[dev.typeparams] cmd/compile: move //go:embed -lang check to noder

User errors should be reported in noder and/or typecheck, we already
know the -lang flag's value during noding, and checking it then works
better for unified IR.

The "multiple files for type" and "cannot apply to var of type" errors
should also be moved to typecheck, but then they'd have to be
duplicated for -G=3 mode (because it avoids typecheck). So those are
left behind for now.

Change-Id: I7caf16163c9faf975784acacdb8147514d2e698e
Reviewed-on: https://go-review.googlesource.com/c/go/+/327609
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

src/cmd/compile/internal/noder/noder.go

@@ -1886,6 +1886,8 @@ func checkEmbed(decl *syntax.VarDecl, haveEmbed, withinFunc bool) error {
 		return errors.New("go:embed cannot apply to var without type")
 	case withinFunc:
 		return errors.New("go:embed cannot apply to var inside func")
+	case !types.AllowsGoVersion(types.LocalPkg, 1, 16):
+		return fmt.Errorf("go:embed requires go1.16 or later (-lang was set to %s; check go.mod)", base.Flag.Lang)
 
 	default:
 		return nil

src/cmd/compile/internal/staticdata/embed.go

@@ -108,13 +108,6 @@ func WriteEmbed(v *ir.Name) {
 	// TODO(mdempsky): User errors should be reported by the frontend.
 
 	commentPos := (*v.Embed)[0].Pos
-	if !types.AllowsGoVersion(types.LocalPkg, 1, 16) {
-		prevPos := base.Pos
-		base.Pos = commentPos
-		base.ErrorfVers("go1.16", "go:embed")
-		base.Pos = prevPos
-		return
-	}
 	if base.Flag.Cfg.Embed.Patterns == nil {
 		base.ErrorfAt(commentPos, "invalid go:embed: build system did not supply embed configuration")
 		return