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Collection expressions: type inference from spread elements #69856

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Sep 12, 2023
Merged

Collection expressions: type inference from spread elements #69856

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b9603dc
Collection expressions: type inference from spread elements
cston Sep 7, 2023
b51dde8
Merge remote-tracking branch 'upstream/main' into inference-spread
cston Sep 12, 2023
3f07874
Address feedback
cston Sep 12, 2023
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25 changes: 25 additions & 0 deletions src/Compilers/CSharp/Portable/Binder/Semantics/OverloadResolution/MethodTypeInference.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -615,6 +615,10 @@ private void MakeExplicitParameterTypeInferences(Binder binder, BoundExpression
{
MakeCollectionExpressionTypeInferences(binder, (BoundUnconvertedCollectionExpression)argument, target, kind, ref useSiteInfo);
}
else if (argument.Kind == BoundKind.CollectionExpressionSpreadElement)
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I find it super confusing that this parameter's name is argument when it seems like it might be any subexpression of an argument. Not for this PR to fix, though.

{
MakeSpreadElementTypeInferences((BoundCollectionExpressionSpreadElement)argument, target, ref useSiteInfo);
}
else if (argument.Kind != BoundKind.TupleLiteral ||
!MakeExplicitParameterTypeInferences(binder, (BoundTupleLiteral)argument, target, kind, ref useSiteInfo))
{
Expand All @@ -639,6 +643,7 @@ private void MakeCollectionExpressionTypeInferences(
ExactOrBoundsKind kind,
ref CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
{
Debug.Assert(target.Type is { });
if (target.Type is null)
{
return;
Expand All @@ -659,6 +664,26 @@ private void MakeCollectionExpressionTypeInferences(
MakeExplicitParameterTypeInferences(binder, element, targetElementType, kind, ref useSiteInfo);
}
}

private void MakeSpreadElementTypeInferences(
BoundCollectionExpressionSpreadElement argument,
TypeWithAnnotations target,
ref CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
{
Debug.Assert(target.Type is { });
if (target.Type is null)
{
return;
}

var enumeratorInfo = argument.EnumeratorInfoOpt;
if (enumeratorInfo is null)
{
return;
}

LowerBoundInference(enumeratorInfo.ElementTypeWithAnnotations, target, ref useSiteInfo);
}
#nullable disable

private bool MakeExplicitParameterTypeInferences(Binder binder, BoundTupleLiteral argument, TypeWithAnnotations target, ExactOrBoundsKind kind, ref CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
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176 changes: 176 additions & 0 deletions src/Compilers/CSharp/Test/Emit2/Semantics/CollectionExpressionTests.cs
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Expand Up @@ -2675,6 +2675,182 @@ static void Main(string[] args)
Diagnostic(ErrorCode.ERR_CantInferMethTypeArgs, "F").WithArguments("Program.F<T>(System.Func<T[]>)").WithLocation(9, 17));
}

[Fact]
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workitem.

public void TypeInference_Spread_01()
{
string source = """
class Program
{
static T[] F<T>(T[] arg) => arg;
static void Main()
{
int[] x = [1, 2];
object[] y = [3];
F([..x]).Report(includeType: true);
F([..x, ..y]).Report(includeType: true);
F([..y, ..x]).Report(includeType: true);
}
}
""";
CompileAndVerify(new[] { source, s_collectionExtensions }, expectedOutput: "(System.Int32[]) [1, 2], (System.Object[]) [1, 2, 3], (System.Object[]) [3, 1, 2], ");
}

[Fact]
public void TypeInference_Spread_02()
{
string source = """
class Program
{
static T[] F<T>(T[] arg) => arg;
static void Main()
{
object[] x = [1, 2];
var y = F([..x, 3]);
y.Report(includeType: true);
}
}
""";
CompileAndVerify(new[] { source, s_collectionExtensions }, expectedOutput: "(System.Object[]) [1, 2, 3], ");
}

[Fact]
public void TypeInference_Spread_03()
{
string source = """
class Program
{
static T[] F<T>(T[] arg) => arg;
static void Main()
{
int[] x = [1, 2];
var y = F([..x, (object)3]);
y.Report(includeType: true);
}
}
""";
CompileAndVerify(new[] { source, s_collectionExtensions }, expectedOutput: "(System.Object[]) [1, 2, 3], ");
}

// If we allow inference from a spread element _expression_ rather than simply
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would def want to do this eventually. I feel like if we can make return [null] "just work" then return [..[null]] should also just work.

