cmd/go: `go mod download -json` should output valid json

[techabstraction]

What version of Go are you using (go version)?

$ go version
go version go1.12.8 darwin/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/jakcollins/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/jakcollins/dev/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/jakcollins/dev/github.expedia.biz/Brand-Expedia/aws_key_gen/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/s4/655pl1x12pjc0c05f43ptjx94hrmpt/T/go-build867894321=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

git clone git@github.com:golang/tools.git
cd tools
go mod download -json

What did you expect to see?

Well formed json output, please click to expand example below.

go mod download -json Output

$ go mod download -json
[
	{
		"Path": "golang.org/x/crypto",
		"Version": "v0.0.0-20190308221718-c2843e01d9a2",
		"Info": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/crypto/@v/v0.0.0-20190308221718-c2843e01d9a2.info",
		"GoMod": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/crypto/@v/v0.0.0-20190308221718-c2843e01d9a2.mod",
		"Zip": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/crypto/@v/v0.0.0-20190308221718-c2843e01d9a2.zip",
		"Dir": "/Users/jakcollins/dev/go/pkg/mod/golang.org/x/crypto@v0.0.0-20190308221718-c2843e01d9a2",
		"Sum": "h1:VklqNMn3ovrHsnt90PveolxSbWFaJdECFbxSq0Mqo2M=",
		"GoModSum": "h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w="
	},
	{
		"Path": "golang.org/x/net",
		"Version": "v0.0.0-20190620200207-3b0461eec859",
		"Info": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/net/@v/v0.0.0-20190620200207-3b0461eec859.info",
		"GoMod": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/net/@v/v0.0.0-20190620200207-3b0461eec859.mod",
		"Zip": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/net/@v/v0.0.0-20190620200207-3b0461eec859.zip",
		"Dir": "/Users/jakcollins/dev/go/pkg/mod/golang.org/x/net@v0.0.0-20190620200207-3b0461eec859",
		"Sum": "h1:R/3boaszxrf1GEUWTVDzSKVwLmSJpwZ1yqXm8j0v2QI=",
		"GoModSum": "h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s="
	},
	{
		"Path": "golang.org/x/sync",
		"Version": "v0.0.0-20190423024810-112230192c58",
		"Info": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/sync/@v/v0.0.0-20190423024810-112230192c58.info",
		"GoMod": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/sync/@v/v0.0.0-20190423024810-112230192c58.mod",
		"Zip": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/sync/@v/v0.0.0-20190423024810-112230192c58.zip",
		"Dir": "/Users/jakcollins/dev/go/pkg/mod/golang.org/x/sync@v0.0.0-20190423024810-112230192c58",
		"Sum": "h1:8gQV6CLnAEikrhgkHFbMAEhagSSnXWGV915qUMm9mrU=",
		"GoModSum": "h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM="
	},
	{
		"Path": "golang.org/x/sys",
		"Version": "v0.0.0-20190215142949-d0b11bdaac8a",
		"Info": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/sys/@v/v0.0.0-20190215142949-d0b11bdaac8a.info",
		"GoMod": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/sys/@v/v0.0.0-20190215142949-d0b11bdaac8a.mod",
		"Zip": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/sys/@v/v0.0.0-20190215142949-d0b11bdaac8a.zip",
		"Dir": "/Users/jakcollins/dev/go/pkg/mod/golang.org/x/sys@v0.0.0-20190215142949-d0b11bdaac8a",
		"Sum": "h1:1BGLXjeY4akVXGgbC9HugT3Jv3hCI0z56oJR5vAMgBU=",
		"GoModSum": "h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY="
	},
	{
		"Path": "golang.org/x/text",
		"Version": "v0.3.0",
		"Info": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/text/@v/v0.3.0.info",
		"GoMod": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/text/@v/v0.3.0.mod",
		"Zip": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/text/@v/v0.3.0.zip",
		"Dir": "/Users/jakcollins/dev/go/pkg/mod/golang.org/x/text@v0.3.0",
		"Sum": "h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=",
		"GoModSum": "h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ="
	},
	{
		"Path": "golang.org/x/xerrors",
		"Version": "v0.0.0-20190717185122-a985d3407aa7",
		"Info": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/xerrors/@v/v0.0.0-20190717185122-a985d3407aa7.info",
		"GoMod": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/xerrors/@v/v0.0.0-20190717185122-a985d3407aa7.mod",
		"Zip": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/xerrors/@v/v0.0.0-20190717185122-a985d3407aa7.zip",
		"Dir": "/Users/jakcollins/dev/go/pkg/mod/golang.org/x/xerrors@v0.0.0-20190717185122-a985d3407aa7",
		"Sum": "h1:9zdDQZ7Thm29KFXgAX/+yaf3eVbP7djjWp/dXAppNCc=",
		"GoModSum": "h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0="
	}
]

What did you see instead?

