Compiling scripts transparently about swift-sh HOT 10 CLOSED

We already have a cache.

So yeah, we could already do this.

Though ideally SwiftPM itself would do this, but we can implement this for now, PR welcome, sources are easy enough to understand and I don't have the time right now.

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I've made some improvements that I will push shortly, times are all for a pre-built unchanged script:

I can do more I believe, since we can check if the script mtime is less than the compiled binary mtime unchanged and then just exec which is how make works, but seems a little risky, but I guess if it's good enough for make it should be good enough for us.

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K got it down to 0.040s with the above. Further optimizations will be hard. There isn’t a lot more happening that isn’t Swift itself. In theory I'm sure more could be gained, but we are talking about an unnoticeable amount of time now at least. Obviously we’d prefer to have negligible overhead, so PRs welcome.

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@mxcl Very cool! Thank you very much, it really boosts usability.

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Notably this introduces a bug that is only present for the Swift 4.2 -> Swift 5.0 transition. I'm not sure as a result if I should fix it.

Because these are not ABI compatible, thus the binaries will fail to run after Xcode is upgraded.

The only fix is to record the swift-tools-version in a file that is then checked before deciding to just run the binary.

However once Swift 5 is installed this no longer becomes necessary… ever again.

I'll think on it.

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I guess I'll make a quick update that disables this optimization if swift < 5. Sucks a bit, but people having broken scripts and no idea what to do about it sucks more.

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Hmm needs to be more than this, I need to detect if a script was built against <5 and now swift is >=5.

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The full solution is to detect the ABI version requirements from the binary somehow and compare that against the current swift version in the path.

Querying swift for it’s version via swift --version is 20ms. Not sure we can skip this unless we can cache that via mtime querying again and that's complicated considering /usr/bin/swift is just a shim.

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So basically I need:

1. Fast active swift version lookup
2. Fast ABI version lookup for binaries†

† could just assume the generated manifest tools version is this, it’s not exact, but if the manifest version is different then either there's a bug or someone edited it by hand.

Otherwise I have to push this patch that makes the exec time closer to 50–60ms.

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Also for reference, I built a simple swift app that execs the same pre-built script I was testing with above and it ran between 32–35ms over multiple runs.

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