[Core] CLI should search classpath root by default

The Cucumber CLI is rather complex to use. To work correctly it needs both
a `--glue` parameter in the form of a package name and a location of a feature
file in form of a classpath uri or path. As a result people often configure
Cucumber incorrectly and are left wondering why their features or glue can not
be found.

This can be simplified as shown by the Cucumber Platform Engine which defaults
to the classpath root and the JUnit and TestNG runners which default to the
package of the runner class.

So it makes sense to do the same with the CLI.

Assuming the following project layout the CLI can discover and execute
all features without needing additional arguments.

```
├── pom.xml
├── src
│   ├── main
│   │   └── java
│   │       └── com/example/Application.java
│   └── test
│       ├── java
│       │   └── com/example/StepDefinitions.java
│       └── resources
│           └── com/example/example.feature
```

This can be with a single maven command:

```
mvn exec:java                                  \
    -Dexec.classpathScope=test                 \
    -Dexec.mainClass=io.cucumber.core.cli.Main
```

Additional benefits can be found in the fact that IDEA often can't work out
which package should be used as glue and does not provide a default. The
Cucumber Eclipse plugin on the other hand always defaults to the class path
root.

Fixes: #1875

Author: mpkorstanje

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ## [Unreleased] (In Git)
 
 ### Added
+ *  [Core] CLI should search classpath root by default ([#1889](https://github.com/cucumber/cucumber-jvm/pull/1889) M.P. Korstanje)
 
 ### Changed
 

core/src/main/java/io/cucumber/core/cli/Main.java

@@ -54,6 +54,8 @@ public static byte run(String[] argv, ClassLoader classLoader) {
 
         RuntimeOptions runtimeOptions = new CommandlineOptionsParser()
             .parse(argv)
+            .addDefaultGlueIfAbsent()
+            .addDefaultFeaturePathIfAbsent()
             .addDefaultFormatterIfAbsent()
             .addDefaultSummaryPrinterIfAbsent()
             .build(systemOptions);

core/src/main/java/io/cucumber/core/options/RuntimeOptions.java

@@ -17,6 +17,8 @@
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
 
+import static io.cucumber.core.resource.ClasspathSupport.rootPackageUri;
+import static java.util.Collections.emptyList;
 import static java.util.Collections.unmodifiableList;
 import static java.util.Collections.unmodifiableMap;
 
@@ -64,6 +66,17 @@ void addDefaultSummaryPrinterIfAbsent(){
         }
     }
 
+    void addDefaultGlueIfAbsent() {
+        if (glue.isEmpty()) {
+            glue.add(rootPackageUri());
+        }
+    }
+
+    void addDefaultFeaturePathIfAbsent() {
+        if (featurePaths.isEmpty()) {
+            featurePaths.add(FeatureWithLines.create(rootPackageUri(), emptyList()));
+        }
+    }
     public int getCount() {
         return count;
     }

core/src/main/java/io/cucumber/core/options/RuntimeOptionsBuilder.java

@@ -32,6 +32,8 @@ public final class RuntimeOptionsBuilder {
     private Class<? extends ObjectFactory> parsedObjectFactoryClass = null;
     private boolean addDefaultSummaryPrinterIfAbsent;
     private boolean addDefaultFormatterIfAbsent;
+    private boolean addDefaultGlueIfAbsent;
+    private boolean addDefaultFeaturePathIfAbsent;
 
     public RuntimeOptionsBuilder addRerun(Collection<FeatureWithLines> featureWithLines) {
         if (parsedRerunPaths == null) {
@@ -134,6 +136,14 @@ public RuntimeOptions build(RuntimeOptions runtimeOptions) {
             runtimeOptions.addDefaultSummaryPrinterIfAbsent();
         }
 
+        if (addDefaultGlueIfAbsent) {
+            runtimeOptions.addDefaultGlueIfAbsent();
+        }
+
+        if (addDefaultFeaturePathIfAbsent) {
+            runtimeOptions.addDefaultFeaturePathIfAbsent();
+        }
+
         return runtimeOptions;
     }
 
@@ -205,6 +215,17 @@ public RuntimeOptionsBuilder addDefaultFormatterIfAbsent() {
         return this;
     }
 
