chore: Replace sort package with slices and cmp packages

[dongjiang1989]

Replace all usage of Go's sort package with the modern slices and cmp packages (Go 1.21+) for more concise and readable sorting code.

Changes

• Remove sort.Interface methods (Len/Less/Swap) from LabelNames, LabelValues, LabelPairs, Fingerprints, Alerts, Samples, Vector, and Matrix types.
• Add Compare methods on *Sample, *SampleStream, *Alert, and *LabelPair for use with slices.SortFunc, eliminating duplicated comparator code at call sites.
• Replace sort.Sort calls with slices.SortFunc (using the new Compare methods or cmp.Compare for simple ordered types), and sort.Strings with slices.Sort.
• Add a depguard rule in .golangci.yml to forbid the sort package and prevent future regressions.
• Fix pre-existing gofumpt formatting issues in config and route packages (uncovered by make lint).

Note

The original Alerts.Less was not a proper strict weak ordering (it used StartsBefore || EndsBefore || FPLess). The new (*Alert).Compare implements a correct hierarchical comparison (StartsAt → EndsAt → Fingerprint). TestSortAlerts expected values were updated accordingly.

Verification

• go build ./... ✅
• go vet ./... ✅
• make lint ✅
• go test ./model/... ./expfmt/... ✅

[bwplotka]

NOTE: This is a breaking change for downstream - we should do it ideally only when we have to

[Copilot]

🟢 Approval recommended

The sorting refactor is consistent and test updates align with the new comparison logic, with only minor doc-comment nits remaining.

Pull request overview

This PR modernizes sorting across the codebase by replacing sort usage with Go 1.21+ slices/cmp, and centralizing comparison logic into Compare methods on key model types.

Changes:

• Replaced sort.Sort / sort.Strings usage with slices.SortFunc / slices.Sort across model and expfmt code.
• Introduced Compare methods on *Sample, *SampleStream, *Alert, and *LabelPair to reuse consistent ordering logic.
• Added a depguard rule to forbid importing sort, preventing reintroduction.

File summaries

File	Description
route/route_test.go	Formatting-only adjustments to method chaining (gofumpt style).
model/value.go	Adds Compare methods and migrates matrix sorting to slices.SortFunc.
model/value_test.go	Updates vector sorting test to use slices.SortFunc with (*Sample).Compare.
model/metric.go	Replaces sort.Strings with slices.Sort for label string ordering.
model/labelset.go	Replaces label-name sorting with slices.SortFunc + cmp.Compare.
model/labels.go	Removes sort.Interface impls and adds (*LabelPair).Compare.
model/labels_test.go	Migrates label sorting tests to slices.SortFunc.
model/fingerprinting.go	Removes sort.Interface impl from Fingerprints (now sorted via slices elsewhere).
model/fingerprinting_test.go	Migrates fingerprint sorting test to slices.SortFunc + cmp.Compare.
model/alert.go	Replaces Alerts.Less with a strict, hierarchical (*Alert).Compare.
model/alert_test.go	Updates alert sorting test to use slices.SortFunc and new expected order.
expfmt/decode_test.go	Updates sample sorting in decoder tests to use (*model.Sample).Compare.
config/tls_config_test.go	Formatting-only cast simplification for TLSVersion.
config/http_config.go	Formatting-only cast simplification and gofumpt-style trailing commas in varargs calls.
.golangci.yml	Adds depguard deny rule for sort imports.

Review details

• Files reviewed: 15/15 changed files
• Comments generated: 4
• Review effort level: Lite

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[bboreham]

Agree with Bartek - it's quite a breaking change to make all these types no longer implement sort.Interface. Suggest to leave them in, maybe with a comment that they are for backwards-compatibility only. You could have Less call the new Compare.

Can you explain a bit more about the change to Alert ordering? This will be another breaking change; we'd need a strong justification.

Fix pre-existing gofumpt formatting issues in config and route packages (uncovered by make lint).

Do this in a separate PR. It's extra work to review changes for multiple different reasons at the same time.

Also, it might be neater to use cmp.Or in the Compare methods.

[bboreham]

This change is not covered by the PR title.

[bboreham]

Spurious change

[dongjiang1989]

Thanks for the review @bwplotka @bboreham.

Understood. I'll restore Len/Less/Swap methods as a compatibility layer, delegating to the new Compare().

I will make these changes in the next push:

1. Fix doc comments and remove the wrong cmp.Comparator reference.
2. Restore sort.Interface methods (Len/Less/Swap) as a compatibility layer, delegating to Compare().
3. Rewrite multi-level comparisons using cmp.Or.
4. Strip unrelated gofumpt formatting changes to a separate PR, clean up spurious diffs.
5. The old Alert sort had invalid ordering. The new ordering fixes this bug, which is a behavioral change. I will add a changelog note for this.