fix goroot (#74)

mage/main.go

@@ -101,6 +101,7 @@ func ParseAndRun(dir string, stdout, stderr io.Writer, stdin io.Reader, args []s
 		log.Println(initFile, "created")
 		return 0
 	}
+
 	return Invoke(inv)
 }
 
@@ -183,6 +184,7 @@ func Invoke(inv Invocation) int {
 	for i := range files {
 		fnames = append(fnames, filepath.Base(files[i]))
 	}
+
 	info, err := parse.Package(inv.Dir, fnames)
 	if err != nil {
 		log.Println("Error:", err)
@@ -264,24 +266,8 @@ func Magefiles(dir string) ([]string, error) {
 
 // Compile uses the go tool to compile the files into an executable at path.
 func Compile(path string, stdout, stderr io.Writer, gofiles []string) error {
-	// we explicitly set GOROOT on the command because go build will fail
-	// without it.
-	goroot := os.Getenv("GOROOT")
-	if goroot == "" {
-		c := exec.Command("go", "env", "GOROOT")
-		c.Stderr = stderr
-		b, err := c.Output()
-		if err != nil {
-			return fmt.Errorf("failed to get GOROOT from 'go env': %v", err)
-		}
-		goroot = strings.TrimSpace(string(b))
-		if goroot == "" {
-			return errors.New("could not determine GOROOT")
-		}
-	}
-
 	c := exec.Command("go", append([]string{"build", "-o", path}, gofiles...)...)
-	c.Env = append(os.Environ(), "GOROOT="+goroot)
+	c.Env = os.Environ()
 	c.Stderr = stderr
 	c.Stdout = stdout
 	err := c.Run()

parse/parse.go

@@ -3,12 +3,14 @@ package parse
 import (
 	"fmt"
 	"go/ast"
+	"go/build"
 	"go/doc"
 	"go/parser"
 	"go/token"
 	"go/types"
 	"log"
 	"os"
+	"os/exec"
 	"strings"
 )
 
@@ -105,7 +107,7 @@ func getPackage(path string, files []string, fset *token.FileSet) (*ast.Package,
 
 	pkgs, err := parser.ParseDir(fset, path, filter, parser.ParseComments)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("failed to parse directory: %v", err)
 	}
 
 	for name, pkg := range pkgs {
@@ -117,6 +119,21 @@ func getPackage(path string, files []string, fset *token.FileSet) (*ast.Package,
 }
 
 func makeInfo(dir string, fset *token.FileSet, files map[string]*ast.File) (types.Info, error) {
+	goroot := os.Getenv("GOROOT")
+	if goroot == "" {
+		c := exec.Command("go", "env", "GOROOT")
+		b, err := c.Output()
+		if err != nil {
+			return types.Info{}, fmt.Errorf("failed to get GOROOT from 'go env': %v", err)
+		}
+		goroot = strings.TrimSpace(string(b))
+		if goroot == "" {
+			return types.Info{}, fmt.Errorf("could not determine GOROOT")
+		}
+	}
+
+	build.Default.GOROOT = goroot
+
 	cfg := types.Config{
 		Importer: getImporter(fset),
 	}
@@ -133,7 +150,10 @@ func makeInfo(dir string, fset *token.FileSet, files map[string]*ast.File) (type
 	}
 
 	_, err := cfg.Check(dir, fset, fs, &info)
-	return info, err
+	if err != nil {
+		return info, fmt.Errorf("failed to check types in directory: %v", err)
+	}
+	return info, nil
 }
 
 // errorOrVoid filters the list of functions to only those that return only an