fix: stop copying targets, consume directly

Since we have downloaded_file_path that points to the actual jar name
in our http_file invocations we can directly consume from those targets
instead of copying, this has an impact not just in IO as we reduce
copying, but also reduces the amount of targets bazel is aware as we
don't need an extra node, reducing the amount of RAM needed for
rules_jvm_external slightly.

In large maven repositories we use at Booking.com we saw a decrease in
the disk cache from 2.4GB to 300MB, which aligns with a repository_cache
of roughly 2.1GB. The time it takes to do a `bazel build @maven//...`
went from 120 seconds to 50 seconds on a i9-13900H using 75% of the cores.

Author: manuelnaranjo

private/dependency_tree_parser.bzl

@@ -66,6 +66,13 @@ def _find_repository_url(artifact_url, repositories):
                 longest_match = repository
     return longest_match
 
+_ARTIFACT_JAR = """
+alias(
+    name = "{artifact_path}",
+    actual = "{source}",
+    visibility = ["//visibility:public"],
+)"""
+
 def _generate_target(
         repository_ctx,
         jar_versionless_target_labels,
@@ -87,7 +94,7 @@ def _generate_target(
     # (jvm|aar)_import(
     #
     packaging = artifact_path.split(".").pop()
-    if packaging == "jar":
+    if packaging == "jar" or artifact_path.endswith("//file"):
         # Regular `java_import` invokes ijar on all JARs, causing some Scala and
         # Kotlin compile interface JARs to be incorrect. We replace java_import
         # with a simple jvm_import Starlark rule that skips ijar.
@@ -120,7 +127,7 @@ def _generate_target(
     # 	srcjar = "https/repo1.maven.org/maven2/org/hamcrest/hamcrest-library/1.3/hamcrest-library-1.3-sources.jar",
     #
     is_dylib = False
-    if packaging == "jar":
+    if packaging == "jar" or artifact_path.endswith("//file"):
         target_import_string.append("\tjars = [\"%s\"]," % artifact_path)
         if srcjar_paths != None and target_label in srcjar_paths:
             target_import_string.append("\tsrcjar = \"%s\"," % srcjar_paths[target_label])
@@ -320,18 +327,6 @@ genrule(
     to_return.append("alias(\n\tname = \"%s\",\n\tactual = \"%s\",\n%s)" %
                      (versioned_target_alias_label, target_label, alias_visibility))
 
-    # 11. If using maven_install.json, use a genrule to copy the file from the http_file
-    # repository into this repository.
-    #
-    # genrule(
-    #     name = "org_hamcrest_hamcrest_library_1_3_extension",
-    #     srcs = ["@org_hamcrest_hamcrest_library_1_3//file"],
-    #     outs = ["@maven//:v1/https/repo1.maven.org/maven2/org/hamcrest/hamcrest-library/1.3/hamcrest-library-1.3.jar"],
-    #     cmd = "cp $< $@",
-    # )
-    if repository_ctx.attr.maven_install_json:
-        to_return.append(_genrule_copy_artifact_from_http_file(artifact, default_visibilities))
-
     return to_return
 
 # Generate BUILD file with jvm_import and aar_import for each artifact in
@@ -351,6 +346,8 @@ def _generate_imports(repository_ctx, dependencies, explicit_artifacts, neverlin
     # seen_imports :: string -> bool
     seen_imports = {}
 
+    added_aliases = {}
+
     # A list of versionless target labels for jar artifacts. This is used for
     # generating a compatibility layer for repositories. For example, if we generate
     # @maven//:junit_junit, we also generate @junit_junit//jar as an alias to it.
@@ -378,8 +375,6 @@ def _generate_imports(repository_ctx, dependencies, explicit_artifacts, neverlin
                     seen_imports[artifact_path] = True
                     target_label = escape(strip_packaging_and_classifier_and_version(artifact["coordinates"]))
                     srcjar_paths[target_label] = artifact_path
-                    if repository_ctx.attr.maven_install_json:
-                        all_imports.append(_genrule_copy_artifact_from_http_file(artifact, default_visibilities))
 
     # Iterate through the list of artifacts, and generate the target declaration strings.
     for artifact in dependencies:
@@ -409,23 +404,18 @@ def _generate_imports(repository_ctx, dependencies, explicit_artifacts, neverlin
             all_imports.append(
                 "alias(\n\tname = \"%s\",\n\tactual = \"%s\",\n\tvisibility = [\"//visibility:public\"],\n)" % (target_label, versioned_target_alias_label),
             )
-            if repository_ctx.attr.maven_install_json:
-                all_imports.append(_genrule_copy_artifact_from_http_file(artifact, default_visibilities))
         elif target_label in labels_to_override:
             # Override target labels with the user provided mapping, instead of generating
             # a jvm_import/aar_import based on information in dep_tree.
             seen_imports[target_label] = True
             all_imports.append(
-                "alias(\n\tname = \"%s\",\n\tactual = \"%s\",\n\tvisibility = [\"//visibility:public\"],)" % (target_label, labels_to_override.get(target_label)),
+                "alias(\n\tname = \"%s\",\n\tactual = \"%s\",\n\tvisibility = [\"//visibility:public\"],\n)" % (target_label, labels_to_override.get(target_label)),
             )
-            if repository_ctx.attr.maven_install_json:
-                # Provide the downloaded artifact as a file target.
-                all_imports.append(_genrule_copy_artifact_from_http_file(artifact, default_visibilities))
             raw_artifact = dict(artifact)
             raw_artifact["coordinates"] = "original_" + artifact["coordinates"]
             raw_artifact["maven_coordinates"] = artifact["coordinates"]
             raw_artifact["out"] = "original_" + artifact["file"]
-
+            raw_artifact["file"] = "@%s//file" % escape(artifact["coordinates"])
             all_imports.extend(_generate_target(
                 repository_ctx,
                 jar_versionless_target_labels,
@@ -439,7 +429,18 @@ def _generate_imports(repository_ctx, dependencies, explicit_artifacts, neverlin
                 raw_artifact,
             ))
 
+
         elif artifact_path != None:
+            if artifact["file"] not in added_aliases:
+                added_aliases[artifact["file"]] = True
+                repo = escape(artifact["coordinates"])
+                all_imports.append(
+                    _ARTIFACT_JAR.format(
+                        artifact_path = artifact["file"],
+                        source = "@%s//file" % repo
+                    )
+                )
+
             all_imports.extend(_generate_target(
                 repository_ctx,
                 jar_versionless_target_labels,

private/rules/jvm_import.bzl

@@ -25,7 +25,7 @@ def _jvm_import_impl(ctx):
 
     injar = ctx.files.jars[0]
     if ctx.attr._stamp_manifest[StampManifestProvider].stamp_enabled:
-        outjar = ctx.actions.declare_file("processed_" + injar.basename, sibling = injar)
+        outjar = ctx.actions.declare_file("processed_" + injar.basename)
         args = ctx.actions.args()
         args.add_all(["--source", injar, "--output", outjar])
         args.add_all(["--manifest-entry", "Target-Label:{target_label}".format(target_label = label)])
@@ -40,7 +40,7 @@ def _jvm_import_impl(ctx):
     else:
         outjar = injar
 
-    compilejar = ctx.actions.declare_file("header_" + injar.basename, sibling = injar)
+    compilejar = ctx.actions.declare_file("header_" + injar.basename)
     args = ctx.actions.args()
     args.add_all(["--source", outjar, "--output", compilejar])