Test of "too new" diagnostics from the stdversion analyzer.

This test references go1.21 and go1.22 symbols from std.

It uses a txtar file due to golang/go#37054.

See also gopls/internal/test/marker/testdata/diagnostics/stdversion.txt
which runs the same test within the gopls analysis driver, to ensure
coverage of per-file Go version support.

-- go.work --
go 1.21

use .
use sub
use sub20
use old

-- go.mod --
module example.com

go 1.21

-- a/a.go --
package a

import "go/types"

func _() {
	// old package-level type
	var _ types.Info // ok: defined by go1.0

	// new field of older type
	_ = new(types.Info).FileVersions // want `types.FileVersions requires go1.22 or later \(module is go1.21\)`

	// new method of older type
	new(types.Info).PkgNameOf // want `types.PkgNameOf requires go1.22 or later \(module is go1.21\)`

	// new package-level type
	var a types.Alias // want `types.Alias requires go1.22 or later \(module is go1.21\)`

	// new method of new type
	a.Underlying() // no diagnostic
}

-- sub/go.mod --
module example.com/sub

go 1.21

-- sub/sub.go --
package sub

import "go/types"

func _() {
	// old package-level type
	var _ types.Info // ok: defined by go1.0

	// new field of older type
	_ = new(types.Info).FileVersions // want `types.FileVersions requires go1.22 or later \(module is go1.21\)`

	// new method of older type
	new(types.Info).PkgNameOf // want `types.PkgNameOf requires go1.22 or later \(module is go1.21\)`

	// new package-level type
	var a types.Alias // want `types.Alias requires go1.22 or later \(module is go1.21\)`

	// new method of new type
	a.Underlying() // no diagnostic
}

invalid syntax // exercise RunDespiteErrors

-- sub/tagged.go --
//go:build go1.22

package sub

import "go/types"

func _() {
	// old package-level type
	var _ types.Info

	// new field of older type
	_ = new(types.Info).FileVersions

	// new method of older type
	new(types.Info).PkgNameOf

	// new package-level type
	var a types.Alias

	// new method of new type
	a.Underlying()
}

-- old/go.mod --
module example.com/old

go 1.5

-- old/old.go --
package old

import "go/types"

var _ types.Alias // no diagnostic: go.mod is too old for us to care

-- sub/oldtagged.go --
// The file Go version (1.16) overrides the go.mod Go version (1.21),
// even when this means a downgrade (#67123).
// (stdversion is silent for go.mod versions before 1.21:
// before the forward compatibility regime, the meaning
// of the go.mod version was not clearly defined.)

//go:build go1.16

package sub

import "bytes"
import "go/types"

var _ = bytes.Clone // want `bytes.Clone requires go1.20 or later \(file is go1.16\)`
var _ = types.Alias // want `types.Alias requires go1.22 or later \(file is go1.16\)`

-- sub20/go.mod --
module example.com/sub20

go 1.20

-- sub20/oldtagged.go --
// Same test again, but with a go1.20 mod,
// before the forward compatibility regime:
// The file's build tag effects selection, but
// not language semantics, so stdversion is silent.

//go:build go1.16

package sub

import "bytes"
import "go/types"

var _ = bytes.Clone
var _ = types.Alias