cmd/compile/internal/types2: add test for imported constraints pre-1.18

But exclude the test when running unified build for now
(the unified builder's importers are not yet updated to
handle extended interfaces).
Also, fix respective error position.

Fixes #47967.

Change-Id: I4e3d829b5c12001c024b9eefcc27f97b10c1d1e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/363834
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

src/cmd/compile/internal/types2/check_test.go

@@ -25,6 +25,7 @@ package types2_test
 import (
 	"cmd/compile/internal/syntax"
 	"flag"
+	"internal/buildcfg"
 	"internal/testenv"
 	"os"
 	"path/filepath"
@@ -93,11 +94,27 @@ func asGoVersion(s string) string {
 	return ""
 }
 
+// excludedForUnifiedBuild lists files that cannot be tested
+// when using the unified build's export data.
+// TODO(gri) enable as soon as the unified build supports this.
+var excludedForUnifiedBuild = map[string]bool{
+	"issue47818.go2": true,
+}
+
 func testFiles(t *testing.T, filenames []string, colDelta uint, manual bool) {
 	if len(filenames) == 0 {
 		t.Fatal("no source files")
 	}
 
+	if buildcfg.Experiment.Unified {
+		for _, f := range filenames {
+			if excludedForUnifiedBuild[filepath.Base(f)] {
+				t.Logf("%s cannot be tested with unified build - skipped", f)
+				return
+			}
+		}
+	}
+
 	var mode syntax.Mode
 	if strings.HasSuffix(filenames[0], ".go2") || manual {
 		mode |= syntax.AllowGenerics

src/cmd/compile/internal/types2/decl.go

@@ -570,7 +570,7 @@ func (check *Checker) typeDecl(obj *TypeName, tdecl *syntax.TypeDecl, def *Named
 		check.validType(obj.typ, nil)
 		// If typ is local, an error was already reported where typ is specified/defined.
 		if check.isImportedConstraint(rhs) && !check.allowVersion(check.pkg, 1, 18) {
-			check.versionErrorf(tdecl.Type.Pos(), "go1.18", "using type constraint %s", rhs)
+			check.versionErrorf(tdecl.Type, "go1.18", "using type constraint %s", rhs)
 		}
 	}).describef(obj, "validType(%s)", obj.Name())
 

src/cmd/compile/internal/types2/testdata/fixedbugs/issue47818.go2

@@ -8,6 +8,8 @@
 
 package go1_17
 
+import "constraints"
+
 type T[P /* ERROR type parameters require go1\.18 or later */ any /* ERROR undeclared name: any \(requires version go1\.18 or later\) */ ] struct{}
 
 // for init (and main, but we're not in package main) we should only get one error
@@ -56,4 +58,4 @@ type (
 	_ = C2
 )
 
-// TODO(gri) need test cases for imported constraint types (see also issue #47967)
+type Ordered constraints /* ERROR using type constraint constraints\.Ordered requires go1\.18 or later */ .Ordered