Libraries: Revert changes that were necessitated by a new rule we have decided not to introduce.
Parser:
- Support mixed constructors/bindings in types.
- Disallow zero-length hex sequences in character escapes: `\x`, `\u`, `\u{}`, `\U`, `\U{}` are no longer legal synonyms for `\0` (matches old parser behavior).
Ensure all tokens from the input are represented in trees resulting from invalid inputs--tests now cover every reachable code line that creates an `Invalid` node. (Also implemented stricter validation, mainly of `import`/`export` statements.)
See: https://www.pivotaltracker.com/story/show/183405907
Fix bugs in `TreeToIr` (rewrite) and parser. Implement more undocumented features in parser. Emulate some old parser bugs and quirks for compatibility.
Changes in libs:
- Fix some bugs.
- Clean up some odd syntaxes that the old parser translates idiosyncratically.
- Constructors are now required to precede methods.
# Important Notes
Out of 221 files:
- 215 match the old parser
- 6 contain complex types the old parser is known not to handle correctly
So, compared to the old parser, the new parser parses 103% of files correctly.
- Special precedence rules for case-of so that `:` operator works without parens or nospace-grouping.
- Support an old-lambda syntax: `x->x-> x`. According to the usual rules, the first nospace group would be parsed as an operator section. The expression now parses as a lambda that contains a lambda.
- Match old parser treatment of # in doc comments.
- Tweak precedence so (a : B = c) works.
- Documented constructors.
- Implement macro-contexts-lite (`from` is now only a keyword at the beginning of a line)
- Support special nospace-group handling for old lambdas (so expressions like this work: `x-> y-> x + y`)
- Fix a text-escape incompatibility
# Important Notes
- There is now an `OperatorFunction`, which is like a `Function` but has an operator for a name, and likewise an `OperatorTypeSignature`.
