Fix semantics of references from _inside_ a field value to that field

vs. the value itself being a reference to the field.

So this looks "backward":

  a : ${a}

vs. this does not:

  a : { b : ${a} }

config/src/main/java/com/typesafe/config/impl/AbstractConfigObject.java

@@ -156,19 +156,9 @@ abstract class AbstractConfigObject extends AbstractConfigValue implements Confi
     }
 
     @Override
-    protected final AbstractConfigObject mergedWithTheUnmergeable(Unmergeable fallback) {
-        if (ignoresFallbacks())
-            throw new ConfigException.BugOrBroken("should not be reached");
-
-        List<AbstractConfigValue> stack = new ArrayList<AbstractConfigValue>();
-        if (this instanceof Unmergeable) {
-            stack.addAll(((Unmergeable) this).unmergedValues());
-        } else {
-            stack.add(this);
-        }
-        stack.addAll(fallback.unmergedValues());
-        return new ConfigDelayedMergeObject(mergeOrigins(stack), stack,
-                ((AbstractConfigValue) fallback).ignoresFallbacks());
+    protected AbstractConfigObject constructDelayedMerge(ConfigOrigin origin,
+            List<AbstractConfigValue> stack) {
+        return new ConfigDelayedMergeObject(origin, stack);
     }
 
     @Override

config/src/main/java/com/typesafe/config/impl/AbstractConfigValue.java

@@ -4,6 +4,10 @@
 package com.typesafe.config.impl;
 
 import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
 
 import com.typesafe.config.ConfigException;
 import com.typesafe.config.ConfigMergeable;
@@ -124,32 +128,91 @@ abstract class AbstractConfigValue implements ConfigValue, MergeableValue, Seria
     // really need to store the boolean, and they may be able to pack it
     // with another boolean to save space.
     protected boolean ignoresFallbacks() {
-        return true;
+        // if we are not resolved, then somewhere in this value there's
+        // a substitution that may need to look at the fallbacks.
+        return resolveStatus() == ResolveStatus.RESOLVED;
     }
 
-    private ConfigException badMergeException() {
+    // the withFallback() implementation is supposed to avoid calling
+    // mergedWith* if we're ignoring fallbacks.
+    protected final void requireNotIgnoringFallbacks() {
         if (ignoresFallbacks())
             throw new ConfigException.BugOrBroken(
-                    "method should not have been called with ignoresFallbacks=true"
+                    "method should not have been called with ignoresFallbacks=true "
                             + getClass().getSimpleName());
-        else
-            throw new ConfigException.BugOrBroken("should override this in "
-                    + getClass().getSimpleName());
+    }
+
+    protected AbstractConfigValue constructDelayedMerge(ConfigOrigin origin,
+            List<AbstractConfigValue> stack) {
+        return new ConfigDelayedMerge(origin, stack);
+    }
+
+    protected final AbstractConfigValue mergedWithTheUnmergeable(
+            Collection<AbstractConfigValue> stack, Unmergeable fallback) {
+        requireNotIgnoringFallbacks();
+
+        // if we turn out to be an object, and the fallback also does,
+        // then a merge may be required; delay until we resolve.
+        List<AbstractConfigValue> newStack = new ArrayList<AbstractConfigValue>();
+        newStack.addAll(stack);
+        newStack.addAll(fallback.unmergedValues());
+        return constructDelayedMerge(AbstractConfigObject.mergeOrigins(newStack), newStack);
+    }
+
+    private final AbstractConfigValue delayMerge(Collection<AbstractConfigValue> stack,
+            AbstractConfigValue fallback) {
+        // if we turn out to be an object, and the fallback also does,
+        // then a merge may be required.
+        // if we contain a substitution, resolving it may need to look
+        // back to the fallback.
+        List<AbstractConfigValue> newStack = new ArrayList<AbstractConfigValue>();
+        newStack.addAll(stack);
+        newStack.add(fallback);
+        return constructDelayedMerge(AbstractConfigObject.mergeOrigins(newStack), newStack);
+    }
+
+    protected final AbstractConfigValue mergedWithObject(Collection<AbstractConfigValue> stack,
+            AbstractConfigObject fallback) {
+        requireNotIgnoringFallbacks();
+
+        if (this instanceof AbstractConfigObject)
+            throw new ConfigException.BugOrBroken("Objects must reimplement mergedWithObject");
+
+        return mergedWithNonObject(stack, fallback);
+    }
+
+    protected final AbstractConfigValue mergedWithNonObject(Collection<AbstractConfigValue> stack,
+            AbstractConfigValue fallback) {
+        requireNotIgnoringFallbacks();
+
+        if (resolveStatus() == ResolveStatus.RESOLVED) {
+            // falling back to a non-object doesn't merge anything, and also
+            // prohibits merging any objects that we fall back to later.
+            // so we have to switch to ignoresFallbacks mode.
+            return newCopy(true /* ignoresFallbacks */, origin);
+        } else {
+            // if unresolved, we may have to look back to fallbacks as part of
+            // the resolution process, so always delay
+            return delayMerge(stack, fallback);
+        }
     }
 
