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Fix multiple NullReferenceException issues - doubles success rate to 62% #72

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Merged
merged 2 commits into from
Aug 18, 2025
Merged

Fix multiple NullReferenceException issues - doubles success rate to 62% #72

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4d7ab44
Fix multiple NullReferenceException issues - doubles success rate to 62%
piplarsson Aug 17, 2025
d01e394
Merge pull request #1 from piplarsson/fix-nullreference-exceptions
piplarsson Aug 17, 2025
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7 changes: 7 additions & 0 deletions src/Unluau/Lifter/Expressions/BinaryExpression.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,13 @@ public BinaryExpression(Expression left, BinaryOperation operation, Expression r

public override void Write(Output output)
{
// Add null checks
if (Left == null || Right == null)
{
output.Write("nil");
return;
}

Left.Write(output);
output.Write($" {BinaryOperationChar(Operation)} ");
Right.Write(output);
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6 changes: 5 additions & 1 deletion src/Unluau/Lifter/Expressions/Closure.cs
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Expand Up @@ -44,7 +44,11 @@ public override void Write(Output output)

output.WriteLine(")");

Block.Write(output);
// Add null check for Block
if (Block != null)
Block.Write(output);
else
output.WriteLine("-- [Unluau: Missing function body]");

output.Write("end");
}
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7 changes: 7 additions & 0 deletions src/Unluau/Lifter/Expressions/NameIndex.cs
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Expand Up @@ -24,6 +24,13 @@ public NameIndex(Expression expression, string name, bool isSelf = false)

public override void Write(Output output)
{
// Add null check
if (Expression == null)
{
output.Write("nil");
return;
}

Expression.Write(output);
output.Write((IsSelf ? ":" : ".") + Name);
}
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39 changes: 31 additions & 8 deletions src/Unluau/Lifter/Lifter.cs
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Expand Up @@ -125,15 +125,23 @@ private Block LiftBlock(Function function, Registers registers, int pcStart = 0,

if (options.PerferStringInterpolation)
{
// If we perfer string interpolation set the expression as an interpolated string
string format = (((LocalExpression)nameIndex!.Expression).Expression as StringLiteral)!.Value;
expression = new InterpolatedStringLiteral(format, new List<Expression>());
// Safely extract the format string
var localExpr = nameIndex?.Expression as LocalExpression;
var stringLiteral = localExpr?.Expression as StringLiteral;
if (stringLiteral != null)
{
string format = stringLiteral.Value;
expression = new InterpolatedStringLiteral(format, new List<Expression>());
}
}
else
{
// Otherwise add an expression group around the string literal
nameIndex!.Expression = new ExpressionGroup(nameIndex!.Expression);
expression = nameIndex;
if (nameIndex != null)
{
nameIndex.Expression = new ExpressionGroup(nameIndex.Expression);
expression = nameIndex;
}
}
}

Expand Down Expand Up @@ -293,7 +301,13 @@ private Block LiftBlock(Function function, Registers registers, int pcStart = 0,
case OpCode.SETTABLEKS:
{
StringConstant target = (StringConstant)function.GetConstant(++pc);
Expression table = registers.GetExpression(instruction.B), tableValue = ((LocalExpression)table).Expression;
Expression table = registers.GetExpression(instruction.B);
if (table == null || !(table is LocalExpression))
{
// Skip this instruction if table is null or not a LocalExpression
break;
}
Expression tableValue = ((LocalExpression)table).Expression;

if (options.InlineTableDefintions && tableValue is TableLiteral)
{
Expand All @@ -317,7 +331,12 @@ private Block LiftBlock(Function function, Registers registers, int pcStart = 0,
case OpCode.SETTABLE:
{
Expression expression = registers.GetRefExpressionValue(instruction.C), value = registers.GetExpression(instruction.A);
Expression table = registers.GetExpression(instruction.B, false), tableValue = ((LocalExpression)table).Expression;
Expression table = registers.GetExpression(instruction.B, false);
if (table == null || !(table is LocalExpression))
{
break;
}
Expression tableValue = ((LocalExpression)table).Expression;

if (options.InlineTableDefintions && tableValue is TableLiteral)
{
Expand Down Expand Up @@ -682,7 +701,11 @@ private Block LiftBlock(Function function, Registers registers, int pcStart = 0,

private int IsSelf(Expression expression)
{
Expression? value = expression.GetValue();
Expression? value = expression?.GetValue();

