Allow implicitly casting enum types to bool. (shader-slang#4739)

* Allow implicitly casting enum types to bool.

* Fix.

Author: csyonghe

source/slang/core.meta.slang

@@ -751,6 +751,14 @@ extension bool : IRangedValue
     __intrinsic_op($(kIROp_CastPtrToBool))
     __init(Ptr<T> ptr);
 
+    __generic<T : __EnumType>
+    __implicit_conversion($(kConversionCost_IntegerTruncate))
+    [__unsafeForceInlineEarly]
+    __init(T v)
+    {
+        return __slang_noop_cast<T.__Tag>(v) != __intCast<T.__Tag>(0);
+    }
+
     static const bool maxValue = true;
     static const bool minValue = false;
 }

tests/language-feature/enums/implicit-cast-to-bool.slang

@@ -0,0 +1,43 @@
+// Test enums can be implicitly casted to bool. 
+
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK): -shaderobj
+
+[Flags]
+enum BitFlags
+{
+    One,
+    Two,
+    Three
+}
+
+int test<let n : bool>()
+{
+    return n;
+}
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<int> outputBuffer;
+
+[numthreads(4, 1, 1)]
+void computeMain(int3 dispatchThreadID : SV_DispatchThreadID)
+{
+    BitFlags x = BitFlags.One | BitFlags.Two;
+    if (x & BitFlags.One)
+        outputBuffer[0] = 1;
+    else
+        outputBuffer[0] = 0;
+    if (x & BitFlags.Three)
+        outputBuffer[1] = 1;
+    else
+        outputBuffer[1] = 0;
+    if (x & BitFlags.Two)
+        outputBuffer[2] = 1;
+    else
+        outputBuffer[2] = 0;
+
+    outputBuffer[3] = test<BitFlags.One & BitFlags.One>();
+    // CHECK: 1
+    // CHECK: 0
+    // CHECK: 1
+    // CHECK: 1
+}