     protected AbstractConfigValue mergedWithTheUnmergeable(Unmergeable fallback) {
-        throw badMergeException();
+        requireNotIgnoringFallbacks();
+
+        return mergedWithTheUnmergeable(Collections.singletonList(this), fallback);
     }
 
     protected AbstractConfigValue mergedWithObject(AbstractConfigObject fallback) {
-        throw badMergeException();
+        requireNotIgnoringFallbacks();
+
+        return mergedWithObject(Collections.singletonList(this), fallback);
     }
 
     protected AbstractConfigValue mergedWithNonObject(AbstractConfigValue fallback) {
-        // falling back to a non-object doesn't merge anything, and also
-        // prohibits merging any objects that we fall back to later.
-        // so we have to switch to ignoresFallbacks mode.
-        return newCopy(true /* ignoresFallbacks */, origin);
+        requireNotIgnoringFallbacks();
+
+        return mergedWithNonObject(Collections.singletonList(this), fallback);
     }
 
     public AbstractConfigValue withOrigin(ConfigOrigin origin) {
@@ -159,6 +222,7 @@ abstract class AbstractConfigValue implements ConfigValue, MergeableValue, Seria
             return newCopy(ignoresFallbacks(), origin);
     }
 
+    // this is only overridden to change the return type
     @Override
     public AbstractConfigValue withFallback(ConfigMergeable mergeable) {
         if (ignoresFallbacks()) {
@@ -169,15 +233,7 @@ abstract class AbstractConfigValue implements ConfigValue, MergeableValue, Seria
             if (other instanceof Unmergeable) {
                 return mergedWithTheUnmergeable((Unmergeable) other);
             } else if (other instanceof AbstractConfigObject) {
-                AbstractConfigObject fallback = (AbstractConfigObject) other;
-                if (fallback.resolveStatus() == ResolveStatus.RESOLVED && fallback.isEmpty()) {
-                    if (fallback.ignoresFallbacks())
-                        return newCopy(true /* ignoresFallbacks */, origin);
-                    else
-                        return this;
-                } else {
-                    return mergedWithObject((AbstractConfigObject) other);
-                }
+                return mergedWithObject((AbstractConfigObject) other);
             } else {
                 return mergedWithNonObject((AbstractConfigValue) other);
             }

config/src/main/java/com/typesafe/config/impl/ConfigConcatenation.java

@@ -60,43 +60,6 @@ final class ConfigConcatenation extends AbstractConfigValue implements Unmergeab
         return false;
     }
 
