The `AnyError` placeholder error can cause tests to succeed for errors
other than what was expected. That is, the use of `AnyError` can mask
bugs in a unit test. So replace it with the specific error, or error type,
the test expects to be raised.
This does not remove the anyError structure because it is used in
the TestCase.DoesNotCompile() method. To keep the size of this change
as small as possible I want to defer updating that use to a separate
change. However, remove the public AnyError var so future test writers
don't attempt to use it.
This also replaces the slightly awkward "arguments here" reason with
"argument count" as the "what" for a typical errs.ArityMismatch
exception. It also reformats most of the constructors so that the "what"
is on the same line. This makes `grep errs.ArityMismatch **.go` more
useful as a result.
This change makes feeding output to commands which handle NUL terminated
"lines" (e.g., `fzf -read0` or `xargs -0`) extremely fast compared to
using an explicit Elvish loop that does `print $val"\x00"`. Similarly for
handling input from commands that produce NUL terminated "lines" (e.g.,
`find . -print0`) compared to an Elvish loop using `read-upto "\x00"`.
Resolves#1070
Related #1053
There is more work to be done but this should address 99.9999% of the
expected uses of a `printf` builtin. Some corner cases which don't have
a POSIX analog, such as support for Elvish bool types will be implemented
in future changes.
Resolves#1132
This will likely become a basic operation in future that can support more types
than exceptions, so putting it in the builtin namespace is appropriate.
Also remove the exc: module altogether as it contains nothing now. All the
introspection features are now implemented as fields of the exception values and
the reason values.
