From fae6e48a596f311132961b69d3dd5a064fc9cef3 Mon Sep 17 00:00:00 2001
From: mnhock <martin.hock.de@gmail.com>
Date: Tue, 11 Jun 2024 20:43:28 +0200
Subject: [PATCH] Provide a New Java Rule checking fields by disallowing public
 fields

Closes gh-18
---
 docs/USERGUIDE.md                             | 11 ++++++++
 .../taikai/java/FieldsShouldNotBePublic.java  | 28 +++++++++++++++++++
 .../enofex/taikai/java/JavaConfigurer.java    | 10 +++++++
 .../com/enofex/taikai/ArchitectureTest.java   |  1 +
 4 files changed, 50 insertions(+)
 create mode 100644 src/main/java/com/enofex/taikai/java/FieldsShouldNotBePublic.java

diff --git a/docs/USERGUIDE.md b/docs/USERGUIDE.md
index f8cf559..e129b61 100644
--- a/docs/USERGUIDE.md
+++ b/docs/USERGUIDE.md
@@ -84,6 +84,17 @@ Taikai.builder()
     .check();
 ```
 
+- **Fields Should Not Be Public**: Ensure that no fields in your Java classes are declared as `public`, except constants.
+
+```java
+Taikai.builder()
+    .namespace("com.enofex.taikai")
+    .java(java -> java
+        .fieldsShouldNotBePublic())
+    .build()
+    .check();
+```
+
 - **Imports Configuration**: Ensure that there are no cyclic dependencies in imports and disallow specific imports.
 
 ```java
diff --git a/src/main/java/com/enofex/taikai/java/FieldsShouldNotBePublic.java b/src/main/java/com/enofex/taikai/java/FieldsShouldNotBePublic.java
new file mode 100644
index 0000000..3fdcb1b
--- /dev/null
+++ b/src/main/java/com/enofex/taikai/java/FieldsShouldNotBePublic.java
@@ -0,0 +1,28 @@
+package com.enofex.taikai.java;
+
+import com.tngtech.archunit.core.domain.JavaField;
+import com.tngtech.archunit.core.domain.JavaModifier;
+import com.tngtech.archunit.lang.ArchCondition;
+import com.tngtech.archunit.lang.ConditionEvents;
+import com.tngtech.archunit.lang.SimpleConditionEvent;
+
+final class FieldsShouldNotBePublic {
+
+  private FieldsShouldNotBePublic() {
+  }
+
+  static ArchCondition<JavaField> notBePublic() {
+    return new ArchCondition<>("not be public") {
+      @Override
+      public void check(JavaField field, ConditionEvents events) {
+        if (!field.getModifiers().contains(JavaModifier.STATIC)
+            && field.getModifiers().contains(JavaModifier.PUBLIC)) {
+          String message = String.format("Field %s in class %s is public",
+              field.getName(),
+              field.getOwner().getFullName());
+          events.add(SimpleConditionEvent.violated(field, message));
+        }
+      }
+    };
+  }
+}
diff --git a/src/main/java/com/enofex/taikai/java/JavaConfigurer.java b/src/main/java/com/enofex/taikai/java/JavaConfigurer.java
index eaa8bad..119560e 100644
--- a/src/main/java/com/enofex/taikai/java/JavaConfigurer.java
+++ b/src/main/java/com/enofex/taikai/java/JavaConfigurer.java
@@ -1,11 +1,13 @@
 package com.enofex.taikai.java;
 
 import static com.enofex.taikai.java.Deprecations.notUseDeprecatedAPIs;
+import static com.enofex.taikai.java.FieldsShouldNotBePublic.notBePublic;
 import static com.enofex.taikai.java.HashCodeAndEquals.implementHashCodeAndEquals;
 import static com.enofex.taikai.java.UtilityClasses.beFinal;
 import static com.enofex.taikai.java.UtilityClasses.havePrivateConstructor;
 import static com.enofex.taikai.java.UtilityClasses.utilityClasses;
 import static com.tngtech.archunit.lang.syntax.ArchRuleDefinition.classes;
+import static com.tngtech.archunit.lang.syntax.ArchRuleDefinition.fields;
 import static com.tngtech.archunit.lang.syntax.ArchRuleDefinition.methods;
 
 import com.enofex.taikai.TaikaiRule;
@@ -66,6 +68,14 @@ public JavaConfigurer classesShouldImplementHashCodeAndEquals(Configuration conf
     return addRule(TaikaiRule.of(classes().should(implementHashCodeAndEquals()), configuration));
   }
 
+  public JavaConfigurer fieldsShouldNotBePublic() {
+    return fieldsShouldNotBePublic(null);
+  }
+
+  public JavaConfigurer fieldsShouldNotBePublic(Configuration configuration) {
+    return addRule(TaikaiRule.of(fields().should(notBePublic()), configuration));
+  }
+
   @Override
   public void disable() {
     disable(ImportsConfigurer.class);
diff --git a/src/test/java/com/enofex/taikai/ArchitectureTest.java b/src/test/java/com/enofex/taikai/ArchitectureTest.java
index c364039..e8cb648 100644
--- a/src/test/java/com/enofex/taikai/ArchitectureTest.java
+++ b/src/test/java/com/enofex/taikai/ArchitectureTest.java
@@ -17,6 +17,7 @@ void shouldFulfilConstrains() {
             .classesShouldImplementHashCodeAndEquals()
             .methodsShouldNotThrowGenericException()
             .utilityClassesShouldBeFinalAndHavePrivateConstructor()
+            .fieldsShouldNotBePublic()
             .imports(imports -> imports
                 .shouldHaveNoCycles()
                 .shouldNotImport("..shaded..")