## Summary

- Fix stale `name` variable in warning print — it referenced the last
package from a previous loop, not the package with the unresolvable dep
- Only print a warning when version resolution fails for
**non-optional** deps, which indicates a genuine problem
- Skip the warning for optional deps behind disabled feature flags,
since failing to resolve is expected behavior

## Context

During version resolution, the code iterates all `possible_deps`
(including optional ones) and attempts to resolve each dep's version
against the lockfile. When an optional dependency's version requirement
doesn't match any version in the lockfile, this is expected — the dep is
behind a disabled feature flag and no crate in the workspace actually
uses it at that version.

For example, `serde_with 3.14.0` has three optional renamed deps on
`schemars` at different versions
([source](https://github.com/jonasbb/serde_with/blob/v3.14.0/serde_with/Cargo.toml)):

```toml
schemars_0_8 = { package = "schemars", version = "0.8.16", optional = true, default-features = false }
schemars_0_9 = { package = "schemars", version = "0.9.0", optional = true, default-features = false }
schemars_1   = { package = "schemars", version = "1.0.2", optional = true, default-features = false }
```

If the lockfile only contains `schemars` at versions `0.9.0` and `1.0.3`
(used by other crates), the `schemars_0_8` dep's `^0.8.16` req correctly
fails to resolve since `^0.8.16` means `>=0.8.16, <0.9.0`. Due to the
stale `name` variable, this produced the misleading message:

```
DEBUG: .../extensions.bzl: zstd-sys schemars ["0.9.0", "1.0.3"] ^0.8.16
```

The `name` variable was set in a previous loop (line 254) and never
reassigned in the version resolution loop (line 415), so it always
printed the last package from the first loop. With the name variable fix
alone, the correct message would be:

```
WARNING: serde_with: could not resolve schemars ^0.8.16 among ["0.9.0", "1.0.3"]
```

But since this dep is optional and not enabled by any feature, it's not
actionable. The existing `continue` already handles it correctly (the
dep never gets a `bazel_target`, so the resolver skips it, and the
post-resolution validation would `fail()` if any feature tried to
activate it). So we suppress the warning for optional deps entirely.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 <[email protected]>

Let me know what you think. Feel free to ignore / rewrite