Add reject_continue to PlaceResult and make SKIP short-circuit in ofChain (#63)

ofChain survival placement had a bug where SKIP (returned when a block
already exists) would not stop the chain, causing fallback alternatives
to replace already valid blocks , for example:
<img width="436" height="477" alt="image"
src="https://github.com/user-attachments/assets/7ff3d6fa-de98-4716-823f-3ad2abab7394"
/>

SKIP now short-circuits the chain, remaining alternatives are skipped
because the position is already valid.
To keep correct behavior for elements without autobuild (which
previously returned SKIP as a "no implementation" signal), a new
REJECT_CONTINUE value is added, which: continues silently like SKIP (no
error, not counted) in the walker and in the chain tries the next
alternative like REJECT
Default survivalPlaceBlock and IStructureElementCheckOnly now return
REJECT_CONTINUE instead of SKIP for unhandled paths.

Tested this with the example above, and fixed the issue:
<img width="435" height="498" alt="image"
src="https://github.com/user-attachments/assets/d92bce4d-b5ad-4051-af79-ffd8c819f9f7"
/>
survival placement also still works:
<img width="1234" height="916" alt="image"
src="https://github.com/user-attachments/assets/632d5556-524d-4dc5-a7f5-75c859cb6b70"
/>

this should ideally merged before
https://github.com/GTNewHorizons/GT5-Unofficial/pull/6922 , to fix this
underlying bug, but if possible not be tagged without the other PR,
which would cause all NEI previews of multis with water to not show any
water anymore

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

src/main/java/com/gtnewhorizon/structurelib/structure/IStructureElement.java

@@ -5,6 +5,7 @@ import static com.gtnewhorizon.structurelib.StructureLib.PANIC_MODE;
 
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.List;
 import java.util.function.Consumer;
 import java.util.function.Predicate;
 
@@ -42,6 +43,30 @@ public interface IStructureElement<T> {
         return true;
     }
 
+    /**
+     * Returns a human-readable description of what block(s) this element accepts. Used for diagnostic messages when
+     * structure checks fail (e.g. "expected Input Bus at (1, 2, 3)").
+     * <p>
+     * Unlike {@link #getBlocksToPlace}, which returns the full set of concrete block variants for autoplacing (e.g.
+     * every tier of Input Bus), this method returns <b>category-level</b> descriptions suitable for display to the
+     * player (e.g. just "Input Bus"). It also requires no parameters, no world, trigger item, or environment, making it
+     * usable in contexts where those are unavailable.
+     * <p>
+     * Implementations should return <b>lang keys</b> (e.g. {@code "tile.blockGlass.name"}) rather than pre-translated
+     * display names. The caller is responsible for translating these keys on the client side via
+     * {@code StatCollector.translateToLocal()}. If a key has no matching translation, {@code translateToLocal} returns
+     * the input string unchanged, so pre-translated fallback strings also work.
+     *
+     * @param context the context object (e.g. the multiblock controller), used to determine state-dependent
+     *                descriptions
+     * @return a list of accepted block descriptions as lang keys (or display names as fallback), or null if no
+     *         description is available
+     */
+    @Nullable
+    default List<String> getDescription(T context) {
+        return null;
+    }
+
     boolean spawnHint(T t, World world, int x, int y, int z, ItemStack trigger);
 
     boolean placeBlock(T t, World world, int x, int y, int z, ItemStack trigger);
@@ -71,7 +96,7 @@ public interface IStructureElement<T> {
                 "Default implementation of survivalPlaceBlock hit! Things aren't going to work well! IStructureElement class: {}",
                 getClass().getName());
         if (!StructureLibAPI.isBlockTriviallyReplaceable(world, x, y, z, actor)) return PlaceResult.REJECT;
-        return PlaceResult.SKIP;
+        return PlaceResult.REJECT_CONTINUE;
     }
 
