use AST order to report missing names (#44)

switch.go

@@ -5,7 +5,6 @@ import (
 	"go/ast"
 	"go/types"
 	"regexp"
-	"sort"
 	"strings"
 
 	"golang.org/x/tools/go/analysis"
@@ -262,19 +261,30 @@ func analyzeCaseClauseExpr(e ast.Expr, info *types.Info, found func(val constant
 
 // diagnosticMissingMembers constructs the list of missing enum members,
 // suitable for use in a reported diagnostic message.
+// Order is the same as in enumMembers.Names.
 func diagnosticMissingMembers(missingMembers map[string]struct{}, em enumMembers) []string {
-	missingByConstVal := make(map[constantValue][]string) // missing members, keyed by constant value.
-	for m := range missingMembers {
-		val := em.NameToValue[m]
-		missingByConstVal[val] = append(missingByConstVal[val], m)
+	missingNamesGroupedByValue := make([][]string, len(em.Names)) // empty groups will be filtered out later
+	firstIndex := make(map[constantValue]int, len(em.ValueToNames))
+	for i, name := range em.Names {
+		value := em.NameToValue[name]
+		j, ok := firstIndex[value]
+		if !ok {
+			firstIndex[value] = i
+			j = i
+		}
+
+		if _, missing := missingMembers[name]; missing {
+			missingNamesGroupedByValue[j] = append(missingNamesGroupedByValue[j], name)
+		}
 	}
 
-	var out []string
-	for _, names := range missingByConstVal {
-		sort.Strings(names)
+	out := make([]string, 0, len(missingMembers))
+	for _, names := range missingNamesGroupedByValue {
+		if len(names) == 0 {
+			continue
+		}
 		out = append(out, strings.Join(names, "|"))
 	}
-	sort.Strings(out)
 	return out
 }
 

switch_test.go

@@ -60,7 +60,7 @@ func TestDiagnosticMissingMembers(t *testing.T) {
 
 	t.Run("missing some: unique or unknown values", func(t *testing.T) {
 		got := diagnosticMissingMembers(map[string]struct{}{"Yamuna": {}, "Kaveri": {}}, em)
-		want := []string{"Kaveri", "Yamuna"}
+		want := []string{"Yamuna", "Kaveri"}
 		if !reflect.DeepEqual(want, got) {
 			t.Errorf("want %v, got %v", want, got)
 		}
@@ -75,7 +75,7 @@ func TestDiagnosticMissingMembers(t *testing.T) {
 
 	t.Run("missing all", func(t *testing.T) {
 		got := diagnosticMissingMembers(map[string]struct{}{"Ganga": {}, "Kaveri": {}, "Yamuna": {}, "Unspecified": {}}, em)
-		want := []string{"Ganga|Unspecified", "Kaveri", "Yamuna"}
+		want := []string{"Ganga|Unspecified", "Yamuna", "Kaveri"}
 		if !reflect.DeepEqual(want, got) {
 			t.Errorf("want %v, got %v", want, got)
 		}
@@ -114,7 +114,7 @@ func TestMakeDiagnostic(t *testing.T) {
 	want := analysis.Diagnostic{
 		Pos:     1,
 		End:     11,
-		Message: "missing cases in switch of type enumpkg.Biome: Desert, Savanna",
+		Message: "missing cases in switch of type enumpkg.Biome: Savanna, Desert",
 	}
 	if !reflect.DeepEqual(want, got) {
 		t.Errorf("want %+v, got %+v", want, got)

testdata/src/duplicate-enum-value/otherpkg/otherpkg.go

@@ -37,7 +37,7 @@ func _r() {
 	}
 
 	var s d.State
-	switch s { // want "^missing cases in switch of type duplicateenumvalue.State: DefaultState\\|TamilNadu, Kerala$"
+	switch s { // want "^missing cases in switch of type duplicateenumvalue.State: TamilNadu\\|DefaultState, Kerala$"
 	case d.Karnataka:
 	}
 }

testdata/src/general/x/general.go

@@ -162,7 +162,7 @@ func _q() {
 	fi, err := os.Lstat(".")
 	fmt.Println(err)
 
-	switch fi.Mode() { // want "^missing cases in switch of type fs.FileMode: ModeDevice, ModePerm, ModeSetgid, ModeSetuid, ModeType$"
+	switch fi.Mode() { // want "^missing cases in switch of type fs.FileMode: ModeDevice, ModeSetuid, ModeSetgid, ModeType, ModePerm$"
 	case os.ModeDir:
 	case os.ModeAppend:
 	case os.ModeExclusive:

testdata/src/ignore-enum-member/same_value.go

@@ -13,6 +13,6 @@ const (
 // The member Standard, though it has the same constant value as User, must
 // still be reported in the diagnostic.
 func _c(a Access) {
-	switch a { // want "^missing cases in switch of type Access: Group, Standard$"
+	switch a { // want "^missing cases in switch of type Access: Standard, Group$"
 	}
 }