cmd/go: add global ignore mechanism for Go tooling ecosystem

[burdiyan]

UPDATE: The summary of the accepted proposal at: #42965 (comment).

---

Problem

For non-trivial (often multi-language) projects it's often desirable to make all the Go tools (including gopls) ignore certain directories.

Some of the examples could be the huge amount of files within node_modules, or bazel-* directories generated by Bazel. This causes many operations with ./... wildcards taking longer than desired. Also gopls often eats up a lot of CPU in VS Code depending on what you are doing.

Prior Art

This is something that has been discussed in several issues before, but seems like people couldn't get agree on a solution.

• proposal: cmd/go: ignore directories containing .goignore in file scans #30058
• x/tools/imports: should not scan bazel-out directories #35914
• x/tools/gopls: add a setting to ignore certain directories #42473

Some tools started to have their own solutions which causes fragmentation and is cumbersome.

For example goimports have its own machinery for this - .goimportsignore file in this case. But it's not working with Go Modules.

Other tools have a hard-coded list of directories to ignore, like .git and so on.

It seems like having a global solution that all the Go ecosystem could understand would make sense to solve this kind of problem.

Recently a workaround for this was to place a dummy go.mod file in the directories you wanted to ignore. But this is not easily portable between users of the project, because often these directories can be re-created on the user's machine and aren't even checked-in. Asking people to sprinkle some go.mod files all around every time is cumbersome.

@robpike was against of creating more dot files (#30058 (comment)).

Proposed Solution

Here're some of the options that this could be implemented with.

1. Use go.mod file for specifying directories to ignore. (Rejected because go.mod is not a catch-all config file like package.json in NodeJS).
2. Use a separate .goignore file. (This would go against Rob's desire to avoid new dot files, and although being in the spirit with other tools: .dockerignore, .gitignore, .bazelignore, etc. is concerning. The concerns are discussed in this thread).
3. Use the go.work file that's coming in the next Go 1.18 release.
4. Have a separate go.ignore file that would specify directories to ignore.

/cc @tj @stamblerre

[mvdan]

But this is not easily portable between users of the project, because often these directories can be re-created on the user's machine and aren't even checked-in. Asking people to sprinkle some go.mod files all around every time is cumbersome.

I'm not sure that I understand this argument. Presumably, it's a program that creates and fills those directories, since they have to contain a significant amount of files for you to really want to ignore them in Go. If they were just a handful of files created manually by a human, it would be a negligible cost for Go to walk those and realise there are no Go packages there.

So, given that it is a program or script creating those large directories, why not add a touch ${dir}/go.mod at the end? That seems easy enough at a high level, at least.

I'm proposing to add this configuration into the existing go.mod file.

This is unlikely to happen, see #42343 (comment).

Another solution could be a global .goignore file. This would go against Rob's desire to avoid new dot files, but would be in the spirit with other tools like that have files like .dockerignore, .gitignore, .bazelignore, etc.

I have to admit that I dislike this option. It's bad enough that all these other tools use separate ignore files.

[burdiyan]

I'm not sure that I understand this argument. Presumably, it's a program that creates and fills those directories, since they have to contain a significant amount of files for you to really want to ignore them in Go. If they were just a handful of files created manually by a human, it would be a negligible cost for Go to walk those and realise there are no Go packages there.

So, given that it is a program or script creating those large directories, why not add a touch ${dir}/go.mod at the end? That seems easy enough at a high level, at least.

@mvdan It is indeed a program that creates these directories. But it's a program that you don't control normally. Wrapping well-known tools like nom install with your own script only to put an empty go.mod in there doesn't seem right.

On the other hand by placing arbitrary files in these directories you're invading the territory of other tools. What if that program checks the integrity of the directory and would break seeing a random unknown file? It's not the case with node_modules but breaking into structures created by other programs, only to work around your own problem doesn't seem right either.

I understand the objection about go.mod. I was not aware about @rsc's statement.

I have to admit that I dislike this option. It's bad enough that all these other tools use separate ignore files.

Could you elaborate on why do you think it's bad? It may not be the most elegant solution, but it's common practice, well-understood and somewhat expected.

If we already have .goimportsignore, why not standardizing it into something that can be handled and understood by all the ecosystem of Go tools?

[bcmills]

It is indeed a program that creates these directories. But it's a program that you don't control normally. Wrapping well-known tools like nom install with your own script only to put an empty go.mod in there doesn't seem right.

Wouldn't you need to wrap the tool to add a .goignore file anyway? (Given that you need to inject a file, why does it matter whether it is named .goignore or go.mod?)

[burdiyan]

@bcmills My proposal is to add a file in the root of the project, not in the directory being ignored. So it would be checked in. Like .gitignore in Git. Basically the idea is to list the paths to ignore in that file, and check it in.