     /**
@@ -181,7 +206,7 @@ public interface IStructureElement<T> {
         if (StructureLibAPI.isDebugEnabled()) LOGGER.info(
                 "Fallback shim code of survivalPlaceBlock hit! Things aren't going to work well! IStructureElement class: {}",
                 getClass().getName());
-        return PlaceResult.SKIP;
+        return PlaceResult.REJECT_CONTINUE;
     }
 
     /**
@@ -204,6 +229,12 @@ public interface IStructureElement<T> {
             public boolean spawnHint(T t, World world, int x, int y, int z, ItemStack trigger) {
                 return IStructureElement.this.spawnHint(t, world, x, y, z, trigger);
             }
+
+            @Nullable
+            @Override
+            public List<String> getDescription(T context) {
+                return IStructureElement.this.getDescription(context);
+            }
         };
     }
 
@@ -237,16 +268,21 @@ public interface IStructureElement<T> {
 
     enum PlaceResult {
         /**
-         * This element either exists already, or does not yet have an implementation for survivalPlaceBlock, or some
-         * other unforeseen situations. TODO this definition doesn't seem right. Should we separate SKIP from EXISTS, or
-         * SKIP from ERROR?
+         * The element's check passed, the position is already valid. No placement is needed. In the walker: continue
+         * iteration (no error, not counted as placed). In ofChain: short-circuits, remaining alternatives are skipped.
          */
         SKIP,
         /**
-         * This element's space is occupied by other stuff and require player attention, or player missing required
-         * resource, or the block cannot be placed due to obscure mechanisms, or some other unforeseen situations.
+         * The element cannot handle this position (occupied, missing resources, etc.). In the walker: stop iteration
+         * with error particles. In ofChain: try next alternative.
          */
         REJECT,
+        /**
+         * This element has no survivalPlaceBlock implementation (default fallback), or otherwise cannot place but is
+         * not an error condition. In the walker: continue iteration silently (like SKIP). In ofChain: try next
+         * alternative (like REJECT), so a better-suited element can handle it.
+         */
+        REJECT_CONTINUE,
         /**
          * Autoplace cannot proceed within this tick. To proceed further would require stopping the placement and wait
          * for next round.

src/main/java/com/gtnewhorizon/structurelib/structure/IStructureElementChain.java

@@ -1,7 +1,9 @@
 package com.gtnewhorizon.structurelib.structure;
 
 import java.util.ArrayList;
+import java.util.LinkedHashSet;
 import java.util.List;
+import java.util.Set;
 import java.util.function.Consumer;
 import java.util.function.Predicate;
 
@@ -61,6 +63,19 @@ public interface IStructureElementChain<T> extends IStructureElement<T> {
         return false;
     }
 
+    @Nullable
+    @Override
+    default List<String> getDescription(T context) {
+        Set<String> descriptions = new LinkedHashSet<>();
+        for (IStructureElement<T> fallback : fallbacks()) {
+            List<String> desc = fallback.getDescription(context);
+            if (desc != null) {
+                descriptions.addAll(desc);
+            }
+        }
+        return descriptions.isEmpty() ? null : new ArrayList<>(descriptions);
+    }
+
     @Nullable
     @Override
     default BlocksToPlace getBlocksToPlace(T t, World world, int x, int y, int z, ItemStack trigger,
@@ -82,47 +97,51 @@ public interface IStructureElementChain<T> extends IStructureElement<T> {
     @Override
     default PlaceResult survivalPlaceBlock(T t, World world, int x, int y, int z, ItemStack trigger, IItemSource s,
             EntityPlayerMP actor, Consumer<IChatComponent> chatter) {
-        boolean haveSkip = false;
+        boolean allContinue = true;
         List<IChatComponent> bufferedNoise = new ArrayList<>();
         for (IStructureElement<T> fallback : fallbacks()) {
             PlaceResult result = fallback.survivalPlaceBlock(t, world, x, y, z, trigger, s, actor, bufferedNoise::add);
             switch (result) {
+                case REJECT_CONTINUE:
+                    break;
                 case REJECT:
+                    allContinue = false;
                     break;
                 case SKIP:
-                    haveSkip = true;
-                    break;
+                    bufferedNoise.forEach(chatter);
+                    return PlaceResult.SKIP;
                 default:
                     return result;
             }
         }
         // dump all that noise back into upstream
         bufferedNoise.forEach(chatter);
-        // TODO need reconsider to ensure this is the right course of action
-        return haveSkip ? PlaceResult.SKIP : PlaceResult.REJECT;
+        return allContinue ? PlaceResult.REJECT_CONTINUE : PlaceResult.REJECT;
     }
 
