After the previous commit, nushell uses PrettyDebug and
PrettyDebugWithSource for our pretty-printed display output.
PrettyDebug produces a structured `pretty.rs` document rather than
writing directly into a fmt::Formatter, and types that implement
`PrettyDebug` have a convenience `display` method that produces a string
(to be used in situations where `Display` is needed for compatibility
with other traits, or where simple rendering is appropriate).
This commit extracts Tag, Span, Text, as well as source-related debug
facilities into a new crate called nu_source.
This change is much bigger than one might have expected because the
previous code relied heavily on implementing inherent methods on
`Tagged<T>` and `Spanned<T>`, which is no longer possible.
As a result, this change creates more concrete types instead of using
`Tagged<T>`. One notable example: Tagged<Value> became Value, and Value
became UntaggedValue.
This change clarifies the intent of the code in many places, but it does
make it a big change.
Adds modules for internal, external, and dynamic commands, as well as
the pipeline functionality. These are exported as their old names from
the classified module so as to keep its "interface" the same.
fixes#969, admittedly without a --delimiter alias
moves from_structured_data.rs to from_delimited_data.rs to better
identify its scope and adds to_delimited_data.rs. Now csv and tsv both
use the same code, tsv passes in a fixed '\t' argument where csv passes
in the value of --separator
`save` attempts to convert input based on the target filename extension,
and expects a stream of text otherwise. However the error message is
unclear and provides little guidance, hopefully this is less confusing
to new users.
It might be worthwhile to also add a hint about adding an extension,
though I'm not sure if it's possible to emit multiple diagnostics.
