JDK 13 Compatibility (#116)

* Add jdk 13 to build matrix

* Adjust indentation

* Adjust indentation

* Bump kemitix-maven-tiles from 1.2.0 to 2.4.1

* Fix TypeAlias.equals(Object) does not check for null argument

net.kemitix.mon.TypeAlias.equals(Object) does not check for null argument [net.kemitix.mon.TypeAlias] At TypeAlias.java:[lines 82-88] NP_EQUALS_SHOULD_HANDLE_NULL_ARGUMENT

* Fix TypeAlias.flatMap(Function) declares unbound method template parameter

[ERROR] Method net.kemitix.mon.TypeAlias.flatMap(Function) declares unbound method template parameter(s) [net.kemitix.mon.TypeAlias] At TypeAlias.java:[line 72] UMTP_UNBOUND_METHOD_TEMPLATE_PARAMETER

* Fix Lazy has a circular dependency with other classes

[ERROR] Class net.kemitix.mon.lazy.Lazy has a circular dependency with other classes [net.kemitix.mon.lazy.Lazy] At Lazy.java:[lines 36-46] FCCD_FIND_CLASS_CIRCULAR_DEPENDENCY

* Fix Synchronization performed on AtomicReference

[ERROR] Synchronization performed on java.util.concurrent.atomic.AtomicReference in net.kemitix.mon.lazy.LazySupplier.value() [net.kemitix.mon.lazy.LazySupplier] At LazySupplier.java:[line 61] JLM_JSR166_UTILCONCURRENT_MONITORENTER

* Fix Just.orElseThrow(Supplier) declares throwing an exception that isn't thrown

[ERROR] Non derivable method net.kemitix.mon.maybe.Just.orElseThrow(Supplier) declares throwing an exception that isn't thrown [net.kemitix.mon.maybe.Just] At Just.java:[line 102] BED_BOGUS_EXCEPTION_DECLARATION

* Fix Maybe has a circular dependency with other classes

[ERROR] Class net.kemitix.mon.maybe.Maybe has a circular dependency with other classes [net.kemitix.mon.maybe.Maybe] At Maybe.java:[lines 40-94] FCCD_FIND_CLASS_CIRCULAR_DEPENDENCY

* Fix Maybe.findFirst(Stream) uses immediate execution of a block

[ERROR] Method net.kemitix.mon.maybe.Maybe.findFirst(Stream) uses immediate execution of a block of code that is often not used [net.kemitix.mon.maybe.Maybe] At Maybe.java:[line 94] OI_OPTIONAL_ISSUES_USES_IMMEDIATE_EXECUTION

* Fix Success/Result/Err has a circular dependency

[ERROR] Class net.kemitix.mon.result.Err has a circular dependency with other classes [net.kemitix.mon.result.Err] At Err.java: FCCD_FIND_CLASS_CIRCULAR_DEPENDENCY

* Fix GeneralisedTree has a circular dependency

[ERROR] Class net.kemitix.mon.tree.GeneralisedTree has a circular dependency with other classes [net.kemitix.mon.tree.GeneralisedTree] At GeneralisedTree.java:[lines 39-80] FCCD_FIND_CLASS_CIRCULAR_DEPENDENCY

* Supress warning about boxing a boolean

NAB_NEEDLESS_BOOLEAN_CONSTANT_CONVERSION

Without creating a whole reimplemention of Maybe/Just/Nothing purely for `boolean` primitives, we can’t avoid this boxing.

* Supress store before return warnings in Lombok generate hashCode

USBR_UNNECESSARY_STORE_BEFORE_RETURN

The annotation has to be used at the class level, which unfortunately means we have no store-before-return checks for the rest of the class.

* Suppress warning about unused parameter

The type parameter for `Tree.builder(type)` is used to specify the parameterised type of the return value.

