLoop.IsFirstIterationSufficient(model, assumptions) == true;
var isLastSufficient = forLoop.IsLastIterationSufficient(model, assumptions) == true;
var firstVsLast = isFirstSufficient ? "First"
: isLastSufficient ? "Last"
: null;
if (firstVsLast == null) yield break;
// do we know how to translate?
var loopStatements = forLoop.Statement.Statements();
var rawThenStatements = loopStatements.SkipLast(loopStatements.Last().IsIntraLoopJump() ? 1 : 0).ToArray();
if (rawThenStatements.Any(e => e.HasTopLevelIntraLoopJumps())) yield break; // don't know how to translate jumps that aren't at the end
// wrap collection items in a type with a new null value (so that a null result definitively indicates an empty collection)
var iteratorType = ((LocalSymbol)model.GetDeclaredSymbol(forLoop)).Type;
var nuller = GetNullabledQueryAndValueGetter(iteratorType, forLoop.Identifier, forLoop.Expression);
var nullableQuery = nuller.Item1;
var valueGetter = nuller.Item2;
var tempNullableLocalName = Syntax.Identifier("_" + forLoop.Identifier.ValueText);
var tempNullableLocalGet = Syntax.IdentifierName(tempNullableLocalName);
// build replacement
var iteratorReads = forLoop.Statement.ReadsOfLocalVariable(forLoop.Identifier).ToArray();
var desiredIterationQuery = nullableQuery.Accessing(firstVsLast + "OrDefault").Invoking();
var condition = tempNullableLocalGet.BOpNotEquals(Syntax.LiteralExpression(SyntaxKind.NullLiteralExpression));
var useDenulledLocal = iteratorReads.Length > 2;
var thenStatement = useDenulledLocal
? rawThenStatements.Prepend(forLoop.Identifier.VarInit(valueGetter(tempNullableLocalGet))).Block()
: rawThenStatements.Select(e => e.ReplaceNodes(iteratorReads, (n, a) => valueGetter(tempNullableLocalGet))).Block();
var replacementStatements = new StatementSyntax[] {
tempNullableLocalName.VarInit(desiredIterationQuery),
condition.IfThen(thenStatement)
};
// expose as code action/issue
yield return forLoop.MakeReplaceStatementWithManyAction(
replacementStatements,
"Execute " + firstVsLast + " if any");
}