On an up-to-date Tumbleweed (20190809) install, no additional repos,

`zypper in clang`

would install

```
The following 12 NEW packages are going to be installed:
  clang clang6-checker clang8 glibc-devel libclang6 libclang8 libLLVM6 libLTO8
  libstdc++6-devel-gcc9 libstdc++-devel libxcrypt-devel linux-glibc-devel

The following recommended package was automatically selected:
  clang6-checker
```

while `zypper in clang8` would install

```
The following 11 NEW packages are going to be installed:
  clang6-checker clang8 glibc-devel libclang6 libclang8 libLLVM6 libLTO8
  libstdc++6-devel-gcc9 libstdc++-devel libxcrypt-devel linux-glibc-devel

The following recommended package was automatically selected:
  clang6-checker

The following package is recommended, but will not be installed due to
conflicts or dependency issues:
  clang8-checker
```

and `zypper in clang clang-checker` would install

```
The following 6 NEW packages are going to be installed:
  clang clang8 clang8-checker clang-checker libclang8 libLTO8

The following recommended package was automatically selected:
  clang8-checker
```

In my opinion all three zypper commands should resolve to the same packages and
preferably the latter (no clang6*, libstdc++6* deps).