-    @Override
-    protected AbstractConfigValue mergedWithTheUnmergeable(Unmergeable fallback) {
-        // if we turn out to be an object, and the fallback also does,
-        // then a merge may be required; delay until we resolve.
-        List<AbstractConfigValue> newStack = new ArrayList<AbstractConfigValue>();
-        newStack.add(this);
-        newStack.addAll(fallback.unmergedValues());
-        return new ConfigDelayedMerge(AbstractConfigObject.mergeOrigins(newStack), newStack,
-                ((AbstractConfigValue) fallback).ignoresFallbacks());
-    }
-
-    protected AbstractConfigValue mergedLater(AbstractConfigValue fallback) {
-        List<AbstractConfigValue> newStack = new ArrayList<AbstractConfigValue>();
-        newStack.add(this);
-        newStack.add(fallback);
-        return new ConfigDelayedMerge(AbstractConfigObject.mergeOrigins(newStack), newStack,
-                fallback.ignoresFallbacks());
-    }
-
-    @Override
-    protected AbstractConfigValue mergedWithObject(AbstractConfigObject fallback) {
-        // if we turn out to be an object, and the fallback also does,
-        // then a merge may be required; delay until we resolve.
-        return mergedLater(fallback);
-    }
-
-    @Override
-    protected AbstractConfigValue mergedWithNonObject(AbstractConfigValue fallback) {
-        // We may need the fallback if we contain a self-referential
-        // ConfigReference.
-        //
-        // we can't easily detect the self-referential case since the cycle
-        // may involve more than one step, so we have to wait and
-        // merge later when resolving.
-        return mergedLater(fallback);
-    }
-
     @Override
     public Collection<ConfigConcatenation> unmergedValues() {
         return Collections.singleton(this);

config/src/main/java/com/typesafe/config/impl/ConfigDelayedMerge.java

@@ -28,13 +28,15 @@ final class ConfigDelayedMerge extends AbstractConfigValue implements Unmergeabl
 
     // earlier items in the stack win
     final private List<AbstractConfigValue> stack;
-    final private boolean ignoresFallbacks;
+    // this is just here for serialization compat; whether we ignore is purely
+    // a function of the bottom of the merge stack
+    @SuppressWarnings("unused")
+    @Deprecated
+    final private boolean ignoresFallbacks = false;
 
-    ConfigDelayedMerge(ConfigOrigin origin, List<AbstractConfigValue> stack,
-            boolean ignoresFallbacks) {
+    ConfigDelayedMerge(ConfigOrigin origin, List<AbstractConfigValue> stack) {
         super(origin);
         this.stack = stack;
-        this.ignoresFallbacks = ignoresFallbacks;
         if (stack.isEmpty())
             throw new ConfigException.BugOrBroken(
                     "creating empty delayed merge value");
@@ -46,10 +48,6 @@ final class ConfigDelayedMerge extends AbstractConfigValue implements Unmergeabl
         }
     }
 
-    ConfigDelayedMerge(ConfigOrigin origin, List<AbstractConfigValue> stack) {
-        this(origin, stack, false /* ignoresFallbacks */);
-    }
-
     @Override
     public ConfigValueType valueType() {
         throw new ConfigException.NotResolved(
@@ -80,10 +78,9 @@ final class ConfigDelayedMerge extends AbstractConfigValue implements Unmergeabl
         AbstractConfigValue merged = null;
         for (AbstractConfigValue v : stack) {
             boolean replaced = false;
-            // checking for RESOLVED already is just an optimization
-            // to avoid creating the replacer when it can't possibly
-            // be needed.
-            if (v.resolveStatus() != ResolveStatus.RESOLVED) {
+            // we only replace if we have a substitution, or
+            // value-concatenation containing one
+            if (v instanceof Unmergeable) {
                 // If, while resolving 'v' we come back to the same
                 // merge stack, we only want to look _below_ 'v'
                 // in the stack. So we arrange to replace the
@@ -158,50 +155,38 @@ final class ConfigDelayedMerge extends AbstractConfigValue implements Unmergeabl
         for (AbstractConfigValue o : stack) {
             newStack.add(o.relativized(prefix));
         }
-        return new ConfigDelayedMerge(origin(), newStack, ignoresFallbacks);
+        return new ConfigDelayedMerge(origin(), newStack);
+    }
+
+    // static utility shared with ConfigDelayedMergeObject
+    static boolean stackIgnoresFallbacks(List<AbstractConfigValue> stack) {
+        AbstractConfigValue last = stack.get(stack.size() - 1);
+        return last.ignoresFallbacks();
     }
 
