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Draft implementation for list patterns #49080

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Draft implementation for list patterns #49080

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204 changes: 106 additions & 98 deletions src/Compilers/CSharp/Portable/Binder/Binder_Expressions.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
using System.Reflection;

Expand Down Expand Up @@ -7854,19 +7855,53 @@ private bool TryBindIndexOrRangeIndexer(
var argument = arguments.Arguments[0];

var argType = argument.Type;
bool argIsIndex = TypeSymbol.Equals(argType,
Compilation.GetWellKnownType(WellKnownType.System_Index),
TypeCompareKind.ConsiderEverything);
bool argIsRange = !argIsIndex && TypeSymbol.Equals(argType,
Compilation.GetWellKnownType(WellKnownType.System_Range),
TypeCompareKind.ConsiderEverything);

if ((!argIsIndex && !argIsRange) ||
ThreeState argIsIndexNotRange =
TypeSymbol.Equals(argType, Compilation.GetWellKnownType(WellKnownType.System_Index), TypeCompareKind.ConsiderEverything) ? ThreeState.True :
TypeSymbol.Equals(argType, Compilation.GetWellKnownType(WellKnownType.System_Range), TypeCompareKind.ConsiderEverything) ? ThreeState.False :
ThreeState.Unknown;

if (!argIsIndexNotRange.HasValue() ||
!(receiverOpt?.Type is TypeSymbol receiverType))
{
return false;
}

if (!TryFindIndexOrRangeIndexerPattern(syntax, receiverOpt, receiverType, argIsIndex: argIsIndexNotRange.Value(),
out var lengthOrCountProperty, out var patternSymbol, out var returnType, diagnostics))
{
return false;
}

patternIndexerAccess = new BoundIndexOrRangePatternIndexerAccess(
syntax,
receiverOpt,
lengthOrCountProperty,
patternSymbol,
BindToNaturalType(argument, diagnostics),
returnType);

_ = MessageID.IDS_FeatureIndexOperator.CheckFeatureAvailability(diagnostics, syntax);
if (arguments.Names.Count > 0)
{
diagnostics.Add(
!argIsIndexNotRange.Value()
? ErrorCode.ERR_ImplicitRangeIndexerWithName
: ErrorCode.ERR_ImplicitIndexIndexerWithName,
arguments.Names[0].GetLocation());
}
return true;
}

#nullable enable
private bool TryFindIndexOrRangeIndexerPattern(
SyntaxNode syntax,
BoundExpression? receiverOpt,
TypeSymbol receiverType, bool argIsIndex,
[NotNullWhen(true)] out PropertySymbol? lengthOrCountProperty,
[NotNullWhen(true)] out Symbol? patternSymbol,
[NotNullWhen(true)] out TypeSymbol? returnType,
DiagnosticBag diagnostics)
{
// SPEC:

// An indexer invocation with a single argument of System.Index or System.Range will
Expand All @@ -7877,25 +7912,21 @@ private bool TryBindIndexOrRangeIndexer(
// 2. For Index: Has an accessible indexer with a single int parameter
// For Range: Has an accessible Slice method that takes two int parameters

PropertySymbol lengthOrCountProperty;

var lookupResult = LookupResult.GetInstance();
HashSet<DiagnosticInfo> useSiteDiagnostics = null;
HashSet<DiagnosticInfo>? useSiteDiagnostics = null;

// Look for Length first

if (!tryLookupLengthOrCount(WellKnownMemberNames.LengthPropertyName, out lengthOrCountProperty) &&
!tryLookupLengthOrCount(WellKnownMemberNames.CountPropertyName, out lengthOrCountProperty))
if (!TryLookupLengthOrCount(WellKnownMemberNames.LengthPropertyName, receiverType, lookupResult, out lengthOrCountProperty, ref useSiteDiagnostics) &&
!TryLookupLengthOrCount(WellKnownMemberNames.CountPropertyName, receiverType, lookupResult, out lengthOrCountProperty, ref useSiteDiagnostics))
{
patternSymbol = null;
returnType = null;
return false;
}

Debug.Assert(lengthOrCountProperty is { });

if (argIsIndex)
{
// Look for `T this[int i]` indexer

LookupMembersInType(
lookupResult,
receiverType,
Expand All @@ -7917,43 +7948,32 @@ candidate is PropertySymbol property &&
property.OriginalDefinition is { ParameterCount: 1 } original &&
isIntNotByRef(original.Parameters[0]))
{
patternSymbol = property;
returnType = property.Type;
CheckImplicitThisCopyInReadOnlyMember(receiverOpt, lengthOrCountProperty.GetMethod, diagnostics);
// note: implicit copy check on the indexer accessor happens in CheckPropertyValueKind
patternIndexerAccess = new BoundIndexOrRangePatternIndexerAccess(
syntax,
receiverOpt,
lengthOrCountProperty,
property,
BindToNaturalType(argument, diagnostics),
property.Type);
break;
checkWellKnown(WellKnownMember.System_Index__GetOffset);
return true;
}
}
}
}
else if (receiverType.SpecialType == SpecialType.System_String)
{
Debug.Assert(argIsRange);
Debug.Assert(!argIsIndex);
// Look for Substring
var substring = (MethodSymbol)Compilation.GetSpecialTypeMember(SpecialMember.System_String__Substring);
if (substring is object)
{
patternIndexerAccess = new BoundIndexOrRangePatternIndexerAccess(
syntax,
receiverOpt,
lengthOrCountProperty,
substring,
BindToNaturalType(argument, diagnostics),
substring.ReturnType);
checkWellKnown(WellKnownMember.System_Range__get_Start);
checkWellKnown(WellKnownMember.System_Range__get_End);
patternSymbol = substring;
returnType = substring.ReturnType;
checkWellKnownForRange();
return true;
}
}
else
{
Debug.Assert(argIsRange);
Debug.Assert(!argIsIndex);
// Look for `T Slice(int, int)` indexer

