Automatic discovery of JDK Toolchains

api/maven-api-core/src/main/java/org/apache/maven/api/Toolchain.java

@@ -18,6 +18,7 @@
  */
 package org.apache.maven.api;
 
+import java.nio.file.Path;
 import java.util.Map;
 
 import org.apache.maven.api.annotations.Experimental;
@@ -42,7 +43,7 @@ public interface Toolchain {
      * @param toolName the tool platform independent tool name
      * @return file representing the tool executable, or null if the tool cannot be found
      */
-    String findTool(String toolName);
+    Path findTool(String toolName);
 
     /**
      * Let the toolchain decide if it matches requirements defined

api/maven-api-core/src/main/java/org/apache/maven/api/services/ToolchainManager.java

@@ -36,6 +36,11 @@
 @Experimental
 public interface ToolchainManager extends Service {
 
+    /**
+     * The type identifying JDK toolchains
+     */
+    String TYPE_JDK = "jdk";
+
     /**
      *
      * @param session

api/maven-api-toolchain/src/main/mdo/toolchains.mdo

@@ -61,6 +61,7 @@
                 <![CDATA[
         public static final String USER_LEVEL = "user-level";
         public static final String GLOBAL_LEVEL = "global-level";
+        public static final String DISCOVERED_LEVEL = "discovered-level";
 
         private String sourceLevel = USER_LEVEL;
         private boolean sourceLevelSet = false;
@@ -71,9 +72,10 @@
             {
                 throw new IllegalStateException( "Cannot reset sourceLevel attribute; it is already set to: " + sourceLevel );
             }
-            else if ( !( USER_LEVEL.equals( sourceLevel ) || GLOBAL_LEVEL.equals( sourceLevel ) ) )
+            else if ( !( USER_LEVEL.equals( sourceLevel ) || GLOBAL_LEVEL.equals( sourceLevel )
+                        || DISCOVERED_LEVEL.equals( sourceLevel ) ) )
             {
-                throw new IllegalArgumentException( "sourceLevel must be one of: {" + USER_LEVEL + "," + GLOBAL_LEVEL + "}" );
+                throw new IllegalArgumentException( "sourceLevel must be one of: {" + USER_LEVEL + "," + GLOBAL_LEVEL + "," + DISCOVERED_LEVEL + "}" );
             }
             else
             {

maven-core/src/main/java/org/apache/maven/execution/DefaultMavenExecutionRequestPopulator.java

@@ -23,11 +23,9 @@
 import javax.inject.Singleton;
 
 import java.io.File;
-import java.util.ArrayList;
-import java.util.HashMap;
 import java.util.List;
-import java.util.Map;
 import java.util.Set;
+import java.util.stream.Collectors;
 
 import org.apache.maven.artifact.InvalidRepositoryException;
 import org.apache.maven.artifact.repository.ArtifactRepository;
@@ -60,17 +58,8 @@ public DefaultMavenExecutionRequestPopulator(MavenRepositorySystem repositorySys
     public MavenExecutionRequest populateFromToolchains(MavenExecutionRequest request, PersistedToolchains toolchains)
             throws MavenExecutionRequestPopulationException {
         if (toolchains != null) {
-            Map<String, List<ToolchainModel>> groupedToolchains = new HashMap<>(2);
-
-            for (ToolchainModel model : toolchains.getToolchains()) {
-                if (!groupedToolchains.containsKey(model.getType())) {
-                    groupedToolchains.put(model.getType(), new ArrayList<>());
-                }
-
-                groupedToolchains.get(model.getType()).add(model);
-            }
-
-            request.setToolchains(groupedToolchains);
+            request.setToolchains(
+                    toolchains.getToolchains().stream().collect(Collectors.groupingBy(ToolchainModel::getType)));
         }
         return request;
     }

maven-core/src/main/java/org/apache/maven/internal/impl/DefaultToolchainManager.java

@@ -22,11 +22,14 @@
 import javax.inject.Named;
 import javax.inject.Singleton;
 
