Relax source file attribute check

The purpose of the check is to alert users that they must configure the
compiler to include source file debug info.

Previously all classes were checked to ensure the source file was
present, however it appears there may be some scenarios in which the
source file is omitted when compiling kotlin.

To allow analysis of the remaining classes, the check has been relaxed
so that the info must be present in at least one file, rather than all
files.

pitest-entry/src/main/java/org/pitest/mutationtest/verify/DefaultBuildVerifier.java

@@ -16,7 +16,7 @@
  */
 
 import java.util.Collection;
-import java.util.function.Consumer;
+import java.util.List;
 import java.util.function.Predicate;
 
 import org.pitest.classinfo.ClassInfo;
@@ -29,11 +29,11 @@ public class DefaultBuildVerifier implements BuildVerifier {
 
   @Override
   public void verify(final CodeSource code) {
-    final Collection<ClassInfo> codeClasses = FCollection.filter(code.getCode(), isNotSynthetic());
+    final List<ClassInfo> codeClasses = FCollection.filter(code.getCode(), isNotSynthetic());
 
     if (hasMutableCode(codeClasses)) {
       checkAtLeastOneClassHasLineNumbers(codeClasses);
-      codeClasses.forEach(throwErrorIfHasNoSourceFile());
+      checkAtLeastOneClassHasSourceFile(codeClasses);
     }
   }
 
@@ -54,6 +54,14 @@ private void checkAtLeastOneClassHasLineNumbers(
     }
   }
 
+  private void checkAtLeastOneClassHasSourceFile(List<ClassInfo> codeClasses) {
+    // perform only a weak check for line numbers as
+    // some jvm languages are not guaranteed to include a source file for all classes
+    if (!FCollection.contains(codeClasses, a -> a.getSourceFileName() != null)) {
+      throw new PitHelpError(Help.NO_SOURCE_FILE, codeClasses.get(0).getName().asJavaName());
+    }
+  }
+
   private static Predicate<ClassInfo> aConcreteClass() {
     return a -> !a.isInterface();
   }
@@ -62,14 +70,6 @@ private static Predicate<ClassInfo> aClassWithLineNumbers() {
     return a -> a.getNumberOfCodeLines() != 0;
   }
 
-  private Consumer<ClassInfo> throwErrorIfHasNoSourceFile() {
-    return a -> {
-      if (a.getSourceFileName() == null) {
-        throw new PitHelpError(Help.NO_SOURCE_FILE, a.getName().asJavaName());
-      }
-    };
-  }
-
   private static Predicate<ClassInfo> isNotSynthetic() {
     return a -> !a.isSynthetic();
   }

pitest-entry/src/test/java/org/pitest/mutationtest/verify/DefaultBuildVerifierTest.java

@@ -15,6 +15,7 @@
 
 package org.pitest.mutationtest.verify;
 
+import static org.assertj.core.api.Assertions.assertThatCode;
 import static org.junit.Assert.fail;
 import static org.mockito.Mockito.when;
 
@@ -105,6 +106,12 @@ public void shouldNotThrowAnErrorWhenOnlyInterfacesPresent() {
     }
   }
 
+  @Test
+  public void doesNotErrorWhenNoClassesProvided() {
+    when(this.code.getCode()).thenReturn(Collections.emptyList());
+    assertThatCode(() -> this.testee.verify(this.code)).doesNotThrowAnyException();
+  }
+
   private void setupClassPath(final Class<?> clazz) {
     this.setupClassPath(
         new ClassloaderByteArraySource(IsolationUtils.getContextClassLoader()),