* Checkstyle fixups

* [changelog] updated

.github/workflows/maven-build.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        java: [ 8, 11 ]
+        java: [ 8, 11, 13 ]
     steps:
       - uses: actions/checkout@v2
       - name: Set up JDK ${{ matrix.java }}

CHANGELOG.org

@@ -10,9 +10,11 @@ The format is based on [[https://keepachangelog.com/en/1.0.0/][Keep a Changelog]
 ** Added
 
  * Add github actions config (#113)
+ * Add JDK 13 compatibility (#116)
 
 ** Dependencies
 
+ * Bump kemitix-maven-tiles from 1.2.0 to 2.4.1 (#116)
  * Bump assertj-core from 3.13.2 to 3.15.0 (#106)
  * Bump junit-bom from 5.5.2 to 5.6.0 (#105)
  * Bump tiles-maven-plugin from 2.15 to 2.16 (#101)

pom.xml

@@ -38,11 +38,12 @@
         <assertj.version>3.15.0</assertj.version>
         <lombok.version>1.18.12</lombok.version>
         <tiles-maven-plugin.version>2.16</tiles-maven-plugin.version>
-        <kemitix-maven-tiles.version>1.2.0</kemitix-maven-tiles.version>
+        <kemitix-maven-tiles.version>2.4.1</kemitix-maven-tiles.version>
         <digraph-dependency.basePackage>net.kemitix.mon</digraph-dependency.basePackage>
         <kemitix-checkstyle.version>5.0.0</kemitix-checkstyle.version>
         <pitest-maven-plugin.version>1.5.0</pitest-maven-plugin.version>
         <pitest-junit5-plugin.version>0.12</pitest-junit5-plugin.version>
+        <spotbugs.version>4.0.1</spotbugs.version>
     </properties>
 
     <dependencies>
@@ -75,6 +76,12 @@
             <version>${assertj.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>com.github.spotbugs</groupId>
+            <artifactId>spotbugs-annotations</artifactId>
+            <version>${spotbugs.version}</version>
+            <scope>provided</scope>
+        </dependency>
     </dependencies>
 
     <dependencyManagement>

src/main/java/net/kemitix/mon/TypeAlias.java

@@ -64,11 +64,10 @@ public abstract class TypeAlias<T> {
      * Map the TypeAlias into another TypeAlias.
      *
      * @param f   the function to create the new value
-     * @param <R> the type of the new value within a TypeAlias
      * @param <U> the type of the TypeAlias superclass containing the new value
      * @return a TypeAlias
      */
-    public final <R, U extends TypeAlias<R>> U flatMap(final Function<T, U> f) {
+    public final <U extends TypeAlias<?>> U flatMap(final Function<T, U> f) {
         return f.apply(value);
     }
 
@@ -85,7 +84,7 @@ public abstract class TypeAlias<T> {
             return otherValueClass.equals(getValue().getClass())
                     && other.value.equals(getValue());
         }
-        return map(o::equals);
+        return o != null && map(o::equals);
     }
 
     @Override

src/main/java/net/kemitix/mon/lazy/LazySupplier.java

@@ -38,6 +38,7 @@ class LazySupplier<T> implements Lazy<T> {
     private final Supplier<T> supplier;
     private final AtomicBoolean evaluated = new AtomicBoolean(false);
     private final AtomicReference<T> value = new AtomicReference<>();
+    private final Object lock = new Object();
 
     /**
      * Creates a new Lazy wrapper for the Supplier.
@@ -58,7 +59,7 @@ class LazySupplier<T> implements Lazy<T> {
         if (evaluated.get()) {
             return value.get();
         }
-        synchronized (value) {
+        synchronized (lock) {
             if (!evaluated.get()) {
                 value.set(supplier.get());
                 evaluated.set(true);
@@ -69,7 +70,7 @@ class LazySupplier<T> implements Lazy<T> {
 
     @Override
     public <R> Lazy<R> map(final Function<T, R> f) {
-        return Lazy.of(() -> f.apply(value()));
+        return new LazySupplier<R>(() -> f.apply(value()));
     }
 
 }

src/main/java/net/kemitix/mon/maybe/Just.java

@@ -85,11 +85,12 @@ final class Just<T> implements Maybe<T> {
     }
 
     @Override
+    @SuppressWarnings("unchecked")
     public Maybe<T> filter(final Predicate<T> predicate) {
         if (predicate.test(value)) {
             return this;
         }
-        return Maybe.nothing();
+        return (Maybe<T>) Nothing.INSTANCE;
     }
 
     @Override
@@ -98,7 +99,7 @@ final class Just<T> implements Maybe<T> {
     }
 
     @Override
-    public <X extends Throwable> T orElseThrow(final Supplier<? extends X> e) throws X {
+    public <X extends Throwable> T orElseThrow(final Supplier<? extends X> e) {
         return value;
     }
 

src/main/java/net/kemitix/mon/maybe/Maybe.java

@@ -91,7 +91,7 @@ public interface Maybe<T> extends Functor<T, Maybe<?>> {
     public static <T> Maybe<T> findFirst(Stream<T> stream) {
         return stream.findFirst()
                 .map(Maybe::just)
-                .orElse(Maybe.nothing());
+                .orElseGet(Maybe::nothing);
     }
 
