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Fix modification of readonly locals through ref fields #74255

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merged 5 commits into from
Jul 10, 2024
Merged

Fix modification of readonly locals through ref fields #74255

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a917d8e
Fix modification of readonly locals through ref fields
jjonescz Jul 1, 2024
b4a1047
Extend tests
jjonescz Jul 4, 2024
427c7ae
Improve check
jjonescz Jul 8, 2024
6c3c641
Add query tests
jjonescz Jul 9, 2024
369465f
Merge branch 'main' into 73741-RefForeach
jjonescz Jul 10, 2024
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1 change: 1 addition & 0 deletions src/Compilers/CSharp/Portable/BoundTree/Constructors.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -60,6 +60,7 @@ private static bool NeedsByValueFieldAccess(BoundExpression? receiver, FieldSymb
{
if (fieldSymbol.IsStatic ||
!fieldSymbol.ContainingType.IsValueType ||
fieldSymbol.RefKind is RefKind.Ref ||
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In L76 we are effectively checking RefKind != RefKind.None on the localSymbol, should we also do that here for the fieldSymbol? Is it possible we need this when we have a ref-readonly field whose referent value is changing "during" the expression?

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If we have a ref readonly field, there are binding errors if we try to change its referent value, so I think we cannot observe the difference (the IsByValue computed here is used by Binder.HasHome in codegen to determine whether the field should be stored in a temp but we never get there if we have binding errors). But it makes sense to me to check what you suggest.

receiver == null) // receiver may be null in error cases
{
return false;
Expand Down
120 changes: 120 additions & 0 deletions src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenForEachTests.cs
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Expand Up @@ -5327,5 +5327,125 @@ public static class Extensions
}";
CompileAndVerify(source, parseOptions: TestOptions.Regular9, expectedOutput: "123123");
}

[Fact, WorkItem("https://github.com/dotnet/roslyn/issues/73741")]
public void MutatingThroughRefFields_01()
{
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Consider adding a smoke test for LINQ iteration variables and using variables. They have the same "can't assign" semantics as foreach iteration variables and hence are possibly subject to the same issue.

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@jjonescz jjonescz Jul 9, 2024 •
edited
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There are tests for using variables added in this PR in CodeGenUsingStatementTests.cs.
LINQ iteration variables aren't affected by this bug (the iteration variable is not a LocalSymbol so the BoundFieldAccess has always IsByValue set to false), but I will add similar tests.

var source = """
using System;

V[] arr = new V[3];

foreach (var r in new E(arr))
{
r.V.F++;
}

foreach (var v in arr) Console.Write(v.F);

ref struct E(V[] arr)
{
int i;
public E GetEnumerator() => this;
public R Current => new(ref arr[i - 1]);
public bool MoveNext() => i++ < arr.Length;
}

ref struct R(ref V v)
{
public ref V V = ref v;
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The submitted repro has these as readonly ref fields. Let's add some more tests with different variants of readonlyness sprinkled throughout. It would also be good to test variables that come from ref foreach loops.

}

struct V
{
public int F;
}
""";
CompileAndVerify(source, targetFramework: TargetFramework.Net70,
verify: Verification.Fails,
expectedOutput: ExecutionConditionUtil.IsDesktop ? null : "111").VerifyDiagnostics();
}

[Fact, WorkItem("https://github.com/dotnet/roslyn/issues/73741")]
public void MutatingThroughRefFields_02()
{
var source = """
using System;

V[] arr = new V[3];

foreach (var r in new E(arr))
{
r.V.F += 2;
}

foreach (var v in arr) Console.Write(v.F);

ref struct E(V[] arr)
{
int i;
public E GetEnumerator() => this;
public R Current => new(ref arr[i - 1]);
public bool MoveNext() => i++ < arr.Length;
}

ref struct R(ref V v)
{
public ref V V = ref v;
}

struct V
{
public int F;
}
""";
CompileAndVerify(source, targetFramework: TargetFramework.Net70,
verify: Verification.Fails,
expectedOutput: ExecutionConditionUtil.IsDesktop ? null : "222").VerifyDiagnostics();
}

[Fact, WorkItem("https://github.com/dotnet/roslyn/issues/73741")]
public void MutatingThroughRefFields_03()
{
var source = """
using System;

V[] arr = new V[3];

foreach (var r in new E(arr))
{
r.V.S.Inc();
}

foreach (var v in arr) Console.Write(v.S.F);

ref struct E(V[] arr)
{
int i;
public E GetEnumerator() => this;
public R Current => new(ref arr[i - 1]);
public bool MoveNext() => i++ < arr.Length;
}

ref struct R(ref V v)
{
public ref V V = ref v;
}

struct V
{
public S S;
}

struct S
{
public int F;
public void Inc() => F++;
}
""";
CompileAndVerify(source, targetFramework: TargetFramework.Net70,
verify: Verification.Fails,
expectedOutput: ExecutionConditionUtil.IsDesktop ? null : "111").VerifyDiagnostics();
}
}
}
100 changes: 100 additions & 0 deletions src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenUsingStatementTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@

#nullable disable

using Microsoft.CodeAnalysis.Test.Utilities;
using Roslyn.Test.Utilities;
using Xunit;

Expand Down Expand Up @@ -3136,5 +3137,104 @@ ref struct S
}
}
}

[Fact, WorkItem("https://github.com/dotnet/roslyn/issues/73741")]
public void MutatingThroughRefFields_01()
{
var source = """
using System;

V v = default;

using (var d = new R(ref v))
{
d.V.F++;
}

Console.Write(v.F);

ref struct R(ref V v)
{
public ref V V = ref v;
public void Dispose() { }
}

struct V
{
public int F;
}
""";
CompileAndVerify(source, targetFramework: TargetFramework.Net70,
verify: Verification.FailsPEVerify,
expectedOutput: ExecutionConditionUtil.IsDesktop ? null : "1").VerifyDiagnostics();
}

[Fact, WorkItem("https://github.com/dotnet/roslyn/issues/73741")]
public void MutatingThroughRefFields_02()
{
var source = """
using System;

V v = default;

using (var d = new R(ref v))
{
d.V.F += 2;
}

Console.Write(v.F);

ref struct R(ref V v)
{
public ref V V = ref v;
public void Dispose() { }
}

struct V
{
public int F;
}
""";
CompileAndVerify(source, targetFramework: TargetFramework.Net70,
verify: Verification.FailsPEVerify,
expectedOutput: ExecutionConditionUtil.IsDesktop ? null : "2").VerifyDiagnostics();
}

[Fact, WorkItem("https://github.com/dotnet/roslyn/issues/73741")]
public void MutatingThroughRefFields_03()
{
var source = """
using System;

V v = default;

using (var d = new R(ref v))
{
d.V.S.Inc();
}

Console.Write(v.S.F);

ref struct R(ref V v)
{
public ref V V = ref v;
public void Dispose() { }
}

struct V
{
public S S;
}

struct S
{
public int F;
public void Inc() => F++;
}
""";
CompileAndVerify(source, targetFramework: TargetFramework.Net70,
verify: Verification.FailsPEVerify,
expectedOutput: ExecutionConditionUtil.IsDesktop ? null : "1").VerifyDiagnostics();
}
}
}
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