mirror of
https://github.com/littlefs-project/littlefs.git
synced 2025-12-27 17:40:24 +00:00
a3ac512cc1
This ended up being a pretty in-depth rework of prettyasserts.py to
adopt the shared Parser class. But now prettyasserts.py should be both
more robust and faster.
The tricky parts:
- The Parser class eagerly munches whitespace by default. This is
usually a good thing, but for prettyasserts.py we need to keep track
of the whitespace somehow in order to write it to the output file.
The solution here is a little bit hacky. Instead of complicating the
Parser class, we implicitly add a regex group for whitespace when
compiling our lexer.
Unfortunately this does make last-minute patching of the lexer a bit
messy (for things like -p/--prefix, etc), thanks to Python's
re.Pattern class not being extendable. To work around this, the Lexer
class keeps track of the original patterns to allow recompilation.
- Since we no longer tokenize in a separate pass, we can't use the
None token to match any unmatched tokens.
Fortunately this can be worked around with sufficiently ugly regex.
See the 'STUFF' rule.
It's a good thing Python has negative lookaheads.
On the flip side, this means we no longer need to explicitly specify
all possible tokens when multiple tokens overlap.
- Unlike stack.py/csv.py, prettyasserts.py needs multi-token lookahead.
Fortunately this has a pretty straightforward solution with the
addition of an optional stack to the Parser class.
We can even have a bit of fun with Python's with statements (though I
do wish with statements could have else clauses, so we wouldn't need
double nesting to catch parser exceptions).
---
In addition to adopting the new Parser class, I also made sure to
eliminate intermediate string allocation through heavy use of Python's
io.StringIO class.
This, plus Parser's cheap shallow chomp/slice operations, gives
prettyasserts.py a much needed speed boost.
(Honestly, the original prettyasserts.py was pretty naive, with the
assumption that it wouldn't be the bottleneck during compilation. This
turned out to be wrong.)
These changes cut total compile time in ~half:
real user sys
before (time make test-runner -j): 0m56.202s 2m31.853s 0m2.827s
after (time make test-runner -j): 0m26.836s 1m51.213s 0m2.338s
Keep in mind this includes both prettyasserts.py and gcc -Os (and other
Makefile stuff).