     @Override
     default PlaceResult survivalPlaceBlock(T t, World world, int x, int y, int z, ItemStack trigger,
             AutoPlaceEnvironment env) {
-        boolean haveSkip = false;
+        boolean allContinue = true;
         List<IChatComponent> bufferedNoise = new ArrayList<>();
         for (IStructureElement<T> fallback : fallbacks()) {
             PlaceResult result = fallback
                     .survivalPlaceBlock(t, world, x, y, z, trigger, env.withChatter(bufferedNoise::add));
             switch (result) {
+                case REJECT_CONTINUE:
+                    break;
                 case REJECT:
+                    allContinue = false;
                     break;
                 case SKIP:
-                    haveSkip = true;
-                    break;
+                    bufferedNoise.forEach(env.getChatter());
+                    return PlaceResult.SKIP;
                 default:
                     return result;
             }
         }
         // dump all that noise back into upstream
         bufferedNoise.forEach(env.getChatter());
-        // TODO need reconsider to ensure this is the right course of action
-        return haveSkip ? PlaceResult.SKIP : PlaceResult.REJECT;
+        return allContinue ? PlaceResult.REJECT_CONTINUE : PlaceResult.REJECT;
     }
 }

src/main/java/com/gtnewhorizon/structurelib/structure/IStructureElementCheckOnly.java

@@ -27,12 +27,12 @@ public interface IStructureElementCheckOnly<T> extends IStructureElement<T> {
     @Override
     default PlaceResult survivalPlaceBlock(T t, World world, int x, int y, int z, ItemStack trigger, IItemSource s,
             EntityPlayerMP actor, Consumer<IChatComponent> chatter) {
-        return PlaceResult.SKIP;
+        return PlaceResult.REJECT_CONTINUE;
     }
 
     @Override
     default PlaceResult survivalPlaceBlock(T t, World world, int x, int y, int z, ItemStack trigger,
             AutoPlaceEnvironment env) {
-        return PlaceResult.SKIP;
+        return PlaceResult.REJECT_CONTINUE;
     }
 }

src/main/java/com/gtnewhorizon/structurelib/structure/LazyStructureElement.java

@@ -1,5 +1,6 @@
 package com.gtnewhorizon.structurelib.structure;
 
+import java.util.List;
 import java.util.function.Consumer;
 import java.util.function.Function;
 
@@ -65,4 +66,10 @@ class LazyStructureElement<T> implements IStructureElementDeferred<T> {
             AutoPlaceEnvironment env) {
         return get(t).survivalPlaceBlock(t, world, x, y, z, trigger, env);
     }
+
+    @Nullable
+    @Override
+    public List<String> getDescription(T context) {
+        return elem != null ? elem.getDescription(context) : null;
+    }
 }

