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Support System LambdaExpression invocation targets in LightExpression #570

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Copilot Oct 26, 2026
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Support System lambda invocation in LightExpression
Copilot Oct 26, 2026
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2 changes: 2 additions & 0 deletions src/FastExpressionCompiler.LightExpression/Expression.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1353,6 +1353,8 @@ expression is LambdaExpression lambda
? lambda.ReturnType
: expression is UnaryExpression unExpr && unExpr.NodeType == ExpressionType.Quote && unExpr.Operand is LambdaExpression quotedLambda
? quotedLambda.ReturnType
: expression is ConstantExpression constantExpr && constantExpr.Value is System.Linq.Expressions.LambdaExpression sysLambda
? sysLambda.ReturnType
: expression.Type.FindDelegateInvokeMethod().ReturnType;

[RequiresUnreferencedCode(Trimming.Message)]
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24 changes: 22 additions & 2 deletions src/FastExpressionCompiler/FastExpressionCompiler.cs
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Expand Up @@ -1343,7 +1343,7 @@ public static Result TryCollectInfo(ref CompilerContext context, Expression expr
var invokeExpr = (InvocationExpression)expr;
var invokeArgs = invokeExpr.GetArgExprs();
var invokeArgCount = invokeArgs.GetArgCount();
var invokedExpr = invokeExpr.Expression;
var invokedExpr = GetInvokedExpression(invokeExpr, ref context);
if ((context.CompilerFlags & CompilerFlags.NoInvocationLambdaInlining) == 0 && invokedExpr is LambdaExpression lambdaExpr)
{
var oldIndex = context.CurrentInlinedLambdaInvokeIndex;
Expand Down Expand Up @@ -1617,6 +1617,26 @@ private static Expression CreateInlinedLambdaInvocationExpression(ArgExprs invok
return inlinedBlock;
}

private static Expression GetInvokedExpression(InvocationExpression invokeExpr, ref CompilerContext context)
{
var invokedExpr = invokeExpr.Expression;
#if LIGHT_EXPRESSION
if (invokedExpr is ConstantExpression constantExpr &&
constantExpr.Value is System.Linq.Expressions.LambdaExpression sysLambda)
{
if ((context.CompilerFlags & CompilerFlags.NoInvocationLambdaInlining) != 0)
{
ref var cachedLambda = ref context.InlinedLambdaInvocation.Map.AddOrGetValueRef(invokeExpr, out var found);
if (!found)
cachedLambda = sysLambda.ToLightExpression();
return cachedLambda;
}
return sysLambda.ToLightExpression();
}
#endif
return invokedExpr;
}

private static bool PropagateNonPassedParamsToOuterLambda(ref CompilerContext context, NestedLambdaInfo lambda,
ParamExprs nestedLambdaParamExprs, ref SmallList<ParameterExpression> nestedNonPassedParams)
{
Expand Down Expand Up @@ -5375,7 +5395,7 @@ private static bool TryEmitInvoke(InvocationExpression expr, ILGenerator il, ref

var argExprs = expr.GetArgExprs();
var argCount = argExprs.GetArgCount();
var invokedExpr = expr.Expression;
var invokedExpr = GetInvokedExpression(expr, ref context);
if ((context.CompilerFlags & CompilerFlags.NoInvocationLambdaInlining) == 0 && invokedExpr is LambdaExpression lambdaExpr)
{
parent |= ParentFlags.InlinedLambdaInvoke;
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34 changes: 33 additions & 1 deletion test/FastExpressionCompiler.UnitTests/NestedLambdaTests.cs
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Expand Up @@ -25,14 +25,17 @@ public int Run()
Given_composed_expr_with_closure_over_2_parameters_used_in_2_levels_of_nested_lambda();
Given_composed_expr_with_closure_over_2_same_parameters_used_in_2_levels_of_nested_lambda();
Two_same_nested_lambdas_should_compile_once();
#if LIGHT_EXPRESSION
Invoke_constant_System_lambda();
#endif

Nested_Hoisted_Func_using_outer_parameter();
Nested_Hoisted_Func_using_outer_parameter_and_closed_value();
Nested_Hoisted_Action_using_outer_parameter_and_closed_value();
Nested_Hoisted_lambda_using_outer_parameter_and_closed_value_deeply_nested_lambda();
Given_hoisted_expr_with_closure_over_parameters_in_nested_lambda_should_work();

return 17;
return 18;
}


Expand Down Expand Up @@ -388,6 +391,35 @@ public void Two_same_nested_lambdas_should_compile_once()
Asserts.AreEqual(50, f());
}

#if LIGHT_EXPRESSION
public void Invoke_constant_System_lambda()
{
System.Linq.Expressions.LambdaExpression lambda =
System.Linq.Expressions.Expression.Lambda<Func<int>>(
System.Linq.Expressions.Expression.Constant(42));
var zeroArgExpr = Lambda<Func<int>>(Invoke(Constant(lambda)));

var zeroArgFunc = zeroArgExpr.CompileFast(true);
Asserts.IsNotNull(zeroArgFunc);
Asserts.AreEqual(42, zeroArgFunc());

var value = System.Linq.Expressions.Expression.Parameter(typeof(int), "value");
lambda = System.Linq.Expressions.Expression.Lambda<Func<int, int>>(
System.Linq.Expressions.Expression.Add(value, System.Linq.Expressions.Expression.Constant(2)),
value);
var arg = Parameter(typeof(int), "arg");
var oneArgExpr = Lambda<Func<int, int>>(Invoke(Constant(lambda), arg), arg);

var oneArgFunc = oneArgExpr.CompileFast(true);
Asserts.IsNotNull(oneArgFunc);
Asserts.AreEqual(42, oneArgFunc(40));

oneArgFunc = oneArgExpr.CompileFast(true, CompilerFlags.NoInvocationLambdaInlining);
Asserts.IsNotNull(oneArgFunc);
Asserts.AreEqual(42, oneArgFunc(40));
}
#endif


public void Hmm_I_can_use_the_same_parameter_for_outer_and_nested_lambda()
{
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