debug/pe: added windows-specific test against atmfd imports

This adds a test against atmfd as suggested by Alex Brainman
that proves that file.go has the ability to parse an import
table residing in a section not named .idata.

This test is windows-only and since the atmfd driver itself is
actually provided by Adobe but bundled with all versions of
windows, we're forced to search for the file in the current
PATH and then try to read the symbols from it. If the file
isn't found, the test fails.

src/debug/pe/file_test.go: added test

Author: arizvisa

src/debug/pe/file_test.go

@@ -14,6 +14,7 @@ import (
 	"reflect"
 	"regexp"
 	"runtime"
+	"strings"
 	"strconv"
 	"testing"
 	"text/template"
@@ -532,3 +533,50 @@ func TestBuildingWindowsGUI(t *testing.T) {
 		t.Fatalf("unexpected OptionalHeader type: have %T, but want *pe.OptionalHeader32 or *pe.OptionalHeader64", oh)
 	}
 }
+
+// go through each directory in dirs looking for the file identified by name.
+// returns the index or -1 on error.
+func filenameInDirectories(name string, dirs []string) string {
+	for i, path := range dirs {
+		rp := filepath.Join(path, name)
+		if _, err := os.Stat(rp); !os.IsNotExist(err) {
+			return rp
+		}
+	}
+	return ""
+}
+
+// split an environment variable into its individual paths
+// more likely to be used with "PATH" and nothing else
+func listOfEnvironment(key string) []string {
+	if path, ok := os.LookupEnv(key); ok {
+		return strings.Split(path, string(filepath.ListSeparator))
+	}
+	return []string{"."}
+}
+
+func TestImportTableInUnknownSection(t *testing.T) {
+	if runtime.GOOS != "windows" {
+		t.Skip("skipping windows only test")
+	}
+
+	// first we need to find this font driver
+	const filename = "atmfd.dll"
+	path := filenameInDirectories(filename, listOfEnvironment("PATH"))
+	if path == "" {
+		t.Fatalf("unable to locate required file (%s) in search path.", filename)
+	}
+
+	// now we can open it with debug/pe like so
+	f, err := Open(path)
+	if err != nil {
+		t.Error(err)
+	}
+	defer f.Close()
+
+	// so let's ask for symbols and if it burns, then complain
+	symbols, err := f.ImportedSymbols()
+	if err != nil {
+		t.Error(err)
+	}
+}