read package path from go.mod if it exists (#30)

cmd/grifter.go

@@ -1,14 +1,16 @@
 package cmd
 
 import (
+	"fmt"
+	"github.com/pkg/errors"
+	"github.com/rogpeppe/go-internal/modfile"
 	"html/template"
+	"io/ioutil"
 	"os"
 	"path"
 	"path/filepath"
 	"strings"
 	"sync"
-
-	"github.com/pkg/errors"
 )
 
 const exePath = ".grifter/main.go"
@@ -69,7 +71,24 @@ func newGrifter(name string) (*grifter, error) {
 			return g, errors.Errorf("There is no directory named 'grifts'. Run '%s init' or switch to the appropriate directory", name)
 		}
 		g.GriftsAbsolutePath = filepath.ToSlash(filepath.Join(currentPath, "grifts"))
-		g.GriftsPackagePath = filepath.ToSlash(filepath.Join(path.Base(currentPath), "grifts"))
+
+		// check for go module to see if we can get go.mod
+		if os.Getenv("GO111MODULE") == "on" {
+			moddata, err := ioutil.ReadFile("go.mod")
+			if err != nil {
+				return g, errors.New("go.mod cannot be read or does not exist while go module is enabled.")
+			}
+			packagePath := modfile.ModulePath(moddata)
+			if packagePath == "" {
+				return g, errors.New("go.mod is malformed.")
+			}
+			g.GriftsPackagePath = fmt.Sprintf("%s/grifts", packagePath)
+		} else {
+			// no go module, infer package path from current directory
+			g.GriftsPackagePath = filepath.ToSlash(filepath.Join(path.Base(currentPath), "grifts"))
+		}
+
+
 	}
 
 	return g, nil
@@ -101,3 +120,4 @@ func (g *grifter) Setup() error {
 func (g *grifter) TearDown() error {
 	return os.RemoveAll(filepath.Dir(exePath))
 }
+

go.mod

@@ -4,5 +4,6 @@ require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/pkg/errors v0.8.0
 	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/rogpeppe/go-internal v1.0.0-alpha
 	github.com/stretchr/testify v1.2.2
 )

go.sum

@@ -1,8 +1,15 @@
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
+github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
+github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
 github.com/pkg/errors v0.8.0 h1:WdK/asTD0HN+q6hsWO3/vpuAkAr+tw6aNJNDFFf0+qw=
 github.com/pkg/errors v0.8.0/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/rogpeppe/go-internal v1.0.0-alpha h1:zJtNjia0DW6sKVGzv5i+3TwGRJEJmaPnU9F12IRf/gI=
+github.com/rogpeppe/go-internal v1.0.0-alpha/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=
 github.com/stretchr/testify v1.2.2 h1:bSDNvY7ZPG5RlJ8otE/7V6gMiyenm9RtJ7IUVIAoJ1w=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/errgo.v2 v2.1.0/go.mod h1:hNsd1EY+bozCKY1Ytp96fpM3vjJbqLJn88ws8XvfDNI=