Add java_library statements for providing a lib with transitive deps

README.md

@@ -140,6 +140,50 @@ android_binary(
 )
 ```
 
+### Detailed dependency information specifications
+
+Although you can always give a dependency as a Maven coordinate string, occasionally special
+handling is required in the form of additional directives to properly situate the artifact
+in the dependency tree. For example, a given artifact may need to have one of its dependencies
+excluded to prevent a conflict. 
+
+This situation is provided for by allowing the artifact to be specified as a map containing
+all of the required information. This map can express more information than the coordinate
+strings can, so internally the coordinate strings are parsed into the artifact map with default
+values for the additional items. To assist in generating the maps, you can pull in the file 
+`specs.bzl` alongside `defs.bzl` and import the `maven` struct, which provides several helper
+functions to assist in creating these maps. An example: 
+
+```python
+load("@rules_maven//:defs.bzl", "artifact")
+load("@rules_maven//:specs.bzl", "maven")
+
+maven_install(
+    artifacts = [
+        maven.artifact(
+            group = "com.google.guava",
+            artifact = "guava",
+            version = "27.0-android",
+            exclusions = [
+                ...
+            ]
+        ),
+        "junit:junit:4.12",
+        ...
+    ],
+    repositories = [
+        maven.repository(
+            "https://some.private.maven.re/po",
+            user = "bob",
+            password = "l0bl4w"
+        ),
+        "https://repo1.maven.org/maven2",
+        ...
+    ],
+)
+```
+
+
 ## How it works
 
 Note the lack of explicit packaging type (a la gmaven_rules). `coursier`
@@ -151,13 +195,19 @@ The repository rule then..
 1. creates the repository "@maven"
 1. symlinks the transitive artifacts from the central cache to the repository's
    directory in the output_base
-1. creates a single BUILD file with `java_import`/`aar_import` targets for each
-   transitive artifact (including the top level ones), and their respective deps
-   matching the `<dependencies>` element in the artifact's POM file.
+1. creates a single BUILD file with `java_import`/`aar_import` and `java_library` 
+   transitive library targets for each transitive artifact (including the top level 
+   ones), and their respective deps matching the `<dependencies>` element in the 
+   artifact's POM file.
 
 The `artifact` macro used in the BUILD file translates the artifact fully
 qualified name to the label of the top level `java_import`/`aar_import` target
-in the `@maven` repository.
+in the `@maven` repository. This macro will depend directly on the referenced jar, and
+nothing else. 
+
+The `library` macro accepts the same arguments, but references the `java_library` target
+for the arguments. The library target will contain the referenced jar *and* all of its
+transitive dependencies. 
 
 For example, the generated BUILD file for `com.google.inject:guice:4.0` looks like this:
 

coursier.bzl

@@ -162,15 +162,15 @@ def generate_imports(repository_ctx, dep_tree, srcs_dep_tree = None):
             artifact_deps = artifact["dependencies"]
             # Dedupe dependencies here. Sometimes coursier will return "x.y:z:aar:version" and "x.y:z:version" in the
             # same list of dependencies.
-            seen_dep_labels = {}
+            target_import_labels = []
             for dep in artifact_deps:
                 dep_target_label = _escape(_strip_packaging_and_classifier(dep))
-                if dep_target_label not in seen_dep_labels:
-                    seen_dep_labels[dep_target_label] = True
-                    target_import_string.append("\t\t\":%s\"," % dep_target_label)
-            target_import_string.append("\t],")
+                target_import_labels.append("\t\t\":%s\",\n" % dep_target_label)
+            target_import_labels = _deduplicate_list(target_import_labels)
 
-            # 5. Conclude.
+            target_import_string.append("".join(target_import_labels) + "\t],")
+
+            # 5. Finish the java_import rule.
             #
             # java_import(
             # 	name = "org_hamcrest_hamcrest_library_1_3",
@@ -184,9 +184,45 @@ def generate_imports(repository_ctx, dep_tree, srcs_dep_tree = None):
 
             all_imports.append("\n".join(target_import_string))
 
-            # Also create a versionless alias target
-            target_alias_label = _escape(_strip_packaging_and_classifier_and_version(artifact["coord"]))
-            all_imports.append("alias(\n\tname = \"%s\",\n\tactual = \"%s\",\n)" % (target_alias_label, target_label))
+            # 6. Create a versionless alias target
+            #
+            # alias(
+            #   name = "org_hamcrest_hamcrest_library",
+            #   actual = "org_hamcrest_hamcrest_library_1_3",
+            # )
+            versionless_target_alias_label = _escape(_strip_packaging_and_classifier_and_version(artifact["coord"]))
+            all_imports.append("alias(\n\tname = \"%s\",\n\tactual = \"%s\",\n)" % (versionless_target_alias_label, target_label))
+
+            # 7. Create java_library rule (includes transitive dependencies)
+            #
+            # java_library(
+            #   name = "org_hamcrest_hamcrest_library_lib",
+            #   exports = [
+            #       ":org_hamcrest_hamcrest_core_1_3",
+            #       ":org_hamcrest_hamcrest_library_1_3",
+            #   ]
+            # )
+            transitive_dep_aliases = ["\t\t\":" + versionless_target_alias_label + "\""]
+            for transitive_dep_coord in artifact["dependencies"]:
+                transitive_dep = _find_dependency_by_coord(dep_tree, transitive_dep_coord)
+                if transitive_dep == None:
+                    fail("Could not find transitive dependency of " + artifact["coord"] + ": " + transitive_dep_coord + "\n" +
+                         "Parsed artifact data:" + repr(artifact) + "\n" +
+                         "Parsed dependency output:" + repr(dep_tree))
+
+                transitive_dep_aliases.append("\t\t\":" + _escape(_strip_packaging_and_classifier_and_version(transitive_dep["coord"])) + "\"")
+
+            target_library = \
+"""
+java_library(
+    name = "{}",
+    exports = [
+{}
+    ]
+)
+""".lstrip()
+            transitive_dep_aliases = _deduplicate_list(transitive_dep_aliases)
+            all_imports.append(target_library.format(versionless_target_alias_label + "_lib", ",\n".join(transitive_dep_aliases)))
 
 
         elif absolute_path_to_artifact == None:
@@ -197,6 +233,21 @@ def generate_imports(repository_ctx, dep_tree, srcs_dep_tree = None):
 
     return ("\n".join(all_imports), checksums)
 
+def _deduplicate_list(items):
+    seen_items = {}
+    unique_items = []
+    for item in items:
+        if item not in seen_items:
+            seen_items[item] = True
+            unique_items.append(item)
+    return unique_items
+
+def _find_dependency_by_coord(coursier_report, dep_coord):
+    for artifact in coursier_report["dependencies"]:
+        if artifact["coord"] == dep_coord:
+            return artifact
+    return None
+
 # Generate the base `coursier` command depending on the OS, JAVA_HOME or the
 # location of `java`.
 def _generate_coursier_command(repository_ctx):

defs.bzl

@@ -44,6 +44,13 @@ def artifact(a, repository_name = REPOSITORY_NAME):
 def maven_artifact(a):
     return artifact(a, repository_name = REPOSITORY_NAME)
 
+def library(a, repository_name = REPOSITORY_NAME):
+    artifact_obj = _parse_artifact_str(a) if type(a) == "string" else a
+    return "@%s//:%s" % (repository_name, _escape(artifact_obj["group"] + ":" + artifact_obj["artifact"] + "_lib"))
+
+def maven_library(a):
+    return library(a, repository_name = REPOSITORY_NAME)
+
 def _escape(string):
     return string.replace(".", "_").replace("-", "_").replace(":", "_")