Maven pom.xml to support automatic code generation for ANTLR 4 grammar(s) during an Eclipse build. This configuration does not support (and is not intended for) building using Maven alone.

pom.xml

<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.uiuc</groupId>
  <artifactId>cchistory</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <name>CodeCompletionWithHistory</name>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <antlr4.visitor>true</antlr4.visitor>
    <antlr4.listener>true</antlr4.listener>
  </properties>

  <dependencies>
    <dependency>
      <groupId>org.antlr</groupId>
      <artifactId>antlr4-runtime</artifactId>
      <version>4.0</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.eclipse.jgit</groupId>
      <artifactId>org.eclipse.jgit</artifactId>
      <version>2.1.0.201209190230-r</version>
      <scope>compile</scope>
    </dependency>
  </dependencies>

  <build>
    <sourceDirectory>src</sourceDirectory>
    <outputDirectory>bin</outputDirectory>

    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.0</version>
        <configuration>
          <source>6</source>
          <target>6</target>
          <showWarnings>true</showWarnings>
          <showDeprecation>true</showDeprecation>
          <compilerArguments>
            <Xlint />
          </compilerArguments>
        </configuration>
      </plugin>

      <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>build-helper-maven-plugin</artifactId>
        <version>1.7</version>
        <executions>
          <execution>
            <phase>generate-sources</phase>
            <goals>
              <goal>add-source</goal>
            </goals>
            <configuration>
              <sources>
                <source>target/generated-sources/antlr4</source>
              </sources>
            </configuration>
          </execution>
        </executions>
      </plugin>

      <plugin>
        <groupId>org.antlr</groupId>
        <artifactId>antlr4-maven-plugin</artifactId>
        <version>4.0</version>
        <configuration>
          <sourceDirectory>src</sourceDirectory>
        </configuration>
        <executions>
          <execution>
            <goals>
              <goal>antlr4</goal>
            </goals>
          </execution>
        </executions>
      </plugin>

    </plugins>
    <pluginManagement>
      <plugins>
        <!--This plugin's configuration is used to store Eclipse m2e settings 
          only. It has no influence on the Maven build itself. -->
        <plugin>
          <groupId>org.eclipse.m2e</groupId>
          <artifactId>lifecycle-mapping</artifactId>
          <version>1.0.0</version>
          <configuration>
            <lifecycleMappingMetadata>
              <pluginExecutions>
                <pluginExecution>
                  <pluginExecutionFilter>
                    <groupId>org.antlr</groupId>
                    <artifactId>antlr4-maven-plugin</artifactId>
                    <versionRange>[4.0,)</versionRange>
                    <goals>
                      <goal>antlr4</goal>
                    </goals>
                  </pluginExecutionFilter>
                  <action>
                    <execute>
                      <runOnIncremental>true</runOnIncremental>
                    </execute>
                  </action>
                </pluginExecution>
              </pluginExecutions>
            </lifecycleMappingMetadata>
          </configuration>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>
</project>

You shouldn't use build-helper-maven-plugin here, cause antlr4-maven-plugin already adds the sources to the compile roots.. Furthermore the life cycle mapping for m2e are not needed cause antlr4-maven-plugin (using newer version 4.5.X ?) already contains appropriate mapping in the plugin itself. So it shouldn't be necessary...