Detect missing explicit config

internal/command/command.go

@@ -707,7 +707,8 @@ func LoadAppConfigIfPresent(ctx context.Context) (context.Context, error) {
 	}
 
 	logger := logger.FromContext(ctx)
-	for _, path := range appConfigFilePaths(ctx) {
+	configPaths := appConfigFilePaths(ctx)
+	for _, path := range configPaths {
 		switch cfg, err := appconfig.LoadConfig(path); {
 		case err == nil:
 			logger.Debugf("app config loaded from %s", path)
@@ -726,6 +727,11 @@ func LoadAppConfigIfPresent(ctx context.Context) (context.Context, error) {
 		}
 	}
 
+	// If the user explicitly specified a config file path and we couldn't find it, return an error
+	if configPath := flag.GetAppConfigFilePath(ctx); configPath != "" {
+		return nil, fmt.Errorf("config file not found at specified path: %s (also tried: %s)", configPath, filepath.Join(configPath, appconfig.DefaultConfigFileName))
+	}
+
 	return ctx, nil
 }
 

internal/command/load_app_config_test.go

@@ -0,0 +1,80 @@
+package command
+
+import (
+	"context"
+	"io"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/spf13/pflag"
+	"github.com/superfly/flyctl/internal/appconfig"
+	"github.com/superfly/flyctl/internal/flag"
+	"github.com/superfly/flyctl/internal/flag/flagnames"
+	"github.com/superfly/flyctl/internal/logger"
+	"github.com/superfly/flyctl/internal/state"
+)
+
+func TestLoadAppConfigIfPresent(t *testing.T) {
+	t.Run("missing explicitly specified config returns an error", func(t *testing.T) {
+		configPath := filepath.Join(t.TempDir(), "missing.toml")
+		ctx := loadAppConfigTestContext(t, configPath)
+
+		loadedCtx, err := LoadAppConfigIfPresent(ctx)
+		if err == nil {
+			t.Fatal("expected an error for a missing explicitly specified config")
+		}
+		if loadedCtx != nil {
+			t.Fatal("expected a nil context when loading fails")
+		}
+
+		want := "config file not found at specified path: " + configPath + " (also tried: " + filepath.Join(configPath, appconfig.DefaultConfigFileName) + ")"
+		if got := err.Error(); got != want {
+			t.Fatalf("error = %q, want %q", got, want)
+		}
+	})
+
+	t.Run("missing default config is allowed", func(t *testing.T) {
+		ctx := loadAppConfigTestContext(t, "")
+
+		loadedCtx, err := LoadAppConfigIfPresent(ctx)
+		if err != nil {
+			t.Fatalf("LoadAppConfigIfPresent() error = %v", err)
+		}
+		if loadedCtx != ctx {
+			t.Fatal("expected the original context when no default config exists")
+		}
+	})
+
+	t.Run("existing explicitly specified config is loaded", func(t *testing.T) {
+		configPath := filepath.Join(t.TempDir(), "custom.toml")
+		if err := os.WriteFile(configPath, []byte("app = \"test-app\"\n"), 0o600); err != nil {
+			t.Fatal(err)
+		}
+		ctx := loadAppConfigTestContext(t, configPath)
+
+		loadedCtx, err := LoadAppConfigIfPresent(ctx)
+		if err != nil {
+			t.Fatalf("LoadAppConfigIfPresent() error = %v", err)
+		}
+		if cfg := appconfig.ConfigFromContext(loadedCtx); cfg == nil {
+			t.Fatal("expected the explicit config to be added to the context")
+		}
+	})
+}
+
+func loadAppConfigTestContext(t *testing.T, configPath string) context.Context {
+	t.Helper()
+
+	fs := pflag.NewFlagSet("test", pflag.ContinueOnError)
+	fs.String(flagnames.AppConfigFilePath, "", "")
+	if configPath != "" {
+		if err := fs.Set(flagnames.AppConfigFilePath, configPath); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	ctx := flag.NewContext(context.Background(), fs)
+	ctx = logger.NewContext(ctx, logger.New(io.Discard, logger.NoLogLevel, false))
+	return state.WithWorkingDirectory(ctx, t.TempDir())
+}