Capture some of the invariants around InputType/NarrowedType in patterns

src/Compilers/CSharp/Portable/BoundTree/BoundBinaryPattern.cs

@@ -0,0 +1,28 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics;
+
+namespace Microsoft.CodeAnalysis.CSharp
+{
+    internal partial class BoundBinaryPattern
+    {
+        private partial void Validate()
+        {
+            Debug.Assert(Left.InputType.Equals(InputType, TypeCompareKind.AllIgnoreOptions));
+
+            if (Disjunction)
+            {
+                Debug.Assert(Right.InputType.Equals(InputType, TypeCompareKind.AllIgnoreOptions));
+                // Is it worth asserting that NarrowedType is either the InputType, or or the NarrowedType
+                // of one of the leaves in the Disjunction hierarchy?
+            }
+            else
+            {
+                Debug.Assert(Right.InputType.Equals(Left.NarrowedType, TypeCompareKind.AllIgnoreOptions));
+                Debug.Assert(NarrowedType.Equals(Right.NarrowedType, TypeCompareKind.AllIgnoreOptions));
+            }
+        }
+    }
+}

src/Compilers/CSharp/Portable/BoundTree/BoundConstantPattern.cs

@@ -0,0 +1,17 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics;
+
+namespace Microsoft.CodeAnalysis.CSharp
+{
+    internal partial class BoundConstantPattern
+    {
+        private partial void Validate()
+        {
+            Debug.Assert(NarrowedType.Equals(InputType, TypeCompareKind.AllIgnoreOptions) ||
+                         NarrowedType.Equals(Value.Type, TypeCompareKind.AllIgnoreOptions));
+        }
+    }
+}

src/Compilers/CSharp/Portable/BoundTree/BoundDeclarationPattern.cs

@@ -0,0 +1,18 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics;
+
+namespace Microsoft.CodeAnalysis.CSharp
+{
+    internal partial class BoundDeclarationPattern
+    {
+        private partial void Validate()
+        {
+            Debug.Assert(DeclaredType is null ?
+                         NarrowedType.Equals(InputType, TypeCompareKind.AllIgnoreOptions) :
+                         NarrowedType.Equals(DeclaredType.Type, TypeCompareKind.AllIgnoreOptions));
+        }
+    }
+}

src/Compilers/CSharp/Portable/BoundTree/BoundDiscardPattern.cs

@@ -0,0 +1,17 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics;
+
+namespace Microsoft.CodeAnalysis.CSharp
+{
+    internal partial class BoundDiscardPattern
+    {
+        private partial void Validate()
+        {
+            Debug.Assert(NarrowedType.Equals(InputType, TypeCompareKind.AllIgnoreOptions));
+        }
+    }
+}
+

src/Compilers/CSharp/Portable/BoundTree/BoundITuplePattern.cs

@@ -0,0 +1,17 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics;
+using Microsoft.CodeAnalysis.CSharp.Symbols;
+
+namespace Microsoft.CodeAnalysis.CSharp
+{
+    internal partial class BoundITuplePattern
+    {
+        private partial void Validate()
+        {
+            Debug.Assert(NarrowedType.IsCompilerServicesTopLevelType() && NarrowedType.Name == "ITuple");
+        }
+    }
+}

src/Compilers/CSharp/Portable/BoundTree/BoundListPattern.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Diagnostics;
+using Microsoft.CodeAnalysis.CSharp.Symbols;
 
 namespace Microsoft.CodeAnalysis.CSharp
 {
@@ -13,6 +14,7 @@ private partial void Validate()
             Debug.Assert(LengthAccess is null or BoundPropertyAccess or BoundBadExpression);
             Debug.Assert(IndexerAccess is null or BoundIndexerAccess or BoundImplicitIndexerAccess or BoundArrayAccess or BoundBadExpression or BoundDynamicIndexerAccess);
             Debug.Assert(Binder.GetIndexerOrImplicitIndexerSymbol(IndexerAccess) is var _);
+            Debug.Assert(NarrowedType.Equals(InputType.StrippedType(), TypeCompareKind.AllIgnoreOptions));
         }
     }
 }

src/Compilers/CSharp/Portable/BoundTree/BoundNegatedPattern.cs

@@ -0,0 +1,17 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics;
+
+namespace Microsoft.CodeAnalysis.CSharp
+{
+    internal partial class BoundNegatedPattern
+    {
+        private partial void Validate()
+        {
+            Debug.Assert(NarrowedType.Equals(InputType, TypeCompareKind.AllIgnoreOptions));
+            Debug.Assert(Negated.InputType.Equals(InputType, TypeCompareKind.AllIgnoreOptions));
+        }
+    }
+}

src/Compilers/CSharp/Portable/BoundTree/BoundNodes.xml

@@ -2389,12 +2389,14 @@
     <Field Name="NarrowedType" Type="TypeSymbol" Null="disallow"/>
   </AbstractNode>
 
