Encoder: try to use pointer type TextMarshaler (#679)

If a type does not implement the encoding.TextMarshaler interface but
its pointer type does, use it if possible.

Fixes #678

marshaler.go

@@ -209,7 +209,12 @@ func (enc *Encoder) encode(b []byte, ctx encoderCtx, v reflect.Value) ([]byte, e
 		}
 	}
 
-	if v.Type().Implements(textMarshalerType) {
+	hasTextMarshaler := v.Type().Implements(textMarshalerType)
+	if hasTextMarshaler || (v.CanAddr() && reflect.PtrTo(v.Type()).Implements(textMarshalerType)) {
+		if !hasTextMarshaler {
+			v = v.Addr()
+		}
+
 		if ctx.isRoot() {
 			return nil, fmt.Errorf("toml: type %s implementing the TextMarshaler interface cannot be a root element", v.Type())
 		}
@@ -657,7 +662,7 @@ func willConvertToTable(ctx encoderCtx, v reflect.Value) bool {
 	if !v.IsValid() {
 		return false
 	}
-	if v.Type() == timeType || v.Type().Implements(textMarshalerType) {
+	if v.Type() == timeType || v.Type().Implements(textMarshalerType) || (v.Kind() != reflect.Ptr && v.CanAddr() && reflect.PtrTo(v.Type()).Implements(textMarshalerType)) {
 		return false
 	}
 

marshaler_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
+	"math/big"
 	"strings"
 	"testing"
 
@@ -798,6 +799,48 @@ func TestIssue590(t *testing.T) {
 	require.NoError(t, err)
 }
 
+func TestIssue571(t *testing.T) {
+	type Foo struct {
+		Float32 float32
+		Float64 float64
+	}
+
+	const closeEnough = 1e-9
+
+	foo := Foo{
+		Float32: 42,
+		Float64: 43,
+	}
+	b, err := toml.Marshal(foo)
+	require.NoError(t, err)
+
+	var foo2 Foo
+	err = toml.Unmarshal(b, &foo2)
+	require.NoError(t, err)
+
+	assert.InDelta(t, 42, foo2.Float32, closeEnough)
+	assert.InDelta(t, 43, foo2.Float64, closeEnough)
+}
+
+func TestIssue678(t *testing.T) {
+	type Config struct {
+		BigInt big.Int
+	}
+
+	cfg := &Config{
+		BigInt: *big.NewInt(123),
+	}
+
+	out, err := toml.Marshal(cfg)
+	require.NoError(t, err)
+	equalStringsIgnoreNewlines(t, "BigInt = '123'", string(out))
+
+	cfg2 := &Config{}
+	err = toml.Unmarshal(out, cfg2)
+	require.NoError(t, err)
+	require.Equal(t, cfg, cfg2)
+}
+
 func ExampleMarshal() {
 	type MyConfig struct {
 		Version int
@@ -822,26 +865,3 @@ func ExampleMarshal() {
 	// Name = 'go-toml'
 	// Tags = ['go', 'toml']
 }
-
-func TestIssue571(t *testing.T) {
-	type Foo struct {
-		Float32 float32
-		Float64 float64
-	}
-
-	const closeEnough = 1e-9
-
-	foo := Foo{
-		Float32: 42,
-		Float64: 43,
-	}
-	b, err := toml.Marshal(foo)
-	require.NoError(t, err)
-
-	var foo2 Foo
-	err = toml.Unmarshal(b, &foo2)
-	require.NoError(t, err)
-
-	assert.InDelta(t, 42, foo2.Float32, closeEnough)
-	assert.InDelta(t, 43, foo2.Float64, closeEnough)
-}

unmarshaler_test.go

@@ -664,6 +664,36 @@ func TestUnmarshal(t *testing.T) {
 				}
 			},
 		},
+		{
+			desc:  "long string array into []string",
+			input: `A = ["0","1","2","3","4","5","6","7","8","9","10","11","12","13","14","15","16","17"]`,
+			gen: func() test {
+				type doc struct {
+					A []string
+				}
+
+				return test{
+					target:   &doc{},
+					expected: &doc{A: []string{"0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14", "15", "16", "17"}},
+				}
+			},
+		},
+		{
+			desc: "long string array into []interface{}",
+			input: `A = ["0","1","2","3","4","5","6","7","8","9","10","11","12","13","14",
+"15","16","17"]`,
+			gen: func() test {
+				type doc struct {
+					A []interface{}
+				}
+
+				return test{
+					target: &doc{},
+					expected: &doc{A: []interface{}{"0", "1", "2", "3", "4", "5", "6",
+						"7", "8", "9", "10", "11", "12", "13", "14", "15", "16", "17"}},
+				}
+			},
+		},
 		{
 			desc: "standard table",
 			input: `[A]