A fix for #1498 implementation to prevent regression failures wrt Exception deserialization

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/databind/cfg/ConstructorDetector.java

@@ -155,7 +155,7 @@ public ConstructorDetector withRequireAnnotation(boolean state) {
                 state, _allowJDKTypeCtors);
     }
 
-    public ConstructorDetector withAllowJDKTypes(boolean state) {
+    public ConstructorDetector withAllowJDKTypeConstructors(boolean state) {
         return new ConstructorDetector(_singleArgMode,
                 _requireCtorAnnotation, state);
     }
@@ -186,12 +186,31 @@ public boolean singleArgCreatorDefaultsToProperties() {
         return _singleArgMode == SingleArgConstructor.PROPERTIES;
     }
 
-    public boolean allowImplicitCreators(Class<?> rawType) {
+    /**
+     * Accessor that combines calls to {@link #allowImplicitCreators} and
+     * {@link #allowJDKTypeConstructors} to determine whether implicit constructor
+     * detection should be enabled or not.
+     * 
+     * @param rawType Value type to consider
+     *
+     * @return True if implicit constructor detection should be enabled; false if not
+     */
+    public boolean shouldIntrospectorImplicitConstructors(Class<?> rawType) {
         // May not allow implicit creator introspection at all:
         if (_requireCtorAnnotation) {
             return false;
         }
         // But if it is allowed, may further limit use for JDK types
-        return _allowJDKTypeCtors || !ClassUtil.isJDKClass(rawType);
+        if (!_allowJDKTypeCtors) {
+            if (ClassUtil.isJDKClass(rawType)) {
+                // 18-Sep-2020, tatu: Looks like must make an exception for Exception
+                //    types (ha!) -- at this point, single-String-arg constructor
+                //    is to be auto-detected
+                if (!Throwable.class.isAssignableFrom(rawType)) {
+                    return false;
+                }
+            }
+        }
+        return true;
     }
 }

src/main/java/com/fasterxml/jackson/databind/deser/BasicDeserializerFactory.java

@@ -252,16 +252,14 @@ protected ValueInstantiator _constructDefaultValueInstantiator(DeserializationCo
         throws JsonMappingException
     {
         final CreatorCollectionState ccState;
-        final boolean findImplicit;
+        final ConstructorDetector ctorDetector;
 
         {
             final DeserializationConfig config = ctxt.getConfig();
             // need to construct suitable visibility checker:
             final VisibilityChecker<?> vchecker = config.getDefaultVisibilityChecker(beanDesc.getBeanClass(),
                     beanDesc.getClassInfo());
-            // 18-Sep-2020, tatu: Although by default implicit introspection is allowed, 2.12
-            //   has settings to prevent that either generally, or at least for JDK types
-            findImplicit = config.getConstructorDetector().allowImplicitCreators(beanDesc.getBeanClass());
+            ctorDetector = config.getConstructorDetector();
 
             // 24-Sep-2014, tatu: Tricky part first; need to merge resolved property information
             //  (which has creator parameters sprinkled around) with actual creator
@@ -278,7 +276,7 @@ protected ValueInstantiator _constructDefaultValueInstantiator(DeserializationCo
         }
 
         // Start with explicitly annotated factory methods
-        _addExplicitFactoryCreators(ctxt, ccState, findImplicit);
+        _addExplicitFactoryCreators(ctxt, ccState, !ctorDetector.requireCtorAnnotation());
 
         // constructors only usable on concrete types:
         if (beanDesc.getType().isConcrete()) {
@@ -300,6 +298,9 @@ protected ValueInstantiator _constructDefaultValueInstantiator(DeserializationCo
                 // TODO: look for `@JsonCreator` annotated ones, throw explicit exception?
                 ;
             } else {
+                // 18-Sep-2020, tatu: Although by default implicit introspection is allowed, 2.12
+                //   has settings to prevent that either generally, or at least for JDK types
+                final boolean findImplicit = ctorDetector.shouldIntrospectorImplicitConstructors(beanDesc.getBeanClass());
                 _addExplicitConstructorCreators(ctxt, ccState, findImplicit);
                 if (ccState.hasImplicitConstructorCandidates()
                         && !ccState.hasExplicitFactories() && !ccState.hasExplicitConstructors()) {

src/test/java/com/fasterxml/jackson/databind/exc/ExceptionDeserializationTest.java

@@ -56,7 +56,8 @@ static class MyNoArgException extends Exception
     public void testIOException() throws IOException
     {
         IOException ioe = new IOException("TEST");
-        String json = MAPPER.writeValueAsString(ioe);
+        String json = MAPPER.writerWithDefaultPrettyPrinter()
+                .writeValueAsString(ioe);
         IOException result = MAPPER.readValue(json, IOException.class);
         assertEquals(ioe.getMessage(), result.getMessage());
     }