/// <summary>
/// This check is entirely to avoid some unnecessary default initializations so the code looks less cluttered and more like the VB did.
/// The caller should default to outputting an initializer which is always safe for equivalence/correctness.
/// </summary>
public static bool IsDefinitelyAssignedBeforeRead(this SemanticModel semanticModel, VariableDeclaratorSyntax localDeclarator, ModifiedIdentifierSyntax name)
{
Func <string, bool> equalsId = s => s.Equals(name.Identifier.ValueText, StringComparison.OrdinalIgnoreCase);
// Find the first and second statements in the method (property, constructor, etc.) which contain the identifier
// This may overshoot where there are multiple identifiers with the same name - this is ok, it just means we could output an initializer where one is not needed
var statements = localDeclarator.GetAncestor <MethodBlockBaseSyntax>().Statements.Where(s =>
s.DescendantTokens().Any(id => ((SyntaxToken)id).IsKind(SyntaxKind.IdentifierToken) && equalsId(id.ValueText))
).Take(2).ToList();
var first = statements.First();
var second = statements.Last();
// Analyze the data flow in this block to see if initialization is required
// If the second statement where the identifier is used is an if block, we look at the condition rather than the whole statement. This is an easy special
// case which catches eg. the if (TryParse()) pattern. This could happen for any node which allows multiple statements.
var dataFlow = second is MultiLineIfBlockSyntax ifBlock
? semanticModel.AnalyzeDataFlow(ifBlock.IfStatement.Condition)
: semanticModel.AnalyzeDataFlow(first, second);
bool alwaysAssigned = dataFlow.AlwaysAssigned.Any(s => equalsId(s.Name));
bool readInside = dataFlow.ReadInside.Any(s => equalsId(s.Name));
bool writtenInside = dataFlow.WrittenInside.Any(s => equalsId(s.Name));
return(alwaysAssigned && !writtenInside || !readInside);
}
