if f := ctxt.SplitPathList; f != nil {
		return f(s)
	}
	return filepath.SplitList(s)
}

// isAbsPath calls ctxt.IsAbsPath (if not nil) or else filepath.IsAbs.
func (ctxt *Context) isAbsPath(path string) bool {
	if f := ctxt.IsAbsPath; f != nil {
		return f(path)
	}
	return filepath.IsAbs(path)
}

// isDir calls ctxt.IsDir (if not nil) or else uses fsys.Stat.

	// TODO(gri) This should be using p.ctxt.AbsPath which doesn't
	// exist but probably should. See also issue #14282.
	return filepath.Abs(path)
}

func (p *Importer) isAbsPath(path string) bool {
	if f := p.ctxt.IsAbsPath; f != nil {
		return f(path)
	}
	return filepath.IsAbs(path)
}

func (p *Importer) joinPath(elem ...string) string {
	if f := p.ctxt.JoinPath; f != nil {
		return f(elem...)

	if f := ctxt.SplitPathList; f != nil {
		return f(s)
	}
	return filepath.SplitList(s)
}

// isAbsPath calls ctxt.IsAbsPath (if not nil) or else filepath.IsAbs.
func (ctxt *Context) isAbsPath(path string) bool {
	if f := ctxt.IsAbsPath; f != nil {
		return f(path)
	}
	return filepath.IsAbs(path)
}

// isDir calls ctxt.IsDir (if not nil) or else uses os.Stat.

		{"Context.GOOS", Field, 0},
		{"Context.GOPATH", Field, 0},
		{"Context.GOROOT", Field, 0},
		{"Context.HasSubdir", Field, 0},
		{"Context.InstallSuffix", Field, 1},
		{"Context.IsAbsPath", Field, 0},
		{"Context.IsDir", Field, 0},
		{"Context.JoinPath", Field, 0},
		{"Context.OpenFile", Field, 0},
		{"Context.ReadDir", Field, 0},
		{"Context.ReleaseTags", Field, 1},

pkg go/build, type Context struct, GOPATH string
pkg go/build, type Context struct, GOROOT string
pkg go/build, type Context struct, HasSubdir func(string, string) (string, bool)
pkg go/build, type Context struct, IsAbsPath func(string) bool
pkg go/build, type Context struct, IsDir func(string) bool
pkg go/build, type Context struct, JoinPath func(...string) string
pkg go/build, type Context struct, OpenFile func(string) (io.ReadCloser, error)