replace OpCall with OpPreCall

also add comments and small code reorg

stdlibs/stdlibs.go

@@ -287,34 +287,32 @@ func InjectPackage(store gno.Store, pn *gno.PackageNode) {
 				// TODO: limit usage in goroutines?
 				// TODO: build a new sub-context instead of patching the root one.
 				//       to support multiple concurrent contexts and advanced flows.
-				arg0 := m.LastBlock().GetParams1().TV
-				fn := arg0.GetFunc()
-
-				ctx := m.Context.(ExecContext)
-				ctx.OrigCaller = ctx.OrigPkgAddr
-
-				backupContext := m.Context.(ExecContext)
 
+				// Push original context first, so it will be reset after the function
+				// call.
+				m.PushOp(gno.OpSetContext)
 				m.PushValue(gno.TypedValue{
-					T: &gno.InterfaceType{},
 					V: gno.ContextValue{
-						Context: backupContext,
+						Context: m.Context,
 					},
 				})
-				m.PushOp(gno.OpSetContext)
 
-				cx := gno.Call(gno.FuncT(nil, nil))
-				m.PushValue(gno.TypedValue{})
-				m.PushFrameCall(cx, fn, gno.TypedValue{})
-				m.PushOp(gno.OpCall)
+				// Push a function call, to execute the function in parameter.
+				m.PushOp(gno.OpPrecall)
+				m.PushExpr(gno.Call(gno.FuncT(nil, nil)))
+				tv := m.LastBlock().GetParams1().TV
+				m.PushValue(*tv)
 
+				// Push an alternate context with OrigCaller=OrigPkgAddr, this will
+				// affect the function call above
+				m.PushOp(gno.OpSetContext)
+				ctx := m.Context.(ExecContext)
+				ctx.OrigCaller = ctx.OrigPkgAddr
 				m.PushValue(gno.TypedValue{
-					T: &gno.InterfaceType{},
 					V: gno.ContextValue{
 						Context: ctx,
 					},
 				})
-				m.PushOp(gno.OpSetContext)
 			},
 		)
 		pn.DefineNative("GetCallerAt",

tests/files/zrealm_std6.gno

@@ -6,14 +6,16 @@ import (
 	"std"
 )
 
-func main() {
-	println(std.GetOrigCaller())
-	std.ExecAsPkg(func() {
-		println(std.GetOrigCaller())
-	})
+func printOrigCaller() {
 	println(std.GetOrigCaller())
 }
 
+func main() {
+	printOrigCaller()
+	std.ExecAsPkg(printOrigCaller)
+	printOrigCaller()
+}
+
 // Output:
 // g1fahslvxakc058u0wa98ytfc9fd6trhe5qfh9ld
 // g157y5v3k529jyzhjjz4fn49tzzhf4gess6v39xg