Hot Reload results in debugger pausing with "PauseInterrupted" instead of "PauseBreakpoint"

[DanTup]

In the Dart-Code integration tests there are some Flutter web tests that perform Hot Reloads and ensure breakpoints are still hit after a reload. Recently (perhaps with the last stable Flutter release?) they've started failing because the pause event is PauseInterrupted instead of PauseBreakpoint (and has no frame information with it) after the reload.

The breakpoint is initially hit (at startup) normally:

{
	"jsonrpc": "2.0",
	"method": "streamNotify",
	"params": {
		"streamId": "Debug",
		"event": {
			"type": "Event",
			"kind": "PauseBreakpoint",
			"timestamp": 1632747746674,
			"isolate": {
				"type": "@Isolate",
				"id": "1",
				"number": "1",
				"name": "main()",
				"isSystemIsolate": false
			},
			"pauseBreakpoints": [
				{
					"type": "Breakpoint",
					"id": "bp/3#49",
					"breakpointNumber": 584,
					"enabled": true,
					"resolved": true,
					"location": {
						"type": "SourceLocation",
						"script": {
							"type": "@Script",
							"id": "3",
							"uri": "package:flutter_hello_world/main.dart"
						},
						"tokenPos": 1438
					}
				}
			],
			"topFrame": {
				"// SNIP...":""
			}
		}
	}
}

But after the reload, but pause event looks like this:

{
	"jsonrpc": "2.0",
	"method": "streamNotify",
	"params": {
		"streamId": "Debug",
		"event": {
			"type": "Event",
			"kind": "PauseInterrupted",
			"timestamp": 1632747768591,
			"isolate": {
				"type": "@Isolate",
				"id": "1",
				"number": "1",
				"name": "main()",
				"isSystemIsolate": false
			}
		}
	}
}

I don't know if this is an intended change, but wanted to raise it before changing anything in Dart-Code.

[annagrin]

@DanTup that does not look intentional but could it be a side effect of the test? The isolate should be paused on a breakpoint after hot restart if it was before. PauseInterrupted usually means that something calls pause on the VM. I presume dart code does not call pause, it just calls hot restart extension?

[DanTup]

I presume dart code does not call pause, it just calls hot restart extension?

Correct. However, with some more testing, I found that a) it doesn't happen on Flutter master, only stable - so whatever it is has likely been fixed and b) it actually seems like the reload might be failing, because the Stop event comes around 90 seconds after the hot reload progress says it completed so I don't think it was the expected event at all:

[11:03:17 AM] [DAP] [Info] ==> {"command":"hotReload"}
[11:03:17 AM] [FlutterRun] ==> [{"id":"2","method":"app.restart","params":{"appId":"06fa34fe-3e26-4d90-b5ba-e17c9761fdd6","fullRestart":false,"pause":true}}]
[11:03:17 AM] [FlutterRun] <== [{"event":"app.progress","params":{"appId":"06fa34fe-3e26-4d90-b5ba-e17c9761fdd6","id":"3","progressId":"hot.restart","message":"Performing hot restart...","finished":false}}]
[11:03:17 AM] [DAP] [Info] <== {"seq":252,"type":"event","event":"dart.progressStart","body":{"progressID":"flutter-06fa34fe-3e26-4d90-b5ba-e17c9761fdd6-hot.restart","message":"Performing hot restart..."}}
[11:03:17 AM] [FlutterRun] <== [{"event":"app.progress","params":{"appId":"06fa34fe-3e26-4d90-b5ba-e17c9761fdd6","id":"4","progressId":null,"message":"Waiting for connection from debug service on Chrome...","finished":false}}]
[11:03:17 AM] [DAP] [Info] <== {"seq":254,"type":"event","event":"dart.progressStart","body":{"progressID":"flutter-06fa34fe-3e26-4d90-b5ba-e17c9761fdd6-null","message":"Waiting for connection from debug service on Chrome..."}}
[11: 03: 17 AM][FlutterRun][Info][Dart & Flutter] <==[{ "event": "app.progress", "params": { "appId": "06fa34fe-3e26-4d90-b5ba-e17c9761fdd6", "id": "4", "progressId": null, "finished": true } }]
// Hot reload completed
[11:03:17 AM] [DAP] [Info] <== {"seq":256,"type":"event","event":"dart.progressEnd","body":{"progressID":"flutter-06fa34fe-3e26-4d90-b5ba-e17c9761fdd6-null"}}
[11:04:10 AM] [CI] [Info] Promise stops_at_a_breakpoint->reload:0->hotReload:breakpoint is still unresolved!
[11:04:20 AM] [CI] [Info] Promise stops_at_a_breakpoint->reload:0->assertStoppedLocation:breakpoint is still unresolved!
[11:04:20 AM] [CI] [Error] Promise stops_at_a_breakpoint->reload:0->assertStoppedLocation:breakpoint not resolved after 60000ms so no longer watching!
[11:04:20 AM] [CI] [Info] Promise stops_at_a_breakpoint->reload:0->hotReload:breakpoint is still unresolved!
[11: 04: 20 AM][CI][Error] Promise stops_at_a_breakpoint -> reload: 0 -> hotReload:breakpoint not resolved after 60000ms so no longer watching!
// PauseInterrupted event
[11:04:43 AM] [VmService] <== {"jsonrpc":"2.0","method":"streamNotify","params":{"streamId":"Debug","event":{"type":"Event","kind":"PauseInterrupted","timestamp":1633514683749,"isolate":{"type":"@Isolate","id":"1","number":"1","name":"main()","isSystemIsolate":false}}}}
[11:04:43 AM] [DAP] [Info] <== {"seq":258,"type":"event","event":"stopped","body":{"reason":"pause","threadId":0}}
[11:04:43 AM] [General] [Info] [stopped] pause
[11:04:43 AM] [CI] [Warn] Promise stops_at_a_breakpoint->reload:0->assertStoppedLocation:breakpoint rejected!
[11:04:43 AM] [CI] [Error] Test flutter run debugger (launch on chrome) stops at a breakpoint after each reload (1) failed after 116278ms
[11:04:43 AM] [CI] [Error] 'pause' == 'breakpoint'
[11:04:43 AM] [CI] [Error] AssertionError [ERR_ASSERTION]: 'pause' == 'breakpoint'

