This is a much cleaner way to expose the new option to disable recovery
added in 62720ad9f9. It also makes it possible to add further
options in the future without further breaking changes.
This is useful to avoid unbounded recursion/iteration while fuzzing.
It's not interesting to learn that the parser hits a stack overflow when
fed a million open parens for example.
My attempt to handle this case in 6f151109b5fdf88eb8b has proven
insufficient, the test case added by this commit was failing.
Solve this with a "start of file" non-terminal in the PEG grammar,
which unfortunately isn't portable but much better reflects the actual
implementation and is much simpler.
Currently the grammar fails to enforce matching whitespace or lack of
whitespace around operators that are immediately preceded by a multiline
string literal and terminating newline.
This script parses a PEG grammar definition and generates a simple
recursive descent parser that recognizes that grammar.
The intent is to use this tool to generate an oracle against which
std.zig.Ast.parse() can be fuzz tested.
Unfortunately, generating a "smith" that can produce all possible valid
source code according to the PEG grammar definition does not seem
feasible due to PEG semantics. In particular, modeling the ordered
choice operator ('/') with a smith is problematic and seems to have
worst-case exponential runtime. Consider that `A / B` is equivalent to
`A / !A B`, it is not sufficient for a smith to choose an option from
the ordered choice at random and generate an input matched by that
sub-expression.
The current handwritten AstSmith.zig implementation does not match the
exact semantics of the PEG grammar. It has some hacks (see the `not_*`
variables) to work around specific instances of the general problem
with ordered choice described above but that is not an acceptable
long term solution in my opinion.
Generating the oracle for the fuzz test automatically from the PEG
makes the oracle correct by construction and gives us a single source of
truth: the PEG definition in the language spec.
Andrew Kelley