cmd/test2json: introduce continuation flag for splited output events

[zolotov]

test2json tool splits long lines into several with src/cmd/internal/test2json/test2json.go#outBuffer limit.

E.g. the output for the following program

package main

import (
	"testing"
)

func Test1(t *testing.T) {
	const expected = "{\\n  \"data\": [\\n    {\\n      \"data\": [\\n        \\n      ],\\n      \"event\": \"sign_up\",\\n      \"search\":{}\\n    },\\n    {\\n      \"data\": [\\n\\n      \\n      ],\\n      \"event\": \"subscribe\",\\n      \"search\": {}\\n    },\\n    {\\n      \"data\": [\\n        {\\n          \"ads_stats\": [],\\n          \"count\": 1,\\n          \"group_value\": \"\",\\n          \"rate\": 0.2,\\n          \"total\": 5\\n        },\\n        {\\n          \"ads_stats\": [],\\n          \"count\": 1,\\n          \"group_value\": \"green\",\\n          \"rate\": 0.2,\\n          \"total\": 5\\n        },\\n        {\\n          \"ads_stats\": [],\\n          \"count\": 1,\\n          \"group_value\": \"orange\",\\n          \"rate\": 0.2,\\n          \"total\": 5\\n        },\\n        {\\n          \"ads_stats\": [],\\n          \"count\": 2,\\n          \"group_value\": \"red\",\\n          \"rate\": 0.4,\\n          \"total\": 5\\n        }\\n      ],\\n      \"event\": \"pageview\",\\n      \"search\": {}\\n    }\\n  ],\\n  \"meta\": {\\n    \"shortlist\": true,\\n    \"source\": \"visitor_data\",\\n    \"total\": 4\\n  },\\n  \"search\": {}\\n}"
	t.Log(expected)
}

contains two Output events:

{"Time":"2019-12-09T19:27:08.985242+01:00","Action":"run","Test":"Test1"}
{"Time":"2019-12-09T19:27:08.986919+01:00","Action":"output","Test":"Test1","Output":"=== RUN   Test1\n"}
{"Time":"2019-12-09T19:27:08.987393+01:00","Action":"output","Test":"Test1","Output":"--- PASS: Test1 (0.00s)\n"}
{"Time":"2019-12-09T19:27:08.987414+01:00","Action":"output","Test":"Test1","Output":"    stepper_test.go:9: {\\n  \"data\": [\\n    {\\n      \"data\": [\\n        \\n      ],\\n      \"event\": \"sign_up\",\\n      \"search\":{}\\n    },\\n    {\\n      \"data\": [\\n\\n      \\n      ],\\n      \"event\": \"subscribe\",\\n      \"search\": {}\\n    },\\n    {\\n      \"data\": [\\n        {\\n          \"ads_stats\": [],\\n          \"count\": 1,\\n          \"group_value\": \"\",\\n          \"rate\": 0.2,\\n          \"total\": 5\\n        },\\n        {\\n          \"ads_stats\": [],\\n          \"count\": 1,\\n          \"group_value\": \"green\",\\n          \"rate\": 0.2,\\n          \"total\": 5\\n        },\\n        {\\n          \"ads_stats\": [],\\n          \"count\": 1,\\n          \"group_value\": \"orange\",\\n          \"rate\": 0.2,\\n          \"total\": 5\\n        },\\n        {\\n          \"ads_stats\": [],\\n          \"count\": 2,\\n          \"group_value\": \"red\",\\n          \"rate\": 0.4,\\n          \"total\": 5\\n        }\\n      ],\\n      \"event\": \"pageview\",\\n      \"search\": {}\\n    }\\n  ],\\n  \"meta\": {\\n    \"shortlist\": true,\\n    \"source\": \"visitor_data\",\\n    \"total"}
{"Time":"2019-12-09T19:27:08.987484+01:00","Action":"output","Test":"Test1","Output":"\": 4\\n  },\\n  \"search\": {}\\n}\n"}
{"Time":"2019-12-09T19:27:08.987494+01:00","Action":"pass","Test":"Test1","Elapsed":0}
{"Time":"2019-12-09T19:27:08.987562+01:00","Action":"output","Output":"PASS\n"}
{"Time":"2019-12-09T19:27:08.98759+01:00","Action":"pass","Elapsed":0.341}

If an external tool wants to parse the output somehow, it has no chance to know that the second event is a continuation of the first one.
It would be nice to have a special event flag that could tell an external tool about it. The same Time or another identification flag for split events also could help.

The real usecase: https://youtrack.jetbrains.com/issue/GO-8141

[toothrot]

/cc @rsc

[trivigy]

anyway to workaround this issue in the meantime?

At the moment the only viable solution I found was to compile a custom golang version with the limits modified.

[rsc]

There is no need for a continuation flag: lines that are continued are already marked by not including a trailing \n in the output text.