Add option to extract proguard configurations in jvm_import

Some jars include proguard specs in META-INF/proguard/
META-INF/com.android.tools
We need to extract these files in order to pass them correctly
to R8 for android builds.
Normally R8 should detect these files automatically inside the jar,
but if proguard specs are specified in META-INF/com.android.tools and
META-INF/proguard the files under META-INF/proguard are ignored.
See https://r8.googlesource.com/r8/+/refs/heads/main/src/main/java/com/android/tools/r8/R8Command.java#1394
Given that bazel uses a single deploy jar when running R8 it is likely
that both directories exist and several needed configs are ignored.

see bazelbuild/bazel#14966 (comment)

private/rules/jvm_import.bzl

@@ -8,6 +8,7 @@
 # [1]: https://github.com/bazelbuild/bazel/issues/4549
 
 load("//settings:stamp_manifest.bzl", "StampManifestProvider")
+load("//settings:extract_proguard_config.bzl", "ExtractProguardConfigProvider")
 
 def _jvm_import_impl(ctx):
     if len(ctx.files.jars) != 1:
@@ -30,6 +31,26 @@ def _jvm_import_impl(ctx):
     else:
         outjar = injar
 
+    proguard_info = []
+    if ctx.attr._extract_proguard_config[ExtractProguardConfigProvider].extract_proguard_config:
+        spec = ctx.actions.declare_file("%s_proguard.pro" % injar.basename.split(".jar")[0])
+
+        args = ctx.actions.args()
+        args.add("--jar_to_spec", "%s:%s" % (injar.path, spec.path))
+
+        ctx.actions.run(
+            inputs = [injar],
+            outputs = [spec],
+            executable = ctx.executable._proguard_config_extractor,
+            arguments = [args],
+            mnemonic = "ExtractProguardSpec",
+            progress_message = "Extracting proguard config of %s" % ctx.label,
+        )
+
+        proguard_info = [
+            ProguardSpecProvider(depset(direct = [spec])),
+        ]
+
     compilejar = ctx.actions.declare_file("header_" + injar.basename, sibling = injar)
     args = ctx.actions.args()
     args.add_all(["--source", outjar, "--output", compilejar])
@@ -69,7 +90,7 @@ def _jvm_import_impl(ctx):
             ],
             neverlink = ctx.attr.neverlink,
         ),
-    ]
+    ] + proguard_info
 
 jvm_import = rule(
     attrs = {
@@ -95,9 +116,17 @@ jvm_import = rule(
             cfg = "exec",
             default = "//private/tools/java/com/github/bazelbuild/rules_jvm_external/jar:AddJarManifestEntry",
         ),
+        "_proguard_config_extractor": attr.label(
+            executable = True,
+            cfg = "exec",
+            default = "//private/tools/java/com/github/bazelbuild/rules_jvm_external/jar:ExtractProguardConfig",
+        ),
         "_stamp_manifest": attr.label(
             default = "@rules_jvm_external//settings:stamp_manifest",
         ),
+        "_extract_proguard_config": attr.label(
+            default = "@rules_jvm_external//settings:extract_proguard_config",
+        ),
     },
     implementation = _jvm_import_impl,
     provides = [JavaInfo],

private/tools/java/com/github/bazelbuild/rules_jvm_external/jar/BUILD

@@ -51,3 +51,14 @@ java_binary(
         "//private/tools/java/com/github/bazelbuild/rules_jvm_external/zip",
     ],
 )
+
+java_binary(
+    name = "ExtractProguardConfig",
+    srcs = [
+        "ExtractProguardConfig.java",
+    ],
+    main_class = "com.github.bazelbuild.rules_jvm_external.jar.ExtractProguardConfig",
+    visibility = [
+        "//visibility:public",
+    ],
+)

private/tools/java/com/github/bazelbuild/rules_jvm_external/jar/ExtractProguardConfig.java

@@ -0,0 +1,94 @@
+package com.github.bazelbuild.rules_jvm_external.jar;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Enumeration;
+import java.util.List;
+import java.util.jar.JarEntry;
+import java.util.jar.JarFile;
+
+public final class ExtractProguardConfig {
+
+    private List<String> jarToSpec;
+
+    // Directories to search for proguard configurations.
+    // The list is sorted from highest priorty to lowest priority
+    // Only the first one is extracted.
+    private List<String> proguardDirs = Arrays.asList(
+            "META-INF/com.android.tools/r8",
+            "META-INF/com.android.tools/proguard",
+            "META-INF/proguard"
+    );
+
+    public ExtractProguardConfig(List<String> jarToSpec) {
+        this.jarToSpec = jarToSpec;
+    }
+
+    private boolean maybeCopySpec(String jarPath, String directoryName, String spec) {
+        try {
+            JarFile jarFile = new JarFile(jarPath);
+            Enumeration<JarEntry> entries = jarFile.entries();
+            while (entries.hasMoreElements()) {
+                JarEntry entry = entries.nextElement();
+                if (!entry.isDirectory() && entry.getName().startsWith(directoryName)) {
+                    File outputFile = new File(spec);
+                    FileOutputStream outputStream = new FileOutputStream(outputFile);
+                    jarFile.getInputStream(entry).transferTo(outputStream);
+
+                    outputStream.close();
+                    return true;
+                }
+            }
+            jarFile.close();
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+        return false;
+    }
+
+    private void extractSpec(String jar, String spec) {
+        boolean hadSpec = false;
+        for (String dir : proguardDirs) {
+            hadSpec = maybeCopySpec(jar, dir, spec);
+            if (hadSpec) {
+                break;
+            }
+        }
+
+        if (!hadSpec) {
+            try {
+                File file = new File(spec);
+                file.createNewFile();
+            } catch (IOException e) {
+                e.printStackTrace();
+            }
+        }
+    }
+
+    public void run() {
+        for (String js : jarToSpec) {
+            String[] parts = js.split(":");
+            if (parts.length != 2) {
+                throw new IllegalArgumentException("Invalid jar_to_spec value: " + js);
+            }
+            extractSpec(parts[0], parts[1]);
+        }
+    }
+
+    public static void main(String[] args) {
+        List<String> jarToSpec = new ArrayList();
+        for (int i = 0; i < args.length; i++) {
+            if (args[i].equals("--jar_to_spec")) {
+                if (i + 1 < args.length) {
+                    jarToSpec.add(args[i + 1]);
+                    i++; 
+                }
+            }
+        }
+
+        new ExtractProguardConfig(jarToSpec).run();
+    }
+}

settings/BUILD

@@ -1,12 +1,21 @@
 load("//settings:stamp_manifest.bzl", "stamp_manifest")
+load("//settings:extract_proguard_config.bzl", "extract_proguard_config")
 
 package(
     default_visibility = ["//visibility:public"],
 )
 
-exports_files(["stamp_manifest.bzl"])
+exports_files([
+    "extract_proguard_config.bzl",
+    "stamp_manifest.bzl",
+])
 
 stamp_manifest(
     name = "stamp_manifest",
     build_setting_default = True,
 )
+
+extract_proguard_config(
+    name = "extract_proguard_config",
+    build_setting_default = False,
+)

settings/extract_proguard_config.bzl

@@ -0,0 +1,9 @@
+ExtractProguardConfigProvider = provider(fields = ["extract_proguard_config"])
+
+def _impl(ctx):
+    return ExtractProguardConfigProvider(extract_proguard_config = ctx.build_setting_value)
+
+extract_proguard_config = rule(
+    implementation = _impl,
+    build_setting = config.bool(flag = True),
+)