[DAP] `--pause-isolates-on-start` and `--pause-isolates-on-exit` flags are not set for attach workflows

[elliette]

If the VM flags --pause-isolates-on-start and --pause-isolates-on-exit are not already set before the DAP attach workflow, then they never get set.

That's because we never set them after looping through all the VM flags here:

sdk/pkg/dds/lib/src/dap/adapters/dart.dart

Line 857 in 238a29d

if (flagName == null || !isPauseIsolatesFlag) continue;

FYI @DanTup - I have a fix prepared and will send it out shortly.

[DanTup]

@elliette I'm not sure I understand why this doesn't work. Wouldn't they be set during the loop?

We enumerate the flags (which comes from getFlagList() and includes all flags), then when we find pauseOnStart/pauseOnExit, the condition on line 857 is false (the name is not null and it is a pause-isolates flag) so we carry on. The condition on 859 is false (the flag is not already true), so we fall into 867 which calls _setVmflagTo (and the booleans like pauseIsolatesOnStartSetByDap defaulted to true so already match)?

(maybe it'll be clearer when I see your fix though :-) )

[elliette]

Hmm in g3 this call to getFlagList is returning an empty list:

sdk/pkg/dds/lib/src/dap/adapters/dart.dart

Line 852 in 238a29d

final flags = (await vmService.getFlagList()).flags ?? <vm.Flag>[];

[elliette]

Hmm in g3 this call to getFlagList is returning an empty list:

sdk/pkg/dds/lib/src/dap/adapters/dart.dart

Line 852 in 238a29d

final flags = (await vmService.getFlagList()).flags ?? <vm.Flag>[];

Ah hah: https://github.com/dart-lang/webdev/blob/15028c4fd1488376de701230bb57ac214549526b/dwds/lib/src/services/chrome_proxy_service.dart#L760-L764

So maybe the right fix is to implement this in DWDS

[DanTup]

Ah, I see. The docs for getFlagList() say:

The getFlagList RPC returns a list of all command line flags in the VM along with their current values.

I don't know if it's reasonable for web to have all the CLI flags in there, but if web has behaviour for pause-on-start/exit then probably it should at least include those there (and with the correct values that were set).