fix(codegen): raise a runtime error when a FUNCTION ends without RETURN

Report the function and its header line, then throw, instead of silently
returning zero. FUNCTION MAIN keeps its implicit result.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/cps/FunctionGen.h b/include/cps/FunctionGen.h
index 6c5c7c0..f5e5ba2 100644
--- a/include/cps/FunctionGen.h
+++ b/include/cps/FunctionGen.h
@@ -86,6 +86,7 @@ private:
     std::function<void(const FuncSig &)> BeforeCall;
     ArrayParamBinder BindArrayParam;
     std::function<void(llvm::Value *, const std::string &, int)> RegisterCopy;
+    std::function<void(int, const std::string &)> MissingReturn;
     ClangABI ABI{Context, Types}; // clang context created on the first EXTERN
 
     void createArgumentAllocas(llvm::Function *F, const std::vector<ParamDecl> &Params, bool IsMethod);
@@ -105,6 +106,12 @@ public:
 
     void setArrayParamBinder(ArrayParamBinder Binder) { BindArrayParam = std::move(Binder); }
 
+    // Called (with the FUNCTION header line and name) where a non-VOID FUNCTION
+    // body can fall off its end; emits the runtime error and throw.
+    void setMissingReturnHandler(std::function<void(int, const std::string &)> Handler) {
+        MissingReturn = std::move(Handler);
+    }
+
     void setCopyRegistrar(std::function<void(llvm::Value *, const std::string &, int)> Registrar) {
         RegisterCopy = std::move(Registrar);
     }