setting gcflags in the .vscode/settings.json disables test debugging

[ran-berenfeld]

Hello

if I set this in the workspace settings :

"go.testFlags": [
    "-gcflags=-l", 
],

then running a test using the "debug test" link will result in :

go test: gcflags flag may be set only once
run "go help test" or "go help testflag" for more information
Process exiting with code: 1

[misha-ridge]

Arguably it's a bug in dlv, as VS Code properly constructs a command-line invocation --build-flags="-gcflags=-l", and dlv adds -gcflags="-N -l", so go build rejects it.

[ramya-rao-a]

Thanks for reporting @ran-berenfeld and for the information on how delve adds the same flag @misha-tectonic

@aarzilli, @derekparker I believe the right thing to do here is for the extension to ignore the gcflags passed by the user?

[aarzilli]

I think delve should not pass its own gcflags argument if build-flags already has it.

[misha-ridge]

@aarzilli This won't work: delve requires -N -l gcflags in order to function.

[aarzilli]

It doesn't require them, it just works better if they are there. If the user specifically passes a different gcflags through build-flags delve should respect it.

Also maybe the VSCode extension should ignore gcflags set in go.testFlags when calling delve.

[ramya-rao-a]

If the user specifically passes a different gcflags through build-flags delve should respect it.

Also maybe the VSCode extension should ignore gcflags set in go.testFlags when calling delve.

@aarzilli That is conflicting advice :) or I am missing something here...

Like @misha-tectonic mentioned above, the extension does pass --build-flags="-gcflags=-l" to delve when the user sets go.testFlags to ["-gcflags=-l"]. So should we log an issue for delve for trying to set gcflags the second time?

[misha-ridge]

Yes, ideally delve should parse passed -gcflags and add any flags it needs to it before passing it to go build.

[aarzilli]

@aarzilli That is conflicting advice :) or I am missing something here...

For me there's two questions here:

1. What should delve do when the user passes a -gcflags parameter inside --build-flags

2. Should VSCode pass -gcflags, if it's part of go.testFlags, inside --build-flags?

For (1) one reasonable choice is to use the gcflags specified by the user instead of ours, another is to leave things as they are and let delve fail, after all the point of having delve build the executable is to have it set gcflags, if you don't want then you can just use go.

For (2) one reasonable answer is to say that go.testFlags don't apply to debug builds (but then how would you set test flags for debug builds?).

Yes, ideally delve should parse passed -gcflags and add any flags it needs to it before passing it to go build.

This gets very complicated when you take into account patterns. What -gcflags=-l says is "disable inlining for the tested package". What delve does is -gcflags=all=-N -l which says "disable inlining and optimizations for every pacakge". What does "adding" mean in this context:

• -gcflags=-l + -gcflags=all=-N -l = -gcflags=all=-N -l
• -gcflags=-l + -gcflags=all=-N -l = "disable inlining for every package, disable optimizations for every package except the tested package"

More complicated gcflags expressions in build-flags would pose more complex problems.

[ramya-rao-a]

I vote for simplicity here and would go with the vscode-go extension should ignore the gcflags set by the user

PRs are welcome to make this change.

Code Pointers:

• Set up local dev environment
• getCodeLensForFunctions is the method in goRunTestCodelens.ts file that creates the debug configuration. This is where we need to ignore -gcFlags