Fix int16_t/uint16_t support for WGSL target (#7692)

* Initial plan

* Implement int16_t/uint16_t support for WGSL target

Co-authored-by: csyonghe <2652293+csyonghe@users.noreply.github.com>

* Change int16_t/uint16_t to emit proper diagnostics instead of auto-promoting

Co-authored-by: csyonghe <2652293+csyonghe@users.noreply.github.com>

* Implement diagnoseOnce to prevent duplicate diagnostics

Co-authored-by: csyonghe <2652293+csyonghe@users.noreply.github.com>

* Optimize diagnoseOnce to use HashSet::add() return value

Co-authored-by: csyonghe <2652293+csyonghe@users.noreply.github.com>

* Apply code formatting to slang-emit-c-like.h

Co-authored-by: csyonghe <2652293+csyonghe@users.noreply.github.com>

* Fix diagnoseOnce to use all parameters instead of first parameter only

Co-authored-by: csyonghe <2652293+csyonghe@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: csyonghe <2652293+csyonghe@users.noreply.github.com>

3 files changed, 45 insertions, 2 deletions

diff --git a/source/slang/slang-diagnostic-defs.h b/source/slang/slang-diagnostic-defs.h
index b3d90f27c..dd7885281 100644
--- a/source/slang/slang-diagnostic-defs.h
+++ b/source/slang/slang-diagnostic-defs.h
@@ -2866,6 +2866,12 @@ DIAGNOSTIC(
     divisionByMatrixNotSupported,
     "division by matrix is not supported for Metal and WGSL targets.")
 
+DIAGNOSTIC(
+    56103,
+    Error,
+    int16NotSupportedInWGSL,
+    "16-bit integer type '$0' is not supported by the WGSL backend.")
+
 DIAGNOSTIC(57001, Warning, spirvOptFailed, "spirv-opt failed. $0")
 DIAGNOSTIC(57002, Error, unknownPatchConstantParameter, "unknown patch constant parameter '$0'.")
 DIAGNOSTIC(57003, Error, unknownTessPartitioning, "unknown tessellation partitioning '$0'.")
diff --git a/source/slang/slang-emit-c-like.h b/source/slang/slang-emit-c-like.h
index 1e9deaa0d..caf1a913b 100644
--- a/source/slang/slang-emit-c-like.h
+++ b/source/slang/slang-emit-c-like.h
@@ -228,6 +228,30 @@ public:
     /// Get the diagnostic sink
     DiagnosticSink* getSink() { return m_codeGenContext->getSink(); }
 
+    /// Diagnose a diagnostic only once per diagnostic ID and all parameters
+    template<typename... Args>
+    void diagnoseOnce(SourceLoc loc, DiagnosticInfo const& diagnostic, Args&&... args)
+    {
+        // For diagnostics with parameters, we'll use all parameters to create a unique key
+        // This prevents duplicate diagnostics while allowing different parameter combinations
+        if constexpr (sizeof...(args) > 0)
+        {
+            String key = String(diagnostic.id);
+            ((key = key + "|" + String(args)), ...); // Fold expression to append all args
+            if (!m_reportedDiagnosticKeys.add(key))
+                return;
+        }
+        else
+        {
+            // For diagnostics without parameters, just use the ID
+            if (!m_reportedDiagnosticIds.add(diagnostic.id))
+                return;
+        }
+
+        // Report the diagnostic
+        getSink()->diagnose(loc, diagnostic, std::forward<Args>(args)...);
+    }
+
     /// Get the code gen target
     CodeGenTarget getTarget() { return m_target; }
     /// Get the source style
@@ -747,6 +771,13 @@ protected:
 
     // Indicates if we are emiting for Optix cooperative vector.
     bool isOptixCoopVec = false;
+
+    // Set of diagnostic IDs that have already been reported to prevent duplicates
+    HashSet<int> m_reportedDiagnosticIds;
+
+    // Set of diagnostic keys (ID + all parameters) that have already been reported to prevent
+    // duplicates
+    HashSet<String> m_reportedDiagnosticKeys;
 };
 
 } // namespace Slang
diff --git a/source/slang/slang-emit-wgsl.cpp b/source/slang/slang-emit-wgsl.cpp
index 97b57d352..fbcb54d10 100644
--- a/source/slang/slang-emit-wgsl.cpp
+++ b/source/slang/slang-emit-wgsl.cpp
@@ -515,8 +515,10 @@ void WGSLSourceEmitter::emitSimpleTypeImpl(IRType* type)
             return;
         }
     case kIROp_Int16Type:
+        diagnoseOnce(SourceLoc(), Diagnostics::int16NotSupportedInWGSL, "int16_t");
+        return;
     case kIROp_UInt16Type:
-        SLANG_UNEXPECTED("16 bit integer value emitted");
+        diagnoseOnce(SourceLoc(), Diagnostics::int16NotSupportedInWGSL, "uint16_t");
         return;
     case kIROp_Int64Type:
     case kIROp_IntPtrType:
@@ -976,9 +978,13 @@ void WGSLSourceEmitter::emitSimpleValueImpl(IRInst* inst)
                         break;
                     }
                 case BaseType::Int16:
+                    {
+                        diagnoseOnce(SourceLoc(), Diagnostics::int16NotSupportedInWGSL, "int16_t");
+                        break;
+                    }
                 case BaseType::UInt16:
                     {
-                        SLANG_UNEXPECTED("16 bit integer value emitted");
+                        diagnoseOnce(SourceLoc(), Diagnostics::int16NotSupportedInWGSL, "uint16_t");
                         break;
                     }
                 case BaseType::Int: