create binary symlinks with relative location

since the installed binary as well as the symlink reside in the
same directory, relative paths should be safe to use without
having to worry about crossing filesystem boundaries.

closes #158

Author: UiP9AV6Y

get.go

@@ -806,7 +806,8 @@ func install(ctx context.Context, logger *log.Logger, r *runner.Runner, modDir s
 	}
 
 	// go install does not define -modfile flag, so we mimic go install with go build -o instead.
-	binPath := filepath.Join(gobin, fmt.Sprintf("%s-%s", name, pkg.Module.Version))
+	binName := fmt.Sprintf("%s-%s", name, pkg.Module.Version)
+	binPath := filepath.Join(gobin, binName)
 
 	// New context with new environment files.
 	modCtx = r.With(ctx, modFile.Filepath(), modDir, pkg.BuildEnvs)
@@ -825,10 +826,11 @@ func install(ctx context.Context, logger *log.Logger, r *runner.Runner, modDir s
 		return nil
 	}
 
-	if err := os.RemoveAll(filepath.Join(gobin, name)); err != nil {
+	lnPath := filepath.Join(gobin, name)
+	if err := os.RemoveAll(lnPath); err != nil {
 		return errors.Wrap(err, "rm")
 	}
-	if err := os.Symlink(binPath, filepath.Join(gobin, name)); err != nil {
+	if err := os.Symlink(binName, lnPath); err != nil {
 		return errors.Wrap(err, "symlink")
 	}
 	return nil