src/main/java/com/gtnewhorizon/structurelib/structure/StructureUtility.java

@@ -707,6 +707,29 @@ public class StructureUtility {
     public static <T, TIER> IStructureElement<T> ofBlocksTiered(ITierConverter<TIER> tierExtractor,
             @Nullable List<Pair<Block, Integer>> allKnownTiers, @Nullable TIER notSet, BiConsumer<T, TIER> setter,
             Function<T, TIER> getter) {
+        List<String> descriptions = null;
+        if (allKnownTiers != null) {
+            descriptions = new java.util.ArrayList<>();
+            for (Pair<Block, Integer> tier : allKnownTiers) {
+                Item item = Item.getItemFromBlock(tier.getLeft());
+                if (item != null) {
+                    descriptions.add(new ItemStack(item, 1, tier.getRight()).getUnlocalizedName() + ".name");
+                }
+            }
+        }
+        return ofBlocksTiered(tierExtractor, allKnownTiers, notSet, setter, getter, descriptions);
+    }
+
+    /**
+     * Like {@link #ofBlocksTiered(ITierConverter, List, Object, BiConsumer, Function)}, but with an explicit
+     * description that will be returned by {@link IStructureElement#getDescription(Object)}.
+     *
+     * @param description the description lang keys to attach to this element, or null for no description
+     * @see #ofBlocksTiered(ITierConverter, List, Object, BiConsumer, Function)
+     */
+    public static <T, TIER> IStructureElement<T> ofBlocksTiered(ITierConverter<TIER> tierExtractor,
+            @Nullable List<Pair<Block, Integer>> allKnownTiers, @Nullable TIER notSet, BiConsumer<T, TIER> setter,
+            Function<T, TIER> getter, @Nullable List<String> description) {
         List<Pair<Block, Integer>> hints = allKnownTiers == null ? Collections.emptyList() : allKnownTiers;
         if (hints.stream().anyMatch(Objects::isNull)) throw new IllegalArgumentException();
         IStructureElementCheckOnly<T> check = ofBlocksTiered(tierExtractor, notSet, setter, getter);
@@ -768,7 +791,7 @@ public class StructureUtility {
             public PlaceResult survivalPlaceBlock(T t, World world, int x, int y, int z, ItemStack trigger,
                     AutoPlaceEnvironment env) {
                 Pair<Block, Integer> hint = getHint(trigger);
-                if (hint == null) return PlaceResult.REJECT; // TODO or SKIP?
+                if (hint == null) return PlaceResult.REJECT;
                 Block block = world.getBlock(x, y, z);
                 int meta = world.getBlockMetadata(x, y, z);
                 TIER tier = tierExtractor.convert(block, meta);
@@ -785,6 +808,24 @@ public class StructureUtility {
                         env.getActor(),
                         env.getChatter());
             }
+
+            @Nullable
+            @Override
+            public List<String> getDescription(T context) {
+                TIER currentTier = getter.apply(context);
+                if (Objects.equals(currentTier, notSet)) return description;
+
+                for (Pair<Block, Integer> pair : hints) {
+                    TIER pairTier = tierExtractor.convert(pair.getKey(), pair.getValue());
+                    if (!Objects.equals(pairTier, currentTier)) continue;
+                    Item item = Item.getItemFromBlock(pair.getKey());
+                    if (item == null) continue;
+                    return Collections
+                            .singletonList(new ItemStack(item, 1, pair.getValue()).getUnlocalizedName() + ".name");
+                }
+                return description;
+            }
+
         };
     }
 