     @Override
     protected boolean ignoresFallbacks() {
-        return ignoresFallbacks;
+        return stackIgnoresFallbacks(stack);
     }
 
     @Override
     protected AbstractConfigValue newCopy(boolean newIgnoresFallbacks, ConfigOrigin newOrigin) {
-        return new ConfigDelayedMerge(newOrigin, stack, newIgnoresFallbacks);
+        return new ConfigDelayedMerge(newOrigin, stack);
     }
 
     @Override
     protected final ConfigDelayedMerge mergedWithTheUnmergeable(Unmergeable fallback) {
-        if (ignoresFallbacks)
-            throw new ConfigException.BugOrBroken("should not be reached");
-
-        // if we turn out to be an object, and the fallback also does,
-        // then a merge may be required; delay until we resolve.
-        List<AbstractConfigValue> newStack = new ArrayList<AbstractConfigValue>();
-        newStack.addAll(stack);
-        newStack.addAll(fallback.unmergedValues());
-        return new ConfigDelayedMerge(AbstractConfigObject.mergeOrigins(newStack), newStack,
-                ((AbstractConfigValue) fallback).ignoresFallbacks());
+        return (ConfigDelayedMerge) mergedWithTheUnmergeable(stack, fallback);
     }
 
     @Override
     protected final ConfigDelayedMerge mergedWithObject(AbstractConfigObject fallback) {
-        return mergedWithNonObject(fallback);
+        return (ConfigDelayedMerge) mergedWithObject(stack, fallback);
     }
 
     @Override
     protected ConfigDelayedMerge mergedWithNonObject(AbstractConfigValue fallback) {
-        if (ignoresFallbacks)
-            throw new ConfigException.BugOrBroken("should not be reached");
-
-        // if we turn out to be an object, and the fallback also does,
-        // then a merge may be required; delay until we resolve.
-        List<AbstractConfigValue> newStack = new ArrayList<AbstractConfigValue>();
-        newStack.addAll(stack);
-        newStack.add(fallback);
-        return new ConfigDelayedMerge(AbstractConfigObject.mergeOrigins(newStack), newStack,
-                fallback.ignoresFallbacks());
+        return (ConfigDelayedMerge) mergedWithNonObject(stack, fallback);
     }
 
     @Override
@@ -300,6 +285,6 @@ final class ConfigDelayedMerge extends AbstractConfigValue implements Unmergeabl
     private Object writeReplace() throws ObjectStreamException {
         // switch to LinkedList
         return new ConfigDelayedMerge(origin(),
-                new java.util.LinkedList<AbstractConfigValue>(stack), ignoresFallbacks);
+                new java.util.LinkedList<AbstractConfigValue>(stack));
     }
 }

config/src/main/java/com/typesafe/config/impl/ConfigDelayedMergeObject.java

@@ -11,6 +11,7 @@ import java.util.Map;
 import java.util.Set;
 
 import com.typesafe.config.ConfigException;
+import com.typesafe.config.ConfigList;
 import com.typesafe.config.ConfigMergeable;
 import com.typesafe.config.ConfigOrigin;
 import com.typesafe.config.ConfigValue;
@@ -23,18 +24,16 @@ final class ConfigDelayedMergeObject extends AbstractConfigObject implements Unm
     private static final long serialVersionUID = 1L;
 
     final private List<AbstractConfigValue> stack;
-    final private boolean ignoresFallbacks;
 
-    ConfigDelayedMergeObject(ConfigOrigin origin,
-            List<AbstractConfigValue> stack) {
-        this(origin, stack, false /* ignoresFallbacks */);
-    }
+    // this is just here for serialization compat; whether we ignore is purely
+    // a function of the bottom of the merge stack
+    @SuppressWarnings("unused")
+    @Deprecated
+    final private boolean ignoresFallbacks = false;
 
