"Unknown" error into the pom.xml file.

Describe the bug When compiling a Maven-based SARL project, the compiler into Eclipse (not on the command-line interface) shows up an “Unknown” error at the first line of the pom.xml file.

To Reproduce Steps to reproduce the behavior:

1. Create a Maven SARL project with the following pom file:

<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>mygroup</groupId>
	<artifactId>myproject</artifactId>
	<version>0.1-SNAPSHOT</version>
	<properties>
		<sarl.version>0.10.0-SNAPSHOT</sarl.version>
		<janus.version>2.0.10.0-SNAPSHOT</janus.version>
		<compiler.level>1.8</compiler.level>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
	</properties>
	<dependencies>
		<dependency>
			<groupId>javafx</groupId>
			<artifactId>jfxrt</artifactId>
			<version>${java.version}</version>
			<scope>system</scope>
			<systemPath>${java.home}/lib/ext/jfxrt.jar</systemPath>
		</dependency>
		<dependency>
			<groupId>io.janusproject</groupId>
			<artifactId>io.janusproject.kernel</artifactId>
			<version>${janus.version}</version>
		</dependency>
		<dependency>
			<groupId>org.arakhne.afc.gis.ui</groupId>
			<artifactId>gisroadfx</artifactId>
			<version>${afc.version}</version>
		</dependency>
		<dependency>
			<groupId>org.arakhne.afc.core</groupId>
			<artifactId>mathphysics</artifactId>
			<version>${afc.version}</version>
		</dependency>
		<dependency>
			<groupId>org.arakhne.afc.core</groupId>
			<artifactId>mathstochastic</artifactId>
			<version>${afc.version}</version>
		</dependency>
		<dependency>
			<groupId>org.arakhne.afc.core</groupId>
			<artifactId>vmutils</artifactId>
			<version>${afc.version}</version>
		</dependency>
		<dependency>
			<groupId>com.dlsc.preferencesfx</groupId>
			<artifactId>preferencesfx-core</artifactId>
			<version>2.1.0</version>
		</dependency>
		<dependency>
			<groupId>org.fxmisc.richtext</groupId>
			<artifactId>richtextfx</artifactId>
			<version>0.10.1</version>
		</dependency>
		<dependency>
			<groupId>com.opencsv</groupId>
			<artifactId>opencsv</artifactId>
			<version>4.6</version>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>3.8.1</version>
				<configuration>
					<source>${compiler.level}</source>
					<target>${compiler.level}</target>
					<encoding>${project.build.sourceEncoding}</encoding>
				</configuration>
			</plugin>
			<plugin>
				<groupId>io.sarl.maven</groupId>
				<artifactId>sarl-maven-plugin</artifactId>
				<version>${sarl.version}</version>
				<extensions>true</extensions>
				<configuration>
					<source>${compiler.level}</source>
					<target>${compiler.level}</target>
					<encoding>${project.build.sourceEncoding}</encoding>
				</configuration>
			</plugin>
		</plugins>
	</build>
	<repositories>
		<repository>
			<name>Arakhne Lastest Builds</name>
			<id>org.arakhne.maven</id>
			<url>http://download.arakhne.org/arakhne/maven</url>
			<releases>
				<enabled>true</enabled>
			</releases>
			<snapshots>
				<enabled>true</enabled>
			</snapshots>
		</repository>
	</repositories>
</project>

1. Compile
2. See error

Expected behavior No error is expected.

Screenshots

System configuration:

• SARL version: 0.9.0 and 0.10.0
• SARL compiler:
• Eclipse compiler without Maven
• Eclipse compiler with Maven
• Maven compiler on the command line
• sarlc compiler
• Java JDK version (with the manufacturer name): 1.8.0_201
• Operating System:
• Linux 64bits
• Linux 32bits
• Windows 64bits
• Windows 32bits
• MacOS 64bits

[gallandarakhneorg]

There is incompatibilities between the version of M2E and the version 3.1.2 of the maven-jar-plugin.

Until the problem is solved by the development teams of M2E or maven-jar-plugins, you have to add in your pom.xml file the following line in order to solve this issue:

</project>
	<build>
		<pluginManagement>
			<plugins>
				<plugin>
					<groupId>org.apache.maven.plugins</groupId>
					<artifactId>maven-jar-plugin</artifactId>
					<version>3.1.1</version>
				</plugin>
			</plugins>
		</pluginManagement>
	</build>
</project>

[gallandarakhneorg]

Seems to be fixed into SARL 0.12, that is based on Eclipse 2020-06. We do not need to specify the maven-jar-plugin anymore.