go/packages: fix incorrect x_test graph in fallback

This change fixes a bug that occured in the golist fallback logic when
an x_test package imported its own package under test. For a package
"a", if "a_test" imported "a", we'd populate "a_test"'s import map
with an entry "a [a.test]" pointing to the test variant of the package
with id "a [a.test]". This change fixes the key to be "a", the correct
import path of the package, not "a [a.test], which is the ID".

Change-Id: If798f2675b01aa537c6ccc129dc35d042d967337
Reviewed-on: https://go-review.googlesource.com/133356
Reviewed-by: Ian Cottrell <iancottrell@google.com>

go/packages/golist_fallback.go

@@ -127,9 +127,11 @@ func golistDriverFallback(cfg *Config, words ...string) (*driverResponse, error)
 					if isRoot {
 						response.Roots = append(response.Roots, xtestID)
 					}
-					for i, imp := range p.XTestImports {
+					// Rewrite import to package under test to refer to test variant.
+					imports := importMap(p.XTestImports)
+					for imp := range imports {
 						if imp == p.ImportPath {
-							p.XTestImports[i] = testID
+							imports[imp] = &Package{ID: testID}
 							break
 						}
 					}
@@ -139,7 +141,7 @@ func golistDriverFallback(cfg *Config, words ...string) (*driverResponse, error)
 						GoFiles:         absJoin(p.Dir, p.XTestGoFiles),
 						CompiledGoFiles: absJoin(p.Dir, p.XTestGoFiles),
 						PkgPath:         pkgpath,
-						Imports:         importMap(p.XTestImports),
+						Imports:         imports,
 					})
 				}
 			}

go/packages/packages110_test.go

@@ -6,6 +6,51 @@
 
 package packages_test
 
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"strings"
+	"testing"
+
+	"golang.org/x/tools/go/packages"
+)
+
 func init() {
 	usesOldGolist = true
 }
+
+func TestXTestImports(t *testing.T) {
+	tmp, cleanup := makeTree(t, map[string]string{
+		"src/a/a_test.go": `package a_test; import "a"`,
+		"src/a/a.go":      `package a`,
+	})
+	defer cleanup()
+
+	cfg := &packages.Config{
+		Mode:  packages.LoadImports,
+		Dir:   tmp,
+		Env:   append(os.Environ(), "GOPATH="+tmp, "GO111MODULE=off"),
+		Tests: true,
+	}
+	initial, err := packages.Load(cfg, "a")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var gotImports bytes.Buffer
+	for _, pkg := range initial {
+		var imports []string
+		for imp, pkg := range pkg.Imports {
+			imports = append(imports, fmt.Sprintf("%q: %q", imp, pkg.ID))
+		}
+		fmt.Fprintf(&gotImports, "%s {%s}\n", pkg.ID, strings.Join(imports, ", "))
+	}
+	wantImports := `a {}
+a [a.test] {}
+a_test [a.test] {"a": "a [a.test]"}
+`
+	if gotImports.String() != wantImports {
+		t.Fatalf("wrong imports: got <<%s>>, want <<%s>>", gotImports.String(), wantImports)
+	}
+}