So I suspect something else was going wrong with the breakpoint so it's not pausing (and then something is timing out 90 seconds later).

In any case, since I can't reproduce it on latest code I'll close this (I tried on both stable and master many times, and it was 100% consistent on stable, and never happened on master). I'll re-open if I see it again in anything newer than current master and do some more digging.

[annagrin]

Ah it is probably related to the weird issue where after hot restart chrome required focus, fixed on master: flutter/flutter#89874. I will see if we can update the stable with that fix.

[DanTup]

Ah! I actually saw that issue when manually testing some other things recently (it wouldn't hot reload until I moved my cursor into the window), but I didn't connect it with the test failures. Thanks!

[DanTup]

I recently removed a skip from a Dart-Code test that I thought was not necessary (Dart-Code/Dart-Code@2e19f1b) but I see that it's failing with the same error described above. I'm not sure why I couldn't repro when I closed it above, but it does seem to be occurring now:

// Reload request from VS Code to DAP
[10:19:53 AM] [DAP] [Info] ==> {"command":"hotReload"}

// DAP restart request to `flutter run` progress
[10:19:53 AM] [DAP] [Info] ==> [Flutter] [{"id":1,"method":"app.restart","params":{"appId":"d177e89a-1d07-43b3-bc01-7ab750a31bf7","fullRestart":false,"pause":true,"reason":null,"debounce":true}}]

// Error from stderr in `flutter run` process
[10:19:53 AM] [DAP] [Info] <== {"seq":3379,"type":"event","body":{"category":"stderr","output":"DebugService: Error serving requestsError: Unsupported operation: Cannot send Null\n"},"event":"output"}
[10:19:54 AM] [DAP] [Info] <== {"seq":3381,"type":"event","body":{"category":"stderr","output":"DebugService: Error serving requestsError: Unsupported operation: Cannot send Null\n"},"event":"output"}

// PauseInterrupted event from VM
[10:19:54 AM] [VmService] [Info] <== [VM] {"jsonrpc":"2.0","method":"streamNotify","params":{"streamId":"Debug","event":{"type":"Event","kind":"PauseInterrupted","timestamp":1756718394060,"isolate":{"type":"@Isolate","id":"1","number":"1","name":"main()","isSystemIsolate":false,"isolateGroupId":""},"topFrame":{"type":"Frame","index":640,"code":{"type":"@Code","id":"1592","name":"postEvent","kind":"Dart"},"location":{"type":"SourceLocation","script":{"type":"@Script","id":"317","uri":"package:flutter/src/foundation/binding.dart"},"tokenPos":286608,"line":845,"column":15},"kind":"AsyncCausal"}}}}

// Pause event back to VS Code
[10:19:54 AM] [DAP] [Info] <== {"seq":3383,"type":"event","body":{"allThreadsStopped":false,"reason":"pause","threadId":1},"event":"stopped"}

[DanTup]

The PauseInterrupted event was removed as part of a fix for another issue:

• [DWDS] Don't send PauseInterrupted event during a hot reload #2695
• Hot Reload opens binding.dart at line 845 on every reload (no errors shown) sdk#61560

So this shouldn't be an issue any more.