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Handle potential null in extension lookup #80621

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333fred merged 3 commits into from
Oct 13, 2025
+112 −8
Merged

Handle potential null in extension lookup #80621

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1a6213d
Handle potential null in extension lookup
333fred Oct 10, 2025
15896a3
Address feedback.
333fred Oct 10, 2025
e58dc95
Invert if
333fred Oct 10, 2025
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1 change: 1 addition & 0 deletions src/Compilers/CSharp/Portable/Binder/Binder_Crefs.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -341,6 +341,7 @@ ImmutableArray<Symbol> computeSortedAndFilteredCrefExtensionMembers(NamespaceOrT

if (result.Kind == LookupResultKind.Viable)
{
Debug.Assert(result.Symbol is not null);
sortedSymbolsBuilder ??= ArrayBuilder<Symbol>.GetInstance();
sortedSymbolsBuilder.Add(result.Symbol);
}
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6 changes: 4 additions & 2 deletions src/Compilers/CSharp/Portable/Binder/Binder_Expressions.cs
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Expand Up @@ -10896,7 +10896,8 @@ private MethodGroupResolution ResolveDefaultMethodGroup(

foreach (SingleLookupResult singleLookupResult in singleLookupResults)
{
Symbol extensionMember = singleLookupResult.Symbol;
var extensionMember = singleLookupResult.Symbol;
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@AlekseyTs AlekseyTs Oct 10, 2025 •
edited
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var

Consider reverting change on this line. #Closed

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@AlekseyTs AlekseyTs Oct 10, 2025

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I realized that it is probably driven by added nullable annotations

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@333fred 333fred Oct 10, 2025

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Yep, that's the reason.

Debug.Assert(extensionMember is not null);
if (IsStaticInstanceMismatchForUniqueSignatureFromMethodGroup(receiver, extensionMember))
{
// Remove static/instance mismatches
Expand Down Expand Up @@ -11109,7 +11110,8 @@ private static bool IsStaticInstanceMismatchForUniqueSignatureFromMethodGroup(Bo
var methods = ArrayBuilder<MethodSymbol>.GetInstance(capacity: singleLookupResults.Count);
foreach (SingleLookupResult singleLookupResult in singleLookupResults)
{
Symbol extensionMember = singleLookupResult.Symbol;
var extensionMember = singleLookupResult.Symbol;
Debug.Assert(extensionMember is not null);
if (IsStaticInstanceMismatchForUniqueSignatureFromMethodGroup(receiver, extensionMember))
{
// Remove static/instance mismatches
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11 changes: 10 additions & 1 deletion src/Compilers/CSharp/Portable/Binder/Binder_Lookup.cs
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Expand Up @@ -208,6 +208,12 @@ internal void EnumerateAllExtensionMembersInSingleBinder(ArrayBuilder<SingleLook
foreach (var candidate in extensionCandidates)
{
SingleLookupResult resultOfThisMember = originalBinder.CheckViability(candidate, arity, options, null, diagnose: true, useSiteInfo: ref useSiteInfo);
if (resultOfThisMember.Kind == LookupResultKind.Empty)
{
continue;
}

Debug.Assert(resultOfThisMember.Symbol is not null);
result.Add(resultOfThisMember);

if (candidate is MethodSymbol { IsStatic: false } shadows &&
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@AlekseyTs AlekseyTs Oct 10, 2025 •
edited
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if (candidate is MethodSymbol { IsStatic: false } shadows &&

It looks like this if belongs inside the if added above #Closed

Expand All @@ -230,7 +236,10 @@ internal void EnumerateAllExtensionMembersInSingleBinder(ArrayBuilder<SingleLook
if (implementationsToShadow is null || !implementationsToShadow.Remove(method.OriginalDefinition))
{
SingleLookupResult resultOfThisMember = originalBinder.CheckViability(method, arity, options, null, diagnose: true, useSiteInfo: ref classicExtensionUseSiteInfo);
result.Add(resultOfThisMember);
if (resultOfThisMember.Kind != LookupResultKind.Empty)
{
result.Add(resultOfThisMember);
}
}
}

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10 changes: 5 additions & 5 deletions src/Compilers/CSharp/Portable/Binder/SingleLookupResult.cs
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Expand Up @@ -2,11 +2,10 @@
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

#nullable disable

using Microsoft.CodeAnalysis.CSharp.Symbols;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Text;
using System.Diagnostics;

namespace Microsoft.CodeAnalysis.CSharp
{
Expand All @@ -22,13 +21,14 @@ internal readonly struct SingleLookupResult
internal readonly LookupResultKind Kind;

// the symbol or null.
internal readonly Symbol Symbol;
internal readonly Symbol? Symbol;

