Maven compile replies 'No sources to compile' for scala project

Question

I have the following (single) scala class

[      14253 Oct 30  8:44]  ./pom.xml
[       9083 Oct 30  8:30]  ./scaladem.iml
[        102 Oct 29 19:21]  ./src
[        102 Oct 29 19:21]  ./src/main
[        102 Oct 29 19:21]  ./src/main/scala
[        102 Oct 29 19:21]  ./src/main/scala/com
[        102 Oct 29 19:21]  ./src/main/scala/com/blazedb
[        102 Oct 30  8:30]  ./src/main/scala/com/blazedb/scalademo
[       4646 Oct 30  8:30]  ./src/main/scala/com/blazedb/scalademo/SDemo.scala

Here is the applicable section of the pom

<plugin>
    <groupId>net.alchim31.maven</groupId>
    <artifactId>scala-maven-plugin</artifactId>
    <version>3.1.6</version>
        <configuration>
          <recompileMode>incremental</recompileMode>
          <javacArgs>
            <javacArg>-Xlint:unchecked</javacArg>
            <javacArg>-Xlint:deprecation</javacArg>
          </javacArgs>
        </configuration>
    <executions>
        <execution>
            <id>scala-compile-first</id>
            <phase>process-resources</phase>
            <goals>
                <goal>add-source</goal>
                <goal>compile</goal>
            </goals>
        </execution>
        <execution>
            <id>scala-test-compile</id>
            <phase>process-test-resources</phase>
            <goals>
                <goal>testCompile</goal>
            </goals>
        </execution>
    </executions>
</plugin>

When we run

mvn compile

We get (notice the 'no sources' ..)

[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building SDemo 1.0
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-compiler-plugin:2.3.2:compile (default-compile) @ scalademo ---
[INFO] No sources to compile
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------

Update: when running the following command

$mvn scala:compile -DdisplayCmd=true

The compilation succeeds.

From suggestion of @badtrumpet I have added the explicit as shown below

<sourceDirectory>src/main/scala</sourceDirectory>

And this works even by mvn compile. But that would be an issue for mixed java/scala projects.

Answer 1

Here's an example (simple) pom.xml which I use as a bit of a boilerplate for Scala compilation and build using Maven:

<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/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>badtrumpet</groupId>
<artifactId>blog</artifactId>
<version>1.0-SNAPSHOT</version>
<inceptionYear>2013</inceptionYear>
<packaging>jar</packaging>
<properties>
    <scala.version>2.10.2</scala.version>
    <commons.codec.version>1.8</commons.codec.version>
    <grizzled.version>1.0.1</grizzled.version>
    <slf4j-log4j12.version>1.7.5</slf4j-log4j12.version>
</properties>

<repositories>
    <repository>
        <id>Sonatype repository</id>
        <name>Sonatype's Maven repository</name>
        <url>http://oss.sonatype.org/content/groups/public</url>
    </repository>
    <repository>
        <id>scala-tools.org</id>
        <name>Scala-Tools Maven2 Repository</name>
        <url>http://scala-tools.org/repo-releases</url>
    </repository>
    <repository>
        <id>milestone.repo.springsource.org</id>
        <name>repo.springsource.org-milestone</name>
        <url>https://repo.springsource.org/libs-milestone</url>
    </repository>
</repositories>

<pluginRepositories>
    <pluginRepository>
        <id>scala-tools.org</id>
        <name>Scala-Tools Maven2 Repository</name>
        <url>http://scala-tools.org/repo-releases</url>
    </pluginRepository>
</pluginRepositories>

<dependencies>
    <dependency>
        <groupId>org.scala-lang</groupId>
        <artifactId>scala-library</artifactId>
        <version>${scala.version}</version>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>3.8.1</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>commons-codec</groupId>
        <artifactId>commons-codec</artifactId>
        <version>${commons.codec.version}</version>
    </dependency>
    <dependency>
        <groupId>org.clapper</groupId>
        <artifactId>grizzled-slf4j_2.10</artifactId>
        <version>${grizzled.version}</version>
    </dependency>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-log4j12</artifactId>
        <version>${slf4j-log4j12.version}</version>
    </dependency>
</dependencies>

<build>
    <sourceDirectory>src/main/scala</sourceDirectory>
    <testSourceDirectory>src/test/scala</testSourceDirectory>
    <plugins>
        <plugin>
            <groupId>org.scala-tools</groupId>
            <artifactId>maven-scala-plugin</artifactId>
            <executions>
                <execution>
                    <goals>
                        <goal>compile</goal>
                        <goal>testCompile</goal>
                    </goals>
                </execution>
            </executions>
            <configuration>
                <scalaVersion>${scala.version}</scalaVersion>
            </configuration>
        </plugin>
    </plugins>
</build>
<reporting>
    <plugins>
        <plugin>
            <groupId>org.scala-tools</groupId>
            <artifactId>maven-scala-plugin</artifactId>
            <configuration>
                <scalaVersion>${scala.version}</scalaVersion>
            </configuration>
        </plugin>
    </plugins>
</reporting>

Answer 2

To add extra source folders to your maven project you can use the build-helper-maven-plugin.

So to add src/main/scala as a source folder you would configure the following in your pom:

<plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>build-helper-maven-plugin</artifactId>
    <version>1.8</version>
    <executions>
        <execution>
            <id>add-source</id>
            <phase>generate-sources</phase>
            <goals>
                <goal>add-source</goal>
            </goals>
            <configuration>
                <sources>
                    <source>${basedir}/src/main/scala</source>
                </sources>
            </configuration>
        </execution>
    </executions>
</plugin>

For a standard maven project this would mean that now both src/main/java and src/main/scala are considered source directories by maven.