@@ -1408,6 +1449,14 @@ public class StructureUtility {
                         AutoPlaceEnvironment env) {
                     return BlocksToPlace.create(block, meta);
                 }
+
+                @Nullable
+                @Override
+                public List<String> getDescription(T context) {
+                    Item item = Item.getItemFromBlock(block);
+                    if (item == null) return null;
+                    return Collections.singletonList(new ItemStack(item, 1, meta).getUnlocalizedName() + ".name");
+                }
             };
         } else {
             return new IStructureElement<T>() {
@@ -1487,6 +1536,14 @@ public class StructureUtility {
                         AutoPlaceEnvironment env) {
                     return BlocksToPlace.create(block, meta);
                 }
+
+                @Nullable
+                @Override
+                public List<String> getDescription(T context) {
+                    Item item = Item.getItemFromBlock(block);
+                    if (item == null) return null;
+                    return Collections.singletonList(new ItemStack(item, 1, meta).getUnlocalizedName() + ".name");
+                }
             };
         }
     }
@@ -1529,6 +1586,14 @@ public class StructureUtility {
                     // there is getSubItems on ItemBlock, but it's client only
                     return BlocksToPlace.create(defaultBlock, defaultMeta);
                 }
+
+                @Nullable
+                @Override
+                public List<String> getDescription(T context) {
+                    Item item = Item.getItemFromBlock(block);
+                    if (item == null) return null;
+                    return Collections.singletonList(new ItemStack(item, 1, 0).getUnlocalizedName() + ".name");
+                }
             };
         } else {
             return new IStructureElement<T>() {
@@ -1561,6 +1626,14 @@ public class StructureUtility {
                     // there is getSubItems on ItemBlock, but it's client only
                     return BlocksToPlace.create(defaultBlock, defaultMeta);
                 }
+
+                @Nullable
+                @Override
+                public List<String> getDescription(T context) {
+                    Item item = Item.getItemFromBlock(block);
+                    if (item == null) return null;
+                    return Collections.singletonList(new ItemStack(item, 1, 0).getUnlocalizedName() + ".name");
+                }
             };
         }
     }
@@ -1824,6 +1897,71 @@ public class StructureUtility {
                     AutoPlaceEnvironment env) {
                 return element.survivalPlaceBlock(t, world, x, y, z, trigger, env);
             }
+
+            @Nullable
+            @Override
+            public List<String> getDescription(T context) {
+                return element.getDescription(context);
+            }
+        };
+    }
+
+    /**
+     * Wraps an element and overrides its description. Useful for providing human-readable names to elements whose
+     * underlying implementation doesn't provide a description (e.g. tiered block elements).
+     *
+     * @param description the description to use, or null to clear any existing description
+     * @param element     the element to wrap
+     */
+    public static <B extends IStructureElement<T>, T> IStructureElement<T> withDescription(
+            @Nullable List<String> description, B element) {
+        return new IStructureElement<T>() {
+
+            @Override
+            public boolean check(T t, World world, int x, int y, int z) {
+                return element.check(t, world, x, y, z);
+            }
+
+            @Override
+            public boolean couldBeValid(T t, World world, int x, int y, int z, ItemStack trigger) {
+                return element.couldBeValid(t, world, x, y, z, trigger);
+            }
+
+            @Override
+            public boolean placeBlock(T t, World world, int x, int y, int z, ItemStack trigger) {
+                return element.placeBlock(t, world, x, y, z, trigger);
+            }
+
+            @Override
+            public boolean spawnHint(T t, World world, int x, int y, int z, ItemStack trigger) {
+                return element.spawnHint(t, world, x, y, z, trigger);
+            }
+
+            @Nullable
+            @Override
+            public BlocksToPlace getBlocksToPlace(T t, World world, int x, int y, int z, ItemStack trigger,
+                    AutoPlaceEnvironment env) {
+                return element.getBlocksToPlace(t, world, x, y, z, trigger, env);
+            }
+
+            @Override
+            @Deprecated
+            public PlaceResult survivalPlaceBlock(T t, World world, int x, int y, int z, ItemStack trigger,
+                    IItemSource s, EntityPlayerMP actor, Consumer<IChatComponent> chatter) {
+                return element.survivalPlaceBlock(t, world, x, y, z, trigger, s, actor, chatter);
+            }
+
+            @Override
+            public PlaceResult survivalPlaceBlock(T t, World world, int x, int y, int z, ItemStack trigger,
+                    AutoPlaceEnvironment env) {
+                return element.survivalPlaceBlock(t, world, x, y, z, trigger, env);
+            }
+
+            @Nullable
+            @Override
+            public List<String> getDescription(T context) {
+                return description;
+            }
         };
     }
 
