cmd/go: fix coverage in xtest of cgo package

Cover-annotated cgo-rebuilt package for xtest was
not linked into package graph and so not being rebuilt.
Link into package graph.

Fixes #13625.

Change-Id: I685f7276f92bbc85fbc4b389111c83d9fe517637
Reviewed-on: https://go-review.googlesource.com/32614
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/go_test.go

@@ -2106,11 +2106,16 @@ func TestCoverageWithCgo(t *testing.T) {
 		t.Skip("skipping because cgo not enabled")
 	}
 
-	tg := testgo(t)
-	defer tg.cleanup()
-	tg.run("test", "-short", "-cover", "./testdata/cgocover")
-	data := tg.getStdout() + tg.getStderr()
-	checkCoverage(tg, data)
+	for _, dir := range []string{"cgocover", "cgocover2", "cgocover3", "cgocover4"} {
+		t.Run(dir, func(t *testing.T) {
+			tg := testgo(t)
+			defer tg.cleanup()
+			tg.setenv("GOPATH", filepath.Join(tg.pwd(), "testdata"))
+			tg.run("test", "-short", "-cover", dir)
+			data := tg.getStdout() + tg.getStderr()
+			checkCoverage(tg, data)
+		})
+	}
 }
 
 func TestCgoDependsOnSyscall(t *testing.T) {

src/cmd/go/test.go

@@ -867,7 +867,7 @@ func (b *builder) test(p *Package) (buildAction, runAction, printAction *action,
 	if err != nil {
 		return nil, nil, nil, err
 	}
-	if len(ptest.GoFiles) > 0 {
+	if len(ptest.GoFiles)+len(ptest.CgoFiles) > 0 {
 		pmain.imports = append(pmain.imports, ptest)
 		t.ImportTest = true
 	}

src/cmd/go/testdata/src/cgocover2/p.go

+package p
+
+/*
+void
+f(void)
+{
+}
+*/
+import "C"
+
+var b bool
+
+func F() {
+	if b {
+		for {
+		}
+	}
+	C.f()
+}

src/cmd/go/testdata/src/cgocover2/x_test.go

+package p_test
+
+import (
+	. "cgocover2"
+	"testing"
+)
+
+func TestF(t *testing.T) {
+	F()
+}

src/cmd/go/testdata/src/cgocover3/p.go

+package p
+
+/*
+void
+f(void)
+{
+}
+*/
+import "C"
+
+var b bool
+
+func F() {
+	if b {
+		for {
+		}
+	}
+	C.f()
+}

src/cmd/go/testdata/src/cgocover3/p_test.go

+package p

src/cmd/go/testdata/src/cgocover3/x_test.go

+package p_test
+
+import (
+	. "cgocover3"
+	"testing"
+)
+
+func TestF(t *testing.T) {
+	F()
+}

src/cmd/go/testdata/src/cgocover4/notcgo.go

+package p

src/cmd/go/testdata/src/cgocover4/p.go

+package p
+
+/*
+void
+f(void)
+{
+}
+*/
+import "C"
+
+var b bool
+
+func F() {
+	if b {
+		for {
+		}
+	}
+	C.f()
+}

src/cmd/go/testdata/src/cgocover4/x_test.go

+package p_test
+
+import (
+	. "cgocover4"
+	"testing"
+)
+
+func TestF(t *testing.T) {
+	F()
+}