// the error of the result, if it is NonViable or Inaccessible
internal readonly DiagnosticInfo Error;
internal readonly DiagnosticInfo? Error;

internal SingleLookupResult(LookupResultKind kind, Symbol symbol, DiagnosticInfo error)
internal SingleLookupResult(LookupResultKind kind, Symbol? symbol, DiagnosticInfo? error)
{
Debug.Assert(symbol is not null || kind == LookupResultKind.Empty);
this.Kind = kind;
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@AlekseyTs AlekseyTs Oct 10, 2025 •
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this.Kind = kind;

Consider adding an assert that symbol is not null unless kind is empty. #Closed

this.Symbol = symbol;
this.Error = error;
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92 changes: 92 additions & 0 deletions src/Compilers/CSharp/Test/Emit3/Semantics/ExtensionTests2.cs
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Expand Up @@ -35085,5 +35085,97 @@ public void SyntaxFacts_01()

Assert.Equal("extension", SyntaxFacts.GetText(SyntaxKind.ExtensionKeyword));
}

[Theory, WorkItem("https://developercommunity.visualstudio.com/t/NRE-in-Roslyn-v500-225451107/10979295")]
[InlineData(LanguageVersion.CSharp10)]
[InlineData(LanguageVersion.Latest)]
public void InvalidReceiverWithOldExtensionInFileClass(LanguageVersion languageVersion)
{
var code = """
#nullable enable
using System.Threading.Tasks;
using N2;
namespace N1
{
class C
{
async Task M(object o)
{
await using var test = await nonExistent.ExtensionMethod(o);
}
}
}
""";

var code2 = """
namespace N2;

file static class E
{
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@333fred 333fred Oct 10, 2025 •
edited by jcouv
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One such "remove without any errors" scenario is when a file class is out of scope:

https://github.com/333fred/roslyn/blob/1a6213d6fe1b37b01bd8816f5a93d681d070e435/src/Compilers/CSharp/Portable/Binder/Binder_Lookup.cs#L1471-L1475

There are other scenarios in which lookup can return a result with a null symbol, but this proved to be the easiest to replicate as @viceroypenguin gave me a dump where he hit it. #Closed

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@jcouv jcouv Oct 10, 2025 •
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Thanks for fixing this. I don't quite understand how the scenario differs from existing InstanceMethodInvocation_VariousScopes_Errors which also has a file-scoped extension (therefore inaccessible) :-/

Update: ah, the receiver is non existent...

public static void ExtensionMethod(this object o) { }
}
""";

var comp = CreateCompilation([(code, "file1.cs"), (code2, "file2.cs")], parseOptions: TestOptions.Regular.WithLanguageVersion(languageVersion));

if (languageVersion == LanguageVersion.CSharp10)
{
comp.VerifyEmitDiagnostics(
// file2.cs(3,19): error CS8936: Feature 'file types' is not available in C# 10.0. Please use language version 11.0 or greater.
// file static class E
Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "E").WithArguments("file types", "11.0").WithLocation(3, 19),
// file1.cs(10,42): error CS0103: The name 'nonExistent' does not exist in the current context
// await using var test = await nonExistent.ExtensionMethod(o);
Diagnostic(ErrorCode.ERR_NameNotInContext, "nonExistent").WithArguments("nonExistent").WithLocation(10, 42)
);
}
else
{
comp.VerifyEmitDiagnostics(
// file1.cs(10,42): error CS0103: The name 'nonExistent' does not exist in the current context
// await using var test = await nonExistent.ExtensionMethod(o);
Diagnostic(ErrorCode.ERR_NameNotInContext, "nonExistent").WithArguments("nonExistent").WithLocation(10, 42)
);
}
}

[Fact, WorkItem("https://developercommunity.visualstudio.com/t/NRE-in-Roslyn-v500-225451107/10979295")]
public void InvalidReceiverWithNewExtensionInFileClass()
{
var code = """
#nullable enable
using System.Threading.Tasks;
using N2;
namespace N1
{
class C
{
async Task M(object o)
{
await using var test = await nonExistent.ExtensionMethod(o);
}
}
}
""";

var code2 = """
namespace N2;

file static class E
{
extension(object o)
{
public void ExtensionMethod(object o2) { }
}
}
""";

var comp = CreateCompilation([(code, "file1.cs"), (code2, "file2.cs")]);
comp.VerifyEmitDiagnostics(
// file1.cs(10,42): error CS0103: The name 'nonExistent' does not exist in the current context
// await using var test = await nonExistent.ExtensionMethod(o);
Diagnostic(ErrorCode.ERR_NameNotInContext, "nonExistent").WithArguments("nonExistent").WithLocation(10, 42)
);
}
}