x/tools/go/packages: all "no Go files in" errors get assigned to single package as a single error

[dominikh]

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

$ go version
go version go1.12.5 linux/amd64
go version devel +c11f6c4929 Fri Jun 21 21:24:47 2019 +0000 linux/amd64

What did you do?

https://play.golang.org/p/Y0ANYGkISpa

What did you expect to see?

Two packages, sandbox/empty1 and sandbox/empty2, each with one error

What did you see instead?

One package, sandbox/empty2, with one error but whose error message contains two errors for two separate packages.

$ go run foo.go
2019/06/24 20:22:59 sandbox/empty2
2019/06/24 20:22:59 1
2019/06/24 20:22:59 packages.Error{Pos:"", Msg:"go build sandbox/empty2: no Go files in /home/dominikh/prj/src/sandbox/empty2\ngo build sandbox/empty1: no Go files in /home/dominikh/prj/src/sandbox/empty1", Kind:0}

/cc @matloob

[dominikh]

The Mode can be further reduced to packages.NeedImports | packages.NeedExportsFile and still reproduce the bug.

The underlying go list call seems to behave correctly:

$ go list -e -json -compiled=false -test=false -export=true -deps=false -find=false -- sandbox/foo
go build sandbox/empty2: no Go files in /home/dominikh/prj/src/sandbox/empty2
go build sandbox/empty1: no Go files in /home/dominikh/prj/src/sandbox/empty1
{
	"Dir": "/home/dominikh/prj/src/sandbox/foo",
	"ImportPath": "sandbox/foo",
	"Name": "pkg",
	"Target": "/home/dominikh/prj/pkg/linux_amd64/sandbox/foo.a",
	"Root": "/home/dominikh/prj/",
	"Match": [
		"sandbox/foo"
	],
	"Incomplete": true,
	"GoFiles": [
		"foo.go"
	],
	"Imports": [
		"sandbox/empty1",
		"sandbox/empty2"
	],
	"Deps": [
		"sandbox/empty1",
		"sandbox/empty2"
	],
	"DepsErrors": [
		{
			"ImportStack": [
				"sandbox/foo",
				"sandbox/empty1"
			],
			"Pos": "/home/dominikh/prj/src/sandbox/foo/foo.go:3:8",
			"Err": "no Go files in /home/dominikh/prj/src/sandbox/empty1"
		},
		{
			"ImportStack": [
				"sandbox/foo",
				"sandbox/empty2"
			],
			"Pos": "/home/dominikh/prj/src/sandbox/foo/foo.go:4:8",
			"Err": "no Go files in /home/dominikh/prj/src/sandbox/empty2"
		}
	]
}

though the extra output on stderr is noteworthy.

[dominikh]

Worse yet, if we attempt to load a healthy package in addition to sandbox/foo – e.g. packages.Load(cfg, "sandbox/foo", "strconv") – then the healthy package will not be returned by packages.Load. We still only get exactly one package, sandbox/empty2, with exactly one packages.Error.

[sauyon]

I'm reasonably sure that this is caused by this special case in the golist driver.

This might be a bug on the older go1.1 version which I assume is supported (?) but doesn't seem to be an issue on my version (go1.12.6).

Either way, I think the correct way to correct this is to add special JSON nodes to stdout, then, when parsing, remove them if there is already a node for them.

[gopherbot]

Change https://golang.org/cl/185077 mentions this issue: Ignore more errors in go list