Example with a java library that doesn't contain any sources

Merge-request: BAZEL-MR-1033
Merged-by: Tomasz Pasternak <Tomasz.Pasternak@jetbrains.com>

example/animals/BUILD

@@ -0,0 +1,18 @@
+load(":generator.bzl", "animals_library_source")
+
+java_library(
+    name = "consumer",
+    srcs = glob(["src/java/org/jetbrains/bsp/example/animals/consumer/LibraryConsumer.java"]),
+    deps = [":animals_lib"],
+)
+
+# This is a jvm library that doesn't have file sources. We must ensure we import it as a library, not as sources
+# even if it is directly referred in projectview's targets section.
+java_library(
+    name = "animals_lib",
+    srcs = [":animals"],
+)
+
+animals_library_source(
+    name = "animals",
+)

example/animals/generator.bzl

@@ -0,0 +1,24 @@
+def _animals_library_source_impl(ctx):
+    tc = ctx.toolchains["@bazel_tools//tools/jdk:toolchain_type"]
+    cat_java = ctx.actions.declare_file("Cat.java")
+    ctx.actions.write(cat_java, """
+                      package org.jetbrains.bsp.example.animals;
+                      public class Cat {};
+                      """)
+    src_jar = ctx.actions.declare_file("animals.srcjar")
+    java_common.pack_sources(ctx.actions, sources = [cat_java], java_toolchain = tc.java, output_source_jar = src_jar)
+
+    return [
+        DefaultInfo(files = depset([src_jar])),
+    ]
+
+animals_library_source = rule(
+    implementation = _animals_library_source_impl,
+    fragments = ["java"],
+    toolchains = ["@bazel_tools//tools/jdk:toolchain_type"],
+    attrs = {
+        "_java_toolchain": attr.label(
+            default = Label("@bazel_tools//tools/jdk:current_java_toolchain"),
+        ),
+    },
+)

example/animals/src/java/org/jetbrains/bsp/example/animals/consumer/LibraryConsumer.java

@@ -0,0 +1,5 @@
+package org.jetbrains.bsp.example.animals.consumer;
+
+class LibraryConsumer {
+    org.jetbrains.bsp.example.animals.Cat cat;
+}