cmd/vet: reporting "composite literal uses unkeyed fields" for slice types

[fsouza]

I have a typed defined from a slice (type TemplateDataList []TemplateData), and when I
create instances of this type

% go version
go version devel +ffe33f1f1f17 Tue Nov 25 15:41:33 2014 +1100 darwin/amd64
% cd $GOPATH/src/golang.org/x/tools
% hg tip
changeset:   1264:e105dadc3014
tag:         tip
user:        Andrew Gerrand <[email protected]>
date:        Wed Nov 26 15:31:30 2014 +1100
summary:     x/tools/cmd/godoc: add golang.org/x/oauth2 import path
% cd -
% cat code_bad.go
package main

import (
    "fmt"
    "github.com/tsuru/tsuru/iaas"
)

type Template struct {
    Name string
    Data iaas.TemplateDataList
}

func main() {
    template := Template{
        Name: "My Template",
        Data: iaas.TemplateDataList{
            {Name: "color", Value: "red"},
            {Name: "size", Value: "100"},
        },
    }
    fmt.Println(template)
}
% go vet code_bad.go
code_bad.go:16: iaas.TemplateDataList composite literal uses unkeyed fields
exit status 1

Here's where TemplateDataList is defined:
https://github.com/tsuru/tsuru/blob/0ac00f9d08f67efa39b679b643f74ff6ebba8530/iaas/template.go#L21

Now, if I copy the TemplateDataList definition to the same file, the error disappears:

% cat code_good.go
package main

import (
    "fmt"
    "github.com/tsuru/tsuru/iaas"
)

type TemplateDataList []iaas.TemplateData

type Template struct {
    Name string
    Data TemplateDataList
}

func main() {
    template := Template{
        Name: "My Template",
        Data: TemplateDataList{
            {Name: "color", Value: "red"},
            {Name: "size", Value: "100"},
        },
    }
    fmt.Println(template)
}
% go vet code_good.go
# no failures

[ianlancetaylor]

Comment 1:

I don't know if there is anything that can be done here.

Labels changed: added repo-tools, release-none.

[robpike]

Comment 2:

With only some of the files in the package presented to vet, it can't get the types
right. Nothing can be done.

Status changed to Unfortunate.

[luan]

@fsouza @ianlancetaylor

I had a conversation with a coworker (@tedsuo) about this today, we have this which doesn't pass vet, but that's really only possible with a slice literal, so I went and tried the following:

    // Check if the CompositeLit contains an unkeyed field.
    allKeyValue := true
    for _, e := range c.Elts {
        if _, ok := e.(*ast.KeyValueExpr); !ok {
            if cl, ok := e.(*ast.CompositeLit); !ok || cl.Type != nil {
                allKeyValue = false
                break
            }
        }
    }
    if allKeyValue {
        return
    }

To detect composite literals with no type, seems like we can use that logic to not show this unfortunate warning on slice type aliases.
Glad to submit code for code review if folks think this is reasonable.

[ianlancetaylor]

Seems plausible. Sure, send a CL.

[luan]

https://go-review.googlesource.com/#/c/22000/

[gopherbot]

CL https://golang.org/cl/22000 mentions this issue.

[gopherbot]

CL https://golang.org/cl/22318 mentions this issue.