Allow direct reference using the current app

Author: jannotti

data/transactions/logic/eval.go

@@ -2804,6 +2804,15 @@ func appReference(cx *evalContext, ref uint64, foreign bool) (basics.AppIndex, e
 				return appID, nil
 			}
 		}
+		// It should be legal to use your own app id, which
+		// can't be in ForeignApps during creation, because it
+		// is unknown then.  But it can be discovered in the
+		// app code.  It's tempting to combine this with the
+		// == 0 test, above, but it must come after the check
+		// for being below len(ForeignApps)
+		if ref == uint64(cx.Ledger.ApplicationID()) {
+			return cx.Ledger.ApplicationID(), nil
+		}
 	} else {
 		// Old rules
 		if foreign {

data/transactions/logic/evalStateful_test.go

@@ -950,6 +950,11 @@ byte 0x414c474f
 	testProg(t, strings.Replace(text, "int 1  // account idx", "byte \"aoeuiaoeuiaoeuiaoeuiaoeuiaoeui01\"", -1), directRefEnabledVersion-1,
 		expect{4, "app_local_get_ex arg 0 wanted type uint64..."})
 	testApp(t, strings.Replace(text, "int 100 // app id", "int 2", -1), now)
+	// Next we're testing if the use of the current app's id works
+	// as a direct reference. The error is because the sender
+	// account is not opted into 123.
+	ledger.appID = basics.AppIndex(123)
+	testApp(t, strings.Replace(text, "int 100 // app id", "int 123", -1), now, "no app for account")
 	testApp(t, strings.Replace(text, "int 100 // app id", "int 2", -1), pre, "no app for account")
 	testApp(t, strings.Replace(text, "int 100 // app id", "int 9", -1), now, "invalid App reference 9")
 	testApp(t, strings.Replace(text, "int 1  // account idx", "byte \"aoeuiaoeuiaoeuiaoeuiaoeuiaoeui00\"", -1), now,
@@ -1107,6 +1112,12 @@ int 4141
 	now.Txn.Txn.ApplicationID = 0
 	now.Txn.Txn.ForeignApps = []basics.AppIndex{100}
 	testApp(t, text, now)
+
+	// Direct reference to the current app also works
+	ledger.appID = basics.AppIndex(100)
+	now.Txn.Txn.ForeignApps = []basics.AppIndex{}
+	testApp(t, strings.Replace(text, "int 1  // ForeignApps index", "int 100", -1), now)
+	testApp(t, strings.Replace(text, "int 1  // ForeignApps index", "global CurrentApplicationID", -1), now)
 }
 
 const assetsTestProgram = `int 0//account