+    public RuntimeOptionsBuilder addDefaultGlueIfAbsent() {
+        this.addDefaultGlueIfAbsent = true;
+        return this;
+    }
+
+    public RuntimeOptionsBuilder addDefaultFeaturePathIfAbsent() {
+        this.addDefaultFeaturePathIfAbsent = true;
+        return this;
+    }
+
+
     public void setObjectFactoryClass(Class<? extends ObjectFactory> objectFactoryClass) {
         this.parsedObjectFactoryClass = objectFactoryClass;
     }

core/src/main/resources/io/cucumber/core/options/USAGE.txt

@@ -6,8 +6,10 @@ Options:
                                            Defaults to 1.
 
   -g, --glue PATH                          Package to load glue code (step
-                                           definitions, hooks and plugins) from.
-                                           E.g: com.example.app
+                                           definitions, hooks and plugins) from
+                                           e.g: com.example.app. When not
+                                           provided Cucumber will search the
+                                           classpath.
 
   -p, --[add-]plugin PLUGIN[:PATH_OR_URL]  Register a plugin.
                                            Built-in formatter PLUGIN types:
@@ -69,6 +71,9 @@ Options:
                                            META-INF/services/io.cucumber.core.backend.ObjectFactory
 
 Feature path examples:
+                                           When no feature path is provided
+                                           cucumber will scan the classpath root
+                                           and its sub directories.
 
   <path>                                   Load the files with the extension
                                            ".feature" for the directory <path>

core/src/test/java/io/cucumber/core/options/RuntimeOptionsTest.java

@@ -35,6 +35,7 @@
 
 import static io.cucumber.core.options.Constants.FILTER_TAGS_PROPERTY_NAME;
 import static io.cucumber.core.options.Constants.OPTIONS_PROPERTY_NAME;
+import static io.cucumber.core.resource.ClasspathSupport.rootPackageUri;
 import static java.util.Arrays.asList;
 import static java.util.Collections.emptyMap;
 import static java.util.Collections.singleton;
@@ -734,6 +735,24 @@ void loads_no_features_when_rerun_file_specified_in_cucumber_options_property_is
         assertThat(options.getFeaturePaths(), emptyCollectionOf(URI.class));
     }
 
+    @Test
+    void scans_class_path_root_for_glue_by_default() {
+        RuntimeOptions options = new CommandlineOptionsParser()
+            .parse()
+            .addDefaultGlueIfAbsent()
+            .build();
+        assertThat(options.getGlue(), is(singletonList(rootPackageUri())));
+    }
+
+    @Test
+    void scans_class_path_root_for_features_by_default() {
+        RuntimeOptions options = new CommandlineOptionsParser()
+            .parse()
+            .addDefaultFeaturePathIfAbsent()
+            .build();
+        assertThat(options.getFeaturePaths(), is(singletonList(rootPackageUri())));
+        assertThat(options.getLineFilters(), is(emptyMap()));
+    }
 
     public static final class AwareFormatter implements StrictAware, ColorAware, EventListener {
 

picocontainer/pom.xml

@@ -1,4 +1,5 @@
-<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>
 
     <parent>
@@ -66,13 +67,14 @@
                         </goals>
                         <configuration>
                             <target>
-                                <echo message="Running CLI test for picocontainer" />
-                                <java classname="io.cucumber.core.cli.Main" fork="true" failonerror="true" newenvironment="true" maxmemory="512m" classpathref="maven.test.classpath">
-                                    <arg value="--plugin" />
-                                    <arg value="progress" />
-                                    <arg value="--glue" />
-                                    <arg value="io.cucumber.picocontainer" />
-                                    <arg value="${basedir}/src/test/resources/io/cucumber/picocontainer" />
+                                <echo message="Running CLI test for picocontainer"/>
+                                <java classname="io.cucumber.core.cli.Main"
+                                      fork="true"
+                                      failonerror="true"
+                                      newenvironment="true"
+                                      maxmemory="512m"
+                                      classpathref="maven.test.classpath"
+                                >
                                 </java>
                             </target>
                         </configuration>