Author(s): Heschi Kreinick, Rebecca Stambler
Last updated: [Date]
Discussion at https://golang.org/issue/32394.
We propose a new workspace model for gopls that supports editing multiple projects at the same time, without compromising editor features.
gopls users may want to edit multiple projects in one editor session. For example, a microservice might depend on a proprietary infrastructure library, and a feature might require working across both. In
GOPATH mode, that's relatively trivial, because all code exists in the same context. In module mode, where multiple versions of dependencies are in play, it is much more difficult.
Consider the following application:
Find References on an
errors.Wrapf call in
app1, I expect to see references in
lib as well. This is especially true if I happen to own
lib, but even if not I may be looking for usage examples. In this situation, supporting that is easy.
Now consider a workspace with two applications.
Again, I would expect a
Find References in either App1 or App2 to find all
Wrapf calls, and there‘s no reason that shouldn’t work in this scenario. In module mode, things can be more difficult. Here's the next step in complexity:
At the level of the type checker,
v1.0.1 of the library are completely unrelated packages that happen to share a name. We as humans expect the APIs to match, but they could be completely different. Nonetheless, in this situation we can simply load both, and if we do a
Find References on
Wrapf there should be no problem finding all of them. That goes away in the next step:
Now there are two versions of
Wrapf. Again, at the type-checking level, these packages have nothing to do with each other. There is no easy way to relate
v0.9.1 with its match from
v0.9.0. We would have to do a great deal of work to correlate all the versions of a package together and match them up. (Wrapf is a simple case; consider how we'd match them if it was a method receiver, or took a complex struct, or a type from another package.) Worse yet, how would a multi-project rename work? Would it rename in all versions?
One final case:
Imagine I start in App1 and
Go To Definition on a function from the utility library. So far, no problem: there‘s only one version of the utility library in scope. Now I
Go To Definition on
Wrapf. Which version should I go to? The answer depends on where I came from, but that information can’t be expressed in the filesystem path of the source file, so there's no way for
gopls to keep track.
We propose to require all projects in a multi-project workspace use the same set of dependency versions. For
GOPATH, this means that all the projects should have the same
GOPATH setting. For module mode, it means creating one super-module that forces all the projects to resolve their dependencies together. Effectively, this would create an on-the-fly monorepo. This rules out users working on projects with mutually conflicting requirements, but that will hopefully be rare. Hopefully
gopls can create this super-module automatically.
The super-module would look something like:
module gopls-workspace require ( example.com/app1 v0.0.0-00010101000000-000000000000 example.com/app2 v0.0.0-00010101000000-000000000000 ) replace ( example.com/app1 => /abs/path/to/app1 example.com/app2 => /abs/path/to/app2 // Further replace directives included from app1 and app2 )
Note the propagation of replace directives from the constituent projects, since they would otherwise not take effect.
For users to get the experience they expect, with all of the scenarios above working, the only possible model is one where there‘s one version of any dependency in scope at a time. We don’t think there are any realistic alternatives to this model. We could try to include multiple versions of packages and then correlate them by name and signature (as discussed above) but that would be error-prone to implement. And if there were any problems matching things up, features like
Find References would silently fail.
No compatibility issues.
The implementation involves (1) finding all of the modules in the view, (2) automatically creating the super-module, and (3) adjusting gopls's go/packages queries and
go command calls to run in the correct modules.
When a view is created, we traverse the view's root folder and search for all of the existing modules. These modules will then be used to programmatically create the super-module. Once each view is created, it will load all of its packages (initial workspace load). As of 2020-08-13, for views in GOPATH or in a module, the initial workspace load takes the form of a
go list ./... query. With the current design, the initial workspace load will need be a query of the form:
go list example.com/app1/... example.com/app12/..., within the super-module. In GOPATH mode, we will not create the super-module.
All go/packages queries should be made from the super-module directory. Only
go mod commands need to be made from the module to which they refer.
As of 2020-08-13,
gopls relies on the
-modfile flag to avoid modifying the user’s existing
go.mod file. We will continue to use the
-modfile flag when running the
go command from within a module, but
-modfile is no longer necessary when we run the
go command from the super-module.
go command does require that its working directory contain a
go.mod file, but we want to run commands from the super-module without exposing super-module‘s
go.mod file to the user. To handle this, we will create a temporary directory containing the super-module’s
go.mod file, to act as the module root for any go/packages queries.
We should allow users to provide their own super-module
go.mod file, for extra control over the developer experience. This can also be used to mitigate any issues with the automatic creation of the super-module. We should detect a
gopls.mod in the view's root folder and use that as the super-module if present.
The authors have not yet considered the full implications of this design on:
module/... will include packages in nested modules inside it, whether the user wants them or not.
If any issues are noted during the implementation process, this document will be updated accordingly.
This design means that there is no longer any need to have multiple views in a session. The
gopls team will need to reconsider whether there is value in offering users a standalone workspace for each workspace folder, rather than merging all workspace folders into one view.
Users have currently been getting support for multiple modules in
gopls by adding each module as its own workspace folder. Once the implementation is complete, we will need to help users transition to this new model--otherwise they will find that memory consumption rises, as
gopls will have loaded the same module into memory multiple times. We will need to detect if a workspace folder is part of multiple views and alert the user to adjust their workspace.
gopls team implements this design, the super-module functionality will be gated behind an opt-in flag.
go.mod editing functionality of
gopls should continue to work as it does today, even in multi-project mode. Most likely it should simply continue to operate in one project at a time.