parse error when setting breakpoint with nestedIdent in GHCi

Summary

The user guide contains an example:

foo s = 'a' : add s
    where add = (++"z")

For which it should be possible to set a breakpoint with one of the following:

:break Main.foo.add
:break foo.add

But both produce an error message:

ghci> :break Main.foo.add

<interactive>:1:9: error: parse error on input ‘.’
ghci> :break foo.add

<interactive>:1:4: error: parse error on input ‘.’

Environment

• GHC version used: 8.10.4

Optional:

• Operating System: NixOS 21.05
• System Architecture: x86_64

Comments

See also this stackoverflow question.