Add more tests for variadic functions

ql/test/library-tests/semmle/go/dataflow/VarArgs/main.go

@@ -11,17 +11,40 @@ type A struct {
 	f string
 }
 
-func functionWithVarArgsOfStructsParameter(s ...A) {
-	sink(s[0].f) // $ MISSING: taintflow dataflow
+func functionWithSliceParameter(s []string) string {
+	return s[1]
+}
+
+func functionWithVarArgsParameter(s ...string) string {
+	return s[1]
+}
+
+func functionWithSliceOfStructsParameter(s []A) string {
+	return s[1].f
+}
+
+func functionWithVarArgsOfStructsParameter(s ...A) string {
+	return s[1].f
 }
 
 func main() {
 	stringSlice := []string{source()}
 	sink(stringSlice[0]) // $ taintflow dataflow
 
-	arrayOfStructs := []A{{f: source()}}
-	sink(arrayOfStructs[0].f) // $ taintflow dataflow
+	s0 := ""
+	s1 := source()
+	sSlice := []string{s0, s1}
+	sink(functionWithSliceParameter(sSlice))      // $ taintflow dataflow
+	sink(functionWithVarArgsParameter(sSlice...)) // $ taintflow dataflow
+	sink(functionWithVarArgsParameter(s0, s1))    // $ MISSING: taintflow dataflow
 
-	a := A{f: source()}
-	functionWithVarArgsOfStructsParameter(a)
+	sliceOfStructs := []A{{f: source()}}
+	sink(sliceOfStructs[0].f) // $ taintflow dataflow
+
+	a0 := A{f: ""}
+	a1 := A{f: source()}
+	aSlice := []A{a0, a1}
+	sink(functionWithSliceOfStructsParameter(aSlice))      // $ taintflow dataflow
+	sink(functionWithVarArgsOfStructsParameter(aSlice...)) // $ taintflow dataflow
+	sink(functionWithVarArgsOfStructsParameter(a0, a1))    // $ MISSING: taintflow dataflow
 }