The most common reason for this issue is improper use of struct tags (eg. `yaml` or `json`). Viper uses [github.com/mitchellh/mapstructure](https://github.com/mitchellh/mapstructure) under the hood for unmarshaling values which uses `mapstructure` tags by default. Please refer to the library's documentation for using other struct tags.
## Cannot find package
Viper installation seems to fail a lot lately with the following (or a similar) error:
```
cannot find package "github.com/hashicorp/hcl/tree/hcl1" in any of:
As the error message suggests, Go tries to look up dependencies in `GOPATH` mode (as it's commonly called) from the `GOPATH`.
Viper opted to use [Go Modules](https://github.com/golang/go/wiki/Modules) to manage its dependencies. While in many cases the two methods are interchangeable, once a dependency releases new (major) versions, `GOPATH` mode is no longer able to decide which version to use, so it'll either use one that's already present or pick a version (usually the `master` branch).
The solution is easy: switch to using Go Modules.
Please refer to the [wiki](https://github.com/golang/go/wiki/Modules) on how to do that.
