Unify syntax error reporting

[scottfrazer]

Each parser context should have a queue of syntax errors. When one is found, the string message is added to the queue based on a SyntaxErrorFormatter.

SyntaxErrorFormatter should be have overridable methods, with a way of getting at source lines with an arrow pointing to a certain column.

There will be other error types that users will add to the list below when processing the AST.

Goals of this task are:

• All language targets should support overridable formatters with reasonable defaults, described below
• As proof of concept, extend the syntax error reporting for Hermes itself. Everything raise Exception in factory.py should now report a syntax error

SyntaxErrorFormatter for each language should have the following syntax errors:

unexpected_token

Currently displayed as: "Unrecognized token on line x, column y..."

Occurs when a we expect one token and get another, This is a LEXER error

file.ext:1:5: error: Unrecognized token

int ♭ain(
    ^

Or add mode information

file.ext:1:2: error: Unrecognized token

Occurred while scanning an object

{♭"abc"
 ^

excess_tokens

Currently displayed as: "Finished parsing without consuming all tokens"

Occurs when we've hit a terminal state parsing but there are still tokens left. This might also be accompanied with an unexpected_symbol.

file.ext:1:2: error: Finished parsing without consuming all tokens

{}}
  ^

unexpected_eof

Currently displayed as: "unexpected end of file"

Occurs when we're parsing a nonterminal and it's supposed to consume tokens but there are none left. What happens if we just continue anyway?

file.ext:1:2: error: Unexpected end of file

Expecting: :string

{
 ^

$object = :lbrace list($key_value_pair, :comma) :rbrace -> Object(values=$1)

no_more_tokens

Currently displayed as: "No more tokens. Expecting ..."

Occurs when we call expect() and there's nothing left in the token stream. This could probably be the error that happens after unexpected_eof

file.ext:1:2: error: No more tokens left to consume

Expecting: :string, :lsquare, :lbrace, :integer

{"key": 
       ^

$key_value_pair = :string :colon $value -> KeyValue(key=$0, value=$2)

invalid_terminal

Currently displayed as: "Invalid symbol ID ..."

Occurs when a terminal is invalid. Probably rarely usedWe should probably consume the token and continue if this is the case.

file.ext:1:2: error: Invalid terminal

Unsure how to process :unknown ("foobar")

$key_value_pair = :string :colon $value -> KeyValue(key=$0, value=$2)

unexpected_symbol

Currently displayed as: "Unexpected symbol (line {line}, col {col}) when parsing parse_{nt} ...")

This is a PARSER error, when we see a token that we weren't expecting. Perhaps throw it away and move on?

file.ext:1:5: error: Unexpected symbol when parsing $key_value_pair

Expecting (:colon) but got (:string)

{"abc" "def"}
        ^