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Formatter: Recycle parsed AST and tokens in between rule invocations when no correction was applied to improve performance by bergmeister · Pull Request #1462 · PowerShell/PSScriptAnalyzer

Christoph Bergmeister

PR Summary

This saves on the expensive calls to the Parser and the rule itself, which are called at the moment for every rule invocation AND after every applied DiagnosticRecord. With this PR, parsing is skipped and the previous result is used if a rule did not return a DiagnosticRecord that changed the analysed script definition string. If there is not DiagnosticRecord returned from a rule during formatting, this simple change can dramatically speed up the formatting time: In the case of a pre-formatted file (always using PowerShell's build.psm1 for reference), formatting is 3 times faster. In reality, I guess it's only around 50%-100% depending on how well formatter the script already is. Because I had to change publicly exposed methods, it is technically speaking a breaking change but I think we can live with that.

Since I haven't written this core logic, I can only guess it was written like this because applying a change invalidates the previous analysis and this explains why one cannot simply run the rules in parallel. However, I imagine, one could write code to not re-parse at all between applying a list of DiagnosticRecords by adapting the line and column numbers (which would also allow for parallelisation of the rules). At the moment one could probably even improve performance further by stopping rule analysis once the first object comes back due to this re-analysis pattern. I've actually tried that locally but it would've broken a few tests so maybe not as easy as it seems to be therefore let's leave that for later now though.

PR Checklist