Check for nil when getting package info

Author: Sauyon Lee

extractor/extractor.go

@@ -148,7 +148,14 @@ func ExtractWithFlags(buildFlags []string, patterns []string) error {
 
 	for _, pkg := range pkgs {
 		info := pkgInfos[pkg.PkgPath]
-		if info.PkgDir == "" {
+		if info == nil {
+			var err error
+			info, err = util.GetPkgInfo(pkg.PkgPath)
+			if err != nil {
+				log.Fatalf("Unable to get a source directory for input package %s: %s", pkg.PkgPath, err)
+			}
+		}
+		if info == nil || info.PkgDir == "" {
 			log.Fatalf("Unable to get a source directory for input package %s.", pkg.PkgPath)
 		}
 		wantedRoots[info.PkgDir] = true

extractor/util/util.go

@@ -114,6 +114,16 @@ func GetPkgsInfo(patterns []string, includingDeps bool, flags ...string) (map[st
 	return pkgInfoMapping, nil
 }
 
+// GetPkgsInfo gets the absolute module and package root directories for the package `pkg`, passing
+// the internal `go list` command the flags specified by `flags`.
+func GetPkgInfo(pkg string, flags ...string) (*PkgInfo, error) {
+	pkgInfos, err := GetPkgsInfo([]string{pkg}, false, flags...)
+	if err != nil {
+		return nil, err
+	}
+	return pkgInfos[pkg], nil
+}
+
 // DepErrors checks there are any errors resolving dependencies for `pkgpath`. It passes the `go
 // list` command the flags specified by `flags`.
 func DepErrors(pkgpath string, flags ...string) bool {