-  <Node Name="BoundConstantPattern" Base="BoundPattern">
+  <!-- NarrowedType is either the InputType, or the Value.Type -->
+  <Node Name="BoundConstantPattern" Base="BoundPattern" HasValidate="true">
     <Field Name="Value" Type="BoundExpression"/>
     <Field Name="ConstantValue" Type="ConstantValue" Null="disallow"/>
   </Node>
 
-  <Node Name="BoundDiscardPattern" Base="BoundPattern">
+  <!-- NarrowedType is always the InputType -->
+  <Node Name="BoundDiscardPattern" Base="BoundPattern" HasValidate="true">
   </Node>
 
   <AbstractNode Name="BoundObjectPattern" Base="BoundPattern">
@@ -2411,19 +2413,22 @@
     <Field Name="VariableAccess" Type="BoundExpression?"/>
   </AbstractNode>
 
-  <Node Name="BoundDeclarationPattern" Base="BoundObjectPattern">
+  <!-- NarrowedType is the DeclaredType if given, or an InputType -->
+  <Node Name="BoundDeclarationPattern" Base="BoundObjectPattern" HasValidate="true">
     <Field Name="DeclaredType" Type="BoundTypeExpression" Null="disallow"/>
     <Field Name="IsVar" Type="bool"/>
   </Node>
 
-  <Node Name="BoundRecursivePattern" Base="BoundObjectPattern">
+  <!-- NarrowedType is the DeclaredType if given, or an InputType, or its underlying type when the InputType is a Nullable of T -->
+  <Node Name="BoundRecursivePattern" Base="BoundObjectPattern" HasValidate="true">
     <Field Name="DeclaredType" Type="BoundTypeExpression?"/>
     <Field Name="DeconstructMethod" Type="MethodSymbol?"/>
     <Field Name="Deconstruction" Type="ImmutableArray&lt;BoundPositionalSubpattern&gt;" Null="allow"/>
     <Field Name="Properties" Type="ImmutableArray&lt;BoundPropertySubpattern&gt;" Null="allow"/>
     <Field Name="IsExplicitNotNullTest" Type="bool"/>
   </Node>
 
+  <!-- NarrowedType is always an InputType, or its underlying type when the InputType is a Nullable of T -->
   <Node Name="BoundListPattern" Base="BoundObjectPattern" HasValidate="true">
     <Field Name="Subpatterns" Type="ImmutableArray&lt;BoundPattern&gt;" Null="disallow"/>
     <Field Name="HasSlice" Type="bool"/>
@@ -2442,6 +2447,7 @@
     <Field Name="ArgumentPlaceholder" Type="BoundListPatternIndexPlaceholder?" SkipInVisitor="true"/>
   </Node>
 
+  <!-- NarrowedType is always the InputType -->
   <Node Name="BoundSlicePattern" Base="BoundPattern" HasValidate="true">
     <Field Name="Pattern" Type="BoundPattern?"/>
 
@@ -2458,7 +2464,8 @@
     <Field Name="ArgumentPlaceholder" Type="BoundSlicePatternRangePlaceholder?" SkipInVisitor="true"/>
   </Node>
 
-  <Node Name="BoundITuplePattern" Base="BoundPattern">
+  <!-- Narrowed type is always System.Runtime.CompilerServices.ITuple -->
+  <Node Name="BoundITuplePattern" Base="BoundPattern" HasValidate="true">
     <Field Name="GetLengthMethod" Type="MethodSymbol" Null="disallow"/>
     <Field Name="GetItemMethod" Type="MethodSymbol" Null="disallow"/>
     <Field Name="Subpatterns" Type="ImmutableArray&lt;BoundPositionalSubpattern&gt;" Null="disallow"/>
@@ -2482,22 +2489,37 @@
     <Field Name="Type" Type="TypeSymbol"/>
   </Node>
 