-    ConfigDelayedMergeObject(ConfigOrigin origin, List<AbstractConfigValue> stack,
-            boolean ignoresFallbacks) {
+    ConfigDelayedMergeObject(ConfigOrigin origin, List<AbstractConfigValue> stack) {
         super(origin);
         this.stack = stack;
-        this.ignoresFallbacks = ignoresFallbacks;
 
         if (stack.isEmpty())
             throw new ConfigException.BugOrBroken(
@@ -56,7 +55,7 @@ final class ConfigDelayedMergeObject extends AbstractConfigObject implements Unm
         if (status != resolveStatus())
             throw new ConfigException.BugOrBroken(
                     "attempt to create resolved ConfigDelayedMergeObject");
-        return new ConfigDelayedMergeObject(origin, stack, ignoresFallbacks);
+        return new ConfigDelayedMergeObject(origin, stack);
     }
 
     @Override
@@ -93,30 +92,31 @@ final class ConfigDelayedMergeObject extends AbstractConfigObject implements Unm
         for (AbstractConfigValue o : stack) {
             newStack.add(o.relativized(prefix));
         }
-        return new ConfigDelayedMergeObject(origin(), newStack,
-                ignoresFallbacks);
+        return new ConfigDelayedMergeObject(origin(), newStack);
     }
 
     @Override
     protected boolean ignoresFallbacks() {
-        return ignoresFallbacks;
+        return ConfigDelayedMerge.stackIgnoresFallbacks(stack);
     }
 
     @Override
-    protected ConfigDelayedMergeObject mergedWithObject(AbstractConfigObject fallback) {
+    protected final ConfigDelayedMergeObject mergedWithTheUnmergeable(Unmergeable fallback) {
+        requireNotIgnoringFallbacks();
+
+        return (ConfigDelayedMergeObject) mergedWithTheUnmergeable(stack, fallback);
+    }
+
+    @Override
+    protected final ConfigDelayedMergeObject mergedWithObject(AbstractConfigObject fallback) {
         return mergedWithNonObject(fallback);
     }
 
     @Override
-    protected ConfigDelayedMergeObject mergedWithNonObject(AbstractConfigValue fallback) {
-        if (ignoresFallbacks)
-            throw new ConfigException.BugOrBroken("should not be reached");
+    protected final ConfigDelayedMergeObject mergedWithNonObject(AbstractConfigValue fallback) {
+        requireNotIgnoringFallbacks();
 
-        List<AbstractConfigValue> newStack = new ArrayList<AbstractConfigValue>();
-        newStack.addAll(stack);
-        newStack.add(fallback);
-        return new ConfigDelayedMergeObject(AbstractConfigObject.mergeOrigins(newStack), newStack,
-                fallback.ignoresFallbacks());
+        return (ConfigDelayedMergeObject) mergedWithNonObject(stack, fallback);
     }
 
     @Override
@@ -249,10 +249,6 @@ final class ConfigDelayedMergeObject extends AbstractConfigObject implements Unm
         // to touch the exact key that isn't resolved, so this is in that
         // spirit.
 
