[ISSUE-179] Improve message regarding duplicated annotated constructors

[MRamonLeon]

Fixes #179

This PR improves the message when you have two annotated constructors in the same class + tests.

The error now is not descriptive:

[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR : 
[INFO] -------------------------------------------------------------
[ERROR] javax.annotation.processing.FilerException: Attempt to reopen a file for path /...ClassXXX.stapler
  	at com.sun.tools.javac.processing.JavacFiler.checkFileReopening(JavacFiler.java:535)

[jglick]

Try something like

diff --git core/src/main/java/org/kohsuke/stapler/jsr269/ConstructorProcessor.java core/src/main/java/org/kohsuke/stapler/jsr269/ConstructorProcessor.java
index 335074db3..c40b32d03 100644
--- core/src/main/java/org/kohsuke/stapler/jsr269/ConstructorProcessor.java
+++ core/src/main/java/org/kohsuke/stapler/jsr269/ConstructorProcessor.java
@@ -30,10 +30,15 @@ public class ConstructorProcessor extends AbstractProcessorImpl {
     public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
         try {
             ElementScanner6<Void, Void> scanner = new ElementScanner6<Void, Void>() {
+                boolean written;
                 @Override
                 public Void visitExecutable(ExecutableElement e, Void aVoid) {
                     if(e.getAnnotation(DataBoundConstructor.class)!=null) {
-                        write(e);
+                        if (written) {
+                            processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, "Only one @DataBoundConstructor is permitted per class", e);
+                        } else {
+                            write(e);
+                        }
                     } else {
                         String javadoc = getJavadoc(e);
                         if(javadoc!=null && javadoc.contains("@stapler-constructor")) {

[MRamonLeon]

@jglick This latest approach fails when the annotation is duplicated because of several annotated constructors in inner classes:

[ERROR] /home/rleon/develop/projects/stapler/core/src/test/java/org/kohsuke/stapler/DataBindingTest.java:[132,16] Only one annotated constructor (@DataBoundConstructor annotation or @stapler-constructor javadoc) is permitted per class

[MRamonLeon]

Back to catching the exception

[jglick]

fails when the annotation is duplicated because of several annotated constructors in inner classes

Nested classes you mean. Adding a @DataBoundConstructor to an inner class would be illegal (and, I hope, reported already).

I think this is simply because the processor is being passed source units (typically meaning one top-level class), so boolean writable would need to be something more like Map<Something, Boolean>.

[jglick]

See #190.