Introduce restart method for interceptors

implementation/src/main/java/io/smallrye/config/ConfigSourceInterceptorContext.java

@@ -11,16 +11,25 @@ public interface ConfigSourceInterceptorContext extends Serializable {
     /**
      * Proceeds to the next interceptor in the chain.
      *
-     * @param name the configuration name to lookup. Can be the original key.
+     * @param name the configuration name to look up (can be the original key)
      * @return a {@link ConfigValue} with information about the name, value, config source and ordinal, or {@code null}
      *         if the value isn't present.
      */
     ConfigValue proceed(String name);
 
     /**
-     * Proceeds to the next interceptor in the chain.
+     * Re-calls the first interceptor in the chain.
+     * If the original name is given, then it is possible to cause a recursive loop, so care must be taken.
+     * This method is intended to be used by relocating and other compatibility-related interceptors.
      *
-     * @return an Iterator of Strings with configuration names.
+     * @param name the configuration name to look up (can be the original key)
+     * @return a {@link ConfigValue} with information about the name, value, config source and ordinal, or {@code null}
+     *         if the value isn't present.
+     */
+    ConfigValue restart(String name);
+
+    /**
+     * {@return an iterator over the configuration names known to this interceptor.
      */
     Iterator<String> iterateNames();
 

implementation/src/main/java/io/smallrye/config/SmallRyeConfig.java

@@ -80,7 +80,7 @@ public class SmallRyeConfig implements Config, Serializable {
     SmallRyeConfig(SmallRyeConfigBuilder builder) {
         // This needs to be executed before everything else to make sure that defaults from mappings are available to all sources
         ConfigMappingProvider mappingProvider = builder.getMappingsBuilder().build();
-        this.configSources = new ConfigSources(builder);
+        this.configSources = new ConfigSources(builder, this);
         this.converters = buildConverters(builder);
         this.configValidator = builder.getValidator();
         this.mappings = new ConcurrentHashMap<>(mappingProvider.mapConfiguration(this));
@@ -672,6 +672,10 @@ public ConfigSource getDefaultValues() {
         return configSources.defaultValues;
     }
 
+    ConfigSourceInterceptorContext interceptorChain() {
+        return configSources.interceptorChain;
+    }
+
     private static class ConfigSources implements Serializable {
         private static final long serialVersionUID = 3483018375584151712L;
 
@@ -686,7 +690,7 @@ private static class ConfigSources implements Serializable {
          * that this constructor must be used when the Config object is being initialized, because interceptors also
          * require initialization.
          */
-        ConfigSources(final SmallRyeConfigBuilder builder) {
+        ConfigSources(final SmallRyeConfigBuilder builder, final SmallRyeConfig config) {
             // Add all sources except for ConfigurableConfigSource types. These are initialized later
             List<ConfigSource> sources = buildSources(builder);
             // Add the default values sources separately, so we can keep a reference to it and add mappings defaults
@@ -698,27 +702,29 @@ private static class ConfigSources implements Serializable {
             List<InterceptorWithPriority> interceptorWithPriorities = buildInterceptors(builder);
 
             // Create the initial chain with initial sources and all interceptors
-            SmallRyeConfigSourceInterceptorContext current = new SmallRyeConfigSourceInterceptorContext(EMPTY, null);
-            current = new SmallRyeConfigSourceInterceptorContext(new SmallRyeConfigSources(mapSources(sources)), current);
+            SmallRyeConfigSourceInterceptorContext current = new SmallRyeConfigSourceInterceptorContext(EMPTY, null, config);
+            current = new SmallRyeConfigSourceInterceptorContext(new SmallRyeConfigSources(mapSources(sources)), current,
+                    config);
             for (InterceptorWithPriority interceptorWithPriority : interceptorWithPriorities) {
                 ConfigSourceInterceptor interceptor = interceptorWithPriority.getInterceptor(current);
                 interceptors.add(interceptor);
-                current = new SmallRyeConfigSourceInterceptorContext(interceptor, current);
+                current = new SmallRyeConfigSourceInterceptorContext(interceptor, current, config);
             }
 
             // Init all late sources
             List<String> profiles = getProfiles(interceptors);
             List<ConfigSourceWithPriority> sourcesWithPriorities = mapLateSources(sources, interceptors, current, profiles,
-                    builder);
+                    builder, config);
             List<ConfigSource> configSources = getSources(sourcesWithPriorities);
 
             // Rebuild the chain with the late sources and new instances of the interceptors
             // The new instance will ensure that we get rid of references to factories and other stuff and keep only
             // the resolved final source or interceptor to use.
-            current = new SmallRyeConfigSourceInterceptorContext(EMPTY, null);
-            current = new SmallRyeConfigSourceInterceptorContext(new SmallRyeConfigSources(sourcesWithPriorities), current);
+            current = new SmallRyeConfigSourceInterceptorContext(EMPTY, null, config);
+            current = new SmallRyeConfigSourceInterceptorContext(new SmallRyeConfigSources(sourcesWithPriorities), current,
+                    config);
             for (ConfigSourceInterceptor interceptor : interceptors) {
-                current = new SmallRyeConfigSourceInterceptorContext(interceptor, current);
+                current = new SmallRyeConfigSourceInterceptorContext(interceptor, current, config);
             }
 
             this.profiles = profiles;
@@ -785,7 +791,7 @@ private static List<ConfigSourceWithPriority> mapLateSources(
                 final List<ConfigSourceInterceptor> interceptors,
                 final ConfigSourceInterceptorContext current,
                 final List<String> profiles,
-                final SmallRyeConfigBuilder builder) {
+                final SmallRyeConfigBuilder builder, final SmallRyeConfig config) {
 
