Bazel: add support for DirectoryFileObject

Previously, the scip-java Bazel support only supported SimpleFileObject
in the Java compiler API and it crashed when encountering other types of
file objects like DirectoryFileObject, which are used in some Bazel
builds in the wild. This commit adds support for DirectoryFileObject.

Additionally, this commit adds more detailed documentation on how to
use scip-java with Bazel.

Author: olafurpg

docs/getting-started.md

@@ -328,9 +328,8 @@ projects, with the following caveats:
 
 ### Bazel
 
-Bazel is supported by scip-java but it requires custom configuration to work
-correctly. Note that the `scip-java index` command does not automatically index
-Bazel builds.
+Bazel is supported by scip-java, but it requires custom configuration to work
+correctly. The `scip-java index` command does not automatically index Bazel builds.
 
 The Bazel integration for scip-java is specifically designed to be compatible
 with the Bazel build cache to enable incremental indexing. To achieve this,
@@ -343,6 +342,38 @@ repository contains an example for how to configure everything.
   configured `java_library` and `java_binary` targets to be indexed with
   scip-java.
 
+Once configured, build the codebase with the SemanticDB compiler plugin.
+```sh
+bazel build //... --@scip_java//semanticdb-javac:enabled=true
+```
+
+Next, run the following command to generate the SCIP index (`index.scip`).
+
+```
+bazel run @scip_java//scip-semanticdb:bazel -- --sourceroot $PWD
+
+# (optional) Validate that SemanticDB files were generated.
+# The command below works for the `examples/bazel-example` directory in the sourcegraph/scip-java repository.
+❯ jar tf bazel-bin/src/main/java/example/libexample.jar | grep semanticdb$
+META-INF/semanticdb/src/main/java/example/Example.java.semanticdb
+ ```
+
+Finally, run the following commands to upload the SCIP index to Sourcegraph.
+
+```
+# 1. Install src
+npm install -g @sourcegraph/src # Or yarn global add @sourcegraph/src
+
+# 2. Authenticate with Sourcegraph
+export SRC_ACCESS_TOKEN=sgp_YOUR_ACCESS_TOKEN
+export SRC_ENDPOINT=https://sourcegraph.example.com
+src login # validate the token authenticates correctly
+
+# 3. Upload SCIP index to Sourcegraph
+src code-intel upload # requires index.scip file to exist
+```
+
+
 Don't hesitate to open an issue in the
 [scip-java repository](https://github.com/sourcegraph/scip-java) if you have any
 questions about using scip-java with Bazel builds.

semanticdb-javac/src/main/java/com/sourcegraph/semanticdb_javac/SemanticdbTaskListener.java

@@ -114,15 +114,19 @@ public static Path absolutePathFromUri(SemanticdbJavacOptions options, JavaFileO
     } else if (options.uriScheme == UriScheme.BAZEL) {
       String toString = file.toString();
       // This solution is hacky, and it would be very nice to use a dedicated API instead.
-      // The Bazel Java compiler constructs `SimpleFileObject` with a "user-friendly" name that
-      // points to the original source file and an underlying/actual file path in a temporary
-      // directory. We're constrained by having to use only public APIs of the Java compiler
-      // and `toString()` seems to be the only way to access the user-friendly path.
-      if (toString.startsWith("SimpleFileObject[") && toString.endsWith("]")) {
-        return Paths.get(toString.substring("SimpleFileObject[".length(), toString.length() - 1));
-      } else {
-        throw new IllegalArgumentException("unsupported source file: " + toString);
+      // The Bazel Java compiler constructs `SimpleFileObject/DirectoryFileObject` with a
+      // "user-friendly" name that points to the original source file and an underlying/actual
+      // file path in a temporary directory. We're constrained by having to use only public APIs of
+      // the Java compiler and `toString()` seems to be the only way to access the user-friendly
+      // path.
+      String[] knownBazelToStringPatterns =
+          new String[] {"SimpleFileObject[", "DirectoryFileObject["};
+      for (String pattern : knownBazelToStringPatterns) {
+        if (toString.startsWith(pattern) && toString.endsWith("]")) {
+          return Paths.get(toString.substring(pattern.length(), toString.length() - 1));
+        }
       }
+      throw new IllegalArgumentException("unsupported source file: " + toString);
     } else {
       return Paths.get(uri);
     }