x/tools/gopls: handle go1.22's go/types.Alias

[adonovan]

This issue tracks the adoption in gopls of go1.22's new types.Alias type. We will need to audit every place that type-switches or type-asserts a types.Type to ensure that it works correctly with the new type. Initially the type checker will not produce instances of these types unless GODEBUG=gotypesalias=1 is set.

Things to resolve:

• go/types: Alias.String should not mention the aliased type #64584 (done)
• waiting for cmd/compile support for writing aliases (done)
• gcimporter support for reading and writing aliases (done)
• sprinkling Unalias in a great many places (done)
• supporting parameterized aliases (for now my goal is just to support with the new representation of simple aliases).
• adding tests to each x/tools package with aliases, both ordinary and parameterized.
• working with @dominikh to upgrade staticcheck in a similar way. (audit staticcheck for GODEBUG=gotypesalias=1 support dominikh/go-tools#1523)
• working with the vulncheck folks to do the same (done)

Related:

• x/tools: get tests passing with GODEBUG=gotypesalias=1 #65294

@gri @findleyr

[gopherbot]

Change https://go.dev/cl/547876 mentions this issue: gopls: updates for go1.22 types.Alias

[adonovan]

I tested gopls using tip GOROOT after hardwiring types.Checker.enablealias to true. (We can't use GODEBUG=gotypesalias=1 to control it yet because this environment variable would be inherited by 'go list' and the Go compiler, which doesn't yet have support for writing out Alias types, so it crashes.)

I added rudimentary support to the gcimporter package used by gopls for reading and writing aliases, and sprinkled lots of Unalias operations throughout the tree, and was able to get all but three tests (of vulncheck and staticheck) to pass. So I think it's in good shape for the 1.22 release, though we have a lot of work to do after the release.

[gopherbot]

Change https://go.dev/cl/574717 mentions this issue: internal/gcimporter: support materialized aliases

[gopherbot]

Change https://go.dev/cl/574737 mentions this issue: go/types: changes to support materialized aliases

[gopherbot]

Change https://go.dev/cl/577576 mentions this issue: internal/apidiff: support materialized aliases

[gopherbot]

Change https://go.dev/cl/579756 mentions this issue: gopls/internal/test/integration/misc: reenable staticcheck test