// from the spread element _type_, and if we allow spread element expressions to
// be collection expressions, then MethodTypeInferrer.MakeOutputTypeInferences
// will probably need to make an output type inference from each element within
// the nested spread element collection expression.
[Fact]
public void TypeInference_Spread_04()
{
string source = """
using System;
class Program
{
static Func<T>[] F<T>(Func<T>[] arg) => arg;
static void Main()
{
var x = F([null, .. [() => 1]]);
x.Report();
}
}
""";
var comp = CreateCompilation(new[] { source, s_collectionExtensions });
comp.VerifyEmitDiagnostics(
// 0.cs(7,29): error CS9176: There is no target type for the collection expression.
// var x = F([null, .. [() => 1]]);
Diagnostic(ErrorCode.ERR_CollectionExpressionNoTargetType, "[() => 1]").WithLocation(7, 29));
}

[Fact]
public void TypeInference_Spread_05()
{
string source = """
class Program
{
static T[] F<T>(T[] arg) => arg;
static void Main()
{
object x = new[] { 2, 3 };
var y = F([..x]);
var z = F([1, ..x]);
}
}
""";
var comp = CreateCompilation(new[] { source, s_collectionExtensions });
comp.VerifyEmitDiagnostics(
// 0.cs(7,22): error CS1579: foreach statement cannot operate on variables of type 'object' because 'object' does not contain a public instance or extension definition for 'GetEnumerator'
// var y = F([..x]);
Diagnostic(ErrorCode.ERR_ForEachMissingMember, "x").WithArguments("object", "GetEnumerator").WithLocation(7, 22),
// 0.cs(8,25): error CS1579: foreach statement cannot operate on variables of type 'object' because 'object' does not contain a public instance or extension definition for 'GetEnumerator'
// var z = F([1, ..x]);
Diagnostic(ErrorCode.ERR_ForEachMissingMember, "x").WithArguments("object", "GetEnumerator").WithLocation(8, 25));
}

[Fact]
public void TypeInference_Spread_06()
{
string source = """
class Program
{
static T[] F<T>(T[] arg) => arg;
static void Main()
{
dynamic x = new[] { 2, 3 };
var y = F([..x]);
y.Report(includeType: true);
var z = F([1, ..x]);
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@RikkiGibson RikkiGibson Sep 8, 2023 •
edited by cston
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nit: might be nice to show a case with multiple spread arguments. #Resolved

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Added to TypeInference_Spread_01.

z.Report(includeType: true);
}
}
""";
CompileAndVerify(
new[] { source, s_collectionExtensions },
references: new[] { CSharpRef },
expectedOutput: "(System.Object[]) [2, 3], (System.Object[]) [1, 2, 3], ");
}

[Fact]
public void TypeInference_Spread_07()
{
string source = """
#nullable enable
class Program
{
static void Main()
{
string[] a = [];
string?[] b = [];
object[] aa = [..a, ..a];
object[] ab = [..a, ..b]; // 1
object[] bb = [..b, ..b]; // 2
}
}
""";
// https://github.com/dotnet/roslyn/issues/68786: Infer nullability from collection expressions in type inference.
var comp = CreateCompilation(source);
comp.VerifyEmitDiagnostics();
}

[Fact]
public void TypeInference_Spread_08()
{
string source = """
#nullable enable
using System.Collections.Generic;
class Program
{
static void Main()
{
IEnumerable<string>[] a = [];
IEnumerable<string?>[] b = [];
IEnumerable<object>[] aa = [..a, ..a];
IEnumerable<object>[] ab = [..a, ..b]; // 1
IEnumerable<object>[] bb = [..b, ..b]; // 2
}
}
""";
// https://github.com/dotnet/roslyn/issues/68786: Infer nullability from collection expressions in type inference.
var comp = CreateCompilation(source);
comp.VerifyEmitDiagnostics();
}

[Fact]
public void MemberAccess_01()
{
Expand Down