Tailscale main now requires go >= 1.26.2, so building the HEAD derper
image against golang:1.26.1-alpine fails with:
go: go.mod requires go >= 1.26.2 (running go 1.26.1; GOTOOLCHAIN=local)
Bump Dockerfile.derper to match the earlier fix for Dockerfile.tailscale-HEAD
in 6390fcee so TestDERPVerifyEndpoint can build the derper container
again. This test is the only consumer of Dockerfile.derper, which is why
the failure was scoped to that single integration job.
This commit upgrades the codebase from Go 1.25.5 to Go 1.26rc2 and
adopts new language features.
Toolchain updates:
- go.mod: go 1.25.5 → go 1.26rc2
- flake.nix: buildGo125Module → buildGo126Module, go_1_25 → go_1_26
- flake.nix: build golangci-lint from source with Go 1.26
- Dockerfile.integration: golang:1.25-trixie → golang:1.26rc2-trixie
- Dockerfile.tailscale-HEAD: golang:1.25-alpine → golang:1.26rc2-alpine
- Dockerfile.derper: golang:alpine → golang:1.26rc2-alpine
- .goreleaser.yml: go mod tidy -compat=1.25 → -compat=1.26
- cmd/hi/run.go: fallback Go version 1.25 → 1.26rc2
- .pre-commit-config.yaml: simplify golangci-lint hook entry
Code modernization using Go 1.26 features:
- Replace tsaddr.SortPrefixes with slices.SortFunc + netip.Prefix.Compare
- Replace ptr.To(x) with new(x) syntax
- Replace errors.As with errors.AsType[T]
Lint rule updates:
- Add forbidigo rules to prevent regression to old patterns