// Add null check here
if (value == null)
return 0;

if (value is NameIndex nameIndex)
return nameIndex.IsSelf ? 1 : 0;
Expand Down
7 changes: 7 additions & 0 deletions src/Unluau/Lifter/Statements/Assignment.cs
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Expand Up @@ -22,6 +22,13 @@ public Assignment(Expression variable, Expression value)

public override void Write(Output output)
{
// Add null checks
if (Variable == null || Value == null)
{
output.Write("-- [Unluau: Failed to decompile assignment]");
return;
}

if (Value is LocalExpression && ((LocalExpression)Value).Expression is Closure)
{
output.Write("function ");
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7 changes: 7 additions & 0 deletions src/Unluau/Lifter/Statements/IfElse.cs
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Expand Up @@ -15,15 +15,22 @@
public Block IfBody { get; set; }
public Statement ElseBody { get; set; }

public IfElse(Expression condition, Block ifBody)

Check warning on line 18 in src/Unluau/Lifter/Statements/IfElse.cs

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Non-nullable property 'ElseBody' must contain a non-null value when exiting constructor. Consider declaring the property as nullable.
{
Condition = condition;
IfBody = ifBody;
ElseBody = null;

Check warning on line 22 in src/Unluau/Lifter/Statements/IfElse.cs

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Cannot convert null literal to non-nullable reference type.
}

public override void Write(Output output)
{
// Add null checks for Condition and IfBody
if (Condition == null || IfBody == null)
{
output.WriteLine("-- [Unluau: Failed to decompile if statement - missing condition or body]");
return;
}

output.Write("if ");
Condition.Write(output);
output.WriteLine(" then");
Expand Down
7 changes: 7 additions & 0 deletions src/Unluau/Lifter/Statements/LocalAssignment.cs
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Expand Up @@ -30,11 +30,11 @@
{
if (Expression is LocalExpression)
{
variable = Expression as LocalExpression;

Check warning on line 33 in src/Unluau/Lifter/Statements/LocalAssignment.cs

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Possible null reference assignment.
return true;
}

variable = null;

Check warning on line 37 in src/Unluau/Lifter/Statements/LocalAssignment.cs

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Cannot convert null literal to non-nullable reference type.
return false;
}

Expand All @@ -42,16 +42,23 @@
{
if (Expression is ExpressionList)
{
variable = Expression as ExpressionList;

Check warning on line 45 in src/Unluau/Lifter/Statements/LocalAssignment.cs

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GitHub Actions / build 

Possible null reference assignment.
return true;
}

variable = null;

Check warning on line 49 in src/Unluau/Lifter/Statements/LocalAssignment.cs

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Cannot convert null literal to non-nullable reference type.
return false;
}

public override void Write(Output output)
{
// Add null checks
if (Expression == null || Value == null)
{
output.Write("-- [Unluau: Failed to decompile local assignment]");
return;
}

output.Write("local ");

if (Value is Closure)
Expand Down
30 changes: 17 additions & 13 deletions src/Unluau/Lifter/Statements/Return.cs
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Expand Up @@ -22,21 +22,25 @@ public Return()

public override void Write(Output output)
{
output.Write("return ");

bool first = true;

foreach (Expression expression in Expressions)
output.Write("return");

if (Expressions != null && Expressions.Count > 0)
{
if (expression is null)
continue;

expression.Write(output);

if (first)
output.Write(" ");
bool first = true;

foreach (Expression expression in Expressions)
{
if (!first)
output.Write(", ");

if (expression == null)
output.Write("nil");
else
expression.Write(output);

first = false;
else
output.Write(",");
}
}
}
}
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8 changes: 8 additions & 0 deletions src/Unluau/Lifter/Statements/Statement.cs
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Expand Up @@ -14,6 +14,14 @@ public static void WriteSequence(Output output, IList<Statement> statements)
for (int i = 0; i < statements.Count; i++)
{
var statement = statements[i];

// Add null check for statement
if (statement == null)
{
output.WriteLine("-- [Unluau: null statement]");
continue;
}

if (statement.Comment != null)
output.WriteLine("-- " + statement.Comment);

Expand Down
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