From 4809d733192875ef3e475e40d36cb75c4782d00f Mon Sep 17 00:00:00 2001
From: Tomasz Tylenda <tomasz.tylenda@sonarsource.com>
Date: Thu, 22 Jan 2026 18:17:18 +0100
Subject: [PATCH] S106 Do not raise on Java 25 compact source files

---
 ...tOrErrUsageCheckCompactOnlyMainSample.java |  5 ++++
 ...OrErrUsageCheckCompactWithClassSample.java | 21 ++++++++++++++++
 .../java/checks/SystemOutOrErrUsageCheck.java | 24 +++++++++++++++----
 .../checks/SystemOutOrErrUsageCheckTest.java  | 16 +++++++++++++
 4 files changed, 62 insertions(+), 4 deletions(-)
 create mode 100644 java-checks-test-sources/default/src/main/java/checks/SystemOutOrErrUsageCheckCompactOnlyMainSample.java
 create mode 100644 java-checks-test-sources/default/src/main/java/checks/SystemOutOrErrUsageCheckCompactWithClassSample.java

diff --git a/java-checks-test-sources/default/src/main/java/checks/SystemOutOrErrUsageCheckCompactOnlyMainSample.java b/java-checks-test-sources/default/src/main/java/checks/SystemOutOrErrUsageCheckCompactOnlyMainSample.java
new file mode 100644
index 00000000000..1b7f921dead
--- /dev/null
+++ b/java-checks-test-sources/default/src/main/java/checks/SystemOutOrErrUsageCheckCompactOnlyMainSample.java
@@ -0,0 +1,5 @@
+void main() {
+  String name = IO.readln("Enter your name: ");
+  IO.println("Hello " + name + "!");
+  System.out.println("Goodbye " + name + "!");
+}
diff --git a/java-checks-test-sources/default/src/main/java/checks/SystemOutOrErrUsageCheckCompactWithClassSample.java b/java-checks-test-sources/default/src/main/java/checks/SystemOutOrErrUsageCheckCompactWithClassSample.java
new file mode 100644
index 00000000000..ebd7f65558a
--- /dev/null
+++ b/java-checks-test-sources/default/src/main/java/checks/SystemOutOrErrUsageCheckCompactWithClassSample.java
@@ -0,0 +1,21 @@
+void main() {
+  String name = IO.readln("Enter your name: ");
+  IO.println("Hello " + name + "!");
+  System.out.println("Goodbye " + name + "!");
+
+  System.out.println(f(6, 7));
+
+  RegularClass rc = new RegularClass();
+  rc.log("This is a log message.");
+}
+
+int f(int x, int y) {
+  System.err.println("Error: x=" + x + ", y=" + y);
+  return x + y;
+}
+
+class RegularClass {
+  void log(String message) {
+    System.out.println(message);
+  }
+}
diff --git a/java-checks/src/main/java/org/sonar/java/checks/SystemOutOrErrUsageCheck.java b/java-checks/src/main/java/org/sonar/java/checks/SystemOutOrErrUsageCheck.java
index 0ff0ca98f0f..dd716f87d66 100644
--- a/java-checks/src/main/java/org/sonar/java/checks/SystemOutOrErrUsageCheck.java
+++ b/java-checks/src/main/java/org/sonar/java/checks/SystemOutOrErrUsageCheck.java
@@ -29,20 +29,36 @@
 @Rule(key = "S106")
 public class SystemOutOrErrUsageCheck extends IssuableSubscriptionVisitor {
 
+  private boolean isCompactSourceFile = false;
+
   @Override
   public List<Tree.Kind> nodesToVisit() {
-    return Collections.singletonList(Tree.Kind.MEMBER_SELECT);
+    return List.of(
+      Tree.Kind.COMPILATION_UNIT,
+      Tree.Kind.IMPLICIT_CLASS,
+      Tree.Kind.MEMBER_SELECT
+    );
   }
 
   @Override
   public void visitNode(Tree tree) {
-    MemberSelectExpressionTree mset = (MemberSelectExpressionTree) tree;
+    if (tree.is(Tree.Kind.COMPILATION_UNIT)) {
+      isCompactSourceFile = false;
+    } else if (tree.is(Tree.Kind.IMPLICIT_CLASS)) {
+      // System.out or System.err is allowed in compact source files.
+      isCompactSourceFile = true;
+    } else if (!isCompactSourceFile && tree instanceof MemberSelectExpressionTree mset) {
+      visitMemberSelectExpression(mset);
+    }
+  }
+
+  private void visitMemberSelectExpression(MemberSelectExpressionTree mset) {
     String name = mset.identifier().name();
 
     if ("out".equals(name) && isSystem(mset.expression())) {
-      reportIssue(tree, "Replace this use of System.out by a logger.");
+      reportIssue(mset, "Replace this use of System.out by a logger.");
     } else if ("err".equals(name) && isSystem(mset.expression())) {
-      reportIssue(tree, "Replace this use of System.err by a logger.");
+      reportIssue(mset, "Replace this use of System.err by a logger.");
     }
   }
 
diff --git a/java-checks/src/test/java/org/sonar/java/checks/SystemOutOrErrUsageCheckTest.java b/java-checks/src/test/java/org/sonar/java/checks/SystemOutOrErrUsageCheckTest.java
index c09fed38453..81b19e26b60 100644
--- a/java-checks/src/test/java/org/sonar/java/checks/SystemOutOrErrUsageCheckTest.java
+++ b/java-checks/src/test/java/org/sonar/java/checks/SystemOutOrErrUsageCheckTest.java
@@ -29,4 +29,20 @@ void test() {
       .withCheck(new SystemOutOrErrUsageCheck())
       .verifyIssues();
   }
+
+  @Test
+  void test_compact_source_file() {
+    CheckVerifier.newVerifier()
+      .onFile(mainCodeSourcesPath("checks/SystemOutOrErrUsageCheckCompactOnlyMainSample.java"))
+      .withCheck(new SystemOutOrErrUsageCheck())
+      .verifyNoIssues();
+  }
+
+  @Test
+  void test_compact_source_file_with_regular_class() {
+    CheckVerifier.newVerifier()
+      .onFile(mainCodeSourcesPath("checks/SystemOutOrErrUsageCheckCompactWithClassSample.java"))
+      .withCheck(new SystemOutOrErrUsageCheck())
+      .verifyNoIssues();
+  }
 }