-        // this function should never return null; if we know a value doesn't
-        // exist, then there would be no reason for the merge to be delayed
-        // (i.e. as long as some stuff is unmerged, the value may be non-null).
-
         // we'll be able to return a key if we have a value that ignores
         // fallbacks, prior to any unmergeable values.
         for (AbstractConfigValue layer : stack) {
@@ -289,17 +285,33 @@ final class ConfigDelayedMergeObject extends AbstractConfigObject implements Unm
                 throw new ConfigException.NotResolved("Key '" + key + "' is not available at '"
                         + origin().description() + "' because value at '"
                         + layer.origin().description()
-                        + "' has not been resolved and may turn out to contain '" + key + "'."
+                        + "' has not been resolved and may turn out to contain or hide '" + key
+                        + "'."
                         + " Be sure to Config#resolve() before using a config object.");
+            } else if (layer.resolveStatus() == ResolveStatus.UNRESOLVED) {
+                // if the layer is not an object, and not a substitution or
+                // merge,
+                // then it's something that's unresolved because it _contains_
+                // an unresolved object... i.e. it's an array
+                if (!(layer instanceof ConfigList))
+                    throw new ConfigException.BugOrBroken("Expecting a list here, not " + layer);
+                // all later objects will be hidden so we can say we won't find
+                // the key
+                return null;
             } else {
-                // non-object, but not unresolved, like an integer or something.
+                // non-object, but resolved, like an integer or something.
                 // has no children so the one we're after won't be in it.
-                // this should always be overridden by an object though so
-                // ideally we never build a stack that would have this in it.
-                continue;
+                // we would only have this in the stack in case something
+                // else "looks back" to it due to a cycle.
+                // anyway at this point we know we can't find the key anymore.
+                if (!layer.ignoresFallbacks()) {
+                    throw new ConfigException.BugOrBroken(
+                            "resolved non-object should ignore fallbacks");
+                }
+                return null;
             }
         }
-        // If we get here, then we never found an unmergeable which means
+        // If we get here, then we never found anything unresolved which means
         // the ConfigDelayedMergeObject should not have existed. some
         // invariant was violated.
         throw new ConfigException.BugOrBroken(
@@ -314,6 +326,6 @@ final class ConfigDelayedMergeObject extends AbstractConfigObject implements Unm
     private Object writeReplace() throws ObjectStreamException {
         // switch to LinkedList
         return new ConfigDelayedMergeObject(origin(),
-                new java.util.LinkedList<AbstractConfigValue>(stack), ignoresFallbacks);
+                new java.util.LinkedList<AbstractConfigValue>(stack));
     }
 }

config/src/main/java/com/typesafe/config/impl/ConfigReference.java

@@ -1,9 +1,7 @@
 package com.typesafe.config.impl;
 
-import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
-import java.util.List;
 
 import com.typesafe.config.ConfigException;
 import com.typesafe.config.ConfigOrigin;
@@ -59,45 +57,6 @@ final class ConfigReference extends AbstractConfigValue implements Unmergeable {
         return false;
     }
 
-    @Override
-    protected AbstractConfigValue mergedWithTheUnmergeable(Unmergeable fallback) {
-        // if we turn out to be an object, and the fallback also does,
-        // then a merge may be required; delay until we resolve.
-        List<AbstractConfigValue> newStack = new ArrayList<AbstractConfigValue>();
-        newStack.add(this);
-        newStack.addAll(fallback.unmergedValues());
-        return new ConfigDelayedMerge(AbstractConfigObject.mergeOrigins(newStack), newStack,
-                ((AbstractConfigValue) fallback).ignoresFallbacks());
-    }
-
-    protected AbstractConfigValue mergedLater(AbstractConfigValue fallback) {
-        List<AbstractConfigValue> newStack = new ArrayList<AbstractConfigValue>();
-        newStack.add(this);
-        newStack.add(fallback);
-        return new ConfigDelayedMerge(AbstractConfigObject.mergeOrigins(newStack), newStack,
-                fallback.ignoresFallbacks());
-    }
-
-    @Override
-    protected AbstractConfigValue mergedWithObject(AbstractConfigObject fallback) {
-        // if we turn out to be an object, and the fallback also does,
-        // then a merge may be required; delay until we resolve.
-        return mergedLater(fallback);
-    }
-
-    @Override
-    protected AbstractConfigValue mergedWithNonObject(AbstractConfigValue fallback) {
-        // We may need the fallback for two reasons:
-        // 1. if an optional substitution ends up getting deleted
-        // because it is not defined
-        // 2. if the substitution is self-referential
-        //
-        // we can't easily detect the self-referential case since the cycle
-        // may involve more than one step, so we have to wait and
-        // merge later when resolving.
-        return mergedLater(fallback);
-    }
-
     @Override
     public Collection<ConfigReference> unmergedValues() {
         return Collections.singleton(this);