The output was not well formed json. It contained a 'go: finding ...' message and the list of module objects was not wrapped in a comma delimited json list. Please click to expand example below.

go mod download -json Output

$ go mod download -json
go: finding golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7
{
	"Path": "golang.org/x/crypto",
	"Version": "v0.0.0-20190308221718-c2843e01d9a2",
	"Info": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/crypto/@v/v0.0.0-20190308221718-c2843e01d9a2.info",
	"GoMod": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/crypto/@v/v0.0.0-20190308221718-c2843e01d9a2.mod",
	"Zip": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/crypto/@v/v0.0.0-20190308221718-c2843e01d9a2.zip",
	"Dir": "/Users/jakcollins/dev/go/pkg/mod/golang.org/x/crypto@v0.0.0-20190308221718-c2843e01d9a2",
	"Sum": "h1:VklqNMn3ovrHsnt90PveolxSbWFaJdECFbxSq0Mqo2M=",
	"GoModSum": "h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w="
}
{
	"Path": "golang.org/x/net",
	"Version": "v0.0.0-20190620200207-3b0461eec859",
	"Info": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/net/@v/v0.0.0-20190620200207-3b0461eec859.info",
	"GoMod": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/net/@v/v0.0.0-20190620200207-3b0461eec859.mod",
	"Zip": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/net/@v/v0.0.0-20190620200207-3b0461eec859.zip",
	"Dir": "/Users/jakcollins/dev/go/pkg/mod/golang.org/x/net@v0.0.0-20190620200207-3b0461eec859",
	"Sum": "h1:R/3boaszxrf1GEUWTVDzSKVwLmSJpwZ1yqXm8j0v2QI=",
	"GoModSum": "h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s="
}
{
	"Path": "golang.org/x/sync",
	"Version": "v0.0.0-20190423024810-112230192c58",
	"Info": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/sync/@v/v0.0.0-20190423024810-112230192c58.info",
	"GoMod": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/sync/@v/v0.0.0-20190423024810-112230192c58.mod",
	"Zip": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/sync/@v/v0.0.0-20190423024810-112230192c58.zip",
	"Dir": "/Users/jakcollins/dev/go/pkg/mod/golang.org/x/sync@v0.0.0-20190423024810-112230192c58",
	"Sum": "h1:8gQV6CLnAEikrhgkHFbMAEhagSSnXWGV915qUMm9mrU=",
	"GoModSum": "h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM="
}
{
	"Path": "golang.org/x/sys",
	"Version": "v0.0.0-20190215142949-d0b11bdaac8a",
	"Info": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/sys/@v/v0.0.0-20190215142949-d0b11bdaac8a.info",
	"GoMod": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/sys/@v/v0.0.0-20190215142949-d0b11bdaac8a.mod",
	"Zip": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/sys/@v/v0.0.0-20190215142949-d0b11bdaac8a.zip",
	"Dir": "/Users/jakcollins/dev/go/pkg/mod/golang.org/x/sys@v0.0.0-20190215142949-d0b11bdaac8a",
	"Sum": "h1:1BGLXjeY4akVXGgbC9HugT3Jv3hCI0z56oJR5vAMgBU=",
	"GoModSum": "h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY="
}
{
	"Path": "golang.org/x/text",
	"Version": "v0.3.0",
	"Info": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/text/@v/v0.3.0.info",
	"GoMod": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/text/@v/v0.3.0.mod",
	"Zip": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/text/@v/v0.3.0.zip",
	"Dir": "/Users/jakcollins/dev/go/pkg/mod/golang.org/x/text@v0.3.0",
	"Sum": "h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=",
	"GoModSum": "h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ="
}
{
	"Path": "golang.org/x/xerrors",
	"Version": "v0.0.0-20190717185122-a985d3407aa7",
	"Info": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/xerrors/@v/v0.0.0-20190717185122-a985d3407aa7.info",
	"GoMod": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/xerrors/@v/v0.0.0-20190717185122-a985d3407aa7.mod",
	"Zip": "/Users/jakcollins/dev/go/pkg/mod/cache/download/golang.org/x/xerrors/@v/v0.0.0-20190717185122-a985d3407aa7.zip",
	"Dir": "/Users/jakcollins/dev/go/pkg/mod/golang.org/x/xerrors@v0.0.0-20190717185122-a985d3407aa7",
	"Sum": "h1:9zdDQZ7Thm29KFXgAX/+yaf3eVbP7djjWp/dXAppNCc=",
	"GoModSum": "h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0="
}

[DisposaBoy]

The output was not well formed json. It contained a 'go: finding ...' message

AFAICT, that output is on stderr so it's fine IMO.

and the list of module objects was not wrapped in a comma delimited json list.

It's a stream of JSON objects? which is in line with JSON output from other sub-commands as well as being idiomatic(tm) and common which also makes it fine IMO.

[jayconrod]

Agree with @DisposaBoy's comment. This is working as intended.

Status messages are printed on stderr so the JSON output can be piped to tools and files separately. Errors are included in the JSON objects (in the Error field).

Printing a stream of JSON objects instead of a single list value is also expected. go list does this as well. Tools like jq work well with this format.

[techabstraction]

Okay, makes sense. Thank you for the explanation.