Problems:
- When iterating over an empty string in a list comprehension, the
result is an empty string. This is a bug, it should be an error.
- When iterating over a non-empty string in a list comprehension, the
expected and unexpected types in the error message are swapped.
- Error messages mention "std.flatMap" when object/list comprehensions
would iterate over a value that is neither array nor string.
```
$ jsonnet --version
Jsonnet commandline interpreter (Go implementation) v0.21.0-rc2
$ jsonnet -e '[a for a in ""]'
""
$ jsonnet -e '[a for a in "b"]'
RUNTIME ERROR: Unexpected type array, expected string
<cmdline>:1:1-17
During evaluation
$ jsonnet -e '{[a]: 1 for a in 2}'
RUNTIME ERROR: std.flatMap second param must be array / string, got number
<cmdline>:1:1-20
<cmdline>:1:1-20
During evaluation
$ jsonnet -e '[a for a in 1]'
RUNTIME ERROR: std.flatMap second param must be array / string, got number
<cmdline>:1:1-15
During evaluation
```
FWIW, the C++ implementation does not have any of these problems. It
gives:
```
RUNTIME ERROR: In comprehension, can only iterate over array.
```
In the Go implementation comprehensions are desugared to a call to
std.flatMap which does accept a string in the "arr" parameter.
The fix: Desugar comprehensions to a call to a new hidden builtin which
only accepts arrays.
manifestYamlDoc takes two optional parameters, `indent_array_in_object` and `quote_keys`. This commit teaches jsonnet-lint about them so that it doesn't raise errors when you use them.
There are other stdlib library functions with this problem; the true solution is probably to auto-generate this from the stdlib AST, but this at least gets the linter happy with this particular function.
There is no reason for external users to directly depend
on parser. It had a few random things exported as well,
namely errors and "children" functions (helpers for AST
traversal).
It was easy to extract the errors package, but I needed to leave
children in parser for now. The errors package was also
made internal, but it's a candidate for making it public
again potentially (if someone wants to display error messages
just like us). For now it's probably too incomplete anyway.
This change has a potential of breaking the existing users
since we technically remove public APIs. These were not needed
or even helpful for actually running Jsonnet code, but perhaps
someone used them anyway.
