In some rare cases, the global predeclarations would clash, for example:
> module spam { export def foo [] { "foo" } }; def foo [] { "bar" }
In the example, the `foo [] { "bar" }` would get predeclared first, then
the predeclaration would be overwritten and consumed by `foo [] {"foo"}`
inside the module, then when parsing the actual `foo [] { "bar" }`, it
would not find its predeclaration.
Hiding definitions now should work correctly with repeated use of 'use',
'def' and 'hide' keywords.
The key change is that 'hide foo' will hide all definitions of foo
that were defined/used within the scope (those from other scopes are
still available). This makes the logic simpler and I found it leads to a
simpler mental map: you don't need to remember the order of defined/used
commands withing the scope -- it just hides all.
* Fixes a panic with defining two commands with the same name caused by
declaration not found after predeclaration.
* Adds a new error if a custom command is defined more than once in one
block.
* Add some tests
* Hiding logic is simplified and fixed so you can hide and unhide the
same def repeatedly.
* Separates predeclared ids into its own data structure to protect them
from hiding. Otherwise, you could hide the predeclared variable and
the actual def would panic.
