feat: Load* and Save functions panic if data is not a pointer to a struct

CHANGELOG.md

@@ -5,6 +5,9 @@
 - Add support for TOML configuration files
 - Add support for HCL configuration files
 - Use stdlib for tests instead of convey
+- Public functions now panic when the data to be marshaled or unmarshaled is not
+  a pointer to a struct. These errors should be caught during deelopment (with
+  unit tests).
 - Update golangci-lint configuration
 
 ## v0.3.0 (2025-01-14)

config.go

@@ -15,14 +15,30 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"reflect"
 )
 
-// ErrUnsupportedFileType is returned when the type of the config file is not
+var (
-// supported.
+	// ErrUnsupportedFileType is returned when the type of the config file is
-var ErrUnsupportedFileType = errors.New("unsupported config type")
+	// not supported.
+	ErrUnsupportedFileType = errors.New("unsupported config type")
+
+	// ErrInvalidMarshalData is returned when the marshaled value is not a
+	// struct.
+	ErrInvalidMarshalData = errors.New("the marshaled value must be a struct")
+
+	// ErrInvalidUnmarshalData is returned when the marshaled value is not a
+	// struct.
+	ErrInvalidUnmarshalData = errors.New(
+		"the unmarshaled value must be a pointer to a struct",
+	)
+)
 
 // LoadFile reads the file at path, parses its json content and fills the struct
 // with the content of the file.
+//
+// LoadFile panics with [ErrInvalidUnmarshalData] if data is not a pointer to a
+// struct, as this error should be caught during dev.
 func LoadFile(path string, data any) error {
 	return read(path, data)
 }
@@ -33,6 +49,9 @@ func LoadFile(path string, data any) error {
 //
 // It returns an error only if the content of a file is invalid, i.e. it
 // cannot be unmarshaled to the struct.
+//
+// LoadFiles panics with [ErrInvalidUnmarshalData] if data is not a pointer to a
+// struct, as this error should be caught during dev.
 func LoadFiles(data any, paths ...string) error {
 	for _, p := range paths {
 		err := read(p, data)
@@ -45,6 +64,9 @@ func LoadFiles(data any, paths ...string) error {
 }
 
 // SaveFile writes the given data serialized in JSON in the given path.
+//
+// SaveFile panics with [ErrInvalidMarshalData] if data is not a struct, as
+// this error should be caught during dev.
 func SaveFile(path string, data any) error {
 	return write(path, data)
 }
@@ -59,6 +81,9 @@ func SaveFile(path string, data any) error {
 //
 // An error is returned only if the config file cannot be
 // written.
+//
+// LoadAndUpdateFile panics with [ErrInvalidUnmarshalData] if data is not a
+// pointer to a struct, as this error should be caught during dev.
 func LoadAndUpdateFile(path string, data any) error {
 	if _, err := os.Stat(path); !os.IsNotExist(err) {
 		err2 := read(path, data)
@@ -85,6 +110,13 @@ type Updater interface {
 }
 
 func read(path string, data any) error {
+	val := reflect.ValueOf(data)
+	indVal := reflect.Indirect(val)
+
+	if val.Kind() != reflect.Ptr || indVal.Kind() != reflect.Struct {
+		panic(ErrInvalidUnmarshalData)
+	}
+
 	content, err := os.ReadFile(filepath.Clean(path))
 	if err != nil {
 		return fmt.Errorf("cannot read config file: %w", err)
@@ -94,6 +126,11 @@ func read(path string, data any) error {
 }
 
 func write(path string, data any) error {
+	v := reflect.Indirect(reflect.ValueOf(data))
+	if v.Kind() != reflect.Struct {
+		panic(ErrInvalidMarshalData)
+	}
+
 	content, err := marshal(getType(path), data)
 	if err != nil {
 		return err

config_test.go

@@ -117,6 +117,31 @@ func testLoadFile(t *testing.T, ext string) {
 			assert.Equal(t, "should not change", c.Invariant)
 		})
 
+		t.Run("with a valid file and invalid data", func(t *testing.T) {
+			t.Parallel()
+
+			file := "test_data/valid." + ext
+
+			assert.PanicsWithError(t, conf.ErrInvalidUnmarshalData.Error(), func() {
+				conf.LoadFile(file, func() {})
+			})
+		})
+
+		t.Run("with a valid file and data is not a pointer", func(t *testing.T) {
+			t.Parallel()
+
+			file := "test_data/valid." + ext
+			c := testconf{
+				String:    "default string",
+				Int:       1,
+				Invariant: "should not change",
+			}
+
+			assert.PanicsWithError(t, conf.ErrInvalidUnmarshalData.Error(), func() {
+				conf.LoadFile(file, c)
+			})
+		})
+
 		t.Run("with an invalid file", func(t *testing.T) {
 			t.Parallel()
 
@@ -206,6 +231,31 @@ func testLoadFiles(t *testing.T, ext string) {
 
 			assert.Equal(t, "", c.String)
 		})
+
+		t.Run("with a valid file and invalid data", func(t *testing.T) {
+			t.Parallel()
+
+			file := "test_data/valid." + ext
+
+			assert.PanicsWithError(t, conf.ErrInvalidUnmarshalData.Error(), func() {
+				conf.LoadFiles(func() {}, file)
+			})
+		})
+
+		t.Run("with a valid file and data is not a pointer", func(t *testing.T) {
+			t.Parallel()
+
+			file := "test_data/valid." + ext
+			c := testconf{
+				String:    "default string",
+				Int:       1,
+				Invariant: "should not change",
+			}
+
+			assert.PanicsWithError(t, conf.ErrInvalidUnmarshalData.Error(), func() {
+				conf.LoadFiles(c, file)
+			})
+		})
 	})
 }
 
@@ -245,8 +295,9 @@ func testSaveFile(t *testing.T, ext string) {
 			tmpDir := t.TempDir()
 			file := filepath.Join(tmpDir, "test."+ext)
 
-			err := conf.SaveFile(file, func() error { return nil })
+			assert.PanicsWithError(t, conf.ErrInvalidMarshalData.Error(), func() {
-			require.Error(t, err)
+				conf.SaveFile(file, func() error { return nil })
+			})
 
 			assert.NoFileExists(t, file)
 		})
@@ -437,7 +488,32 @@ func testLoadAndUpdateFile(t *testing.T, ext string) {
 			require.NoError(t, err)
 			assert.NotContains(t, string(newContent), "Unknown")
 
-			assert.True(t, updated)
+			assert.True(t, updated, "the config file has not been updated")
+		})
+
+		t.Run("with a valid file and invalid data", func(t *testing.T) {
+			t.Parallel()
+
+			file := "test_data/valid." + ext
+
+			assert.PanicsWithError(t, conf.ErrInvalidUnmarshalData.Error(), func() {
+				conf.LoadAndUpdateFile(file, func() {})
+			})
+		})
+
+		t.Run("with a valid file and data is not a pointer", func(t *testing.T) {
+			t.Parallel()
+
+			file := "test_data/valid." + ext
+			c := testconf{
+				String:    "default string",
+				Int:       1,
+				Invariant: "should not change",
+			}
+
+			assert.PanicsWithError(t, conf.ErrInvalidUnmarshalData.Error(), func() {
+				conf.LoadAndUpdateFile(file, c)
+			})
 		})
 	})
 }