remove hardcoded stdlib packages

Signed-off-by: Xiaoyang Tan <tanx@uber.com>

pkg/section/parser.go

@@ -22,7 +22,7 @@ func Parse(data []string) (SectionList, error) {
 		if s == "default" {
 			list = append(list, Default{})
 		} else if s == "standard" {
-			list = append(list, Standard{})
+			list = append(list, NewStandard())
 		} else if s == "newline" {
 			list = append(list, NewLine{})
 		} else if strings.HasPrefix(s, "prefix(") && len(d) > 8 {

pkg/section/section.go

@@ -28,7 +28,7 @@ func (list SectionList) String() []string {
 }
 
 func DefaultSections() SectionList {
-	return SectionList{Standard{}, Default{}}
+	return SectionList{NewStandard(), Default{}}
 }
 
 func DefaultSectionSeparators() SectionList {

pkg/section/standard.go

@@ -3,14 +3,30 @@ package section
 import (
 	"github.com/daixiang0/gci/pkg/parse"
 	"github.com/daixiang0/gci/pkg/specificity"
+	"golang.org/x/tools/go/packages"
 )
 
 const StandardType = "standard"
 
-type Standard struct{}
+type Standard struct {
+	standardPackages map[string]struct{}
+}
+
+func NewStandard() Standard {
+	pkgs, err := packages.Load(nil, "std")
+	if err != nil {
+		panic(err)
+	}
+
+	var standardPackages = make(map[string]struct{})
+	for _, p := range pkgs {
+		standardPackages[p.PkgPath] = struct{}{}
+	}
+	return Standard{standardPackages: standardPackages}
+}
 
 func (s Standard) MatchSpecificity(spec *parse.GciImports) specificity.MatchSpecificity {
-	if isStandard(spec.Path) {
+	if _, ok := s.standardPackages[spec.Path]; ok {
 		return specificity.StandardMatch{}
 	}
 	return specificity.MisMatch{}
@@ -23,8 +39,3 @@ func (s Standard) String() string {
 func (s Standard) Type() string {
 	return StandardType
 }
-
-func isStandard(pkg string) bool {
-	_, ok := standardPackages[pkg]
-	return ok
-}

pkg/section/standard_test.go

@@ -8,13 +8,13 @@ import (
 
 func TestStandardPackageSpecificity(t *testing.T) {
 	testCases := []specificityTestData{
-		{"context", Standard{}, specificity.StandardMatch{}},
-		{"contexts", Standard{}, specificity.MisMatch{}},
-		{"crypto", Standard{}, specificity.StandardMatch{}},
-		{"crypto1", Standard{}, specificity.MisMatch{}},
-		{"crypto/ae", Standard{}, specificity.MisMatch{}},
-		{"crypto/aes", Standard{}, specificity.StandardMatch{}},
-		{"crypto/aes2", Standard{}, specificity.MisMatch{}},
+		{"context", NewStandard(), specificity.StandardMatch{}},
+		{"contexts", NewStandard(), specificity.MisMatch{}},
+		{"crypto", NewStandard(), specificity.StandardMatch{}},
+		{"crypto1", NewStandard(), specificity.MisMatch{}},
+		{"crypto/ae", NewStandard(), specificity.MisMatch{}},
+		{"crypto/aes", NewStandard(), specificity.StandardMatch{}},
+		{"crypto/aes2", NewStandard(), specificity.MisMatch{}},
 	}
 	testSpecificity(t, testCases)
 }