goutil: Ad RelImpPath.

goutil/gotuil.go

@@ -2,11 +2,12 @@
 package goutil
 
 import (
-	"fmt"
 	"go/build"
 	"os"
 	"path/filepath"
 	"strings"
+
+	"github.com/pkg/errors"
 )
 
 // SrcDir tries to locate dir in GOPATH/src/ or GOROOT/src/pkg/ and returns its
@@ -19,7 +20,7 @@ func SrcDir(dir string) (absDir string, err error) {
 			return absDir, nil
 		}
 	}
-	return "", fmt.Errorf("goutil.SrcDir: unable to locate directory (%q) in GOPATH/src/ (%q) or GOROOT/src/pkg/ (%q)", dir, os.Getenv("GOPATH"), os.Getenv("GOROOT"))
+	return "", errors.Errorf("unable to locate directory (%q) in GOPATH/src/ (%q) or GOROOT/src/pkg/ (%q)", dir, os.Getenv("GOPATH"), os.Getenv("GOROOT"))
 }
 
 // AbsImpPath tries to locate the absolute import path based on the provided
@@ -30,7 +31,7 @@ func AbsImpPath(relImpPath string) (absImpPath string, err error) {
 	}
 	absPath, err := filepath.Abs(relImpPath)
 	if err != nil {
-		return "", fmt.Errorf("goutil.AbsImpPath: %v", err)
+		return "", errors.WithStack(err)
 	}
 	for _, srcDir := range build.Default.SrcDirs() {
 		if strings.HasPrefix(absPath, srcDir) {
@@ -41,5 +42,22 @@ func AbsImpPath(relImpPath string) (absImpPath string, err error) {
 			return absImpPath, nil
 		}
 	}
-	return "", fmt.Errorf("goutil.AbsImpPath: unable to locate absolute import path for %q", relImpPath)
+	return "", errors.Errorf("unable to locate absolute import path for %q", relImpPath)
+}
+
+// RelImpPath tries to locate the relative import path of the provided path. A
+// pre-condition is that the given path resides within GOPATH.
+func RelImpPath(path string) (relImpPath string, err error) {
+	if !filepath.IsAbs(path) {
+		path, err = filepath.Abs(path)
+		if err != nil {
+			return "", errors.WithStack(err)
+		}
+	}
+	for _, srcDir := range build.Default.SrcDirs() {
+		if filepath.HasPrefix(path, srcDir) {
+			return path[len(srcDir)+1:], nil
+		}
+	}
+	return "", errors.Errorf("unable to locate path (%q) in GOPATH/src/ (%q) or GOROOT/src/pkg/ (%q)", path, os.Getenv("GOPATH"), os.Getenv("GOROOT"))
 }