Handle removed dependency

antlr4-maven-plugin/src/main/java/org/antlr/mojo/antlr4/GrammarDependencies.java

@@ -150,7 +150,7 @@ class GrammarDependencies {
             Collection<String> usages = e.getValue().getValue();
 
             if (usages.contains(grammarPath)) {
-                if (!Arrays.equals(MojoUtils.checksum(depGrammarFile), checksum)) {
+                if (!depGrammarFile.exists() || !Arrays.equals(MojoUtils.checksum(depGrammarFile), checksum)) {
                     log.debug("  " + grammarPath + ": dependency " +
                         depGrammarFile.getName() + " changed");
 

antlr4-maven-plugin/src/test/java/org/antlr/mojo/antlr4/Antlr4MojoTest.java

@@ -5,6 +5,7 @@ import io.takari.maven.testing.TestResources;
 
 import org.apache.maven.execution.MavenSession;
 import org.apache.maven.plugin.MojoExecution;
+import org.apache.maven.plugin.MojoExecutionException;
 import org.apache.maven.project.MavenProject;
 
 import org.codehaus.plexus.util.xml.Xpp3Dom;
@@ -13,6 +14,7 @@ import static org.junit.Assert.*;
 
 import org.junit.Rule;
 import org.junit.Test;
+import org.junit.rules.ExpectedException;
 
 import java.io.ByteArrayOutputStream;
 import java.io.File;
@@ -31,6 +33,9 @@ import java.util.regex.Pattern;
 
 
 public class Antlr4MojoTest {
+    @Rule
+    public ExpectedException thrown = ExpectedException.none();
+
     @Rule
     public final TestResources resources = new TestResources();
 
@@ -275,6 +280,42 @@ public class Antlr4MojoTest {
         }
     }
 
+    @Test
+    public void processWhenDependencyRemoved() throws Exception {
+        Map.Entry<ByteArrayOutputStream, PrintStream> stdout = redirect();
+        ByteArrayOutputStream output = stdout.getKey();
+
+        try {
+            File baseDir = resources.getBasedir("dependencyRemoved");
+            File antlrDir = new File(baseDir, "src/main/antlr4");
+
+            File baseGrammar = new File(antlrDir, "imports/HelloBase.g4");
+
+            MavenProject project = maven.readMavenProject(baseDir);
+            MavenSession session = maven.newMavenSession(project);
+            MojoExecution exec = maven.newMojoExecution("antlr4");
+
+            maven.executeMojo(session, project, exec);
+
+            String t = text(baseGrammar);
+
+            try {
+                // if the base grammar no longer exists, processing must be performed
+                baseGrammar.delete();
+
+                thrown.expect(MojoExecutionException.class);
+                thrown.expectMessage("ANTLR 4 caught 1 build errors.");
+
+                maven.executeMojo(session, project, exec);
+            } finally {
+                write(baseGrammar, t);
+            }
+        } finally {
+            System.out.flush();
+            System.setOut(stdout.getValue());
+        }
+    }
+
     private List<String> processAndReset(ByteArrayOutputStream output) {
         Pattern pattern = Pattern.compile("Processing grammar: (.+)");
         Matcher matcher = pattern.matcher(output.toString());

antlr4-maven-plugin/src/test/projects/dependencyRemoved/pom.xml

@@ -0,0 +1,27 @@
+<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>deps.removed</groupId>
+  <artifactId>depRemoved</artifactId>
+  <version>1.0-SNAPSHOT</version>
+  <packaging>jar</packaging>
+  <name>Test processing after dependency removed</name>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>4.11</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+  <build>
+    <plugins>
+      <plugin>
+          <artifactId>antlr4-maven-plugin</artifactId>
+        <configuration>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>

antlr4-maven-plugin/src/test/projects/dependencyRemoved/src/main/antlr4/imports/HelloBase.g4

@@ -0,0 +1,16 @@
+lexer grammar TestBaseLexer;
+
+tokens  { Name }
+
+// Default "mode": Everything OUTSIDE of a tag
+Comment     :  '<!--' .*? '-->' ;
+CDSect      :  '<![CDATA[' .*? ']]>' ;
+
+fragment
+Whitespace  :  ' ' | '\n' | '\t' | '\r' ;
+
+fragment
+Hexdigit    :  [a-fA-F0-9] ;
+
+fragment
+Digit       :  [0-9] ;

antlr4-maven-plugin/src/test/projects/dependencyRemoved/src/main/antlr4/test/Hello.g4

@@ -0,0 +1,7 @@
+grammar Hello;
+
+import HelloBase;
+
+r  : 'hello' ID ;
+ID : [a-z]+ ;
+WS : [ \r\t\n]+ -> skip ;