Update AbstractJavaProjectConfigurator.java

 check --enable-preview flag in ${maven.compiler.enablePreview}

Author: RussiaVk

org.eclipse.m2e.jdt.tests/projects/compilerEnablePreviewSettings/pom.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<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
+https://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<groupId>foo.bar</groupId>
+	<artifactId>compilerEnablePreviewSettings</artifactId>
+	<version>0.0.1-SNAPSHOT</version>
+	<properties>
+	        <maven.compiler.enablePreview>true</maven.compiler.enablePreview>
+	        <maven.compiler.release>11</maven.compiler.release>
+	</properties>
+</project>

org.eclipse.m2e.jdt.tests/src/org/eclipse/m2e/jdt/tests/JavaConfigurationTest.java

@@ -124,6 +124,14 @@ public void testSkipNone() throws CoreException, IOException, InterruptedExcepti
 		assertEquals(1, classpathEntriesCount(project, TEST_RESOURCES));
 	}
 
+	
+	@Test
+	public void testComplianceVsEnablePreviewSettings() throws CoreException, IOException, InterruptedException {
+		IJavaProject project = importResourceProject("/projects/compilerEnablePreviewSettings/pom.xml");
+		assertEquals("11", project.getOption(JavaCore.COMPILER_COMPLIANCE, false));
+		assertEquals(JavaCore.ENABLED, project.getOption(JavaCore.COMPILER_PB_ENABLE_PREVIEW_FEATURES, false));
+		assertEquals(JavaCore.IGNORE, project.getOption(JavaCore.COMPILER_PB_REPORT_PREVIEW_FEATURES, false));
+	}
 	// --- utility methods ---
 
 	private static final Predicate<IClasspathEntry> TEST_SOURCES = cp -> cp.isTest()

org.eclipse.m2e.jdt/src/org/eclipse/m2e/jdt/internal/AbstractJavaProjectConfigurator.java

@@ -765,6 +765,17 @@ private boolean isEnablePreviewFeatures(MavenProject mavenProject, MojoExecution
     } catch(CoreException ex) {
       //ignore
     }
+
+    //3nd, check the --enable-preview flag in the ${maven.compiler.enablePreview}
+    try {
+      Boolean enablePreview = maven.getMojoParameterValue(mavenProject, execution, "enablePreview", Boolean.class, //$NON-NLS-1$
+          monitor);
+      if(Boolean.TRUE.equals(enablePreview)) {
+        return true;
+      }
+    } catch(CoreException ex) {
+      //ignore
+    }
     return false;
   }