Playing with an AST

Idea would be to build a light AST as a first pass, then have the
unmarshaler and Document parser do what they need with it.

internal/unmarshaler/parser_test.go

@@ -0,0 +1,50 @@
+package unmarshaler
+
+import (
+	"testing"
+
+	"github.com/pelletier/go-toml/v2/internal/ast"
+	"github.com/stretchr/testify/require"
+)
+
+func TestParser_Simple(t *testing.T) {
+	examples := []struct {
+		desc  string
+		input string
+		ast   ast.Root
+		err   bool
+	}{
+		{
+			desc:  "simple string assignment",
+			input: `A = "hello"`,
+			ast: ast.Root{
+				ast.Node{
+					Kind: ast.KeyValue,
+					Children: []ast.Node{
+						{
+							Kind: ast.Key,
+							Data: []byte(`A`),
+						},
+						{
+							Kind: ast.String,
+							Data: []byte(`hello`),
+						},
+					},
+				},
+			},
+		},
+	}
+
+	for _, e := range examples {
+		t.Run(e.desc, func(t *testing.T) {
+			p := parser{}
+			err := p.parse([]byte(e.input))
+			if e.err {
+				require.Error(t, err)
+			} else {
+				require.NoError(t, err)
+				require.Equal(t, e.ast, p.tree)
+			}
+		})
+	}
+}