+import java.nio.file.Path;
+import java.nio.file.Paths;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 
+import org.apache.maven.api.JavaToolchain;
 import org.apache.maven.api.Session;
 import org.apache.maven.api.Toolchain;
 import org.apache.maven.api.services.ToolchainManager;
@@ -35,6 +38,7 @@
 import org.apache.maven.toolchain.DefaultToolchainManagerPrivate;
 import org.apache.maven.toolchain.MisconfiguredToolchainException;
 import org.apache.maven.toolchain.ToolchainPrivate;
+import org.apache.maven.toolchain.java.JavaToolchainImpl;
 
 @Named
 @Singleton
@@ -70,7 +74,7 @@ public List<Toolchain> getToolchainsForType(Session session, String type) throws
             ToolchainPrivate[] toolchains = toolchainManagerPrivate.getToolchainsForType(type, s);
             return new MappedList<>(Arrays.asList(toolchains), this::toToolchain);
         } catch (MisconfiguredToolchainException e) {
-            throw new ToolchainManagerException("Unable to get toochains for type " + type, e);
+            throw new ToolchainManagerException("Unable to get toolchains for type " + type, e);
         }
     }
 
@@ -83,11 +87,13 @@ public void storeToolchainToBuildContext(Session session, Toolchain toolchain) t
     }
 
     private Toolchain toToolchain(org.apache.maven.toolchain.Toolchain toolchain) {
-        return new ToolchainWrapper(toolchain);
+        return toolchain instanceof JavaToolchainImpl
+                ? new JavaToolchainWrapper((JavaToolchainImpl) toolchain)
+                : new ToolchainWrapper(toolchain);
     }
 
     private static class ToolchainWrapper implements Toolchain {
-        private final org.apache.maven.toolchain.Toolchain toolchain;
+        protected final org.apache.maven.toolchain.Toolchain toolchain;
 
         ToolchainWrapper(org.apache.maven.toolchain.Toolchain toolchain) {
             this.toolchain = toolchain;
@@ -99,13 +105,24 @@ public String getType() {
         }
 
         @Override
-        public String findTool(String toolName) {
-            return toolchain.findTool(toolName);
+        public Path findTool(String toolName) {
+            return Paths.get(toolchain.findTool(toolName));
         }
 
         @Override
         public boolean matchesRequirements(Map<String, String> requirements) {
             return ((ToolchainPrivate) toolchain).matchesRequirements(requirements);
         }
     }
+
+    private static class JavaToolchainWrapper extends ToolchainWrapper implements JavaToolchain {
+        JavaToolchainWrapper(org.apache.maven.toolchain.java.JavaToolchainImpl toolchain) {
+            super(toolchain);
+        }
+
+        @Override
+        public String getJavaHome() {
+            return ((org.apache.maven.toolchain.java.JavaToolchainImpl) toolchain).getJavaHome();
+        }
+    }
 }

maven-core/src/main/java/org/apache/maven/toolchain/DefaultToolchain.java

@@ -83,18 +83,20 @@ public final void addProvideToken(String type, RequirementMatcher matcher) {
 
     @Override
     public boolean matchesRequirements(Map<String, String> requirements) {
-        for (Map.Entry<String, String> requirement : requirements.entrySet()) {
-            String key = requirement.getKey();
-
-            RequirementMatcher matcher = provides.get(key);
-
-            if (matcher == null) {
-                getLog().debug("Toolchain " + this + " is missing required property: " + key);
-                return false;
-            }
-            if (!matcher.matches(requirement.getValue())) {
-                getLog().debug("Toolchain " + this + " doesn't match required property: " + key);
-                return false;
+        if (requirements != null) {
+            for (Map.Entry<String, String> requirement : requirements.entrySet()) {
+                String key = requirement.getKey();
+
+                RequirementMatcher matcher = provides.get(key);
+
+                if (matcher == null) {
+                    getLog().debug("Toolchain " + this + " is missing required property: " + key);
+                    return false;
+                }
+                if (!matcher.matches(requirement.getValue())) {
+                    getLog().debug("Toolchain " + this + " doesn't match required property: " + key);
+                    return false;
+                }
             }
         }
         return true;

