Fix type union logic in generic type inference. (#3852)

6 files changed, 38 insertions, 14 deletions

diff --git a/source/slang/slang-ast-support-types.h b/source/slang/slang-ast-support-types.h
index 196a1d002..93fc3365d 100644
--- a/source/slang/slang-ast-support-types.h
+++ b/source/slang/slang-ast-support-types.h
@@ -140,12 +140,15 @@ namespace Slang
         // Cost of converting a pointer to bool
         kConversionCost_PtrToBool = 400,
 
+        // Cost of converting an integer to int16_t
+        kConversionCost_IntegerTruncate = 450,
+
+        // Cost of converting an integer to a half type
+        kConversionCost_IntegerToHalfConversion = 500,
+
         // Default case (usable for user-defined conversions)
         kConversionCost_Default = 500,
 
-        // Cost of converting an integer to int16_t
-        kConversionCost_IntegerTruncate = 700,
-
         // Catch-all for conversions that should be discouraged
         // (i.e., that really shouldn't be made implicitly)
         //
diff --git a/source/slang/slang-check-constraint.cpp b/source/slang/slang-check-constraint.cpp
index 97dbbcfa3..6a9b0adfa 100644
--- a/source/slang/slang-check-constraint.cpp
+++ b/source/slang/slang-check-constraint.cpp
@@ -105,6 +105,7 @@ namespace Slang
         // through types `X` that are also builtin scalar types.
         //
         Type* bestType = nullptr;
+        ConversionCost bestCost = kConversionCost_Explicit;
         if(auto basicType = dynamicCast<BasicExpressionType>(type))
         {
             for(Int baseTypeFlavorIndex = 0; baseTypeFlavorIndex < Int(BaseType::CountOf); baseTypeFlavorIndex++)
@@ -123,7 +124,8 @@ namespace Slang
                     continue;
 
                 // We only want to consider types where we can implicitly convert from `type`
-                if(!canConvertImplicitly(candidateType, type))
+                auto conversionCost = getConversionCost(candidateType, type);
+                if(!canConvertImplicitly(conversionCost))
                     continue;
 
                 // At this point, we have a candidate type that is usable.
@@ -139,18 +141,16 @@ namespace Slang
                     // Otherwise, we want to pick the "better" type between `candidateType`
                     // and `bestType`.
                     //
-                    // We are going to be a bit loose here, and not worry about the
-                    // case where conversion is allowed in both directions.
+                    // The candidate type that has lower conversion cost from `type` is better.
                     //
-                    // TODO: make this completely robust.
-                    //
-                    if(canConvertImplicitly(bestType, candidateType))
+                    if(conversionCost < bestCost)
                     {
                         // Our candidate can convert to the current "best" type, so
                         // it is logically a more specific type that satisfies our
                         // constraints, therefore we should keep it.
                         //
                         bestType = candidateType;
+                        bestCost = conversionCost;
                     }
                 }
             }
diff --git a/source/slang/slang-check-conversion.cpp b/source/slang/slang-check-conversion.cpp
index aeb964cc9..e55a88077 100644
--- a/source/slang/slang-check-conversion.cpp
+++ b/source/slang/slang-check-conversion.cpp
@@ -1389,13 +1389,22 @@ namespace Slang
     }
 
     bool SemanticsVisitor::canConvertImplicitly(
+        ConversionCost conversionCost)
+    {
+        // Is the conversion cheap enough to be done implicitly?
+        if (conversionCost >= kConversionCost_GeneralConversion)
+            return false;
+        return true;
+    }
+
+    bool SemanticsVisitor::canConvertImplicitly(
         Type* toType,
         QualType fromType)
     {
         auto conversionCost = getConversionCost(toType, fromType);
 
         // Is the conversion cheap enough to be done implicitly?
-        if (conversionCost >= kConversionCost_GeneralConversion)
+        if (canConvertImplicitly(conversionCost))
             return false;
 
         return true;
diff --git a/source/slang/slang-check-impl.h b/source/slang/slang-check-impl.h
index a3ecc28b4..945618f36 100644
--- a/source/slang/slang-check-impl.h
+++ b/source/slang/slang-check-impl.h
@@ -2077,6 +2077,9 @@ namespace Slang
             Type* toType,
             QualType fromType);
 
+        bool canConvertImplicitly(
+            ConversionCost cost);
+
         ConversionCost getConversionCost(Type* toType, QualType fromType);
 
