go.tools/astutil: add Imports, which returns imports grouped by spacing.

R=bradfitz
CC=golang-dev
https://golang.org/cl/23660045

astutil/imports.go

@@ -323,3 +323,33 @@ func isTopName(n ast.Expr, name string) bool {
 	id, ok := n.(*ast.Ident)
 	return ok && id.Name == name && id.Obj == nil
 }
+
+// Imports returns the file imports grouped by paragraph.
+func Imports(fset *token.FileSet, f *ast.File) [][]*ast.ImportSpec {
+	var groups [][]*ast.ImportSpec
+
+	for _, decl := range f.Decls {
+		genDecl, ok := decl.(*ast.GenDecl)
+		if !ok || genDecl.Tok != token.IMPORT {
+			break
+		}
+
+		group := []*ast.ImportSpec{}
+
+		var lastLine int
+		for _, spec := range genDecl.Specs {
+			importSpec := spec.(*ast.ImportSpec)
+			pos := importSpec.Path.ValuePos
+			line := fset.Position(pos).Line
+			if lastLine > 0 && pos > 0 && line-lastLine > 1 {
+				groups = append(groups, group)
+				group = []*ast.ImportSpec{}
+			}
+			group = append(group, importSpec)
+			lastLine = line
+		}
+		groups = append(groups, group)
+	}
+
+	return groups
+}

astutil/imports_test.go

@@ -6,7 +6,8 @@ import (
 	"go/format"
 	"go/parser"
 	"go/token"
-
+	"reflect"
+	"strconv"
 	"testing"
 )
 
@@ -528,3 +529,102 @@ func TestRenameTop(t *testing.T) {
 		}
 	}
 }
+
+var importsTests = []struct {
+	name string
+	in   string
+	want [][]string
+}{
+	{
+		name: "no packages",
+		in: `package foo
+`,
+		want: nil,
+	},
+	{
+		name: "one group",
+		in: `package foo
+
+import (
+	"fmt"
+	"testing"
+)
+`,
+		want: [][]string{{"fmt", "testing"}},
+	},
+	{
+		name: "four groups",
+		in: `package foo
+
+import "C"
+import (
+	"fmt"
+	"testing"
+
+	"appengine"
+
+	"myproject/mylib1"
+	"myproject/mylib2"
+)
+`,
+		want: [][]string{
+			{"C"},
+			{"fmt", "testing"},
+			{"appengine"},
+			{"myproject/mylib1", "myproject/mylib2"},
+		},
+	},
+	{
+		name: "multiple factored groups",
+		in: `package foo
+
+import (
+	"fmt"
+	"testing"
+
+	"appengine"
+)
+import (
+	"reflect"
+
+	"bytes"
+)
+`,
+		want: [][]string{
+			{"fmt", "testing"},
+			{"appengine"},
+			{"reflect"},
+			{"bytes"},
+		},
+	},
+}
+
+func unquote(s string) string {
+	res, err := strconv.Unquote(s)
+	if err != nil {
+		return "could_not_unquote"
+	}
+	return res
+}
+
+func TestImports(t *testing.T) {
+	fset := token.NewFileSet()
+	for _, test := range importsTests {
+		f, err := parser.ParseFile(fset, "test.go", test.in, 0)
+		if err != nil {
+			t.Errorf("%s: %v", test.name, err)
+			continue
+		}
+		var got [][]string
+		for _, block := range Imports(fset, f) {
+			var b []string
+			for _, spec := range block {
+				b = append(b, unquote(spec.Path.Value))
+			}
+			got = append(got, b)
+		}
+		if !reflect.DeepEqual(got, test.want) {
+			t.Errorf("Imports(%s)=%v, want %v", test.name, got, test.want)
+		}
+	}
+}