Add IT for mvn script expanding ${...} in CLI arguments

The eval in the mvn script causes shell expansion of ${...} patterns
in user-provided arguments. This regression test exercises the actual
launcher script via setForkJvm(true) and verifies that ${...} is not
expanded by the shell.

Related: #11978

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ascheman

its/core-it-suite/src/test/java/org/apache/maven/it/MavenITgh11978PlaceholderInCliArgTest.java

@@ -0,0 +1,57 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.maven.it;
+
+import java.nio.file.Path;
+import java.util.Properties;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * This is a test set for <a href="https://github.com/apache/maven/issues/11978">gh-11978</a>.
+ *
+ * Verifies that the launcher script does not expand <code>${...}</code> patterns
+ * in CLI arguments. Regression test for the {@code eval exec} shell expansion
+ * that broke any argument containing Maven property placeholders.
+ */
+class MavenITgh11978PlaceholderInCliArgTest extends AbstractMavenIntegrationTestCase {
+
+    @Test
+    void testIt() throws Exception {
+        Path basedir = extractResources("/gh-11978-placeholder-in-cli-arg")
+                .getAbsoluteFile()
+                .toPath();
+
+        Verifier verifier = newVerifier(basedir.toString());
+        verifier.setForkJvm(true); // NOTE: We want to go through the launcher script
+        // CLI argument with ${...} placeholder that the shell must NOT expand
+        verifier.addCliArgument("-Dtest.placeholder=value_${some.placeholder}");
+        verifier.addCliArgument("validate");
+        verifier.execute();
+        verifier.verifyErrorFreeLog();
+
+        Properties props = verifier.loadProperties("target/pom.properties");
+        // Maven property substitution then resolves ${some.placeholder} (empty here).
+        // The key point: the script did not crash with "bad substitution" and the
+        // literal ${...} arrived at Java for Maven to handle.
+        assertEquals("-value_-", props.getProperty("project.properties.pom.placeholder"));
+    }
+}

its/core-it-suite/src/test/resources/gh-11978-placeholder-in-cli-arg/pom.xml

@@ -0,0 +1,58 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+    Licensed to the Apache Software Foundation (ASF) under one
+    or more contributor license agreements.  See the NOTICE file
+    distributed with this work for additional information
+    regarding copyright ownership.  The ASF licenses this file
+    to you under the Apache License, Version 2.0 (the
+    "License"); you may not use this file except in compliance
+    with the License.  You may obtain a copy of the License at
+
+      http://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing,
+    software distributed under the License is distributed on an
+    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+    KIND, either express or implied.  See the License for the
+    specific language governing permissions and limitations
+    under the License.
+-->
+<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>
+
+  <groupId>org.apache.maven.its.gh11978</groupId>
+  <artifactId>test</artifactId>
+  <version>1.0</version>
+
+  <name>Maven Integration Test :: GH-11978</name>
+  <description>Verify that the launcher script does not expand ${...} placeholders in CLI arguments.</description>
+
+  <properties>
+    <pom.placeholder>-${test.placeholder}-</pom.placeholder>
+  </properties>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.its.plugins</groupId>
+        <artifactId>maven-it-plugin-expression</artifactId>
+        <version>2.1-SNAPSHOT</version>
+        <executions>
+          <execution>
+            <id>test</id>
+            <goals>
+              <goal>eval</goal>
+            </goals>
+            <phase>validate</phase>
+            <configuration>
+              <outputFile>target/pom.properties</outputFile>
+              <expressions>
+                <expression>project/properties</expression>
+              </expressions>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>