Lift backtrace() code into Func.{h,cc}

This is to be re-used by the assertion facility.

src/Func.cc

@@ -903,6 +903,59 @@ FunctionIngredients::FunctionIngredients(ScopePtr _scope, StmtPtr _body,
 		}
 	}
 
+zeek::RecordValPtr make_backtrace_element(std::string_view name, const VectorValPtr args,
+                                          const zeek::detail::Location* loc)
+	{
+	static auto elem_type = id::find_type<RecordType>("BacktraceElement");
+	static auto function_name_idx = elem_type->FieldOffset("function_name");
+	static auto function_args_idx = elem_type->FieldOffset("function_args");
+	static auto file_location_idx = elem_type->FieldOffset("file_location");
+	static auto line_location_idx = elem_type->FieldOffset("line_location");
+
+	auto elem = make_intrusive<RecordVal>(elem_type);
+	elem->Assign(function_name_idx, name.data());
+	elem->Assign(function_args_idx, std::move(args));
+
+	if ( loc )
+		{
+		elem->Assign(file_location_idx, loc->filename);
+		elem->Assign(line_location_idx, loc->first_line);
+		}
+
+	return elem;
+	}
+
+zeek::VectorValPtr get_current_script_backtrace()
+	{
+	static auto backtrace_type = id::find_type<VectorType>("Backtrace");
+
+	auto rval = make_intrusive<VectorVal>(backtrace_type);
+
+	// The body of the following loop can wind up adding items to
+	// the call stack (because MakeCallArgumentVector() evaluates
+	// default arguments, which can in turn involve calls to script
+	// functions), so we work from a copy of the current call stack
+	// to prevent problems with iterator invalidation.
+	auto cs_copy = zeek::detail::call_stack;
+
+	for ( auto it = cs_copy.rbegin(); it != cs_copy.rend(); ++it )
+		{
+		const auto& ci = *it;
+		if ( ! ci.func )
+			// This happens for compiled code.
+			continue;
+
+		const auto& params = ci.func->GetType()->Params();
+		auto args = MakeCallArgumentVector(ci.args, params);
+
+		auto elem = make_backtrace_element(ci.func->Name(), std::move(args),
+		                                   ci.call ? ci.call->GetLocationInfo() : nullptr);
+		rval->Append(std::move(elem));
+		}
+
+	return rval;
+	}
+
 static void emit_builtin_error_common(const char* msg, Obj* arg, bool unwind)
 	{
 	auto emit = [=](const CallExpr* ce)

src/Func.h

@@ -364,6 +364,25 @@ private:
 
 extern std::vector<CallInfo> call_stack;
 
+/**
+ * Create a single BacktraceElement record val.
+ *
+ * @param name the name of the function.
+ * @param args call argument vector created by MakeCallArgumentVector().
+ * @param loc optional location information of the caller.
+ *
+ * @return record value representing a BacktraceElement.
+ */
+zeek::RecordValPtr make_backtrace_element(std::string_view name, const VectorValPtr args,
+                                          const zeek::detail::Location* loc);
+
+/**
+ * Create a Zeek script Backtrace of the current script call_stack.
+ *
+ * @return VectorValPtr containing BacktraceElement entries.
+ */
+zeek::VectorValPtr get_current_script_backtrace();
+
 // This is set to true after the built-in functions have been initialized.
 extern bool did_builtin_init;
 extern std::vector<void (*)()> bif_initializers;

src/zeek.bif

@@ -2368,6 +2368,10 @@ function is_v6_subnet%(s: subnet%): bool
 		return zeek::val_mgr->False();
 	%}
 
+%%{
+#include "zeek/Func.h"
+%%}
+
 ## Returns a representation of the call stack as a vector of call stack
 ## elements, each containing call location information.
 ##
@@ -2375,49 +2379,7 @@ function is_v6_subnet%(s: subnet%): bool
 ##          location information.
 function backtrace%(%): Backtrace
 	%{
-	using zeek::detail::call_stack;
+	return zeek::detail::get_current_script_backtrace();
-	static auto backtrace_type = id::find_type<VectorType>("Backtrace");
-	static auto elem_type = id::find_type<RecordType>("BacktraceElement");
-	static auto function_name_idx = elem_type->FieldOffset("function_name");
-	static auto function_args_idx = elem_type->FieldOffset("function_args");
-	static auto file_location_idx = elem_type->FieldOffset("file_location");
-	static auto line_location_idx = elem_type->FieldOffset("line_location");
-
-	auto rval = make_intrusive<VectorVal>(backtrace_type);
-
-	// The body of the following loop can wind up adding items to
-	// the call stack (because MakeCallArgumentVector() evaluates
-	// default arguments, which can in turn involve calls to script
-	// functions), so we work from a copy of the current call stack
-	// to prevent problems with iterator invalidation.
-	auto cs_copy = call_stack;
-
-	for ( auto it = cs_copy.rbegin(); it != cs_copy.rend(); ++it )
-		{
-		const auto& ci = *it;
-		if ( ! ci.func )
-			// This happens for compiled code.
-			continue;
-
-		auto elem = make_intrusive<RecordVal>(elem_type);
-
-		const auto& params = ci.func->GetType()->Params();
-		auto args = MakeCallArgumentVector(ci.args, params);
-
-		elem->Assign(function_name_idx, ci.func->Name());
-		elem->Assign(function_args_idx, std::move(args));
-
-		if ( ci.call )
-			{
-			auto loc = ci.call->GetLocationInfo();
-			elem->Assign(file_location_idx, loc->filename);
-			elem->Assign(line_location_idx, loc->first_line);
-			}
-
-		rval->Assign(rval->Size(), std::move(elem));
-		}
-
-	return rval;
 	%}
 
 # ===========================================================================