@@ -1880,6 +2018,12 @@ public class StructureUtility {
                     AutoPlaceEnvironment env) {
                 return element.survivalPlaceBlock(t, world, x, y, z, trigger, env);
             }
+
+            @Nullable
+            @Override
+            public List<String> getDescription(T context) {
+                return element.getDescription(context);
+            }
         };
     }
 
@@ -1888,11 +2032,11 @@ public class StructureUtility {
     /**
      * Enable this structure element only if given predicate returns true.
      * <p>
-     * Return SKIP when survival auto place if given predicate returns false.
+     * Return REJECT_CONTINUE when survival auto place if given predicate returns false.
      */
     public static <T> IStructureElement<T> onlyIf(Predicate<? super T> predicate,
             IStructureElement<? super T> downstream) {
-        return onlyIf(predicate, downstream, PlaceResult.SKIP);
+        return onlyIf(predicate, downstream, PlaceResult.REJECT_CONTINUE);
     }
 
     /**
@@ -1949,6 +2093,12 @@ public class StructureUtility {
                 if (predicate.test(t)) return downstream.survivalPlaceBlock(t, world, x, y, z, trigger, env);
                 return placeResultWhenDisabled;
             }
+
+            @Nullable
+            @Override
+            public List<String> getDescription(T context) {
+                return downstream.getDescription(context);
+            }
         };
     }
 
@@ -1961,10 +2111,10 @@ public class StructureUtility {
      * using {@link #isAir()}. It will not attempt to capture any errors though, so next one will not be tried if
      * previous one would crash.
      * <p>
-     * (*): For survival auto place, it will * REJECT, if all structure element REJECT * SKIP, if 1 or more structure
-     * element SKIP and the rest structure element (0 or more) REJECT * any other result, **immediately** upon any
-     * structure element returns these other results. This behavior is not 100% fixed and might change later on, but we
-     * will send the notice on a best effort basis.
+     * (*): For survival auto place, it will: REJECT, if any structure element returns REJECT (and none returned ACCEPT,
+     * STOP, ACCEPT_STOP, or SKIP); REJECT_CONTINUE, if all structure elements return REJECT_CONTINUE (none returned
+     * REJECT); SKIP, as soon as any structure element returns SKIP; any other result, immediately upon any structure
+     * element returning those.
      * <p>
      * Take care while chaining, as it will try to call every structure element until it returns true. If none does it
      * will finally return false.
@@ -2046,6 +2196,12 @@ public class StructureUtility {
                     AutoPlaceEnvironment env) {
                 return elem.survivalPlaceBlock(t.getCurrentContext(), world, x, y, z, trigger, env);
             }
+
+            @Nullable
+            @Override
+            public List<String> getDescription(T context) {
+                return elem.getDescription(context.getCurrentContext());
+            }
         };
     }
     // endregion
@@ -2883,6 +3039,12 @@ public class StructureUtility {
                     warnNoExplicitSubChannel(env.getActor());
                 return backing.survivalPlaceBlock(t, world, x, y, z, newTrigger, env);
             }
+
+            @Nullable
+            @Override
+            public List<String> getDescription(T context) {
+                return backing.getDescription(context);
+            }
         };
     }
     // endregion

src/main/java/com/gtnewhorizon/structurelib/structure/SurvivalBuildStructureWalker.java

@@ -43,9 +43,10 @@ class SurvivalBuildStructureWalker<T> implements IStructureWalker<T> {
         env.offsetABC[2] = c;
         env.setSource(params.getSource());
         PlaceResult placeResult = element.survivalPlaceBlock(object, world, x, y, z, trigger, env);
-        if (placeResult != PlaceResult.SKIP && built == -1) built = 0;
+        if (placeResult != PlaceResult.SKIP && placeResult != PlaceResult.REJECT_CONTINUE && built == -1) built = 0;
         switch (placeResult) {
             case SKIP:
+            case REJECT_CONTINUE:
                 return true;
             case ACCEPT:
                 if (check) element.check(object, world, x, y, z);