Extend noinit to all pointer fields

Makefile

@@ -25,6 +25,7 @@ test-acc:
 	@go test \
 		-count=1 \
 		-race \
+		-shuffle=on \
 		-timeout=10m \
 		-vet="${VETTERS}" \
 		./...

README.md

@@ -260,23 +260,8 @@ Envconfig walks the entire struct, including nested structs, so deeply-nested
 fields are also supported.
 
 If a nested struct is a pointer type, it will automatically be instantianted to
-the non-nil value. To disable this behavior, use the tag `noinit`. E.g.
-
-```go
-type ParentCfg struct {
-  // Without `noinit` tag, `Child` would be set to `&ChildCfg{}` whether
-  // or not `FIELD` is set in the env var.
-  // With `noinit`, `Child` would stay nil if `FIELD` is not set in the env var.
-  Child *ChildCfg `env:",noinit"`
-}
-
-type ChildCfg struct {
-  Field string `env:"FIELD"`
-}
-```
-
-The `noinit` tag is only application for struct pointer fields. Put the tag on
-non-struct-pointer will return an error.
+the non-nil value. To change this behavior, see
+(Initialization)[#Initialization].
 
 
 ### Custom
@@ -307,6 +292,38 @@ if err := envconfig.ProcessWith(ctx, &c, l); err != nil {
 export APP_MYVAR="foo"
 ```
 
+## Initialization
+
+By default, all pointer fields are initialized (allocated) so they are not
+`nil`. To disable this behavior, use the tag the field as `noinit`:
+
+```go
+type MyStruct struct {
+  // Without `noinit`, DeleteUser would be initialized to the default boolean
+  // value. With `noinit`, if the environment variable is not given, the value
+  // is kept as uninitialized (nil).
+  DeleteUser *bool `env:"DELETE_USER, noinit"`
+}
+```
+
+This also applies to nested fields in a struct:
+
+```go
+type ParentConfig struct {
+  // Without `noinit` tag, `Child` would be set to `&ChildConfig{}` whether
+  // or not `FIELD` is set in the env var.
+  // With `noinit`, `Child` would stay nil if `FIELD` is not set in the env var.
+  Child *ChildConfig `env:",noinit"`
+}
+
+type ChildConfig struct {
+  Field string `env:"FIELD"`
+}
+```
+
+The `noinit` tag is only applicable for pointer fields. Putting the tag on a
+non-struct-pointer will return an error.
+
 
 ## Extension
 

envconfig.go

@@ -290,7 +290,8 @@ func ProcessWith(ctx context.Context, i interface{}, l Lookuper, fns ...MutatorF
 				// it means nothing was changed in any sub-fields.
 				// With the noinit opt, we skip setting the empty value
 				// to the original struct pointer (aka. keep it nil).
-				if !reflect.DeepEqual(v.Interface(), empty) || !opts.NoInit {
+				// if !reflect.DeepEqual(v.Interface(), empty) || !opts.NoInit {
+				if !reflect.DeepEqual(v.Interface(), empty) {
 					origin.Set(v)
 				}
 			}
@@ -394,7 +395,7 @@ func ProcessWith(ctx context.Context, i interface{}, l Lookuper, fns ...MutatorF
 		}
 
 		// Set value.
-		if err := processField(val, ef, opts.Delimiter, opts.Separator); err != nil {
+		if err := processField(val, ef, opts.Delimiter, opts.Separator, opts.NoInit); err != nil {
 			return fmt.Errorf("%s(%q): %w", tf.Name, val, err)
 		}
 	}
@@ -544,7 +545,12 @@ func processAsDecoder(v string, ef reflect.Value) (bool, error) {
 	return imp, err
 }
 
-func processField(v string, ef reflect.Value, delimiter, separator string) error {
+func processField(v string, ef reflect.Value, delimiter, separator string, noInit bool) error {
+	// If the input value is empty and initialization is skipped, do nothing.
+	if v == "" && noInit {
+		return nil
+	}
+
 	// Handle pointers and uninitialized pointers.
 	for ef.Type().Kind() == reflect.Ptr {
 		if ef.IsNil() {
@@ -627,12 +633,12 @@ func processField(v string, ef reflect.Value, delimiter, separator string) error
 			mKey, mVal := strings.TrimSpace(pair[0]), strings.TrimSpace(pair[1])
 
 			k := reflect.New(tf.Key()).Elem()
