Report error when generated spirv is empty. (shader-slang#5899)

* Report error when generated spirv is empty.

* format code

---------

Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>
Co-authored-by: Ellie Hermaszewska <ellieh@nvidia.com>

Author: 3 people

source/slang/slang-diagnostic-defs.h

@@ -2452,6 +2452,12 @@ DIAGNOSTIC(
 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'.")
+DIAGNOSTIC(
+    57004,
+    Error,
+    outputSpvIsEmpty,
+    "output SPIR-V contains no exported symbols. Please make sure to specify at least one "
+    "entrypoint.")
 
 // GLSL Compatibility
 DIAGNOSTIC(

source/slang/slang-emit-spirv.cpp

@@ -7964,6 +7964,8 @@ SlangResult emitSPIRVFromIR(
 {
     spirvOut.clear();
 
+    bool symbolsEmitted = false;
+
     auto sink = codeGenContext->getSink();
 
 #if 0
@@ -8008,6 +8010,7 @@ SlangResult emitSPIRVFromIR(
         if (shouldPreserveParams && as<IRGlobalParam>(inst))
         {
             context.ensureInst(inst);
+            symbolsEmitted = true;
         }
         if (generateWholeProgram)
         {
@@ -8016,6 +8019,7 @@ SlangResult emitSPIRVFromIR(
                 if (func->findDecoration<IRDownstreamModuleExportDecoration>())
                 {
                     context.ensureInst(inst);
+                    symbolsEmitted = true;
                 }
             }
         }
@@ -8046,8 +8050,14 @@ SlangResult emitSPIRVFromIR(
     for (auto irEntryPoint : irEntryPoints)
     {
         context.ensureInst(irEntryPoint);
+        symbolsEmitted = true;
     }
 
+    if (!symbolsEmitted)
+    {
+        sink->diagnose(irModule->getModuleInst(), Diagnostics::outputSpvIsEmpty);
+        return SLANG_FAIL;
+    }
 
     // Move forward delcared pointers to the end.
     do

tests/spirv/empty-module.slang

@@ -0,0 +1,7 @@
+//DIAGNOSTIC_TEST:SIMPLE(filecheck=CHECK): -target spirv
+
+// missing entrypoint attribute
+void vertMain()
+{}
+
+// CHECK: error 57004