fix dynamic file path loading

.devcontainer/Dockerfile

@@ -3,13 +3,23 @@ FROM golang:1.25.4-trixie
 # Install basic dependencies
 RUN apt update && \
     apt install -y \
-        git \
         curl \
+        git \
+        tar \
     && \
     rm -rf /var/lib/apt/lists/*
 
 # Install task
-RUN sh -c "$(curl --location https://taskfile.dev/install.sh)" -- -d v3.36.0
+RUN sh -c "$(curl -L https://taskfile.dev/install.sh)" -- -d v3.36.0
 
 # Install golangci-lint
-RUN sh -c "$(curl --location https://raw.githubusercontent.com/golangci/golangci-lint/HEAD/install.sh)" -- v2.6.2
+RUN sh -c "$(curl -L https://raw.githubusercontent.com/golangci/golangci-lint/HEAD/install.sh)" -- v2.6.2
+
+# Install gotestsum
+RUN curl -L https://github.com/gotestyourself/gotestsum/releases/download/v1.13.0/gotestsum_1.13.0_linux_amd64.tar.gz -o gotestsum.tar.gz && \
+    tar -xzf gotestsum.tar.gz -C /usr/local/bin gotestsum && \
+    rm gotestsum.tar.gz
+
+# Install jd
+RUN curl -L https://github.com/josephburnett/jd/releases/download/v2.3.0/jd-amd64-linux -o /usr/local/bin/jd && \
+    chmod +x /usr/local/bin/jd

.devcontainer/devcontainer.json

@@ -1,5 +1,5 @@
 {
-    "image": "ghcr.io/codetent/confless/dev:sha-382640a",
+    "image": "ghcr.io/codetent/confless/dev:sha-6fd6dc8",
     "runArgs": [
         "--platform=linux/amd64"
     ],

.github/workflows/check.yml

@@ -13,7 +13,7 @@ jobs:
   check:
     runs-on: ubuntu-latest
     container:
-      image: ghcr.io/codetent/confless/dev:sha-382640a
+      image: ghcr.io/codetent/confless/dev:sha-6fd6dc8
       env:
         GOFLAGS: -buildvcs=false
     steps:

README.md

@@ -74,6 +74,7 @@ Sources are applied in the following order (later sources override earlier ones)
 1. **Files** (in registration order)
 2. **Command-line flags**
 3. **Environment variables** (highest precedence)
+4. **Dynamically registered files**
 
 ### Files
 
@@ -112,7 +113,9 @@ database:
 
 You can mark a field in your configuration with the `confless:"file"` tag to automatically load it as a configuration file. This is useful for environment-specific configurations.
 
