[swift-generator] skip un-generate-able constants

There is a bug that the swift generator cannot handle certain kinds of constants (e.g. maps that have enums for key or value type). This bug will take a bit of restructuring in the generator to fix properly, but some of the users of the generator don't actually need those constants generated at this point, they just need the generator to keep going instead of break and fail to generate any further types. This change does that.

swift-generator/src/main/java/com/facebook/swift/generator/visitors/ConstantsVisitor.java

@@ -21,6 +21,8 @@
 import com.facebook.swift.generator.util.TemplateLoader;
 import com.facebook.swift.parser.model.Const;
 import com.facebook.swift.parser.visitor.Visitable;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.io.File;
 import java.io.IOException;
@@ -29,6 +31,7 @@
 
 public class ConstantsVisitor extends AbstractTemplateVisitor
 {
+    private static final Logger LOG = LoggerFactory.getLogger(ConstantsVisitor.class);
     private final Set<Const> constants = new HashSet<>();
 
     public ConstantsVisitor(final TemplateLoader templateLoader,
@@ -61,7 +64,12 @@ public void finish()
             final ConstantsContext constantContext = contextGenerator.constantsFromThrift();
 
             for (final Const constant : constants) {
-                constantContext.addConstant(contextGenerator.constantFromThrift(constant));
+                try {
+                    constantContext.addConstant(contextGenerator.constantFromThrift(constant));
+                }
+                catch (IllegalStateException e) {
+                    LOG.error("Could not generate code for constant '{}' due to https://github.com/facebook/swift/issues/209, skipping...", constant.getName());
+                }
             }
             render(constantContext, "constants");
         }