     /**

src/main/java/net/kemitix/mon/maybe/Nothing.java

@@ -50,8 +50,9 @@ final class Nothing<T> implements Maybe<T> {
     }
 
     @Override
+    @SuppressWarnings("unchecked")
     public <R> Maybe<R> flatMap(final Function<T, Maybe<R>> f) {
-        return Maybe.nothing();
+        return (Maybe<R>) INSTANCE;
     }
 
     @Override

src/main/java/net/kemitix/mon/result/Err.java

@@ -54,12 +54,12 @@ class Err<T> implements Result<T> {
 
     @Override
     public <R> Result<R> flatMap(final Function<T, Result<R>> f) {
-        return Result.error(error);
+        return err(error);
     }
 
     @Override
     public <R> Result<R> map(final Function<T, R> f) {
-        return Result.error(error);
+        return err(error);
     }
 
     @Override
@@ -69,7 +69,7 @@ class Err<T> implements Result<T> {
 
     @Override
     public Result<Maybe<T>> maybe(final Predicate<T> predicate) {
-        return Result.error(error);
+        return err(error);
     }
 
     @Override
@@ -108,7 +108,7 @@ class Err<T> implements Result<T> {
 
     @Override
     public <R> Result<R> andThen(final Function<T, Callable<R>> f) {
-        return Result.error(error);
+        return err(error);
     }
 
     @Override
@@ -118,7 +118,7 @@ class Err<T> implements Result<T> {
 
     @Override
     public Result<T> reduce(final Result<T> identify, final BinaryOperator<T> operator) {
-        return Result.error(error);
+        return this;
     }
 
     @Override

src/main/java/net/kemitix/mon/result/Result.java

@@ -49,6 +49,17 @@ public interface Result<T> extends Functor<T, Result<?>> {
                 .orElseGet(() -> Result.error(error.get()));
     }
 
+    /**
+     * Create a Result for an error.
+     *
+     * @param error the error (Throwable)
+     * @param <T>   the type had the result been a success
+     * @return an error Result
+     */
+    public default <T> Result<T> err(final Throwable error) {
+        return new Err<>(error);
+    }
+
     /**
      * Create a Result for an error.
      *
@@ -60,6 +71,22 @@ public interface Result<T> extends Functor<T, Result<?>> {
         return new Err<>(error);
     }
 
+    /**
+     * Create a Result for a output of the Callable.
+     *
+     * @param callable the callable to produce the result
+     * @param <T>      the type of the value
+     * @return a Result
+     */
+    @SuppressWarnings("illegalcatch")
+    public default <T> Result<T> result(final Callable<T> callable) {
+        try {
+            return Result.ok(callable.call());
+        } catch (final Exception e) {
+            return Result.error(e);
+        }
+    }
+
     /**
      * Create a Result for a output of the Callable.
      *
@@ -76,6 +103,17 @@ public interface Result<T> extends Functor<T, Result<?>> {
         }
     }
 
+    /**
+     * Create a Result for a success.
+     *
+     * @param value the value
+     * @param <T>   the type of the value
+     * @return a successful Result
+     */
+    public default <T> Result<T> success(final T value) {
+        return new Success<>(value);
+    }
+
     /**
      * Create a Result for a success.
      *

src/main/java/net/kemitix/mon/result/Success.java

@@ -54,7 +54,7 @@ class Success<T> implements Result<T> {
 
     @Override
     public <R> Result<R> map(final Function<T, R> f) {
-        return Result.ok(f.apply(value));
+        return success(f.apply(value));
     }
 
     @Override
@@ -65,9 +65,9 @@ class Success<T> implements Result<T> {
     @Override
     public Result<Maybe<T>> maybe(final Predicate<T> predicate) {
         if (predicate.test(value)) {
-            return Result.ok(Maybe.just(value));
+            return success(Maybe.just(value));
         }
-        return Result.ok(Maybe.nothing());
+        return success(Maybe.nothing());
     }
 
     @Override
@@ -103,7 +103,7 @@ class Success<T> implements Result<T> {
 
     @Override
     public <R> Result<R> andThen(final Function<T, Callable<R>> f) {
-        return Result.of(f.apply(value));
+        return result(f.apply(value));
     }
 