-			if err := processField(mKey, k, delimiter, separator); err != nil {
+			if err := processField(mKey, k, delimiter, separator, noInit); err != nil {
 				return fmt.Errorf("%s: %w", mKey, err)
 			}
 
 			v := reflect.New(tf.Elem()).Elem()
-			if err := processField(mVal, v, delimiter, separator); err != nil {
+			if err := processField(mVal, v, delimiter, separator, noInit); err != nil {
 				return fmt.Errorf("%s: %w", mVal, err)
 			}
 
@@ -650,7 +656,7 @@ func processField(v string, ef reflect.Value, delimiter, separator string) error
 			s := reflect.MakeSlice(tf, len(vals), len(vals))
 			for i, val := range vals {
 				val = strings.TrimSpace(val)
-				if err := processField(val, s.Index(i), delimiter, separator); err != nil {
+				if err := processField(val, s.Index(i), delimiter, separator, noInit); err != nil {
 					return fmt.Errorf("%s: %w", val, err)
 				}
 			}

envconfig_test.go

@@ -1656,7 +1656,7 @@ func TestProcessWith(t *testing.T) {
 
 		// No init
 		{
-			name: "noinit/no_init_when_sub_fields_set",
+			name: "noinit/no_init_when_sub_fields_unset",
 			input: &struct {
 				Sub *struct {
 					Field string `env:"FIELD"`
@@ -1667,10 +1667,23 @@ func TestProcessWith(t *testing.T) {
 					Field string `env:"FIELD"`
 				} `env:",noinit"`
 			}{
+				// Sub struct ptr shouldn't be initiated because the 'Field' is not set
+				// in the lookuper.
 				Sub: nil,
 			},
-			// 'Sub' struct ptr shouldn't be initiated
-			// because the 'Field' is not set in the lookuper.
+			lookuper: MapLookuper(map[string]string{}),
+		},
+		{
+			name: "noinit/init_when_sub_sub_fields_unset",
+			input: &struct {
+				Lepton *Lepton `env:",noinit"`
+			}{},
+			exp: &struct {
+				Lepton *Lepton `env:",noinit"`
+			}{
+				// Sub-sub fields should not be initiaized when no value is given.
+				Lepton: nil,
+			},
 			lookuper: MapLookuper(map[string]string{}),
 		},
 		{
@@ -1685,18 +1698,63 @@ func TestProcessWith(t *testing.T) {
 					Field string `env:"FIELD"`
 				} `env:",noinit"`
 			}{
+				// Sub struct ptr should be initiated because the 'Field' is set in the
+				// lookuper.
 				Sub: &struct {
 					Field string `env:"FIELD"`
 				}{
 					Field: "banana",
 				},
 			},
-			// 'Sub' struct ptr should be initiated
-			// because the 'Field' is set in the lookuper.
 			lookuper: MapLookuper(map[string]string{
 				"FIELD": "banana",
 			}),
 		},
+		{
+			name: "noinit/init_when_sub_sub_fields_set",
+			input: &struct {
+				Lepton *Lepton `env:",noinit"`
+			}{},
+			exp: &struct {
+				Lepton *Lepton `env:",noinit"`
+			}{
+				// Sub-sub fields should be initiaized when a value is given.
+				Lepton: &Lepton{
+					Quark: &Quark{
+						Value: 5,
+					},
+				},
+			},
+			lookuper: MapLookuper(map[string]string{
+				"QUARK_VALUE": "5",
+			}),
+		},
+		{
+			name: "noinit/non_struct_ptr",
+			input: &struct {
+				Field1 *string  `env:"FIELD1, noinit"`
+				Field2 *int     `env:"FIELD2, noinit"`
+				Field3 *float64 `env:"FIELD3, noinit"`
+				Field4 *bool    `env:"FIELD4"`
+			}{},
+			exp: &struct {
+				Field1 *string  `env:"FIELD1, noinit"`
+				Field2 *int     `env:"FIELD2, noinit"`
+				Field3 *float64 `env:"FIELD3, noinit"`
+				Field4 *bool    `env:"FIELD4"`
+			}{
+				// The pointer fields that had a value should initialize, but the unset
+				// values should remain nil, iff they are set to noinit.
+				Field1: func() *string { x := "banana"; return &x }(),
+				Field2: func() *int { x := 5; return &x }(),
+				Field3: nil,
+				Field4: func() *bool { x := false; return &x }(),
+			},
+			lookuper: MapLookuper(map[string]string{
+				"FIELD1": "banana",
+				"FIELD2": "5",
+			}),
+		},
 		{
 			name: "noinit/error_not_ptr",
 			input: &struct {