From d1e31140cc6b94691ac3eeeeb7544aade9a4cf7d Mon Sep 17 00:00:00 2001
From: LevelX2 <ludwig.hirth@online.de>
Date: Mon, 29 Jun 2020 14:54:29 +0200
Subject: [PATCH] * Fixed a problem that unintended allowed to cast spells with
 alternate cost to cast conditions (fixes #6739).

---
 .../UseAlternateSourceCostsTest.java          | 46 +++++++++++++++++++
 .../costs/AlternativeCostSourceAbility.java   | 12 ++---
 .../main/java/mage/players/PlayerImpl.java    |  3 ++
 3 files changed, 55 insertions(+), 6 deletions(-)

diff --git a/Mage.Tests/src/test/java/org/mage/test/cards/cost/alternate/UseAlternateSourceCostsTest.java b/Mage.Tests/src/test/java/org/mage/test/cards/cost/alternate/UseAlternateSourceCostsTest.java
index 1ecc0ebc70d..fe78134d2c5 100644
--- a/Mage.Tests/src/test/java/org/mage/test/cards/cost/alternate/UseAlternateSourceCostsTest.java
+++ b/Mage.Tests/src/test/java/org/mage/test/cards/cost/alternate/UseAlternateSourceCostsTest.java
@@ -145,6 +145,52 @@ public class UseAlternateSourceCostsTest extends CardTestPlayerBase {
         assertAllCommandsUsed();
     }
 
+    @Test
+    public void test_Playable_WithOpponentGainingLive() {
+        // If you control a Forest, rather than pay Invigorate's mana cost, you may have an opponent gain 3 life.
+        // Target creature gets +4/+4 until end of turn.        
+        addCard(Zone.HAND, playerA, "Invigorate"); // Instant {2}{G}
+        addCard(Zone.BATTLEFIELD, playerA, "Forest");
+        addCard(Zone.BATTLEFIELD, playerA, "Silvercoat Lion");
+        
+        castSpell(1, PhaseStep.PRECOMBAT_MAIN, playerA, "Invigorate", "Silvercoat Lion");
+        setChoice(playerA, "Yes"); // use alternative cost
+        addTarget(playerA, playerB); // Opponent to gain live
+        
+        setStrictChooseMode(true);
+        setStopAt(1, PhaseStep.BEGIN_COMBAT);
+        execute();
+        assertAllCommandsUsed();
+        
+        assertGraveyardCount(playerA, "Invigorate", 1);
+        assertPowerToughness(playerA, "Silvercoat Lion", 6, 6);
+        assertLife(playerB, 23);
+    }
+    
+    @Test
+    public void test_Not_Playable_WithOpponentGainingLive() {
+        // If you control a Forest, rather than pay Invigorate's mana cost, you may have an opponent gain 3 life.
+        // Target creature gets +4/+4 until end of turn.        
+        addCard(Zone.GRAVEYARD, playerA, "Invigorate"); // Instant {2}{G}
+        addCard(Zone.BATTLEFIELD, playerA, "Forest");
+        addCard(Zone.BATTLEFIELD, playerA, "Silvercoat Lion");
+        addCard(Zone.BATTLEFIELD, playerB, "Forest");
+        
+         // can't see as playable because in graveyard
+        checkPlayableAbility("can't", 1, PhaseStep.PRECOMBAT_MAIN, playerA, "Cast Invigorate", false);
+        
+        checkPlayableAbility("can't", 1, PhaseStep.PRECOMBAT_MAIN, playerB, "Cast Invigorate", false);
+        
+        setStrictChooseMode(true);
+        setStopAt(1, PhaseStep.BEGIN_COMBAT);
+        execute();
+        assertAllCommandsUsed();
+        
+        assertGraveyardCount(playerA, "Invigorate", 1);
+        assertPowerToughness(playerA, "Silvercoat Lion", 2, 2);
+        assertLife(playerB, 20);
+    }
+    
     @Test
     @Ignore // TODO: make test to check combo of alternative cost and cost reduction effects
     public void test_Playable_WithCostReduction() {
diff --git a/Mage/src/main/java/mage/abilities/costs/AlternativeCostSourceAbility.java b/Mage/src/main/java/mage/abilities/costs/AlternativeCostSourceAbility.java
index 25ba6f8f4fd..7fc082a4230 100644
--- a/Mage/src/main/java/mage/abilities/costs/AlternativeCostSourceAbility.java
+++ b/Mage/src/main/java/mage/abilities/costs/AlternativeCostSourceAbility.java
@@ -151,11 +151,11 @@ public class AlternativeCostSourceAbility extends StaticAbility implements Alter
                     for (AlternativeCost2 alternateCost : alternativeCostsToCheck) {
                         alternateCost.activate();
                         for (Iterator it = ((Costs) alternateCost).iterator(); it.hasNext(); ) {
-                            Cost costDeailed = (Cost) it.next();
-                            if (costDeailed instanceof ManaCost) {
-                                ability.getManaCostsToPay().add((ManaCost) costDeailed.copy());
-                            } else {
-                                ability.getCosts().add(costDeailed.copy());
+                            Cost costDetailed = (Cost) it.next();
+                            if (costDetailed instanceof ManaCost) {
+                                ability.getManaCostsToPay().add((ManaCost) costDetailed.copy());
+                            } else if (costDetailed != null) {
+                                ability.getCosts().add(costDetailed.copy());
                             }
                         }
                     }
@@ -222,7 +222,7 @@ public class AlternativeCostSourceAbility extends StaticAbility implements Alter
                     sb.append("pay ");
                 }
                 String text = alternativeCost.getText(true);
-                sb.append(Character.toLowerCase(text.charAt(0)) + text.substring(1));
+                sb.append(Character.toLowerCase(text.charAt(0))).append(text.substring(1));
             }
             ++numberCosts;
         }
diff --git a/Mage/src/main/java/mage/players/PlayerImpl.java b/Mage/src/main/java/mage/players/PlayerImpl.java
index 0cba9775d28..7842874ad7f 100644
--- a/Mage/src/main/java/mage/players/PlayerImpl.java
+++ b/Mage/src/main/java/mage/players/PlayerImpl.java
@@ -3207,6 +3207,9 @@ public abstract class PlayerImpl implements Player, Serializable {
         // check "can play" condition as affected controller (BUT play from not own hand zone must be checked as original controller)
         // must check all abilities, not activated only
         for (Ability ability : candidateAbilities) {
+            if (!(ability instanceof ActivatedAbility)) {
+                continue;
+            }
             boolean isPlaySpell = (ability instanceof SpellAbility);
             boolean isPlayLand = (ability instanceof PlayLandAbility);