             ConfigSourceWithPriority.resetLoadPriority();
             List<ConfigSourceWithPriority> currentSources = new ArrayList<>();
@@ -806,10 +812,10 @@ private static List<ConfigSourceWithPriority> mapLateSources(
             Collections.reverse(currentSources);
 
             // Rebuild the chain with the profiles sources, so profiles values are also available in factories
-            ConfigSourceInterceptorContext context = new SmallRyeConfigSourceInterceptorContext(EMPTY, null);
-            context = new SmallRyeConfigSourceInterceptorContext(new SmallRyeConfigSources(currentSources), context);
+            ConfigSourceInterceptorContext context = new SmallRyeConfigSourceInterceptorContext(EMPTY, null, config);
+            context = new SmallRyeConfigSourceInterceptorContext(new SmallRyeConfigSources(currentSources), context, config);
             for (ConfigSourceInterceptor interceptor : interceptors) {
-                context = new SmallRyeConfigSourceInterceptorContext(interceptor, context);
+                context = new SmallRyeConfigSourceInterceptorContext(interceptor, context, config);
             }
 
             // Init remaining sources, coming from SmallRyeConfig

implementation/src/main/java/io/smallrye/config/SmallRyeConfigSourceInterceptorContext.java

@@ -7,19 +7,35 @@ class SmallRyeConfigSourceInterceptorContext implements ConfigSourceInterceptorC
 
     private final ConfigSourceInterceptor interceptor;
     private final ConfigSourceInterceptorContext next;
+    private final SmallRyeConfig config;
+
+    private static final ThreadLocal<RecursionCount> rcHolder = ThreadLocal.withInitial(RecursionCount::new);
 
     SmallRyeConfigSourceInterceptorContext(
             final ConfigSourceInterceptor interceptor,
-            final ConfigSourceInterceptorContext next) {
+            final ConfigSourceInterceptorContext next,
+            final SmallRyeConfig config) {
         this.interceptor = interceptor;
         this.next = next;
+        this.config = config;
     }
 
     @Override
     public ConfigValue proceed(final String name) {
         return interceptor.getValue(next, name);
     }
 
+    @Override
+    public ConfigValue restart(final String name) {
+        RecursionCount rc = rcHolder.get();
+        rc.increment();
+        try {
+            return config.interceptorChain().proceed(name);
+        } finally {
+            rc.decrement();
+        }
+    }
+
     @Override
     public Iterator<String> iterateNames() {
         return interceptor.iterateNames(next);
@@ -29,4 +45,20 @@ public Iterator<String> iterateNames() {
     public Iterator<ConfigValue> iterateValues() {
         return interceptor.iterateValues(next);
     }
+
+    static final class RecursionCount {
+        int count;
+
+        void increment() {
+            int old = count;
+            if (old == 20) {
+                throw new IllegalStateException("Too many recursive interceptor actions");
+            }
+            count = old + 1;
+        }
+
+        void decrement() {
+            count--;
+        }
+    }
 }

implementation/src/main/java/io/smallrye/config/SmallRyeConfigSourceInterceptors.java

@@ -31,6 +31,16 @@ public ConfigValue proceed(final String name) {
                 return interceptors.get(position++).getValue(this, name);
             }
 
+            public ConfigValue restart(final String name) {
+                int old = position;
+                position = 0;
+                try {
+                    return proceed(name);
+                } finally {
+                    position = old;
+                }
+            }
+
             @Override
             public Iterator<String> iterateNames() {
                 return null;
@@ -41,10 +51,13 @@ public Iterator<ConfigValue> iterateValues() {
                 return null;
             }
         };
-
         return context.proceed(name);
     }
 
+    public ConfigValue restart(final String name) {
+        throw new UnsupportedOperationException();
+    }
+
     @Override
     public Iterator<String> iterateNames() {
         return null;

implementation/src/test/java/io/smallrye/config/RelocateConfigSourceInterceptorTest.java

@@ -154,6 +154,10 @@ public ConfigValue proceed(final String name) {
                 return null;
             }
 
+            public ConfigValue restart(final String name) {
+                return null;
+            }
+
             @Override
             public Iterator<String> iterateNames() {
                 return null;
@@ -197,6 +201,10 @@ public ConfigValue proceed(final String name) {
                 return null;
             }
 
+            public ConfigValue restart(final String name) {
+                return null;
+            }
+
             @Override
             public Iterator<String> iterateNames() {
                 return null;