LookupMembersInType(
lookupResult,
receiverType,
Expand All @@ -7977,50 +7997,35 @@ method.OriginalDefinition is var original &&
isIntNotByRef(original.Parameters[0]) &&
isIntNotByRef(original.Parameters[1]))
{
patternSymbol = method;
returnType = method.ReturnType;
CheckImplicitThisCopyInReadOnlyMember(receiverOpt, lengthOrCountProperty.GetMethod, diagnostics);
CheckImplicitThisCopyInReadOnlyMember(receiverOpt, method, diagnostics);
patternIndexerAccess = new BoundIndexOrRangePatternIndexerAccess(
syntax,
receiverOpt,
lengthOrCountProperty,
method,
BindToNaturalType(argument, diagnostics),
method.ReturnType);
checkWellKnown(WellKnownMember.System_Range__get_Start);
checkWellKnown(WellKnownMember.System_Range__get_End);
break;
checkWellKnownForRange();
return true;
}
}
}
}

cleanup(lookupResult, ref useSiteDiagnostics);
if (patternIndexerAccess is null)
{
return false;
}

_ = MessageID.IDS_FeatureIndexOperator.CheckFeatureAvailability(diagnostics, syntax);
checkWellKnown(WellKnownMember.System_Index__GetOffset);
if (arguments.Names.Count > 0)
{
diagnostics.Add(
argIsRange
? ErrorCode.ERR_ImplicitRangeIndexerWithName
: ErrorCode.ERR_ImplicitIndexIndexerWithName,
arguments.Names[0].GetLocation());
}
return true;

static void cleanup(LookupResult lookupResult, ref HashSet<DiagnosticInfo> useSiteDiagnostics)
{
lookupResult.Free();
useSiteDiagnostics = null;
}
lookupResult.Free();
useSiteDiagnostics = null;
patternSymbol = null;
returnType = null;
return false;

#pragma warning disable CS8762 // Parameter may not have a null value when exiting in some condition.
static bool isIntNotByRef(ParameterSymbol param)
=> param.Type.SpecialType == SpecialType.System_Int32 &&
param.RefKind == RefKind.None;
#pragma warning restore CS8762 // Parameter may not have a null value when exiting in some condition.

void checkWellKnownForRange()
{
checkWellKnown(WellKnownMember.System_Range__get_Start);
checkWellKnown(WellKnownMember.System_Range__get_End);
checkWellKnown(WellKnownMember.System_Index__GetOffset);
}

void checkWellKnown(WellKnownMember member)
{
Expand All @@ -8029,39 +8034,42 @@ void checkWellKnown(WellKnownMember member)
// the user from getting surprising errors when optimizations fail
_ = GetWellKnownTypeMember(Compilation, member, diagnostics, syntax: syntax);
}
}

private bool TryLookupLengthOrCount(
string propertyName, TypeSymbol receiverType, LookupResult lookupResult,
[NotNullWhen(true)] out PropertySymbol? valid, ref HashSet<DiagnosticInfo>? useSiteDiagnostics)
{
LookupMembersInType(
lookupResult,
receiverType,
propertyName,
arity: 0,
basesBeingResolved: null,
LookupOptions.Default,
originalBinder: this,
diagnose: false,
useSiteDiagnostics: ref useSiteDiagnostics);

bool tryLookupLengthOrCount(string propertyName, out PropertySymbol valid)
if (lookupResult.IsSingleViable &&
lookupResult.Symbols[0] is PropertySymbol property &&
property.GetOwnOrInheritedGetMethod()?.OriginalDefinition is MethodSymbol getMethod &&
getMethod.ReturnType.SpecialType == SpecialType.System_Int32 &&
getMethod.RefKind == RefKind.None &&
!getMethod.IsStatic &&
IsAccessible(getMethod, ref useSiteDiagnostics))
{
LookupMembersInType(
lookupResult,
receiverType,
propertyName,
arity: 0,
basesBeingResolved: null,
LookupOptions.Default,
originalBinder: this,
diagnose: false,
useSiteDiagnostics: ref useSiteDiagnostics);

if (lookupResult.IsSingleViable &&
lookupResult.Symbols[0] is PropertySymbol property &&
property.GetOwnOrInheritedGetMethod()?.OriginalDefinition is MethodSymbol getMethod &&
getMethod.ReturnType.SpecialType == SpecialType.System_Int32 &&
getMethod.RefKind == RefKind.None &&
!getMethod.IsStatic &&
IsAccessible(getMethod, ref useSiteDiagnostics))
{
lookupResult.Clear();
useSiteDiagnostics = null;
valid = property;
return true;
}
lookupResult.Clear();
useSiteDiagnostics = null;
valid = null;
return false;
valid = property;
return true;
}
lookupResult.Clear();
useSiteDiagnostics = null;
valid = null;
return false;
}
#nullable restore

private ErrorPropertySymbol CreateErrorPropertySymbol(ImmutableArray<PropertySymbol> propertyGroup)
{
Expand Down
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