Be more graceful about cross-repo navigation error (#660)

Author: keynmol

Diff for: docs/manual-configuration.md

@@ -163,6 +163,7 @@ one of the following files in the SemanticDB _targetroot_ directory (the path in
 
 - `javacopts.txt`: line-separated list of Java compiler options that got passed
   to the compiler. For example,
+
   ```sh
   $ cat $TARGETROOT/javacopts.txt
   -Xlint
@@ -172,22 +173,25 @@ one of the following files in the SemanticDB _targetroot_ directory (the path in
   /path/to/classes/directory
   /path/to/com/example/Main.java
   ```
+
   The `javacopts.txt` file format can only be used if the jars on the dependency
   classpath have sibling `.pom` files. In some build tools like Gradle, the POM
   files are not siblings to the jars on the classpath so the `javacopts.txt`
   format cannot be used.
+
 - `dependencies.txt`: a tab-separated values file where the columns are: group
   ID, artifact ID, version and jar path. For example,
+
   ```sh
   $ cat $TARGETROOT/dependencies.txt
   junit junit 4.13.2  /path/to/junit.jar
   org.hamcrest hamcrest-core 1.3  /path/to/hamcrest-core.jar
   ```
+
   The `dependencies.txt` format is used by scip-java to map symbols such as
-  `org.junit.Assert` to Maven co-ordinates like `junit:junit:4.13.2`. As long as
+  `org.junit.Assert` to Maven coordinates like `junit:junit:4.13.2`. As long as
   your Sourcegraph instance has another repository that defines that symbol, the
-  cross-repository navigation should succeed. Only jar files are supported at
-  the moment, classes directories are ignored.
+  cross-repository navigation should succeed. 
 
 Cross-repository navigation is a feature that allows "goto definition" and "find
 references" to show results from multiple repositories.

Diff for: semanticdb-gradle-plugin/src/main/scala/SemanticdbGradlePlugin.scala

@@ -5,7 +5,7 @@ import java.nio.file.Paths
 import java.{util => ju}
 
 import scala.jdk.CollectionConverters._
-import scala.util.control.NonFatal
+import scala.util._
 
 import com.sourcegraph.scip_java.BuildInfo
 import org.gradle.api.DefaultTask
@@ -416,42 +416,56 @@ class WriteDependencies extends DefaultTask {
     // List the project itself as a dependency so that we can assign project name/version to symbols that are defined in this project.
     // The code below is roughly equivalent to the following with Groovy:
     //   deps += "$publication.groupId $publication.artifactId $publication.version $sourceSets.main.output.classesDirectory"
-    try {
-      for {
-        classesDirectory <- project
-          .getExtensions()
-          .getByType(classOf[SourceSetContainer])
-          .getByName("main")
-          .getOutput()
-          .getClassesDirs()
-          .getFiles()
-          .asScala
-          .toList
-          .map(_.getAbsolutePath())
-          .sorted
-          .take(1)
-        publication <-
+
+    Try(
+      project
+        .getExtensions()
+        .findByType(classOf[PublishingExtension])
+        .getPublications()
+        .withType(classOf[MavenPublication])
+        .asScala
+    ) match {
+      case Failure(exception) =>
+        System
+          .err
+          .println(
+            s"""
+               |Failed to extract Maven publication from the project `${project
+              .getName()}`. 
+               |This will not prevent a SCIP index from being created, but the symbols 
+               |extracted from this project won't be available for cross-repository navigation,
+               |as this project doesn't define any Maven coordinates by which it can be referred back to.
+               |See here for more details: https://sourcegraph.github.io/scip-java/docs/manual-configuration.html#step-5-optional-enable-cross-repository-navigation
+               |Here's the raw error message:
+               |  "${exception.getMessage()}"
+               |Continuing without cross-repository support.
+          """.stripMargin.trim()
+          )
+
+      case Success(publications) =>
+        publications.foreach { publication =>
           project
             .getExtensions()
-            .findByType(classOf[PublishingExtension])
-            .getPublications()
-            .withType(classOf[MavenPublication])
+            .getByType(classOf[SourceSetContainer])
+            .getByName("main")
+            .getOutput()
+            .getClassesDirs()
+            .getFiles()
             .asScala
-      } {
-        deps +=
-          List(
-            publication.getGroupId(),
-            publication.getArtifactId(),
-            publication.getVersion(),
-            classesDirectory
-          ).mkString("\t")
-      }
-    } catch {
-      case NonFatal(ex) =>
-        println(
-          s"Failed to extract publication from project ${project.getName()}"
-        )
-        ex.printStackTrace()
+            .toList
+            .map(_.getAbsolutePath())
+            .sorted
+            .take(1)
+            .foreach { classesDirectory =>
+              deps +=
+                List(
+                  publication.getGroupId(),
+                  publication.getArtifactId(),
+                  publication.getVersion(),
+                  classesDirectory
+                ).mkString("\t")
+            }
+        }
     }
 
     project