expose value of constant integers in module reflection (#6367)

* Expose value of constant integers in module reflection

This commit adds `VariableReflection::getDefaultValueInt` to get the value of a variable if it is a compile-time constant integer.
TODO: currently it works only if the initializer expression is an integer literal, references to other constant values are not handled.

* Update VarDecl folded constant value during DeclBodyVisitor

Constant folding for integer values is already done internally by _validateCircularVarDefinition, this just reuses the result.

* Address review comments & formatting

* Formatting

---------

Co-authored-by: Yong He <yonghe@outlook.com>

3 files changed, 30 insertions, 5 deletions

diff --git a/source/slang/slang-check-decl.cpp b/source/slang/slang-check-decl.cpp
index 0c42817c8..1659a161b 100644
--- a/source/slang/slang-check-decl.cpp
+++ b/source/slang/slang-check-decl.cpp
@@ -1430,7 +1430,7 @@ bool SemanticsVisitor::shouldSkipChecking(Decl* decl, DeclCheckState state)
     return false;
 }
 
-void SemanticsVisitor::_validateCircularVarDefinition(VarDeclBase* varDecl)
+IntVal* SemanticsVisitor::_validateCircularVarDefinition(VarDeclBase* varDecl)
 {
     // The easiest way to test if the declaration is circular is to
     // validate it as a constant.
@@ -1444,8 +1444,11 @@ void SemanticsVisitor::_validateCircularVarDefinition(VarDeclBase* varDecl)
     //
     //
     if (!isScalarIntegerType(varDecl->type))
-        return;
-    tryConstantFoldDeclRef(DeclRef<VarDeclBase>(varDecl), ConstantFoldingKind::LinkTime, nullptr);
+        return nullptr;
+    return tryConstantFoldDeclRef(
+        DeclRef<VarDeclBase>(varDecl),
+        ConstantFoldingKind::LinkTime,
+        nullptr);
 }
 
 void SemanticsDeclModifiersVisitor::visitStructDecl(StructDecl* structDecl)
@@ -2350,7 +2353,13 @@ void SemanticsDeclBodyVisitor::checkVarDeclCommon(VarDeclBase* varDecl)
         // a constant with a circular definition.
         //
         varDecl->setCheckState(DeclCheckState::DefinitionChecked);
-        _validateCircularVarDefinition(varDecl);
+
+        // Update constant value
+        //
+        if (!varDecl->val)
+        {
+            varDecl->val = _validateCircularVarDefinition(varDecl);
+        }
     }
     else
     {
diff --git a/source/slang/slang-check-impl.h b/source/slang/slang-check-impl.h
index edb199299..ba3792af7 100644
--- a/source/slang/slang-check-impl.h
+++ b/source/slang/slang-check-impl.h
@@ -1496,7 +1496,7 @@ public:
     /// by calling a function that indirectly reads the variable) will be allowed and then
     /// exhibit undefined behavior at runtime.
     ///
-    void _validateCircularVarDefinition(VarDeclBase* varDecl);
+    IntVal* _validateCircularVarDefinition(VarDeclBase* varDecl);
 
     bool shouldSkipChecking(Decl* decl, DeclCheckState state);
 
diff --git a/source/slang/slang-reflection-api.cpp b/source/slang/slang-reflection-api.cpp
index 52047a751..9295bfdf6 100644
--- a/source/slang/slang-reflection-api.cpp
+++ b/source/slang/slang-reflection-api.cpp
@@ -3164,6 +3164,22 @@ SLANG_API bool spReflectionVariable_HasDefaultValue(SlangReflectionVariable* inV
     return false;
 }
 
+SLANG_API SlangResult
+spReflectionVariable_GetDefaultValueInt(SlangReflectionVariable* inVar, int64_t* rs)
+{
+    auto decl = convert(inVar).getDecl();
+    if (auto varDecl = as<VarDeclBase>(decl))
+    {
+        if (auto constantVal = as<ConstantIntVal>(varDecl->val))
+        {
+            *rs = constantVal->getValue();
+            return 0;
+        }
+    }
+
+    return SLANG_E_INVALID_ARG;
+}
+
 SLANG_API SlangReflectionGeneric* spReflectionVariable_GetGenericContainer(
     SlangReflectionVariable* var)
 {