cmd/go: generate: be more informative/verbose

[adonovan]

Running go generate ./... can take a while in a large project, but it is not easy to know why. It doesn't print a summary of what commands it ran, and neither -x nor -v lead to intelligible output. It would be nice if -v would print additional logging of the start and end time of each command, along with the location of the directive that triggered it, in a format such as this:

internal/protocol/command/interface.go:5: go run -tags=generate generate.go [start] 
...logs...
internal/protocol/command/interface.go:5: go run -tags=generate generate.go [success, 1.23s] 

@matloob

[matloob]

cc @samthanawalla

One option could be to put that information into a -json flag.

[adonovan]

One option could be to put that information into a -json flag.

I don't think JSON output is appropriate. The consumer is always a human, never a machine.

[rsc]

Why does -x not lead to appropriate output?

[adonovan]

Why does -x not lead to appropriate output?

It tells me neither the package nor file on whose behalf a command is being executed, nor the timing of the commands, which would be helpful to understand why my generators are conspicuously slow.

[matloob]

I think -json could be useful because we could make tools that can parse the go test (and go build once it's added) output and show the performance of the steps. I think it would be nice if the same tools could be used when looking at the performance of a test, build, or generate.

[adonovan]

I think -json could be useful

Build and test seem like things that you want to parse in your CI system so that you can present a fancy dashboard UI, but CI systems don't generally run go generate (because in general it is non-hermetic, requiring tools and data that don't exist in the repo). So I don't really see it. Don't let me stop you from adding -json, but I don't think it solves the problem of this issue.

[matloob]

Hm, we shouldn't add -json if it doesn't help. We'll have to think about this.

[mvdan]

#69487 does not duplicate nor replace this issue, but it does overlap. Note that I would still find go generate -exec helpful as a generic hook even if some other flag like -x or -json produced timing results.

[seankhliao]

Somewhat related:

when running go generate -n ./... to see what commands would be run
I'd like to know which packages / directories the commands would be run in.

E.g. when working on x/text, it did a lot of go run gen.go, but figuring out which one was doing what was difficult.