2 files changed, 85 insertions, 0 deletions
diff --git a/internal/enumtest/enumtest.go b/internal/enumtest/enumtest.go
new file mode 100644
index 0000000..cccb09c
--- /dev/null
+++ b/internal/enumtest/enumtest.go
@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// Package enumtest reads the constants of an enum type from Go source, so
+// a test can check that every value is handled - and fails when a value is
+// added without the code that needs it. Only tests import it.
+package enumtest
+
+import (
+	"fmt"
+	"go/ast"
+	"go/parser"
+	"go/token"
+)
+
+// Names returns, in declaration order, the constants declared with type typ
+// in the Go file at path, including those an iota block types implicitly.
+// A type with no constants there is an error, so a renamed file or type
+// cannot make a test pass by finding nothing.
+func Names(path, typ string) ([]string, error) {
+	f, err := parser.ParseFile(token.NewFileSet(), path, nil, 0)
+	if err != nil {
+		return nil, err
+	}
+	var names []string
+	for _, decl := range f.Decls {
+		g, ok := decl.(*ast.GenDecl)
+		if !ok || g.Tok != token.CONST {
+			continue
+		}
+		inType := false
+		for _, spec := range g.Specs {
+			vs, ok := spec.(*ast.ValueSpec)
+			if !ok {
+				continue
+			}
+			switch {
+			case vs.Type != nil:
+				id, ok := vs.Type.(*ast.Ident)
+				inType = ok && id.Name == typ
+			case len(vs.Values) > 0:
+				inType = false
+			}
+			if inType {
+				for _, n := range vs.Names {
+					names = append(names, n.Name)
+				}
+			}
+		}
+	}
+	if len(names) == 0 {
+		return nil, fmt.Errorf("%s: no constants of type %s", path, typ)
+	}
+	return names, nil
+}
diff --git a/internal/enumtest/enumtest_test.go b/internal/enumtest/enumtest_test.go
new file mode 100644
index 0000000..6a7bd69
--- /dev/null
+++ b/internal/enumtest/enumtest_test.go
@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package enumtest
+
+import (
+	"os"
+	"path/filepath"
+	"reflect"
+	"testing"
+)
+
+// TestNames: typed constants are found in declaration order, those an iota
+// block types implicitly included; untyped constants and other types are
+// not.
+func TestNames(t *testing.T) {
+	src := "package x\n\ntype K int\ntype Other int\n\nconst (\n\tA K = iota\n\tB\n\tC\n)\n\nconst (\n\tX Other = iota\n\tY\n)\n\nconst Z K = 9\n\nconst (\n\tP K = 1\n\tQ = 2\n)\n"
+	path := filepath.Join(t.TempDir(), "x.go")
+	if err := os.WriteFile(path, []byte(src), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	got, err := Names(path, "K")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if want := []string{"A", "B", "C", "Z", "P"}; !reflect.DeepEqual(got, want) {
+		t.Errorf("Names = %v, want %v", got, want)
+	}
+	if _, err := Names(path, "Missing"); err == nil {
+		t.Error("a type with no constants should be an error")
+	}
+}