> Shadowing is another concept that made this issue less visible.

There is no shadowing here, Go can only shadow in different scopes, `ctx` is just rebound (overwritten). Zig does not prevent reusing variables that I know. However I believe zig parameters are implicitly `const`, which would have prevented thoughtlessly updating the local in-place. Same in Rust.

> If you've ever heard of linear types, and never saw their utility, that's actually exactly what they are good for: a variable gets 'consumed' by a function, and the type system prevents us from using it after that point. Conceptually, g.Wait(ctx) consumes ctx and there is no point using this ctx afterwards.

I don't believe linear types would prevent this issue per-se since `errgroup.WithContext` specifically creates a derived context.

Depending on the affordance they might make the issue clearer but they also might not: a linear errgroup.WithContext could consume its input leaving you only with the sub-context and thinking little more of it, so you'd have to think to create derived context on the caller side. Would you think of this issue when doing that?

TBH this seems more of a design issue in errgroup's API: why is the context returned from the errgroup instead of being an attribute? That would limit namespace pollution and would make the relationship (and possible effects) much clearer. But I don't know what drove the API to be designed as it is.

But in all honesty I'd say the main error in the snippet is that `checkHaveIBeenPawned` swallows all http client errors, without even logging them. That is the part which struck out to me, it only returns an error if it positively finds that the password was a hit on HIBP. So you'd have hit the exact same issue if the `NewRequestWithContext` was otherwise malformed e.g. typo in the method or URL. And of course that points out to an other issue, this time with type-erased errors and error information not necessarily being programmatically accessible or at least idiomatically checked: I would assume the goal was to avoid triggering an error if HIBP is unavailable (DNS lookup or connection error).