         Type* _tryJoinTypeWithInterface(
diff --git a/source/slang/slang-stdlib.cpp b/source/slang/slang-stdlib.cpp
index 2bc24d8ec..3c8b48e00 100644
--- a/source/slang/slang-stdlib.cpp
+++ b/source/slang/slang-stdlib.cpp
@@ -222,7 +222,12 @@ namespace Slang
         {
             return kConversionCost_IntegerToFloatConversion;
         }
-
+        else if (toInfo.conversionKind == kBaseTypeConversionKind_Float
+            && toInfo.conversionRank >= kBaseTypeConversionRank_Int16
+            && fromInfo.conversionRank >= kBaseTypeConversionRank_Int8)
+        {
+            return kConversionCost_IntegerToHalfConversion;
+        }
         // All other cases are considered as "general" conversions,
         // where we don't consider any one conversion better than
         // any others.
diff --git a/source/slang/slang.natvis b/source/slang/slang.natvis
index b1b52bc5c..c86faa065 100644
--- a/source/slang/slang.natvis
+++ b/source/slang/slang.natvis
@@ -439,7 +439,6 @@
             <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::ResourceType">(Slang::ResourceType*)&amp;astNodeType</ExpandedItem>
             <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::TextureTypeBase">(Slang::TextureTypeBase*)&amp;astNodeType</ExpandedItem>
             <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::TextureType">(Slang::TextureType*)&amp;astNodeType</ExpandedItem>
-            <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::TextureSamplerType">(Slang::TextureSamplerType*)&amp;astNodeType</ExpandedItem>
             <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::GLSLImageType">(Slang::GLSLImageType*)&amp;astNodeType</ExpandedItem>
             <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::SamplerStateType">(Slang::SamplerStateType*)&amp;astNodeType</ExpandedItem>
             <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::BuiltinGenericType">(Slang::BuiltinGenericType*)&amp;astNodeType</ExpandedItem>
@@ -504,6 +503,13 @@
             <Item Name="[Raw View]">(Slang::Type*)this,!</Item>
         </Expand>
     </Type>
+    <Type Name="Slang::DirectDeclRef">
+        <DisplayString>DirectDeclRef{(Decl*)m_operands.m_buffer[0].values.nodeOperand}</DisplayString>
+        <Expand>
+            <ExpandedItem>(Decl*)m_operands.m_buffer[0].values.nodeOperand</ExpandedItem>
+
+        </Expand>
+    </Type>
     <Type Name="Slang::SubstitutionSet">
         <DisplayString>SubstitutionSet{declRef,en}</DisplayString>
         <Expand>
@@ -581,7 +587,6 @@
         <DisplayString Condition="astNodeType == Slang::ASTNodeType::ResourceType">{*(Slang::ResourceType*)this}</DisplayString>
         <DisplayString Condition="astNodeType == Slang::ASTNodeType::TextureTypeBase">{*(Slang::TextureTypeBase*)this}</DisplayString>
         <DisplayString Condition="astNodeType == Slang::ASTNodeType::TextureType">{*(Slang::TextureType*)this}</DisplayString>
-        <DisplayString Condition="astNodeType == Slang::ASTNodeType::TextureSamplerType">{*(Slang::TextureSamplerType*)this}</DisplayString>
         <DisplayString Condition="astNodeType == Slang::ASTNodeType::GLSLImageType">{*(Slang::GLSLImageType*)this}</DisplayString>
         <DisplayString Condition="astNodeType == Slang::ASTNodeType::SamplerStateType">{*(Slang::SamplerStateType*)this}</DisplayString>
         <DisplayString Condition="astNodeType == Slang::ASTNodeType::BuiltinGenericType">{*(Slang::BuiltinGenericType*)this}</DisplayString>
@@ -666,7 +671,6 @@
             <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::ResourceType">(Slang::ResourceType*)&amp;astNodeType</ExpandedItem>
             <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::TextureTypeBase">(Slang::TextureTypeBase*)&amp;astNodeType</ExpandedItem>
             <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::TextureType">(Slang::TextureType*)&amp;astNodeType</ExpandedItem>
-            <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::TextureSamplerType">(Slang::TextureSamplerType*)&amp;astNodeType</ExpandedItem>
             <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::GLSLImageType">(Slang::GLSLImageType*)&amp;astNodeType</ExpandedItem>
             <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::SamplerStateType">(Slang::SamplerStateType*)&amp;astNodeType</ExpandedItem>
             <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::BuiltinGenericType">(Slang::BuiltinGenericType*)&amp;astNodeType</ExpandedItem>