x/tools/go/astutil: PathEnclosingInterval omits FuncType for intervals in the function signature

[adonovan]

Invoking PathEnclosingInterval on the extent of x in this program:

package p

func f(x int)

gives this result:

Path enclosing interval #18-19 [exact=true]:
[0] *ast.Ident @ 3:8-3:9 (#18-19)
[1] *ast.Field @ 3:8-3:13 (#18-23)
[2] *ast.FieldList @ 3:7-3:14 (#17-24)
[3] *ast.FuncDecl @ 3:1-3:14 (#11-24) Type.Scope={x}
[4] *ast.File @ 1:1-3:14 (#0-24) Scope={}

The FuncType--FuncDecl.Type, which holds the Params FieldList--is nowhere to be seen.

I'm sure this is because the invariant that each node contains its children has an edge case for FuncType: the FuncDecl for func f(x int) has a FuncType that includes the func token and the (x int) signature but not the name f (FuncDecl.Name), or the receiver for a method.

I'm amazed we haven't noticed this before.

[gopherbot]

Change https://go.dev/cl/595195 mentions this issue: go/ast/astutil: PathEnclosingInterval: add missing FuncType nodes

[gopherbot]

Change https://go.dev/cl/595196 mentions this issue: gopls/internal/golang: splitlines: remove workaround for golang/go#68202

[findleyr]

I'm not surprised we've missed this. We typically care about idents, fields, and decls only. FuncType is a somewhat arbitrary nesting.