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Enable indexing operations on objects that implement ITuple (PowerS…
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…hell#7633)

This change enables index operations on objects that implement `ITuple` and other interfaces that have `DefaultMemberAttribute` declared, including slicing and negative indexing.
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@SeeminglyScience @daxian-dbw
SeeminglyScience authored and daxian-dbw committed Aug 30, 2018
1 parent eb0c1d5 commit 5c2faaf
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Showing 2 changed files with 73 additions and 15 deletions.
72 changes: 57 additions & 15 deletions src/System.Management.Automation/engine/runtime/Binding/Binders.cs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3928,6 +3928,8 @@ public override DynamicMetaObject FallbackGetIndex(DynamicMetaObject target, Dyn
return GetIndexArray(target, indexes, errorSuggestion).WriteToDebugLog(this);
}

var defaultMember = target.LimitType.GetCustomAttributes<DefaultMemberAttribute>(true).FirstOrDefault();
PropertyInfo lengthProperty = null;
foreach (var i in target.LimitType.GetInterfaces())
{
if (i.IsGenericType && i.GetGenericTypeDefinition() == typeof(IDictionary<,>))
Expand All @@ -3938,12 +3940,23 @@ public override DynamicMetaObject FallbackGetIndex(DynamicMetaObject target, Dyn
return result.WriteToDebugLog(this);
}
}

// If the type explicitly implements an indexer specified by an interface
// then the DefaultMemberAttribute will not carry over to the implementation.
// This check will catch those cases.
if (defaultMember == null)
{
defaultMember = i.GetCustomAttributes<DefaultMemberAttribute>(inherit: false).FirstOrDefault();
if (defaultMember != null)
{
lengthProperty = i.GetProperty("Count") ?? i.GetProperty("Length");
}
}
}

var defaultMember = target.LimitType.GetCustomAttributes<DefaultMemberAttribute>(true).FirstOrDefault();
if (defaultMember != null)
{
return InvokeIndexer(target, indexes, errorSuggestion, defaultMember.MemberName).WriteToDebugLog(this);
return InvokeIndexer(target, indexes, errorSuggestion, defaultMember.MemberName, lengthProperty).WriteToDebugLog(this);
}

return errorSuggestion ?? CannotIndexTarget(target, indexes).WriteToDebugLog(this);
Expand Down Expand Up @@ -4027,9 +4040,29 @@ private DynamicMetaObject GetIndexDictionary(DynamicMetaObject target,
bindingRestrictions);
}

internal static bool CanIndexFromEndWithNegativeIndex(DynamicMetaObject target)
{
var limitType = target.LimitType;
internal static bool CanIndexFromEndWithNegativeIndex(
DynamicMetaObject target,
MethodInfo indexer,
ParameterInfo[] getterParams)
{
// PowerShell supports negative indexing for types that meet the following criteria:
// - Indexer method accepts one parameter that is typed as int
// - The int parameter is not a type argument from a constructed generic type
// (this is to exclude indexers for types that could use a negative index as
// a valid key like System.Linq.ILookup)
// - Declares a "Count" or "Length" property
// - Does not inherit from IDictionary<> as that is handled earlier in the binder
// For those types, generate special code to check for negative indices, otherwise just generate
// the call. Before we test for the above criteria explicitly, we will determine if the
// target is of a type known to be compatible. This is done to avoid the call to Module.ResolveMethod
// when possible.

if (getterParams.Length != 1 || getterParams[0].ParameterType != typeof(int))
{
return false;
}

Type limitType = target.LimitType;
if (limitType.IsArray || limitType == typeof(string) || limitType == typeof(StringBuilder))
{
return true;
Expand All @@ -4046,7 +4079,16 @@ internal static bool CanIndexFromEndWithNegativeIndex(DynamicMetaObject target)
}

// target implements IList<T>?
return limitType.GetInterfaces().Any(i => i.IsGenericType && i.GetGenericTypeDefinition() == typeof(IList<>));
if (limitType.GetInterfaces().Any(i => i.IsGenericType && i.GetGenericTypeDefinition() == typeof(IList<>)))
{
return true;
}

// Get the base method definition of the indexer to determine if the int
// parameter is a generic type parameter. Module.ResolveMethod is used
// because the indexer could be a method from a constructed generic type.
MethodBase baseMethod = indexer.Module.ResolveMethod(indexer.MetadataToken);
return !baseMethod.GetParameters()[0].ParameterType.IsGenericParameter;
}

private DynamicMetaObject IndexWithNegativeChecks(
Expand All @@ -4055,8 +4097,6 @@ private DynamicMetaObject IndexWithNegativeChecks(
PropertyInfo lengthProperty,
Func<Expression, Expression, Expression> generateIndexOperation)
{
Diagnostics.Assert(CanIndexFromEndWithNegativeIndex(target), "Unexpected target type to index from end with negative value");

// Generate:
// try {
// len = obj.Length
Expand Down Expand Up @@ -4197,7 +4237,8 @@ private DynamicMetaObject GetIndexMultiDimensionArray(DynamicMetaObject target,
private DynamicMetaObject InvokeIndexer(DynamicMetaObject target,
DynamicMetaObject[] indexes,
DynamicMetaObject errorSuggestion,
string methodName)
string methodName,
PropertyInfo lengthProperty)
{
MethodInfo getter = PSInvokeMemberBinder.FindBestMethod(target, indexes, "get_" + methodName, false, _constraints);

Expand Down Expand Up @@ -4258,13 +4299,14 @@ private DynamicMetaObject InvokeIndexer(DynamicMetaObject target,
target.CombineRestrictions(indexes));
}

if (getterParams.Length == 1 && getterParams[0].ParameterType == typeof(int) && CanIndexFromEndWithNegativeIndex(target))
if (CanIndexFromEndWithNegativeIndex(target, getter, getterParams))
{
// PowerShell supports negative indexing for some types (specifically, types implementing IList or IList<T>).
// For those types, generate special code to check for negative indices, otherwise just generate
// the call.
PropertyInfo lengthProperty = target.LimitType.GetProperty("Count") ??
target.LimitType.GetProperty("Length"); // for string
if (lengthProperty == null)
{
// Count is declared by most supported types, Length will catch some edge cases like strings.
lengthProperty = target.LimitType.GetProperty("Count") ??
target.LimitType.GetProperty("Length");
}

if (lengthProperty != null)
{
Expand Down
16 changes: 16 additions & 0 deletions test/powershell/Language/Scripting/Indexer.Tests.ps1
View file
Original file line number Diff line number Diff line change
Expand Up @@ -24,4 +24,20 @@ Describe 'Tests for indexers' -Tags "CI" {
$service = Get-WmiObject -List -Amended Win32_Service
$service.Properties["Hello There"] | Should -BeNullOrEmpty
}

It 'ITuple implementations can be indexed' {
$tuple = [Tuple]::Create(10, 'Hello')
$tuple[0] | Should -Be 10
$tuple[1] | Should -BeExactly 'Hello'
}

It 'ITuple objects can be spliced' {
$tuple = [Tuple]::Create(10, 'Hello')
$tuple[0..1] | Should -Be @(10, 'Hello')
}

It 'Index of -1 should return the last item for ITuple objects' {
$tuple = [Tuple]::Create(10, 'Hello')
$tuple[-1] | Should -BeExactly 'Hello'
}
}

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