[bcmills]

...ok? But why would you not also check in the injected go.mod files?

[mvdan]

Could you elaborate on why do you think it's bad? It may not be the most elegant solution, but it's common practice, well-understood and somewhat expected.

The common practice is to litter repositories with dot files. That does not mean we should do the same, making the problem worse :) Go already has multiple mechanisms to ignore entire directories (. or _ prefixes, and dropping empty go.mod files), so there needs to be a really good reason to add another method.

[burdiyan]

...ok? But why would you not also check in the injected go.mod files?

@bcmills because often directories to ignore aren't checked in.

[burdiyan]

The common practice is to litter repositories with dot files. That does not mean we should do the same, making the problem worse :) Go already has multiple mechanisms to ignore entire directories (. or _ prefixes, and dropping empty go.mod files), so there needs to be a really good reason to add another method.

@mvdan IMHO, having a dot file in one place, that is trackable, is less of an evil, than sprinkling empty go.mod files all over the place, ad-hoc, and breaking into opinions of other tools.

Thinking about pros and cons of implementing such a feature, I'm struggling to see any cons (probably due to my ignorance), besides having to spend the time to implement it. I'd appreciate if anyone could bring some light into this to understand the implications.

[psigen]

I have a use case where I have a multi-language repo where not all of the developers are touching the go components.

I don't think it is reasonable to ask my docker, bazel, and nodejs developers to all wrap their normal tooling in scripts that touch extra files in their build directories, nor ask them to try to rename their standard build directories to match existing go conventions, some of which conflict with the other tool conventions.

It seems like there should be a way to specify how to ignore certain files or directories that does not require modifying the content of those files or directories, because the ignored content is not being managed by go and may have its own conflicting conventions and lifecycle.

[rsc]

@psigen Go wants a directory tree that belongs to it. In a multi-language repo, why not create a top-level go/ directory?

[psigen]

@rsc: because my projects are not organized that way. I have services like:

service1/
    backend/  # golang
    debug-cli/
    proto/
service2/
    backend/  #python
    debug-ui/
    proto/
webapp/
    frontend/ 

I know what you are asking, which is why not reorganize to:

proto/
    service1/
    service2/
golang/
    service1-svc/
    service1-cli/
python/
    service2/
nodejs/
    webapp/
    service1/debug-ui/

And the answer, (besides "that's a lot of work right now") is that it is not how our ownership is structured.

It is not convenient to have duplication in the CODEOWNERS files, .gitignore patterns that look like **/service1/foo*, cross-directory-tree docs links, etc. all in service of golang. It makes PR reviews harder when related changes happen all over the directory tree. It forces docker build contexts to all need to be at the root of the entire source tree, and makes live-rebuilds in tools like Tilt and Skaffold much more difficult to author.

I could go on, but I'm really just reiterating the core premise of this proposal:

For non-trivial (often multi-language) projects it's often desirable to make all the Go tools (including gopls) ignore certain directories.

[4k1k0]

I use the serverless framework to deploy lambdas on AWS. Some plugins that I have to use contains go files. So when I run go mod download or go mod tidy I add dependencies to my go.mod file that are required by the go files inside the node_modules directory. It would be great to define a way to exclude directories from go modules.

node_modules
  serverless
    lib
      plugins
        create
          templates
            aws-go
              main.go
cmd
  main.go
pkg
  dirA
  dirB
  dirC

[cespare]

@rsc

@psigen Go wants a directory tree that belongs to it. In a multi-language repo, why not create a top-level go/ directory?

Reading this statement does not make me happy. It goes against the entire premise of the code organization at my company.

We use a monorepo with projects in several languages. Some Go programs live inside projects written in other languages. Sometimes we rewrite a project from one language to another. Some projects use a combination of Go and other languages (imagine a website written using both Go and JavaScript extensively). We already have an organizational hierarchy within the monorepo that is based around purpose and ownership, not language.

This all worked fine with $GOPATH: the repo was inside its own single $GOPATH segment and a top-level vendor directory contained a single version of all shared dependencies.

Moving to modules has raised some challenges, but mostly it has worked. The whole repo is one module so we use a fixed, shared set of dependencies. One issue we faced is that the go mod tidy and other commands printed out a bunch of irrelevant spam (#35941) -- we sent a fix for that. Other issues we see involve various kinds of slowness in gopls (#46438 describes one particular issue I have). But mostly it works fine, and ISTM that the remaining issues are surmountable if the folks working on the tools care about making them work well in the presence of mixed-language source trees (and until now it seemed to me that they mostly do!).

But when I read "Go wants a directory tree that belongs to it", it sounds like you don't think this use case matters as far as the standard Go tools are concerned. I don't know how we could possibly adapt our repo to a "Go code all belongs in its own tree" model. Probably we wouldn't -- I imagine that if push came to shove, we'd look into alternative build tools.