pathtools: add Prefixes helper function #2152
Conversation
In the fix for bazel-contrib#2132, I'll need to iterate over the prefixes of a given slash-separated path. Rather than duplicate the logic from Walk2, let's extract it into pathtools. Prefixes returns an iterator over prefixes to avoid needing to allocate a slice. The code should be much simpler after we adopt Go 1.23 and can use range-over-iterator loops. For bazel-contrib#2132
|
Go 1.23 is needed before we can use |
|
You could also use channels instead 🤷 I've avoided using iterators/yield in a few places where I've noticed they add a lot more overhead then channels. |
Right, it's a new language feature. Older compilers don't support it.
I'd be really surprised if that were true. Do you have an example with a benchmark? Channels are synchronization primitives. Many operations on them involve flushing parts of the cache and context switching. They should not be used for iteration. Iterators are not a zero cost abstraction, but they're implemented with stackless coroutines which are pretty cheap. I think they're usually a good choice when they help avoid allocating a slice or a map like this. |
I can't reproduce it atm, so maybe I'm wrong or misremembering? Using sequences sure is a lot nicer when analyzing profiles like what I'm staring at right now though. Lets ignore my original comment for now... |
I accidentally pushed this onto #2153 instead. About to merge that, so we'll end up in the same place. |
…2153) **What type of PR is this?** > Bug fix **What package or component does this PR mostly affect?** > walk **What does this PR do? Why is it needed?** GetDirInfo was intended to help expand glob expressions in resolve.Resolver.Imports implementations. globs may cover subdirectories, especially when gazelle:generate_mode is used, so GetDirInfo must be able to read contents of subdirectories that may not have been visited yet. Previously, the contract of GetDirInfo did not allow visiting directories that hadn't been visited yet, but it would still sometimes succeed walker.populateCache won the race. This change fully allows GetDirInfo to be called in directories that haven't been visited yet. **Which issues(s) does this PR fix?** Fixes #2132 **Other notes for review** This PR is based on #2152. I tried to split them for easier review, but GitHub doesn't let me set the base to a branch in a forked repo, so I'm sorry if this makes things more difficult.
What type of PR is this?
What package or component does this PR mostly affect?
What does this PR do? Why is it needed?
In the fix for #2132, I'll need to iterate over the prefixes of a given
slash-separated path. Rather than duplicate the logic from Walk2,
let's extract it into pathtools.
Prefixes returns an iterator over prefixes to avoid needing to allocate
a slice. The code should be much simpler after we adopt Go 1.23 and can
use range-over-iterator loops.
Which issues(s) does this PR fix?
Fixes #2132
Other notes for review