First pass at implementation of nullish coalescing #488
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Progress toward #461 Tech plan at https://github.com/alangpierce/sucrase/wiki/Sucrase-Optional-Chaining-and-Nullish-Coalescing-Technical-Plan Some details: * In the parser, operator parsing now keeps track of the start token index so that when we observe a `??` operator, we can mark the first token as being the start of an optional chain. * The token format now has fields for the number of optional chain starts and ends for each token, which the transformer will use to inject code. * Optional chaining code needs to use the HelperManager system, so I refactored it to be on the RootTransformer instead of just on one of them. * The actual start/end code injection is done by the token system so that it works alongside all existing transforms. * Since TokenProcessor now needs a HelperManager, I had to break the dependency cycle by making NameManager no longer depend on TokenProcessor, since it was only barely using it anyway. Some quick perf benchmarks show this as having potentially a 4% slowdown even for code not using nullish coalescing, though I wasn't able to track down any specific area of code responsible, and it may have been partially due to variability or other factors. Except for more egregious cases, I'll leave performance work as a follow-up.
Codecov Report
@@ Coverage Diff @@
## master #488 +/- ##
=========================================
+ Coverage 82.08% 82.29% +0.2%
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Files 52 53 +1
Lines 5202 5466 +264
Branches 1210 1214 +4
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+ Hits 4270 4498 +228
- Misses 647 681 +34
- Partials 285 287 +2
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Progress toward #461
Tech plan at https://github.com/alangpierce/sucrase/wiki/Sucrase-Optional-Chaining-and-Nullish-Coalescing-Technical-Plan
Some details:
that when we observe a
??operator, we can mark the first token as being thestart of an optional chain.
ends for each token, which the transformer will use to inject code.
it to be on the RootTransformer instead of just on one of them.
works alongside all existing transforms.
cycle by making NameManager no longer depend on TokenProcessor, since it was
only barely using it anyway.
Some quick perf benchmarks show this as having potentially a 4% slowdown even
for code not using nullish coalescing, though I wasn't able to track down any
specific area of code responsible, and it may have been partially due to
variability or other factors. Except for more egregious cases, I'll leave
performance work as a follow-up.