go-sqlite-default-path

Answer

The divergence: config.DefaultSQLitePath was ./memory.db while the docs promised ~/.dexdat-memory/memory.db. Four coordinated changes align code to docs without weakening explicit configuration.

1. Default path (config.go) — default to the documented home-relative path, expand ~ at load time:

const DefaultSQLitePath = "~/.dexdat-memory/memory.db"

func expandHome(p string) (string, error) {
    if p == "~" || strings.HasPrefix(p, "~/") {
        home, err := os.UserHomeDir()
        if err != nil {
            return "", fmt.Errorf("resolve home directory: %w", err)
        }
        if p == "~" {
            return home, nil
        }
        return filepath.Join(home, strings.TrimPrefix(p, "~/")), nil
    }
    return p, nil // explicit relative/absolute paths stay as the operator wrote them
}

2. Explicit-vs-default detection — a config struct carries IsDefault, computed from the config file (v.InConfig, not v.IsSet — viper's IsSet reports true for keys that only have a default) plus a direct SQLITE_DB_PATH env check. An empty SQLITE_DB_PATH counts as unset (matches viper's default allow-empty-env=false):

v.SetDefault("sqlite.path", DefaultSQLitePath)
_ = v.BindEnv("sqlite.path", EnvSQLitePath) // SQLITE_DB_PATH

explicit := os.Getenv(EnvSQLitePath) != "" || v.InConfig("sqlite.path")
cfg := &Config{SQLite: SQLiteConfig{Path: expanded, IsDefault: !explicit}}

3. Auto-create only for zero-config; fail-fast otherwise (sqlite.go) — MkdirAll guarded by IsDefault; explicit paths that point at a missing directory error at startup instead of silently creating directories the operator never asked for:

func Open(ctx context.Context, cfg *config.Config, log *slog.Logger) (*sql.DB, error) {
    if cfg.SQLite.IsDefault {
        dir := filepath.Dir(cfg.SQLite.Path)
        if err := os.MkdirAll(dir, 0o700); err != nil {
            return nil, fmt.Errorf("create data dir %q: %w", dir, err)
        }
    }
    // ... sql.Open + PingContext as before
}

4. Startup log (main.go) — the canonical "where is my data" answer:

log.Info("starting dexdat-memory",
    "sqlite_path", cfg.SQLite.Path,
    "sqlite_path_is_default", cfg.SQLite.IsDefault,
)

5. viper v1.19 missing-config quirk — with SetConfigFile on a missing file, v1.19 returns a raw *fs.PathError (*os.PathError is an alias) instead of ConfigFileNotFoundError; treat both as "no config present", anything else is a real error:

if err := v.ReadInConfig(); err != nil {
    var notFound viper.ConfigFileNotFoundError
    var pathErr *fs.PathError
    switch {
    case errors.As(err, &notFound), errors.As(err, &pathErr):
        // no config file: zero-config mode, defaults apply
    default:
        return nil, fmt.Errorf("read config: %w", err)
    }
}

6. README — added a Data location section documenting ~/.dexdat-memory/memory.db as default, SQLITE_DB_PATH/sqlite.path override, the auto-create-only-for-default rule, and the startup log line.