     @Override
@@ -113,7 +113,7 @@ class Success<T> implements Result<T> {
 
     @Override
     public Result<T> reduce(final Result<T> identity, final BinaryOperator<T> operator) {
-        return flatMap(a -> identity.flatMap(b -> Result.of(() -> operator.apply(a, b))));
+        return flatMap(a -> identity.flatMap(b -> result(() -> operator.apply(a, b))));
     }
 
     @Override

src/main/java/net/kemitix/mon/tree/GeneralisedTree.java

@@ -21,6 +21,7 @@
 
 package net.kemitix.mon.tree;
 
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import lombok.EqualsAndHashCode;
 import net.kemitix.mon.maybe.Maybe;
 
@@ -36,6 +37,7 @@ import java.util.function.Function;
  *
  * @author Paul Campbell (pcampbell@kemitix.net)
  */
+@SuppressFBWarnings("USBR_UNNECESSARY_STORE_BEFORE_RETURN")
 @EqualsAndHashCode
 class GeneralisedTree<T> implements Tree<T>, TreeMapper<T> {
 
@@ -62,7 +64,7 @@ class GeneralisedTree<T> implements Tree<T>, TreeMapper<T> {
      */
     @Override
     public <R> Tree<R> map(final Function<T, R> f) {
-        return Tree.of(f.apply(item), mapTrees(f, subTrees()));
+        return new GeneralisedTree<>(f.apply(item), mapTrees(f, subTrees()));
     }
 
     @Override

src/main/java/net/kemitix/mon/tree/MutableTree.java

@@ -21,6 +21,7 @@
 
 package net.kemitix.mon.tree;
 
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import lombok.EqualsAndHashCode;
 import net.kemitix.mon.maybe.Maybe;
 
@@ -37,6 +38,7 @@ import java.util.stream.Collectors;
  *
  * @author Paul Campbell (pcampbell@kemitix.net)
  */
+@SuppressFBWarnings("USBR_UNNECESSARY_STORE_BEFORE_RETURN")
 @EqualsAndHashCode
 @SuppressWarnings("methodcount")
 class MutableTree<T> implements Tree<T>, TreeMapper<T> {

src/main/java/net/kemitix/mon/tree/MutableTreeBuilder.java

@@ -21,6 +21,7 @@
 
 package net.kemitix.mon.tree;
 
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import net.kemitix.mon.maybe.Maybe;
 
 import java.util.function.Function;
@@ -84,8 +85,14 @@ class MutableTreeBuilder<T> implements TreeBuilder<T> {
                         .map(Tree::builder));
     }
 
-    private Boolean matchesItem(final T childItem, final MutableTree<T> tree) {
+    @SuppressFBWarnings("NAB_NEEDLESS_BOOLEAN_CONSTANT_CONVERSION")
-        return tree.item().map(childItem::equals).orElse(false);
+    private boolean matchesItem(
+            final T childItem,
+            final MutableTree<T> tree
+    ) {
+        return tree.item()
+                .map(childItem::equals)
+                .orElse(false);
     }
 
 }

src/main/java/net/kemitix/mon/tree/Tree.java

@@ -21,6 +21,7 @@
 
 package net.kemitix.mon.tree;
 
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import net.kemitix.mon.Functor;
 import net.kemitix.mon.maybe.Maybe;
 
@@ -70,6 +71,8 @@ public interface Tree<T> extends Functor<T, Tree<?>> {
      *
      * @return a TreeBuilder
      */
+    @SuppressFBWarnings(value = "UP_UNUSED_PARAMETER",
+            justification = "Use the type parameter to fingerprint the return type")
     public static <B> TreeBuilder<B> builder(final Class<B> type) {
         return new MutableTreeBuilder<>();
     }

src/test/java/net/kemitix/mon/TypeAliasTest.java

@@ -1,6 +1,7 @@
 package net.kemitix.mon;
 
 import org.assertj.core.util.Strings;
+import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
 
 import java.util.Arrays;
@@ -116,6 +117,17 @@ class TypeAliasTest {
         assertThat(value).isEqualTo("'text'");
     }
 
+    @Test
+    @DisplayName("equals other is null then not equals")
+    void whenOtherNullEqualsIsFalse() {
+        //given
+        final AnAlias anAlias = AnAlias.of("text");
+        //then
+        boolean result = anAlias.equals(null);
+        //then
+        assertThat(result).isFalse();
+    }
+
     private static class AnAlias extends TypeAlias<String> {
 
         /**