fix(config): tighten --config path handling

internal/command/command.go

@@ -648,16 +648,61 @@ func LoadAppConfigIfPresent(ctx context.Context) (context.Context, error) {
 		return ctx, nil
 	}
 
+	explicitPath := flag.GetAppConfigFilePath(ctx)
+	var candidates []string
+
+	if explicitPath != "" {
+		if err := validateConfigPath(explicitPath); err != nil {
+			return nil, err
+		}
+		candidates = []string{explicitPath}
+	} else {
+		candidates = buildDefaultCandidates(ctx)
+	}
+
+	return loadConfig(ctx, candidates, explicitPath)
+}
+
+func validateConfigPath(path string) error {
+	stat, err := os.Stat(path)
+	if err != nil {
+		if errors.Is(err, fs.ErrNotExist) {
+			return fmt.Errorf("the path given with --config (%q) does not exist", path)
+		}
+		return fmt.Errorf("failed to stat %q: %w", path, err)
+	}
+
+	if stat.IsDir() {
+		return fmt.Errorf("the path given with --config (%q) is a directory, not a file", path)
+	}
+
+	return nil
+}
+
+func buildDefaultCandidates(ctx context.Context) []string {
+	wd := state.WorkingDirectory(ctx)
+	base := filepath.Join(wd, appconfig.DefaultConfigFileName)
+	pathNoExt := strings.TrimSuffix(base, filepath.Ext(base))
+
+	return []string{
+		base,
+		pathNoExt + ".json",
+		pathNoExt + ".yaml",
+	}
+}
+
+func loadConfig(ctx context.Context, candidates []string, explicitPath string) (context.Context, error) {
 	logger := logger.FromContext(ctx)
-	for _, path := range appConfigFilePaths(ctx) {
+
+	for _, path := range candidates {
 		switch cfg, err := appconfig.LoadConfig(path); {
 		case err == nil:
 			logger.Debugf("app config loaded from %s", path)
 			if err := cfg.SetMachinesPlatform(); err != nil {
-				logger.Warnf("WARNING the config file at '%s' is not valid: %s", path, err)
+				logger.Warnf("config at '%s' is not valid: %s", path, err)
 			}
 			metrics.IsUsingGPU = cfg.IsUsingGPU()
-			return appconfig.WithConfig(ctx, cfg), nil // we loaded a configuration file
+			return appconfig.WithConfig(ctx, cfg), nil
 		case errors.Is(err, fs.ErrNotExist):
 			logger.Debugf("no app config found at %s; skipped.", path)
 			continue
@@ -666,27 +711,11 @@ func LoadAppConfigIfPresent(ctx context.Context) (context.Context, error) {
 		}
 	}
 
-	return ctx, nil
-}
-
-// appConfigFilePaths returns the possible paths at which we may find a fly.toml
-// in order of preference. it takes into consideration whether the user has
-// specified a command-line path to a config file.
-func appConfigFilePaths(ctx context.Context) (paths []string) {
-	if p := flag.GetAppConfigFilePath(ctx); p != "" {
-		paths = append(paths, p, filepath.Join(p, appconfig.DefaultConfigFileName))
-
-		return
+	if explicitPath != "" {
+		return nil, fmt.Errorf("no app config could be loaded from %q", explicitPath)
 	}
 
-	wd := state.WorkingDirectory(ctx)
-	paths = append(paths,
-		filepath.Join(wd, appconfig.DefaultConfigFileName),
-		filepath.Join(wd, strings.Replace(appconfig.DefaultConfigFileName, ".toml", ".json", 1)),
-		filepath.Join(wd, strings.Replace(appconfig.DefaultConfigFileName, ".toml", ".yaml", 1)),
-	)
-
-	return
+	return ctx, nil
 }
 
 var ErrRequireAppName = fmt.Errorf("the config for your app is missing an app name, add an app field to the fly.toml file or specify with the -a flag")

internal/command/command_config_test.go

@@ -0,0 +1,77 @@
+package command
+
+import (
+	"bytes"
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/spf13/pflag"
+	"github.com/stretchr/testify/require"
+
+	"github.com/superfly/flyctl/internal/appconfig"
+	"github.com/superfly/flyctl/internal/flag"
+	"github.com/superfly/flyctl/internal/logger"
+	"github.com/superfly/flyctl/internal/state"
+)
+
+func writeFlyToml(tb testing.TB, dir string) string {
+	tb.Helper()
+	path := filepath.Join(dir, appconfig.DefaultConfigFileName)
+	content := []byte("app = \"myapp\"\n")
+	require.NoError(tb, os.WriteFile(path, content, 0o644))
+	return path
+}
+
+func newTestContext(wd string, fs *pflag.FlagSet) context.Context {
+	ctx := context.Background()
+	l := logger.New(&bytes.Buffer{}, logger.Debug, false)
+	ctx = logger.NewContext(ctx, l)
+	ctx = state.WithWorkingDirectory(ctx, wd)
+	ctx = flag.NewContext(ctx, fs)
+	return ctx
+}
+
+func TestLoadAppConfigIfPresent_ExplicitFile(t *testing.T) {
+	tmp := t.TempDir()
+	filePath := writeFlyToml(t, tmp)
+
+	fs := pflag.NewFlagSet("test", pflag.ContinueOnError)
+	fs.StringP("config", "c", "", "")
+	require.NoError(t, fs.Set("config", filePath))
+
+	ctxIn := newTestContext(tmp, fs)
+	ctxOut, err := LoadAppConfigIfPresent(ctxIn)
+	require.NoError(t, err)
+
+	cfg := appconfig.ConfigFromContext(ctxOut)
+	require.NotNil(t, cfg)
+	require.Equal(t, "myapp", cfg.AppName)
+}
+
+func TestLoadAppConfigIfPresent_NonExistentPath(t *testing.T) {
+	tmp := t.TempDir()
+	nonExist := filepath.Join(tmp, "does-not-exist.toml")
+
+	fs := pflag.NewFlagSet("test", pflag.ContinueOnError)
+	fs.StringP("config", "c", "", "")
+	require.NoError(t, fs.Set("config", nonExist))
+
+	ctxIn := newTestContext(tmp, fs)
+	_, err := LoadAppConfigIfPresent(ctxIn)
+	require.Error(t, err)
+}
+
+func TestLoadAppConfigIfPresent_AutoDiscovery(t *testing.T) {
+	tmp := t.TempDir()
+	_ = writeFlyToml(t, tmp)
+
+	fs := pflag.NewFlagSet("test", pflag.ContinueOnError)
+
+	ctxIn := newTestContext(tmp, fs)
+	ctxOut, err := LoadAppConfigIfPresent(ctxIn)
+	require.NoError(t, err)
+	cfg := appconfig.ConfigFromContext(ctxOut)
+	require.NotNil(t, cfg)
+}