-The format can be specified explicitly in the tag (`confless:"file,format=json"`) otherwise it defaults to JSON.
+The format can be specified explicitly in the tag (`confless:"file,format=yaml"`) otherwise it defaults to JSON.
+
+Note that dynamically registered files are loaded at the end, while statically registered files are loaded first.
 
 ```go
 type Config struct {

Taskfile.yml

@@ -1,9 +1,15 @@
 version: '3'
 
+includes:
+  examples:
+    dir: examples
+    taskfile: examples/Taskfile.yml
+
 tasks:
   test:
     cmds:
-      - go test -v ./...
+      - gotestsum --format testdox
+      - task: examples:test
 
   lint:
     cmds:

confless.go

@@ -6,6 +6,12 @@ var (
 	defaultLoader = NewLoader()
 )
 
+// Configure the default loader with the given options.
+// Note that reconfiguring the default loader will reset the registered sources.
+func Configure(opts ...loaderOption) {
+	defaultLoader = NewLoader(opts...)
+}
+
 // Register an environment variable prefix to load.
 // Names are converted to dot-separated paths (e.g. "MY_FLAG" -> "my.flag").
 func RegisterEnv(pre string) {

examples/Taskfile.yml

@@ -0,0 +1,17 @@
+version: '3'
+
+tasks:
+  test:
+    cmds:
+      - cmd: |
+          cd {{ .ITEM.dir }} &&
+          {{ .ITEM.cmd }} | jd {{ .ITEM.expected }}
+        for:
+          - dir: simple
+            cmd: >-
+              APP_DATABASE_USERNAME=user
+              APP_DATABASE_PASSWORD=pass
+              go run main.go
+              --debug
+              --config=files/override.yaml
+            expected: expected.json

examples/simple/expected.json

@@ -0,0 +1,13 @@
+{
+    "name": "app",
+    "host": "0.0.0.0",
+    "port": 8080,
+    "debug": true,
+    "database": {
+        "host": "db.example.com",
+        "port": 5432,
+        "username": "user",
+        "password": "pass"
+    },
+    "Config": "files/override.yaml"
+}

examples/simple/files/config.json

@@ -0,0 +1,5 @@
+{
+  "name": "app",
+  "host": "0.0.0.0",
+  "port": 8080
+}

examples/simple/files/override.yaml

@@ -0,0 +1,4 @@
+database:
+  host: db.example.com
+  port: 5432
+  ssl: true

examples/simple/main.go

@@ -0,0 +1,67 @@
+package main
+
+import (
+	"encoding/json"
+	"flag"
+	"log"
+	"os"
+
+	"github.com/codetent/confless"
+)
+
+type Config struct {
+	Name  string `json:"name"`
+	Host  string `json:"host"`
+	Port  int    `json:"port"`
+	Debug bool   `json:"debug"`
+
+	Database struct {
+		Host     string `json:"host"`
+		Port     int    `json:"port"`
+		Username string `json:"username"`
+		Password string `json:"password"`
+	} `json:"database"`
+
+	Config string `confless:"file,format=yaml"`
+}
+
+func main() {
+	// Define command-line flags
+	flag.String("host", "", "Server host")
+	flag.Int("port", 0, "Server port")
+	flag.Bool("debug", false, "Enable debug mode")
+	flag.String("database-host", "", "Database host")
+	flag.Int("database-port", 0, "Database port")
+	flag.Bool("database-ssl", false, "Enable SSL for database")
+	flag.String("config", "", "Path to configuration file")
+
+	// Set default values
+	config := &Config{
+		Name:  "default",
+		Host:  "localhost",
+		Port:  8080,
+		Debug: false,
+	}
+
+	// Read configuration from command-line flags
+	confless.RegisterFlags(flag.CommandLine)
+	// Read configuration from environment variables starting with "APP_"
+	confless.RegisterEnv("APP")
+	// Read configuration from config.json
+	confless.RegisterFile("files/config.json", confless.FileFormatJSON)
+
+	// Parse flags before loading
+	flag.Parse()
+
+	// Load configuration from all registered sources
+	err := confless.Load(config)
+	if err != nil {
+		log.Fatalf("Failed to load configuration: %v", err)
+	}
+
+	// Print the final configuration to stdout
+	enc := json.NewEncoder(os.Stdout)
+	if err := enc.Encode(config); err != nil {
+		log.Fatalf("Failed to encode config as JSON: %v", err)
+	}
+}

loader.go

@@ -69,29 +69,8 @@ func (l *loader) RegisterFlags(f *flag.FlagSet) {
 
 // Populate the object by applying the registered sources.
 func (l *loader) Load(obj any) error {
-	files := make([]*configFile, 0, len(l.files))
-	files = append(files, l.files...)
-
-	// Add file paths from tagged fields.
-	for field, format := range findFileFields(obj) {
-		path := field.String()
-		if path == "" {
-			continue
-		}
-
-		format := fileFormat(format)
-		if format == "" {
-			format = FileFormatJSON
-		}
-
-		files = append(files, &configFile{
-			path:   path,
-			format: format,
-		})
-	}
-
 	// Load the files.
-	for _, file := range files {
+	for _, file := range l.files {
 		// Open the file.
 		f, err := l.fs.Open(file.path)
 		if err != nil {
@@ -127,5 +106,36 @@ func (l *loader) Load(obj any) error {
 		}
 	}
 
+	// Load dynamically files.
+	for field, format := range findFileFields(obj) {
+		path := field.String()
+		if path == "" {
+			continue
+		}
+
+		format := fileFormat(format)
+		if format == "" {
+			format = FileFormatJSON
+		}
+
+		// Open the file.
+		f, err := l.fs.Open(path)
+		if err != nil {
+			if os.IsNotExist(err) {
+				// Skip if file does not exist.
+				continue
+			}
+
+			return fmt.Errorf("failed to open file: %w", err)
+		}
+
+		// Populate the object by the file.
+		err = populateByFile(f, string(format), obj)
+		_ = f.Close()
+		if err != nil {
+			return fmt.Errorf("failed to load file: %w", err)
+		}
+	}
+
 	return nil
 }