Add test for dataflow through switches

Author: owen-mc

go/ql/test/library-tests/semmle/go/dataflow/Switch/DataFlow.expected

@@ -0,0 +1,3 @@
+import go
+import TestUtilities.InlineFlowTest
+import DefaultFlowTest

go/ql/test/library-tests/semmle/go/dataflow/Switch/DataFlow.ql

@@ -0,0 +1,102 @@
+package main
+
+type Type1 struct {
+	field1 string
+}
+type Type2 struct {
+	field2 string
+}
+type Type3 struct {
+	field3 string
+}
+
+func source() string {
+	return "source"
+}
+
+func sink(s string) {
+}
+
+func typeSwitch1(input any, defaultValue string) string {
+	switch x := input.(type) {
+	case *Type1:
+		return x.field1
+	case *Type2, *Type3:
+		if x3, ok := x.(*Type2); ok {
+			return x3.field2
+		}
+		if x4, ok := x.(*Type3); ok {
+			return x4.field3
+		}
+		return ""
+	default:
+		_ = x
+		return defaultValue
+	}
+}
+
+func typeSwitch2(input any, defaultValue string) string {
+	switch input.(type) {
+	case *Type1:
+		return input.(*Type1).field1
+	case *Type2, *Type3:
+		if x3, ok := input.(*Type2); ok {
+			return x3.field2
+		}
+		if x4, ok := input.(*Type3); ok {
+			return x4.field3
+		}
+		return ""
+	default:
+		_ = input
+		return defaultValue
+	}
+}
+
+func expressionSwitch1(input string, defaultValue string) string {
+	switch input {
+	case "0":
+		return "0"
+	case "1", "2":
+		return "1 or 2"
+	case "3":
+		fallthrough
+	default:
+		return defaultValue
+	}
+}
+
+func expressionSwitch2(input string, defaultValue string) string {
+	switch def := defaultValue; input {
+	case "0":
+		return "0"
+	case "1", "2":
+		return "1 or 2"
+	case "3":
+		fallthrough
+	default:
+		return def
+	}
+}
+
+func main() {
+	sink(typeSwitch1(&Type1{source()}, "default")) // $ MISSING: hasValueFlow="call to typeSwitch1"
+	sink(typeSwitch1(&Type2{source()}, "default")) // $ MISSING: hasValueFlow="call to typeSwitch1"
+	sink(typeSwitch1(&Type3{source()}, "default")) // $ MISSING: hasValueFlow="call to typeSwitch1"
+	sink(typeSwitch1(nil, source()))               // $ hasValueFlow="call to typeSwitch1"
+
+	sink(typeSwitch2(&Type1{source()}, "default")) // $ hasValueFlow="call to typeSwitch2"
+	sink(typeSwitch2(&Type2{source()}, "default")) // $ hasValueFlow="call to typeSwitch2"
+	sink(typeSwitch2(&Type3{source()}, "default")) // $ hasValueFlow="call to typeSwitch2"
+	sink(typeSwitch2(nil, source()))               // $ hasValueFlow="call to typeSwitch2"
+
+	sink(expressionSwitch1("1", source())) // $ SPURIOUS: hasValueFlow="call to expressionSwitch1"
+	sink(expressionSwitch1("2", source())) // $ SPURIOUS: hasValueFlow="call to expressionSwitch1"
+	sink(expressionSwitch1("3", source())) // $ hasValueFlow="call to expressionSwitch1"
+	sink(expressionSwitch1("4", source())) // $ hasValueFlow="call to expressionSwitch1"
+
+	sink(expressionSwitch2("1", source())) // $ SPURIOUS: hasValueFlow="call to expressionSwitch2"
+	sink(expressionSwitch2("2", source())) // $ SPURIOUS: hasValueFlow="call to expressionSwitch2"
+	sink(expressionSwitch2("3", source())) // $ hasValueFlow="call to expressionSwitch2"
+	sink(expressionSwitch2("4", source())) // $ hasValueFlow="call to expressionSwitch2"
+}