Add MarshalJSON to xtime.Duration

[sueun-dev]

Duration has an UnmarshalJSON that expects a human-readable string (it strips the surrounding quotes and calls ParseDuration), but no MarshalJSON. json.Marshal therefore emits the raw int64 nanoseconds, which UnmarshalJSON cannot read back:

b, _ := json.Marshal(xtime.Duration(time.Hour))   // "3600000000000"
var d xtime.Duration
json.Unmarshal(b, &d)                              // missing unit in duration "60000000000"

The type is documented as supporting YAML and JSON. #136 added MarshalYAML to match the existing UnmarshalYAML; this does the same for JSON, emitting the human-readable string that UnmarshalJSON reads.

Tested with go test -race ./xtime/ (the existing TestDuration_Marshal is extended to cover the JSON marshal output and a round-trip). gofmt, go vet, and golangci-lint are clean.

Summary by CodeRabbit

• New Features
  • Custom durations now serialize to JSON as readable duration strings.
  • Added coverage to ensure duration values round-trip correctly through JSON, including pointer fields.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: e3587b99-f55b-4143-8d34-492b6726b80d

📥 Commits

Reviewing files that changed from the base of the PR and between d166243 and 334c275.

📒 Files selected for processing (2)

• xtime/time.go
• xtime/time_unmarshal_test.go

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📝 Walkthrough

Walkthrough

Adds a MarshalJSON method to the Duration type in xtime/time.go, serializing durations as human-readable strings via time.Duration.String(). The corresponding test file is updated to verify JSON marshaling output and round-trip unmarshaling correctness.

Changes

Duration JSON Marshaling

Layer / File(s)	Summary
MarshalJSON implementation and round-trip test xtime/time.go, xtime/time_unmarshal_test.go	Adds encoding/json import and Duration.MarshalJSON method returning the string form of the duration; test now marshals a testDuration struct to JSON, checks the exact expected output, and unmarshals it back to verify fields including a non-nil pointer round-trip.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Poem

A hop, a skip, a JSON hop,
Durations now in strings will pop!
"2h", "30m", so neat and clear,
Marshaled out without a fear.
Test cases checked, round-trip complete —
This bunny's work is small but sweet. 🐰

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and accurately summarizes the main change: adding MarshalJSON to xtime.Duration.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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