Run parser twice; enable invalid_* rules only on the second run

[lysnikolaou]

BPO	42123
Nosy	@gvanrossum, @terryjreedy, @lysnikolaou, @pablogsal
PRs	bpo-42123: Run the parser two times and only enable invalid rules on the second run #22111 [3.9] bpo-42123: Run the parser two times and only enable invalid rules on the second run (GH-22111) #23011

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/lysnikolaou'
closed_at = <Date 2020-10-26.22:42:38.482>
created_at = <Date 2020-10-22.23:35:43.266>
labels = ['interpreter-core', '3.10', 'performance']
title = 'Run parser twice; enable invalid_* rules only on the second run'
updated_at = <Date 2020-10-28.00:14:18.810>
user = 'https://github.com/lysnikolaou'

bugs.python.org fields:

activity = <Date 2020-10-28.00:14:18.810>
actor = 'lys.nikolaou'
assignee = 'lys.nikolaou'
closed = True
closed_date = <Date 2020-10-26.22:42:38.482>
closer = 'lys.nikolaou'
components = ['Interpreter Core']
creation = <Date 2020-10-22.23:35:43.266>
creator = 'lys.nikolaou'
dependencies = []
files = []
hgrepos = []
issue_num = 42123
keywords = ['patch']
message_count = 5.0
messages = ['379384', '379508', '379697', '379698', '379811']
nosy_count = 4.0
nosy_names = ['gvanrossum', 'terry.reedy', 'lys.nikolaou', 'pablogsal']
pr_nums = ['22111', '23011']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue42123'
versions = ['Python 3.10']

[lysnikolaou]

We can avoid having to go through all the invalid rules (which might be a significant performance boost, since these may call expensive rules like primary or others), if we run the parser two times.

On the first run, all the invalid rules are disabled and do not get expanded. If a parse failure occurs anywhere, then we run the parser a second time with all these rules enabled, in order to get the correct error message.

Some benchmarking by Pablo show a ~4% speedup in the stdlib benchmark and a ~10% in the xxl benchmark.

[terryjreedy]

Since I do a lot of interactive compiling, I appreciate faster feedback. How much will the slowdown be on errors?

[lysnikolaou]

We do not have a big corpus of SyntaxErrors to test against, but some manual testing of running a file with a SyntaxError after a long complex line 1000 times shows no slowdown.

We keep the token stream for the second run, so we don't need to run the tokenizer all over again and the parsing is done much more quickly.

[lysnikolaou]

New changeset bca7014 by Lysandros Nikolaou in branch 'master':
bpo-42123: Run the parser two times and only enable invalid rules on the second run (GH-22111)
bca7014

[lysnikolaou]

New changeset 24a7c29 by Lysandros Nikolaou in branch '3.9':
[3.9] bpo-42123: Run the parser two times and only enable invalid rules on the second run (GH-22111) (GH-23011)
24a7c29