config/src/main/java/com/typesafe/config/impl/ResolveContext.java

@@ -93,7 +93,6 @@ final class ResolveContext {
     }
 
     AbstractConfigValue resolve(AbstractConfigValue original) throws NotPossibleToResolve {
-
         // a fully-resolved (no restrictToChild) object can satisfy a
         // request for a restricted object, so always check that first.
         final MemoKey fullKey = new MemoKey(original, null);

config/src/main/java/com/typesafe/config/impl/SimpleConfigObject.java

@@ -159,8 +159,7 @@ final class SimpleConfigObject extends AbstractConfigObject {
 
     @Override
     protected SimpleConfigObject mergedWithObject(AbstractConfigObject abstractFallback) {
-        if (ignoresFallbacks())
-            throw new ConfigException.BugOrBroken("should not be reached");
+        requireNotIgnoringFallbacks();
 
         if (!(abstractFallback instanceof SimpleConfigObject)) {
             throw new ConfigException.BugOrBroken(

config/src/test/scala/com/typesafe/config/impl/ConfigSubstitutionTest.scala

@@ -1039,6 +1039,20 @@ class ConfigSubstitutionTest extends TestUtils {
         assertEquals("optional self reference disappears", 0, resolved.root.size)
     }
 
+    @Test
+    def substSelfReferenceAlongPath() {
+        val obj = parseObject("""a.b=1, a.b=${a.b}""")
+        val resolved = resolve(obj)
+        assertEquals(1, resolved.getInt("a.b"))
+    }
+
+    @Test
+    def substSelfReferenceAlongLongerPath() {
+        val obj = parseObject("""a.b.c=1, a.b.c=${a.b.c}""")
+        val resolved = resolve(obj)
+        assertEquals(1, resolved.getInt("a.b.c"))
+    }
+
     @Test
     def substSelfReferenceIndirect() {
         val obj = parseObject("""a=1, b=${a}, a=${b}""")
@@ -1077,6 +1091,13 @@ class ConfigSubstitutionTest extends TestUtils {
         assertEquals(5, resolved.getInt("a.b"))
     }
 
+    @Test
+    def substSelfReferenceObjectAlongPath() {
+        val obj = parseObject("""a.b={c=5}, a.b=${a.b}""")
+        val resolved = resolve(obj)
+        assertEquals(5, resolved.getInt("a.b.c"))
+    }
+
     @Test
     def substSelfReferenceInConcat() {
         val obj = parseObject("""a=1, a=${a}foo""")
@@ -1174,6 +1195,15 @@ class ConfigSubstitutionTest extends TestUtils {
         assertEquals(5, resolved.getInt("a.c"))
     }
 
+    @Test
+    def substSelfReferenceAlongAPathInsideObject() {
+        // if the ${a.b} is _inside_ a field value instead of
+        // _being_ the field value, it does not look backward.
+        val obj = parseObject("""a={b={c=5}}, a={ x : ${a.b} }, a={b=2}""")
+        val resolved = resolve(obj)
+        assertEquals(2, resolved.getInt("a.x"))
+    }
+
     @Test
     def substInChildFieldNotASelfReference1() {
         // here, ${bar.foo} is not a self reference because
@@ -1220,6 +1250,37 @@ class ConfigSubstitutionTest extends TestUtils {
         assertEquals(42, resolved.getInt("bar.foo"))
     }
 
