[release-branch.go1.8] cmd/go: do not install broken libraries during 'go test -i -race'

Manual port of CL 37598 (submitted for Go 1.9) to Go 1.8.1.

Fixes #19133.
Fixes #19151.

Change-Id: I51707ea35068a393022f554b391ee2638dba16b5
Reviewed-on: https://go-review.googlesource.com/39617
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

src/cmd/go/pkg.go

@@ -955,10 +955,6 @@ func (p *Package) load(stk *importStack, bp *build.Package, err error) *Package
 		if p.Name == "main" && goarch == "arm" {
 			importPaths = append(importPaths, "math")
 		}
-		// In coverage atomic mode everything depends on sync/atomic.
-		if testCoverMode == "atomic" && (!p.Standard || (p.ImportPath != "runtime/cgo" && p.ImportPath != "runtime/race" && p.ImportPath != "sync/atomic")) {
-			importPaths = append(importPaths, "sync/atomic")
-		}
 	}
 
 	// Runtime and its internal packages depend on runtime/internal/sys,

src/cmd/go/test.go

@@ -545,6 +545,10 @@ func runTest(cmd *Command, args []string) {
 
 	// Prepare build + run + print actions for all packages being tested.
 	for _, p := range pkgs {
+		// sync/atomic import is inserted by the cover tool. See #18486
+		if testCover && testCoverMode == "atomic" {
+			ensureImport(p, "sync/atomic")
+		}
 		buildTest, runTest, printTest, err := b.test(p)
 		if err != nil {
 			str := err.Error()
@@ -636,6 +640,23 @@ func runTest(cmd *Command, args []string) {
 	b.do(root)
 }
 
+// ensures that package p imports the named package.
+func ensureImport(p *Package, pkg string) {
+	for _, d := range p.deps {
+		if d.Name == pkg {
+			return
+		}
+	}
+
+	a := loadPackage(pkg, &importStack{})
+	if a.Error != nil {
+		fatalf("load %s: %v", pkg, a.Error)
+	}
+	computeStale(a)
+
+	p.imports = append(p.imports, a)
+}
+
 func contains(x []string, s string) bool {
 	for _, t := range x {
 		if t == s {