Ignore stderr when parsing javac version from toolchain (#471)

* Ignore stderr when parsing javac version from toolchain
* parse version from stdout, fall back to stderr for older javac


---------

Co-authored-by: Slawomir Jaranowski <s.jaranowski@gmail.com>

Author: jaredstehler

src/it/github-470/invoker.properties

@@ -0,0 +1,20 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+invoker.toolchain.jdk.version = 17
+
+invoker.environmentVariables.JAVA_TOOL_OPTIONS = -XX:ActiveProcessorCount=1

src/it/github-470/pom.xml

@@ -0,0 +1,60 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  Licensed to the Apache Software Foundation (ASF) under one
+  or more contributor license agreements.  See the NOTICE file
+  distributed with this work for additional information
+  regarding copyright ownership.  The ASF licenses this file
+  to you under the Apache License, Version 2.0 (the
+  "License"); you may not use this file except in compliance
+  with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing,
+  software distributed under the License is distributed on an
+  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+  KIND, either express or implied.  See the License for the
+  specific language governing permissions and limitations
+  under the License.
+-->
+<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>org.apache.maven.plugins</groupId>
+  <artifactId>gh-470</artifactId>
+  <name>gh-470</name>
+  <packaging>jar</packaging>
+  <version>1.0-SNAPSHOT</version>
+  <organization>
+    <name>jar plugin it</name>
+  </organization>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-toolchains-plugin</artifactId>
+        <version>3.1.0</version>
+        <executions>
+          <execution>
+            <goals>
+              <goal>toolchain</goal>
+            </goals>
+          </execution>
+        </executions>
+        <configuration>
+          <toolchains>
+            <jdk>
+              <version>17</version>
+            </jdk>
+          </toolchains>
+        </configuration>
+      </plugin>
+
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-jar-plugin</artifactId>
+        <version>@project.version@</version>
+      </plugin>
+    </plugins>
+  </build>
+</project>

src/it/github-470/src/main/java/myproject/HelloWorld.java

@@ -0,0 +1,36 @@
+package myproject;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/**
+ * The classic Hello World App.
+ */
+public class HelloWorld {
+
+  /**
+     * Main method.
+     *
+     * @param args Not used
+     */
+    public static void main( String[] args )
+    {
+        System.out.println( "Hi!" );
+    } 
+}

src/it/github-470/verify.groovy

@@ -0,0 +1,26 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import java.util.jar.JarFile
+
+def mrjar = new JarFile(new File(basedir, 'target/gh-470-1.0-SNAPSHOT.jar'))
+def manifest = mrjar.manifest.mainAttributes
+
+assert manifest.getValue("Build-Jdk-Spec") == "17"
+assert manifest.getValue("Build-Tool-Jdk-Spec") == System.getProperty("java.specification.version")

src/main/java/org/apache/maven/plugins/jar/ToolchainsJdkSpecification.java

@@ -71,22 +71,26 @@ private Path getCanonicalPath(Path path) {
     private String getSpecForPath(Path path) {
         try {
             ProcessBuilder processBuilder = new ProcessBuilder(path.toString(), "-version");
-            processBuilder.redirectErrorStream(true);
+            processBuilder.redirectErrorStream(false);
             Process process = processBuilder.start();
-            String version = readOutput(process.getInputStream()).trim();
+            String stdout = readOutput(process.getInputStream()).trim();
+            String stderr = readOutput(process.getErrorStream()).trim();
             process.waitFor();
 
-            if (version.startsWith("javac ")) {
-                version = version.substring(6);
-                if (version.startsWith("1.")) {
-                    version = version.substring(0, 3);
-                } else {
-                    version = version.substring(0, 2);
-                }
-                return version;
-            } else {
-                logger.warn("Unrecognized output from {}: {}", processBuilder.command(), version);
+            String version = tryParseVersion(stdout);
+            if (version == null) {
+                version = tryParseVersion(stderr);
+            }
+
+            if (version == null) {
+                logger.warn(
+                        "Unrecognized output from {}: stdout: {}, stderr: {}",
+                        processBuilder.command(),
+                        stdout,
+                        stderr);
             }
+
+            return version;
         } catch (IndexOutOfBoundsException | IOException e) {
             logger.warn("Failed to execute: {} - {}", path, e.getMessage());
         } catch (InterruptedException e) {
@@ -96,6 +100,19 @@ private String getSpecForPath(Path path) {
         return null;
     }
 
+    private String tryParseVersion(String version) {
+        if (version.startsWith("javac ")) {
+            version = version.substring(6);
+            if (version.startsWith("1.")) {
+                version = version.substring(0, 3);
+            } else {
+                version = version.substring(0, 2);
+            }
+            return version;
+        }
+        return null;
+    }
+
     private String readOutput(InputStream inputstream) throws IOException {
         BufferedReader br = new BufferedReader(new InputStreamReader(inputstream));