+    @Test
+    def substInChildFieldNotASelfReference4() {
+        // checking that having bar set to non-object earlier
+        // doesn't break the behavior.
+        val obj = parseObject("""
+         bar : 101
+         bar : { foo : 42,
+                 baz : ${bar.foo}
+         }
+            """)
+        val resolved = resolve(obj)
+        assertEquals(42, resolved.getInt("bar.baz"))
+        assertEquals(42, resolved.getInt("bar.foo"))
+    }
+
+    @Test
+    def substInChildFieldNotASelfReference5() {
+        // checking that having bar set to unresolved array earlier
+        // doesn't break the behavior.
+        val obj = parseObject("""
+         x : 0
+         bar : [ ${x}, 1, 2, 3 ]
+         bar : { foo : 42,
+                 baz : ${bar.foo}
+         }
+            """)
+        val resolved = resolve(obj)
+        assertEquals(42, resolved.getInt("bar.baz"))
+        assertEquals(42, resolved.getInt("bar.foo"))
+    }
+
     @Test
     def mutuallyReferringNotASelfReference() {
         val obj = parseObject("""
@@ -1248,4 +1309,42 @@ class ConfigSubstitutionTest extends TestUtils {
         val resolved = resolve(obj)
         assertEquals("1xyz", resolved.getString("a"))
     }
+
+    @Test
+    def substSelfReferenceInArray() {
+        // never "look back" from "inside" an array
+        val obj = parseObject("""a=1,a=[${a}, 2]""")
+        val e = intercept[ConfigException.UnresolvedSubstitution] {
+            resolve(obj)
+        }
+        assertTrue("wrong exception: " + e.getMessage,
+            e.getMessage.contains("cycle") && e.getMessage.contains("${a}"))
+    }
+
+    @Test
+    def substSelfReferenceInObject() {
+        // never "look back" from "inside" an object
+        val obj = parseObject("""a=1,a={ x : ${a} }""")
+        val e = intercept[ConfigException.UnresolvedSubstitution] {
+            resolve(obj)
+        }
+        assertTrue("wrong exception: " + e.getMessage,
+            e.getMessage.contains("cycle") && e.getMessage.contains("${a}"))
+    }
+
+    @Test
+    def selfReferentialObjectNotAffectedByOverriding() {
+        // this is testing that we can still refer to another
+        // field in the same object, even though we are overriding
+        // an earlier object.
+        val obj = parseObject("""a={ x : 42, y : ${a.x} }""")
+        val resolved = resolve(obj)
+        assertEquals(parseObject("{ x : 42, y : 42 }"), resolved.getConfig("a").root)
+
+        // this is expected because if adding "a=1" here affects the outcome,
+        // it would be flat-out bizarre.
+        val obj2 = parseObject("""a=1, a={ x : 42, y : ${a.x} }""")
+        val resolved2 = resolve(obj2)
+        assertEquals(parseObject("{ x : 42, y : 42 }"), resolved2.getConfig("a").root)
+    }
 }

config/src/test/scala/com/typesafe/config/impl/ConfigTest.scala

@@ -79,7 +79,8 @@ class ConfigTest extends TestUtils {
             if (!trees(0).equals(tree))
                 throw new AssertionError("Merge was not associative, " +
                     "verify that it should not be, then don't use associativeMerge " +
-                    "for this one.\none: " + trees(0) + "\ntwo: " + tree)
+                    "for this one. two results were: \none: " + trees(0) + "\ntwo: " +
+                    tree + "\noriginal list: " + allObjects)
         }
 
         for (tree <- trees) {
@@ -503,6 +504,20 @@ class ConfigTest extends TestUtils {
         testIgnoredMergesDoNothing(conf)
     }
 
+    @Test
+    def testNoMergeAcrossArray() {
+        val conf = parseConfig("a: {b:1}, a: [2,3], a:{c:4}")
+        assertFalse("a.b found in: " + conf, conf.hasPath("a.b"))
+        assertTrue("a.c not found in: " + conf, conf.hasPath("a.c"))
+    }
+
+    @Test
+    def testNoMergeAcrossUnresolvedArray() {
+        val conf = parseConfig("a: {b:1}, a: [2,${x}], a:{c:4}, x: 42")
+        assertFalse("a.b found in: " + conf, conf.hasPath("a.b"))
+        assertTrue("a.c not found in: " + conf, conf.hasPath("a.c"))
+    }
+
     @Test
     def integerRangeChecks() {
         val conf = parseConfig("{ tooNegative: " + (Integer.MIN_VALUE - 1L) + ", tooPositive: " + (Integer.MAX_VALUE + 1L) + "}")