config.go

@@ -1,6 +1,6 @@
 // Package config provides layered configuration management for the Core framework.
 //
-// Configuration values are resolved in priority order: defaults -> file -> env -> flags.
+// Configuration values are resolved in priority order: defaults -> file -> env -> Set().
 // Values are stored in a YAML file at ~/.core/config.yaml by default.
 //
 // Keys use dot notation for nested access:
@@ -11,6 +11,7 @@
 package config
 
 import (
+	"errors"
 	"iter"
 	"maps"
 	"os"
@@ -101,24 +102,21 @@ func New(opts ...Option) (*Config, error) {
 }
 
 // LoadFile reads a configuration file from the given medium and path and merges it into the current config.
-// It supports YAML and environment files (.env).
+// It supports YAML, JSON, TOML, and environment files (.env).
 func (c *Config) LoadFile(m coreio.Medium, path string) error {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 
+	configType, err := configTypeForPath(path)
+	if err != nil {
+		return coreerr.E("config.LoadFile", "unsupported config file type: "+path, err)
+	}
+
 	content, err := m.Read(path)
 	if err != nil {
 		return coreerr.E("config.LoadFile", "failed to read config file: "+path, err)
 	}
 
-	ext := filepath.Ext(path)
-	configType := "yaml"
-	if ext == "" && filepath.Base(path) == ".env" {
-		configType = "env"
-	} else if ext != "" {
-		configType = strings.TrimPrefix(ext, ".")
-	}
-
 	// Load into file-backed viper
 	c.f.SetConfigType(configType)
 	if err := c.f.MergeConfig(strings.NewReader(content)); err != nil {
@@ -134,6 +132,24 @@ func (c *Config) LoadFile(m coreio.Medium, path string) error {
 	return nil
 }
 
+func configTypeForPath(path string) (string, error) {
+	ext := filepath.Ext(path)
+	switch {
+	case ext == "" && filepath.Base(path) == ".env":
+		return "env", nil
+	case ext == "":
+		return "yaml", nil
+	}
+
+	configType := strings.TrimPrefix(ext, ".")
+	switch configType {
+	case "yaml", "yml", "json", "toml", "env":
+		return configType, nil
+	default:
+		return "", errors.New("unsupported config file type")
+	}
+}
+
 // Get retrieves a configuration value by dot-notation key and stores it in out.
 // If key is empty, it unmarshals the entire configuration into out.
 // The out parameter must be a pointer to the target type.

config_test.go

@@ -246,6 +246,50 @@ func TestConfig_LoadFile_Env(t *testing.T) {
 	assert.Equal(t, "bar", foo)
 }
 
+func TestConfig_LoadFile_JSON_Good(t *testing.T) {
+	m := coreio.NewMockMedium()
+	m.Files["/tmp/test/config.json"] = `{"service":{"name":"core"}}`
+
+	cfg, err := New(WithMedium(m), WithPath("/config.yaml"))
+	assert.NoError(t, err)
+
+	err = cfg.LoadFile(m, "/tmp/test/config.json")
+	assert.NoError(t, err)
+
+	var name string
+	err = cfg.Get("service.name", &name)
+	assert.NoError(t, err)
+	assert.Equal(t, "core", name)
+}
+
+func TestConfig_LoadFile_TOML_Good(t *testing.T) {
+	m := coreio.NewMockMedium()
+	m.Files["/tmp/test/config.toml"] = "service = { name = \"core\" }\n"
+
+	cfg, err := New(WithMedium(m), WithPath("/config.yaml"))
+	assert.NoError(t, err)
+
+	err = cfg.LoadFile(m, "/tmp/test/config.toml")
+	assert.NoError(t, err)
+
+	var name string
+	err = cfg.Get("service.name", &name)
+	assert.NoError(t, err)
+	assert.Equal(t, "core", name)
+}
+
+func TestConfig_LoadFile_Unsupported_Bad(t *testing.T) {
+	m := coreio.NewMockMedium()
+	m.Files["/tmp/test/config.txt"] = "service = core\n"
+
+	cfg, err := New(WithMedium(m), WithPath("/config.yaml"))
+	assert.NoError(t, err)
+
+	err = cfg.LoadFile(m, "/tmp/test/config.txt")
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "unsupported config file type")
+}
+
 func TestConfig_WithEnvPrefix(t *testing.T) {
 	t.Setenv("MYAPP_SETTING", "secret")
 

docs/index.md

@@ -5,7 +5,7 @@ description: Layered configuration management for the Core framework with file,
 
 # config
 
-`forge.lthn.ai/core/config` provides layered configuration management for applications built on the Core framework. It resolves values through a priority chain -- defaults, file, environment variables, flags -- so that the same codebase works identically across local development, CI, and production without code changes.
+`forge.lthn.ai/core/config` provides layered configuration management for applications built on the Core framework. It resolves values through a priority chain -- defaults, file, environment variables, and explicit `Set()` calls -- so that the same codebase works identically across local development, CI, and production without code changes.
 
 ## Module Path
 
@@ -85,7 +85,7 @@ Values are resolved in ascending priority order:
 1. **Defaults** -- hardcoded fallbacks (via `Set()` before any file load)
 2. **File** -- YAML loaded from `~/.core/config.yaml` (or a custom path)
 3. **Environment variables** -- prefixed with `CORE_CONFIG_` by default
-4. **Explicit Set()** -- in-memory overrides applied at runtime
+4. **Explicit `Set()`** -- in-memory overrides applied at runtime
 
 Environment variables always override file values. An explicit `Set()` call overrides everything.