From 6e32976de513d4e039c5a2b492cb8ea78f43c321 Mon Sep 17 00:00:00 2001
From: Yong He <yonghe@outlook.com>
Date: Wed, 28 Aug 2024 22:32:04 -0700
Subject: Fix partial inference of variadic generic functions. (#4956)

---
 source/slang/core.meta.slang                       |  4 +++-
 source/slang/slang-check-overload.cpp              | 18 ++++++++++++++--
 .../generics/variadic-partial-inference.slang      | 25 ++++++++++++++++++++++
 3 files changed, 44 insertions(+), 3 deletions(-)
 create mode 100644 tests/language-feature/generics/variadic-partial-inference.slang

diff --git a/source/slang/core.meta.slang b/source/slang/core.meta.slang
index 919c21473..67fb201fe 100644
--- a/source/slang/core.meta.slang
+++ b/source/slang/core.meta.slang
@@ -156,6 +156,8 @@ interface IInteger : IArithmetic, ILogical
     int64_t toInt64();
     uint toUInt();
     uint64_t toUInt64();
+    __init(int val);
+    __init(int64_t val);
 }
 
 interface IFloat : IArithmetic, IDifferentiable
@@ -220,7 +222,7 @@ interface __BuiltinSignedArithmeticType : __BuiltinArithmeticType {}
 /// A type that can represent integers
 [sealed]
 [builtin]
-interface __BuiltinIntegerType : __BuiltinArithmeticType
+interface __BuiltinIntegerType : __BuiltinArithmeticType, IInteger
 {}
 
 /// A type that can represent non-integers
diff --git a/source/slang/slang-check-overload.cpp b/source/slang/slang-check-overload.cpp
index 743d518af..6d376dba3 100644
--- a/source/slang/slang-check-overload.cpp
+++ b/source/slang/slang-check-overload.cpp
@@ -466,8 +466,22 @@ namespace Slang
                 Val* val = nullptr;
                 if (aa >= matchedArgs.getCount())
                 {
-                    // If we run out of matched args, we will just create an empty pack.
-                    val = m_astBuilder->getTypePack(ArrayView<Type*>());
+                    if (allowPartialGenericApp)
+                    {
+                        // If we have run out of arguments and the decl allows
+                        // partial specialization, then we don't apply any more
+                        // checks at this step. We will instead attempt to
+                        // *infer* an argument at this position at a later
+                        // stage.
+                        //
+                        candidate.flags |= OverloadCandidate::Flag::IsPartiallyAppliedGeneric;
+                        break;
+                    }
+                    else
+                    {
+                        // Otherwise, we will just create an empty pack.
+                        val = m_astBuilder->getTypePack(ArrayView<Type*>());
+                    }
                 }
                 else
                 {
diff --git a/tests/language-feature/generics/variadic-partial-inference.slang b/tests/language-feature/generics/variadic-partial-inference.slang
new file mode 100644
index 000000000..003d22424
--- /dev/null
+++ b/tests/language-feature/generics/variadic-partial-inference.slang
@@ -0,0 +1,25 @@
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK): -shaderobj -output-using-type
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK): -cpu -shaderobj -output-using-type
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK): -vk -shaderobj -output-using-type
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+void aggregate(inout int v, int u)
+{
+    v = v * u;
+}
+
+T test<T:IInteger, each U : IInteger>(T t, expand each U u)
+{
+    int v = 1;
+    expand aggregate(v, (each u).toInt());
+    return t + T(v);
+}
+
+[numthreads(1, 1, 1)]
+void computeMain()
+{
+    // CHECK: 11
+    outputBuffer[0] = test<int>(5, 1, 2, 3);
+}
\ No newline at end of file
-- 
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