feat: --debug prints time it takes to parse a file

[bartlomieju]

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[ ] Documentation update
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Closes #15585

I think this is enough debug output, if parsing takes less <1ms then its cost is negligible anyway.

[mdjermanovic]

Espree (default parser) doesn't provide parseResult.scopeManager, so this would include time spent in a separate scope analysis (by eslint-scope), which might be a significant % of the total time between these two debug logs.

I don't know if this makes more sense for your analysis, just want to check if the intent is to calculate parsing time + scope analysis time, or it might be better to split them with more debug logs?

For context, some parsers, like @typescript-eslint/parser, provide their own scope analysis (as parseResult.scopeManager) so in that case there would be no difference since both parsing and scope analysis are done in parser.parseForESLint().

[bartlomieju]

That's a good point, I think it might be useful to have time taken for both steps logged separately. Could you hint how this could be solved generically that would handle built-in parser as well as @typescript-eslint/parser?

[mdjermanovic]

how this could be solved generically that would handle built-in parser as well as @typescript-eslint/parser

We can add one pair of debug logs around const parseResult = ..., and another pair around const scopeManager = ....

When the built-in parser is used, that would log parse time and scope time separately.

When @typescript-eslint/parser is used, parse time and scope time would be both included in the first log (the second would be ~0 time) and it doesn't seem there's anything we can do to split them here. The only solution might be to ask @typescript-eslint/parser to add logs around this line. Then, it would be possible to see parse + scope time (logged by ESLint) and scope time (logged by @typescript-eslint/parser) ,

[mdjermanovic]

The only solution might be to ask @typescript-eslint/parser to add logs around this line. Then, it would be possible to see parse + scope time (logged by ESLint) and scope time (logged by @typescript-eslint/parser) ,

In this case, since both packages are using the same debug library, you could set environment variable DEBUG=eslint:linter,typescript-eslint:parser:parser and run eslint without --debug to see logs from both modules.

[bartlomieju]

Thanks @mdjermanovic, I applied your suggestions

[mdjermanovic]

LGTM, thanks!