-  <Node Name="BoundTypePattern" Base="BoundPattern">
+  <!-- NarrowedType is always the DeclaredType -->
+  <Node Name="BoundTypePattern" Base="BoundPattern" HasValidate="true">
     <Field Name="DeclaredType" Type="BoundTypeExpression"/>
     <Field Name="IsExplicitNotNullTest" Type="bool"/>
   </Node>
 
-  <Node Name="BoundBinaryPattern" Base="BoundPattern">
+  <!-- 
+       For Disjunction
+           NarrowedType is the least specific NarrowedType type across all leafs of constituent disjunctions, or
+                        the InputType if one cannot be determined
+           Left.InputType is the InputType 
+           Right.InputType is the InputType 
+
+       For Conjunction
+           NarrowedType is the Right.NarrowedType
+           Left.InputType is the InputType 
+           Right.InputType is the Left.NarrowedType 
+  -->
+  <Node Name="BoundBinaryPattern" Base="BoundPattern" HasValidate="true">
     <Field Name="Disjunction" Type="bool"/>
     <Field Name="Left" Type="BoundPattern"/>
     <Field Name="Right" Type="BoundPattern"/>
   </Node>
 
-  <Node Name="BoundNegatedPattern" Base="BoundPattern">
+  <!-- NarrowedType is always the InputType -->
+  <Node Name="BoundNegatedPattern" Base="BoundPattern" HasValidate="true">
     <Field Name="Negated" Type="BoundPattern"/>
   </Node>
 
-  <Node Name="BoundRelationalPattern" Base="BoundPattern">
+  <!-- NarrowedType is either the InputType, or the Value.Type -->
+  <Node Name="BoundRelationalPattern" Base="BoundPattern" HasValidate="true">
     <Field Name="Relation" Type="BinaryOperatorKind"/>
     <Field Name="Value" Type="BoundExpression"/>
     <Field Name="ConstantValue" Type="ConstantValue" Null="disallow"/>

src/Compilers/CSharp/Portable/BoundTree/BoundRecursivePattern.cs

@@ -0,0 +1,19 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics;
+using Microsoft.CodeAnalysis.CSharp.Symbols;
+
+namespace Microsoft.CodeAnalysis.CSharp
+{
+    internal partial class BoundRecursivePattern
+    {
+        private partial void Validate()
+        {
+            Debug.Assert(DeclaredType is null ?
+                         NarrowedType.Equals(InputType.StrippedType(), TypeCompareKind.AllIgnoreOptions) :
+                         NarrowedType.Equals(DeclaredType.Type, TypeCompareKind.AllIgnoreOptions));
+        }
+    }
+}

src/Compilers/CSharp/Portable/BoundTree/BoundRelationalPattern.cs

@@ -0,0 +1,17 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics;
+
+namespace Microsoft.CodeAnalysis.CSharp
+{
+    internal partial class BoundRelationalPattern
+    {
+        private partial void Validate()
+        {
+            Debug.Assert(NarrowedType.Equals(InputType, TypeCompareKind.AllIgnoreOptions) ||
+                         NarrowedType.Equals(Value.Type, TypeCompareKind.AllIgnoreOptions));
+        }
+    }
+}

src/Compilers/CSharp/Portable/BoundTree/BoundSlicePattern.cs

@@ -12,6 +12,7 @@ private partial void Validate()
         {
             Debug.Assert(IndexerAccess is null or BoundIndexerAccess or BoundImplicitIndexerAccess or BoundArrayAccess or BoundBadExpression or BoundDynamicIndexerAccess);
             Debug.Assert(Binder.GetIndexerOrImplicitIndexerSymbol(IndexerAccess) is var _);
+            Debug.Assert(NarrowedType.Equals(InputType, TypeCompareKind.AllIgnoreOptions));
         }
     }
 }

src/Compilers/CSharp/Portable/BoundTree/BoundTypePattern.cs

@@ -0,0 +1,16 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics;
+
+namespace Microsoft.CodeAnalysis.CSharp
+{
+    internal partial class BoundTypePattern
+    {
+        private partial void Validate()
+        {
+            Debug.Assert(NarrowedType.Equals(DeclaredType.Type, TypeCompareKind.AllIgnoreOptions));
+        }
+    }
+}