maven-embedder/src/main/java/org/apache/maven/cli/MavenCli.java

@@ -91,6 +91,7 @@
 import org.apache.maven.shared.utils.logging.MessageUtils;
 import org.apache.maven.toolchain.building.DefaultToolchainsBuildingRequest;
 import org.apache.maven.toolchain.building.ToolchainsBuilder;
+import org.apache.maven.toolchain.building.ToolchainsBuildingRequest;
 import org.apache.maven.toolchain.building.ToolchainsBuildingResult;
 import org.codehaus.plexus.ContainerConfiguration;
 import org.codehaus.plexus.DefaultContainerConfiguration;
@@ -133,6 +134,8 @@ public class MavenCli {
 
     public static final String MULTIMODULE_PROJECT_DIRECTORY = "maven.multiModuleProjectDirectory";
 
+    public static final String TOOLCHAINS_DISCOVERY_MODE = "maven.toolchainsDiscoveryMode";
+
     public static final String USER_HOME = System.getProperty("user.home");
 
     public static final File USER_MAVEN_CONFIGURATION_HOME = new File(USER_HOME, ".m2");
@@ -1198,6 +1201,14 @@ void toolchains(CliRequest cliRequest) throws Exception {
         if (userToolchainsFile.isFile()) {
             toolchainsRequest.setUserToolchainsSource(new FileSource(userToolchainsFile));
         }
+        String discoveryModeStr = cliRequest.getUserProperties().getProperty(TOOLCHAINS_DISCOVERY_MODE);
+        if (discoveryModeStr == null) {
+            discoveryModeStr = cliRequest.getSystemProperties().getProperty(TOOLCHAINS_DISCOVERY_MODE);
+        }
+        if (discoveryModeStr == null) {
+            discoveryModeStr = ToolchainsBuildingRequest.DiscoveryMode.IfNoneConfigured.toString();
+        }
+        toolchainsRequest.setDiscoveryMode(ToolchainsBuildingRequest.DiscoveryMode.valueOf(discoveryModeStr));
 
         eventSpyDispatcher.onEvent(toolchainsRequest);
 

maven-toolchain-builder/pom.xml

@@ -51,11 +51,20 @@ under the License.
       <groupId>org.codehaus.plexus</groupId>
       <artifactId>plexus-interpolation</artifactId>
     </dependency>
+    <dependency>
+      <groupId>org.slf4j</groupId>
+      <artifactId>slf4j-api</artifactId>
+    </dependency>
     <dependency>
       <groupId>org.mockito</groupId>
       <artifactId>mockito-core</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.slf4j</groupId>
+      <artifactId>slf4j-simple</artifactId>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 
   <build>

maven-toolchain-builder/src/main/java/org/apache/maven/toolchain/building/DefaultToolchainsBuilder.java

@@ -28,11 +28,13 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 
 import org.apache.maven.building.Problem;
 import org.apache.maven.building.ProblemCollector;
 import org.apache.maven.building.ProblemCollectorFactory;
 import org.apache.maven.building.Source;
+import org.apache.maven.toolchain.discovery.ToolchainDiscoverer;
 import org.apache.maven.toolchain.io.ToolchainsParseException;
 import org.apache.maven.toolchain.io.ToolchainsReader;
 import org.apache.maven.toolchain.io.ToolchainsWriter;
@@ -54,23 +56,37 @@ public class DefaultToolchainsBuilder implements ToolchainsBuilder {
     private final MavenToolchainMerger toolchainsMerger = new MavenToolchainMerger();
     private final ToolchainsWriter toolchainsWriter;
     private final ToolchainsReader toolchainsReader;
+    private final List<ToolchainDiscoverer> toolchainDiscoverers;
 
