[Core] Extract Plugin module (#1774)

## Summary

With the introduction of v5 we will break the plugin API by moving
packages from `cucumber.core` to `io.cucumber.core`. We can use this
as an opportunity to extract the plugin and event classes to separate
modules.

This change moves `io.cucumber.core.plugin` to `io.cucumber.plugin` and
`io.cucumber.core.event` to `io.cucumber.plugin.event`. While on its own this
change provides little value it will allow us in the future to provide
better support for plugins.

With the introduction of JPMS we will want to expose these classes for
plugin developers. However we also want to avoid the use of core by most
end users. By moving these classes to their own modules we can avoid the
use of core and future proof the introduction of JPMS.

Closes #1773.

Author: mpkorstanje

core/pom.xml

@@ -37,6 +37,10 @@
             <groupId>io.cucumber</groupId>
             <artifactId>datatable</artifactId>
         </dependency>
+        <dependency>
+            <groupId>io.cucumber</groupId>
+            <artifactId>cucumber-plugin</artifactId>
+        </dependency>
         <dependency>
             <groupId>io.cucumber</groupId>
             <artifactId>docstring</artifactId>

core/src/main/java/io/cucumber/core/backend/ParameterInfo.java

@@ -1,7 +1,10 @@
 package io.cucumber.core.backend;
 
+import org.apiguardian.api.API;
+
 import java.lang.reflect.Type;
 
+@API(status = API.Status.STABLE)
 public interface ParameterInfo {
 
     /**

core/src/main/java/io/cucumber/core/backend/Scenario.java

@@ -1,6 +1,5 @@
 package io.cucumber.core.backend;
 
-import io.cucumber.core.event.Status;
 import org.apiguardian.api.API;
 
 import java.util.Collection;
@@ -10,7 +9,7 @@
  * It allows writing text and embedding media into reports, as well as inspecting results (in an After block).
  * <p>
  * Note: This class is not intended to be used to create reports. To create custom reports use
- * the {@code io.cucumber.core.plugin.Plugin} class. The plugin system provides a much richer access to Cucumbers then
+ * the {@code io.cucumber.plugin.Plugin} class. The plugin system provides a much richer access to Cucumbers then
  * hooks after could provide. For an example see {@code io.cucumber.core.plugin.PrettyFormatter}.
  */
 @API(status = API.Status.STABLE)
@@ -86,4 +85,5 @@ public interface Scenario {
      * the Scenario Outline.
      */
     Integer getLine();
+
 }

core/src/main/java/io/cucumber/core/backend/Status.java

@@ -0,0 +1,31 @@
+package io.cucumber.core.backend;
+
+import org.apiguardian.api.API;
+
+@API(status = API.Status.STABLE)
+public enum Status {
+    PASSED,
+    SKIPPED,
+    PENDING,
+    UNDEFINED,
+    AMBIGUOUS,
+    FAILED,
+    UNUSED;
+
+    public boolean is(Status status) {
+        return this == status;
+    }
+
+    public boolean isOk(boolean isStrict) {
+        return hasAlwaysOkStatus() || !isStrict && hasOkWhenNotStrictStatus();
+    }
+
+    private boolean hasAlwaysOkStatus() {
+        return is(PASSED) || is(SKIPPED);
+    }
+
+    private boolean hasOkWhenNotStrictStatus() {
+        return is(UNDEFINED) || is(PENDING);
+    }
+
+}

core/src/main/java/io/cucumber/core/backend/StepDefinition.java

@@ -5,7 +5,8 @@
 import java.util.List;
 
 @API(status = API.Status.STABLE)
-public interface StepDefinition extends io.cucumber.core.event.StepDefinition {
+public interface StepDefinition {
+
     /**
      * Invokes the step definition. The method should raise a Throwable
      * if the invocation fails, which will cause the step to fail.
@@ -27,4 +28,17 @@ public interface StepDefinition extends io.cucumber.core.event.StepDefinition {
      */
     List<ParameterInfo> parameterInfos();
 
+    /**
+     * The source line where the step definition is defined.
+     * Example: com/example/app/Cucumber.test():42
+     *
+     * @return The source line of the step definition.
+     */
+    String getLocation();
+
+    /**
+     * @return the pattern associated with this instance. Used for error reporting only.
+     */
+    String getPattern();
+
 }

core/src/main/java/io/cucumber/core/eventbus/AbstractEventBus.java

@@ -1,6 +1,6 @@
 package io.cucumber.core.eventbus;
 
-import io.cucumber.core.event.Event;
+import io.cucumber.plugin.event.Event;
 
 public abstract class AbstractEventBus extends AbstractEventPublisher implements EventBus {
 

core/src/main/java/io/cucumber/core/eventbus/AbstractEventPublisher.java

@@ -1,8 +1,8 @@
 package io.cucumber.core.eventbus;
 
-import io.cucumber.core.event.Event;
-import io.cucumber.core.event.EventHandler;
-import io.cucumber.core.event.EventPublisher;
+import io.cucumber.plugin.event.Event;
+import io.cucumber.plugin.event.EventHandler;
+import io.cucumber.plugin.event.EventPublisher;
 
 import java.util.ArrayList;
 import java.util.HashMap;

core/src/main/java/io/cucumber/core/eventbus/EventBus.java

@@ -2,8 +2,8 @@
 
 import java.time.Instant;
 
-import io.cucumber.core.event.Event;
-import io.cucumber.core.event.EventPublisher;
+import io.cucumber.plugin.event.Event;
+import io.cucumber.plugin.event.EventPublisher;
 
 public interface EventBus extends EventPublisher {
 

core/src/main/java/io/cucumber/core/feature/Argument.java

@@ -1,5 +1,7 @@
 package io.cucumber.core.feature;
 
-public interface Argument extends io.cucumber.core.event.StepArgument {
+import io.cucumber.plugin.event.StepArgument;
+
+public interface Argument extends StepArgument {
 
 }

core/src/main/java/io/cucumber/core/feature/CucumberStep.java

@@ -6,7 +6,7 @@
 import gherkin.pickles.PickleString;
 import gherkin.pickles.PickleTable;
 
-public final class CucumberStep implements io.cucumber.core.event.CucumberStep {
+public final class CucumberStep implements io.cucumber.plugin.event.CucumberStep {
 
     private final PickleStep pickleStep;
     private final String keyWord;