Make it possible to use the detected properties before reading pom.xml (

#59)

Motivation:

It's currently not possible to use the detected properties to activate profiles.

Modifications:

PR implements afterSessionStart in addition to afterProjectsRead. This makes it possible to use the detected properties to activate profiles.

```
...
<profile>
  <id>Ubuntu</id>
  <activation>
    <property>
      <name>os.detected.release</name>
      <value>ubuntu</value>
    </property>
  </activation>
...
  <!-- Now you can do Ubuntu-specific work -->
...
</profile>
```

Result:

`os-maven-plugin` is now capable of injecting the detected properties even before reading `pom.xml`.

pom.xml

@@ -56,6 +56,9 @@
   <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <maven.javadoc.failOnError>false</maven.javadoc.failOnError>
+
+    <!-- Using the same java.home for IT -->
+    <invoker.javaHome>${java.home}</invoker.javaHome>
   </properties>
 
   <dependencies>
@@ -190,6 +193,36 @@
           </archive>
         </configuration>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-invoker-plugin</artifactId>
+        <version>3.2.2</version>
+        <configuration>
+          <debug>true</debug>
+          <cloneProjectsTo>${project.build.directory}/it</cloneProjectsTo>
+          <pomIncludes>
+            <pomInclude>*/pom.xml</pomInclude>
+          </pomIncludes>
+          <postBuildHookScript>verify</postBuildHookScript>
+<!--          <settingsFile>src/it/settings.xml</settingsFile>-->
+          <streamLogs>true</streamLogs>
+          <goals>
+            <goal>clean</goal>
+            <goal>package</goal>
+          </goals>
+        </configuration>
+        <executions>
+          <execution>
+            <id>integration-test</id>
+            <phase>integration-test</phase>
+            <goals>
+              <goal>install</goal>
+              <goal>integration-test</goal>
+              <goal>verify</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
     </plugins>
   </build>
 </project>

src/it/test-activate-profile/.mvn/extensions.xml

@@ -0,0 +1,8 @@
+<extensions xmlns="http://maven.apache.org/EXTENSIONS/1.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+            xsi:schemaLocation="http://maven.apache.org/EXTENSIONS/1.0.0 http://maven.apache.org/xsd/core-extensions-1.0.0.xsd">
+    <extension>
+        <groupId>@project.groupId@</groupId>
+        <artifactId>@project.artifactId@</artifactId>
+        <version>@project.version@</version>
+    </extension>
+</extensions>

src/it/test-activate-profile/pom.xml

@@ -0,0 +1,83 @@
+<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>kr.motd.maven.it</groupId>
+    <artifactId>test-activate-profile</artifactId>
+    <version>1.0-SNAPSHOT</version>
+
+    <description>
+        An integration test that checks whether the profile can be activated by detected properties. If the
+        project.properties file contains the "active.profile" property and it has the expected value, the test is
+        considered successful.
+    </description>
+
+    <prerequisites>
+        <!-- (since Maven 3.3.1) configure your extension in .mvn/extensions.xml -->
+        <!-- https://maven.apache.org/examples/maven-3-lifecycle-extensions.html -->
+        <maven>3.3.1</maven>
+    </prerequisites>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.codehaus.mojo</groupId>
+                <artifactId>properties-maven-plugin</artifactId>
+                <version>1.0.0</version>
+                <executions>
+                    <execution>
+                        <id>write-project-properties</id>
+                        <phase>validate</phase>
+                        <goals>
+                            <goal>write-project-properties</goal>
+                        </goals>
+                        <configuration>
+                            <outputFile>${project.build.directory}/project.properties</outputFile>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+
+    <profiles>
+        <profile>
+            <id>detected-windows</id>
+            <activation>
+                <property>
+                    <name>os.detected.name</name>
+                    <value>windows</value>
+                </property>
+            </activation>
+            <properties>
+                <active.profile>detected-windows</active.profile>
+            </properties>
+        </profile>
+
+        <profile>
+            <id>detected-ubuntu</id>
+            <activation>
+                <property>
+                    <name>os.detected.release</name>
+                    <value>ubuntu</value>
+                </property>
+            </activation>
+            <properties>
+                <active.profile>detected-ubuntu</active.profile>
+            </properties>
+        </profile>
+
+        <profile>
+            <id>detected-osx</id>
+            <activation>
+                <property>
+                    <name>os.detected.name</name>
+                    <value>osx</value>
+                </property>
+            </activation>
+            <properties>
+                <active.profile>detected-osx</active.profile>
+            </properties>
+        </profile>
+    </profiles>
+</project>

src/it/test-activate-profile/verify.groovy

@@ -0,0 +1,24 @@
+import org.apache.commons.io.FileUtils
+import org.apache.commons.lang3.SystemUtils
+
+def projectPropertiesFile = new File(basedir, "target/project.properties")
+
+assert projectPropertiesFile.exists() : "project.properties not found"
+assert projectPropertiesFile.canRead() : "project.properties cannot be read"
+
+Properties projectProperties = new Properties()
+projectPropertiesFile.withInputStream {
+    projectProperties.load(it)
+}
+
+if (SystemUtils.IS_OS_WINDOWS) {
+    assert projectProperties."active.profile" == 'detected-windows'
+} else if (SystemUtils.IS_OS_LINUX) {
+    String osReleaseContent = FileUtils.readFileToString(new File("/etc/os-release"))
+
+    if (osReleaseContent.contains("ID=ubuntu")) {
+        assert projectProperties."active.profile" == 'detected-ubuntu'
+    }
+} else if (SystemUtils.IS_OS_MAC) {
+    assert projectProperties."active.profile" == 'detected-osx'
+}

src/main/java/kr/motd/maven/os/DetectExtension.java

@@ -90,8 +90,17 @@ protected void logProperty(String name, String value) {
         };
     }
 
+    @Override
+    public void afterSessionStart(MavenSession session) throws MavenExecutionException {
+        injectProperties(session);
+    }
+
     @Override
     public void afterProjectsRead(MavenSession session) throws MavenExecutionException {
+        injectProperties(session);
+    }
+
+    private void injectProperties(MavenSession session) throws MavenExecutionException {
         // Detect the OS and CPU architecture.
         final Properties sessionProps = new Properties();
         sessionProps.putAll(session.getSystemProperties());
@@ -118,8 +127,10 @@ public void afterProjectsRead(MavenSession session) throws MavenExecutionExcepti
         injectSession(session, dict);
 
         /// Perform the interpolation for the properties of all dependencies.
-        for (MavenProject p: session.getProjects()) {
-            interpolate(dict, p);
+        if (session.getProjects() != null) {
+            for (MavenProject p : session.getProjects()) {
+                interpolate(dict, p);
+            }
         }
     }
 
@@ -131,7 +142,11 @@ private static List<String> getClassifierWithLikes(MavenSession session) {
         // Check to see if the project defined the
         final Properties props = new Properties();
         props.putAll(session.getUserProperties());
-        props.putAll(session.getCurrentProject().getProperties());
+
+        if (session.getCurrentProject() != null) {
+            props.putAll(session.getCurrentProject().getProperties());
+        }
+
         return DetectMojo.getClassifierWithLikes(
             props.getProperty(DetectMojo.CLASSIFIER_WITH_LIKES_PROPERTY));
     }