Fix the issue in resolving the overload functions (shader-slang#5060)

source/slang/slang-check-overload.cpp

@@ -1,4 +1,5 @@
 // slang-check-overload.cpp
+#include "slang-ast-base.h"
 #include "slang-check-impl.h"
 
 #include "slang-lookup.h"
@@ -1199,6 +1200,28 @@ namespace Slang
         return parent;
     }
 
+    void countDistanceToGloablScope(DeclRef<Slang::Decl> const& leftDecl,
+                                    DeclRef<Slang::Decl> const& rightDecl,
+                                    int& leftDistance, int& rightDistance)
+    {
+        leftDistance = 0;
+        rightDistance = 0;
+
+        DeclRef<Decl> decl = leftDecl;
+        while(decl)
+        {
+            leftDistance++;
+            decl = decl.getParent();
+        }
+
+        decl = rightDecl;
+        while(decl)
+        {
+            rightDistance++;
+            decl = decl.getParent();
+        }
+    }
+
     // Returns -1 if left is preferred, 1 if right is preferred, and 0 if they are equal.
     //
     int SemanticsVisitor::CompareLookupResultItems(
@@ -1324,6 +1347,24 @@ namespace Slang
             }
         }
 
+        // We need to consider the distance of the declarations to the global scope to resolve this case:
+        //      float f(float x);
+        //      struct S
+        //      {
+        //          float f(float x);
+        //          float g(float y) { return f(y); }   // will call S::f() instead of ::f()
+        //      }
+        // We don't need to know the call site of 'f(y)', but only need to count the two candidates' distance to the global scope,
+        // because this function will only choose the valid candidates. So if there is situation like this:
+        //  void main() {  S s; s.f(1.0);} or
+        //  struct T { float g(y) { f(y); } }, there won't be ambiguity.
+        //  So we just need to count which declaration is farther from the global scope and favor the farther one.
+        int leftDistance = 0;
+        int rightDistance = 0;
+        countDistanceToGloablScope(left.declRef, right.declRef, leftDistance, rightDistance);
+        if (leftDistance != rightDistance)
+            return leftDistance > rightDistance ? -1 : 1;
+
         // TODO: We should generalize above rules such that in a tie a declaration
         // A::m is better than B::m when all other factors are equal and
         // A inherits from B.

tests/bugs/overload-ambiguous.slang

@@ -0,0 +1,48 @@
+// https://github.com/shader-slang/slang/issues/4476
+
+//TEST(compute):COMPARE_COMPUTE_EX(filecheck-buffer=BUF):-cuda -compute -shaderobj
+//TEST(compute):COMPARE_COMPUTE_EX(filecheck-buffer=BUF):-cpu -compute -shaderobj
+//TEST(compute):COMPARE_COMPUTE_EX(filecheck-buffer=BUF):-slang -compute -shaderobj
+//TEST(compute):COMPARE_COMPUTE_EX(filecheck-buffer=BUF):-slang -compute -dx12 -shaderobj
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX(filecheck-buffer=BUF):-vk -compute -shaderobj
+
+//TEST_INPUT:ubuffer(data=[0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<uint> outputBuffer;
+
+
+uint getData()
+{
+    return 1u;
+}
+
+struct DataObtainer
+{
+    uint data;
+    uint getData()
+    {
+        return data;
+    }
+
+    uint getValue()
+    {
+        return getData(); // will call DataObtainer::getData()
+    }
+
+    uint getValue2()
+    {
+        return ::getData(); // will call global getData()
+    }
+}
+
+RWStructuredBuffer<uint> output;
+
+[numthreads(1, 1, 1)]
+[shader("compute")]
+void computeMain(uint3 threadID: SV_DispatchThreadID)
+{
+    DataObtainer obtainer = {2u};
+    outputBuffer[0] = obtainer.getValue();
+    outputBuffer[1] = obtainer.getValue2();
+    // BUF: 2
+    // BUF-NEXT: 1
+}