     @Inject
-    public DefaultToolchainsBuilder(ToolchainsWriter toolchainsWriter, ToolchainsReader toolchainsReader) {
-        this.toolchainsWriter = toolchainsWriter;
-        this.toolchainsReader = toolchainsReader;
+    public DefaultToolchainsBuilder(
+            ToolchainsWriter toolchainsWriter,
+            ToolchainsReader toolchainsReader,
+            List<ToolchainDiscoverer> toolchainDiscoverers) {
+        this.toolchainsWriter = Objects.requireNonNull(toolchainsWriter);
+        this.toolchainsReader = Objects.requireNonNull(toolchainsReader);
+        this.toolchainDiscoverers = Objects.requireNonNull(toolchainDiscoverers);
     }
 
     @Override
     public ToolchainsBuildingResult build(ToolchainsBuildingRequest request) throws ToolchainsBuildingException {
         ProblemCollector problems = ProblemCollectorFactory.newInstance(null);
 
-        PersistedToolchains globalToolchains = readToolchains(request.getGlobalToolchainsSource(), request, problems);
-
         PersistedToolchains userToolchains = readToolchains(request.getUserToolchainsSource(), request, problems);
 
+        PersistedToolchains globalToolchains = readToolchains(request.getGlobalToolchainsSource(), request, problems);
         toolchainsMerger.merge(userToolchains, globalToolchains, TrackableBase.GLOBAL_LEVEL);
 
+        if (request.getDiscoveryMode() == ToolchainsBuildingRequest.DiscoveryMode.Always
+                || request.getDiscoveryMode() == ToolchainsBuildingRequest.DiscoveryMode.IfNoneConfigured
+                        && userToolchains.getToolchains().isEmpty()) {
+
+            for (ToolchainDiscoverer discoverer : toolchainDiscoverers) {
+                PersistedToolchains toolchains = discoverer.discoverToolchains();
+                toolchainsMerger.merge(userToolchains, toolchains, TrackableBase.DISCOVERED_LEVEL);
+            }
+        }
+
         problems.setSource("");
 
         userToolchains = interpolate(userToolchains, problems);

maven-toolchain-builder/src/main/java/org/apache/maven/toolchain/building/DefaultToolchainsBuildingRequest.java

@@ -31,6 +31,8 @@ public class DefaultToolchainsBuildingRequest implements ToolchainsBuildingReque
 
     private Source userToolchainsSource;
 
+    private DiscoveryMode discoveryMode = DiscoveryMode.IfNoneConfigured;
+
     @Override
     public Source getGlobalToolchainsSource() {
         return globalToolchainsSource;
@@ -52,4 +54,15 @@ public ToolchainsBuildingRequest setUserToolchainsSource(Source userToolchainsSo
         this.userToolchainsSource = userToolchainsSource;
         return this;
     }
+
+    @Override
+    public DiscoveryMode getDiscoveryMode() {
+        return discoveryMode;
+    }
+
+    @Override
+    public ToolchainsBuildingRequest setDiscoveryMode(DiscoveryMode discoveryMode) {
+        this.discoveryMode = discoveryMode;
+        return this;
+    }
 }

maven-toolchain-builder/src/main/java/org/apache/maven/toolchain/building/ToolchainsBuildingRequest.java

@@ -28,6 +28,16 @@
  */
 public interface ToolchainsBuildingRequest {
 
+    /** Toolchains discovery mode */
+    enum DiscoveryMode {
+        /** Always add discovered toolchains */
+        Always,
+        /** Discover toolchains if none are configured */
+        IfNoneConfigured,
+        /** Never discover toolchains */
+        Never
+    }
+
     /**
      * Gets the global toolchains source.
      *
@@ -59,4 +69,8 @@ public interface ToolchainsBuildingRequest {
      * @return This request, never {@code null}.
      */
     ToolchainsBuildingRequest setUserToolchainsSource(Source userToolchainsSource);
+
+    DiscoveryMode getDiscoveryMode();
+
+    ToolchainsBuildingRequest setDiscoveryMode(DiscoveryMode discoveryMode);
 }