Restore outer variable bindings after nested block redeclarations

src/FastExpressionCompiler/FastExpressionCompiler.cs

@@ -853,7 +853,7 @@ public void PopBlock()
                 for (var i = 0; i < varCount; ++i)
                 {
                     ref var varBlocks = ref _varInBlock.Map.GetSurePresentEntryRef(i);
-                    if (varBlocks.Value.Count == _blockCount)
+                    if (varBlocks.Value.Count != 0 && (varBlocks.Value.GetLastSurePresentRef() >>> 16) == _blockCount - 1)
                         varBlocks.Value.RemoveLastSurePresent();
                 }
                 --_blockCount;

test/FastExpressionCompiler.TestsRunner.Net472/Program.cs

@@ -34,6 +34,7 @@ static void RunLightExpressionTests(object state)
                 var justLightTestsStopwatch = Stopwatch.StartNew();
 
                 var t = (LightExpression.TestRun)state;
+                t.Run(new LightExpression.UnitTests.BlockVariableBindingRegressionTests());
                 t.Run(new LightExpression.UnitTests.NestedStructFieldAddressRegressionTests());
                 t.Run(new LightExpression.IssueTests.Issue183_NullableDecimal());
                 t.Run(new LightExpression.IssueTests.Issue398_Optimize_Switch_with_OpCodes_Switch());
@@ -60,6 +61,7 @@ static void RunLightExpressionTests(object state)
             var fecTestsStopwatch = Stopwatch.StartNew();
 
             var fecTests = new TestRun();
+            fecTests.Run(new BlockVariableBindingRegressionTests());
             fecTests.Run(new NestedStructFieldAddressRegressionTests());
             fecTests.Run(new Issue183_NullableDecimal());
             fecTests.Run(new Issue468_Optimize_the_delegate_access_to_the_Closure_object_for_the_modern_NET());

test/FastExpressionCompiler.TestsRunner/Program.cs

@@ -63,6 +63,7 @@ public static void Main(string[] args)
             var ltTask = Task.Run(() =>
             {
                 var ltStopwatch = Stopwatch.StartNew();
+                lt.Run(new LightExpression.UnitTests.BlockVariableBindingRegressionTests());
 #if NET8_0_OR_GREATER
                 lt.Run(new LightExpression.UnitTests.NestedStructFieldAddressRegressionTests());
                 lt.Run(new LightExpression.IssueTests.Issue490_Regression_in_compiling_lambdas_with_ref_struct_parameters());
@@ -86,6 +87,7 @@ public static void Main(string[] args)
             });
 
             var stStopwatch = Stopwatch.StartNew();
+            st.Run(new BlockVariableBindingRegressionTests());
             st.Run(new NestedStructFieldAddressRegressionTests());
             st.Run(new Issue499_InvalidProgramException_for_Sorting_and_comparison_function());
             st.Run(new Issue561_NonBooleanEqualityOperator());

test/FastExpressionCompiler.UnitTests/BlockVariableBindingRegressionTests.cs

@@ -0,0 +1,82 @@
+using System;
+using System.Collections.Generic;
+using S = System.Linq.Expressions.Expression;
+#if LIGHT_EXPRESSION
+namespace FastExpressionCompiler.LightExpression.UnitTests;
+#else
+namespace FastExpressionCompiler.UnitTests;
+#endif
+
+public struct BlockVariableBindingRegressionTests : ITestX
+{
+    private static readonly CompilerFlags[] Flags =
+    {
+        CompilerFlags.Default, CompilerFlags.NoInvocationLambdaInlining,
+        CompilerFlags.EnableDelegateDebugInfo | CompilerFlags.ThrowOnNotSupportedExpression
+    };
+
+    public void Run(TestRun t)
+    {
+        Leaving_nested_binding_restores_outer_value(t);
+        Sibling_redeclarations_restore_outer_value(t);
+        Direct_nested_and_distinct_bindings_keep_their_values(t);
+    }
+
+    public void Leaving_nested_binding_restores_outer_value(TestContext t)
+    {
+        var value = S.Variable(typeof(int), "value");
+        var middle = S.Variable(typeof(int), "middle");
+        var tree = S.Lambda<Func<int>>(S.Block(new[] { value },
+            S.Assign(value, S.Constant(1)),
+            S.Block(new[] { middle }, S.Assign(middle, S.Constant(0)),
+                S.Block(new[] { value }, S.Assign(value, S.Constant(2))), value)));
+        var expected = tree.Compile()();
+        t.AreEqual(1, expected);
+        foreach (var flags in Flags)
+        {
+            var fast = tree.FromSysExpression().CompileFast(true, flags);
+            if (t.IsNotNull(fast)) t.AreEqual(expected, fast());
+        }
+    }
+
+    public void Sibling_redeclarations_restore_outer_value(TestContext t)
+    {
+        var value = S.Variable(typeof(int), "value");
+        var sum = S.Variable(typeof(int), "sum");
+        var statements = new List<System.Linq.Expressions.Expression>
+        {
+            S.Assign(value, S.Constant(1)), S.Assign(sum, S.Constant(0))
+        };
+        for (var i = 0; i < 3; ++i)
+        {
+            var middle = S.Variable(typeof(int), "middle");
+            statements.Add(S.Block(new[] { middle }, S.Assign(middle, S.Constant(0)),
+                S.Block(new[] { value }, S.Assign(value, S.Constant(i + 10))), S.AddAssign(sum, value)));
+        }
+        statements.Add(sum);
+        var tree = S.Lambda<Func<int>>(S.Block(new[] { value, sum }, statements));
+        var expected = tree.Compile()();
+        t.AreEqual(3, expected);
+        foreach (var flags in Flags)
+        {
+            var fast = tree.FromSysExpression().CompileFast(true, flags);
+            if (t.IsNotNull(fast)) t.AreEqual(expected, fast());
+        }
+    }
+
+    public void Direct_nested_and_distinct_bindings_keep_their_values(TestContext t)
+    {
+        var value = S.Variable(typeof(int), "value");
+        var other = S.Variable(typeof(int), "other");
+        var tree = S.Lambda<Func<int>>(S.Block(new[] { value }, S.Assign(value, S.Constant(1)),
+            S.Block(new[] { value }, S.Assign(value, S.Constant(2))),
+            S.Block(new[] { other }, S.Assign(other, S.Constant(3))), value));
+        var expected = tree.Compile()();
+        t.AreEqual(1, expected);
+        foreach (var flags in Flags)
+        {
+            var fast = tree.FromSysExpression().CompileFast(true, flags);
+            if (t.IsNotNull(fast)) t.AreEqual(expected, fast());
+        }
+    }
+}