Extract r8 rules based on version by snazhmudinov · Pull Request #511 · bazelbuild/rules_android

snazhmudinov · 2026-05-22T08:50:38Z

Addresses #491.
Additional info used: https://developer.android.com/topic/performance/app-optimization/library-optimization#support-different

Add runfiles dependency and data attribute to both AAR and JAR proguard extractor targets, and read the R8 version from r8.version at runtime.

Thread r8_version from main() through _Main and into all proguard_extractor_lib functions. No behavioral change yet.

ExtractEmbeddedProguardFromJar now matches r8-from-X-upto-Y directories against the actual R8 version and only extracts rules whose version range covers the current R8 version. Falls back to legacy META-INF/proguard/ rules when no targeted range matches.

Update ExtractEmbeddedProguardFromAar to prioritize version-targeted R8 rules from classes.jar, falling back to proguard.txt at the AAR root when no targeted range matches. Remove unused ExtractR8Rules and ExtractEmbeddedProguardFromAarLegacy functions.

snazhmudinov · 2026-05-22T09:31:26Z

+    outs = [
+        "r8.version",
+    ],
+    cmd = "$(location :r8) --version | awk -F' ' '{ print $$2 }' >$(OUTS)",


This isn't very robust - it assumes the version format is R8 8.9.35 (build ...) (which is the case today, but can change in the future).

Maybe could use the r8-version.properties resource?

e.g.

unzip -p $(location r8_jar) r8-version.properties | sed -En 's/^version.version=(.+)$/\1/p'

The result looks a bit odd to me:

version.sha=afec818d6658b003ba394e10107b7dfc565dd94b releaser=go/r8bot (luci-r8-custom-ci-archive-0-stqp) version-file.version.code=1

Came up with this: 5e30c57

Ah I see. In my case there was also a version.version property key with the specific version. I suppose when it's built from an untagged version that doesn't exist.

damianw

Amazing!

Fwiw this doesn't fully solve #491. Beyond respecting the R8 version, the prioritization of rules vs proguard/proguard.txt are also part of that issue. Solving that would require extracting the rules from individual jars instead of a single deploy jar.

damianw · 2026-05-22T15:36:44Z

Specifically, this is where the rules are currently being extracted. It can't really be done here, because all the resources are in one jar. So applying logic for "if has com.android.tools, ..." etc doesn't really make sense since the classpath is all jumbled together. The rule file selection would need to happen on the original library jars.

snazhmudinov · 2026-05-22T20:37:13Z

Extract rules from each jar

Ah that makes sense. I tried to run the extractor on jars, which get merged into deploy.jar. Commit.

…ava class

damianw · 2026-05-26T15:43:33Z

Great! That all makes sense to me.

Depending on @bazel_tools//tools/python/runfiles puts the bazel_tools repository root on the Python path, and its tools package shadows this repository's tools package when rules_android is used as an external repository. The extractors then fail with "No module named 'tools.android'". Rlocation("rules_android/...") also misses the canonical rules_android+ directory under Bzlmod. Read r8.version from next to the extractor script instead, falling back to the runfiles manifest when there is no runfiles tree.

Extracting from each runtime JAR puts one --input_jars flag per JAR on the command line. Large apps have more than 10,000 runtime JARs, which exceeds the OS argument length limit ("Argument list too long"). Pass the flags in an absl --flagfile instead.

Match AGP's FilterShrinkerRulesTransform and AarTransform: - Accept every directory form: r8, r8-from-<X>, r8-upto-<Y> and r8-from-<X>-upto-<Y>. Only the two-sided form matched, so libraries such as kotlinx-coroutines-android (r8-from-1.6.0, r8-upto-3.0.0) fell back to their legacy rules, which keep AndroidDispatcherFactory. - Match directory names case-insensitively, accept versions with a suffix such as 8.0.0-alpha01 or 9.5.2-dev, and treat a bound that can't be parsed as no constraint instead of failing. - If a JAR, or an AAR's classes.jar, has any R8-targeted rules, use only the matching ones and skip the legacy rules even if none match.

aar_import only passes --extract_r8_rules when --aar_import_extract_r8_rules is set (off by default), but the extractor stopped reading it, so every AAR's classes.jar rules were used and the flag did nothing. Only consider classes.jar rules when it is set again, and use proguard.txt otherwise, as before.

nathan3d · 2026-11-04T10:37:10Z

I tried this out on a large app with R8 9.5.28 and found a few issues. I've opened fixes as PRs against your branch, so you can take whichever you want:

Read the R8 version without the runfiles library snazhmudinov/rules_android#1: read the R8 version without the runfiles library. When rules_android is an external repository, the extractors fail with ModuleNotFoundError: No module named
'tools.android'. The @bazel_tools runfiles dependency puts bazel_tools' own tools package on the path, and Rlocation("rules_android/…") also misses the rules_android+ directory under Bzlmod.
Pass embedded proguard extractor inputs in a param file snazhmudinov/rules_android#2: pass the extractor inputs in a param file. Extracting from each runtime JAR fails with "Argument list too long" once an app has enough JARs (ours has about
13,500).
Select embedded R8 rules the way AGP does snazhmudinov/rules_android#3: select rules the way AGP does.
- Matches every directory form: r8, r8-from-X, r8-upto-Y, r8-from-X-upto-Y. Without that, kotlinx-coroutines-android (r8-from-1.6.0 / r8-upto-3.0.0) still got its legacy rules.
- Handles case, version suffixes and bounds that can't be parsed.
- Follows AGP's precedence rule: if a JAR has R8-targeted rules, the legacy rules are never used.
- Makes the AAR extractor honour --extract_r8_rules again.

The three PRs merge cleanly in any order. With all three, our app's coroutines dispatcher is constructed directly (no ServiceLoader), and the DEX is slightly smaller than with our previous
patch.

Read the R8 version without the runfiles library

Pass embedded proguard extractor inputs in a param file

Select embedded R8 rules the way AGP does

ted-xie · 2026-11-04T17:55:54Z

+
+public class R8Version {
+  public static void main(String[] args) {
+    System.out.println(com.android.tools.r8.Version.LABEL);


I am really not a fan of specializing behavior based on the R8 version. It's unclear to me why this needs to happen, both from the linked issue and the body of the PR.

Agreed, rules_android shouldn't need to know R8 versions at all. R8 already picks META-INF/com.android.tools/r8-from-*-upto-* rules against its own version: it does that for each program input (EmbeddedRulesExtractor), and it ships the same logic as a command-line tool, com.android.tools.r8.ExtractR8Rules.

The bug in #491 is that the choice is made per library. If a JAR has rules for the running R8, its legacy META-INF/proguard rules are ignored. Because rules_android gives R8 one merged deploy JAR, that choice is made for the whole app: once any library ships R8-targeted rules, every other library's legacy rules are dropped.

I've opened a draft: #585 as an alternative. When r8_extract_embedded_proguard_specs is on, it runs ExtractR8Rules from the toolchain's R8 on each runtime JAR.

snazhmudinov added 4 commits May 22, 2026 10:48

Read R8 version from runfiles in proguard extractors

32e17ef

Add runfiles dependency and data attribute to both AAR and JAR proguard extractor targets, and read the R8 version from r8.version at runtime.

Pass r8_version through extractor function signatures

3958338

Thread r8_version from main() through _Main and into all proguard_extractor_lib functions. No behavioral change yet.

snazhmudinov mentioned this pull request May 22, 2026

Extracted proguard rules do not respect priority #491

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Handle the case, when r8_version is missing

7b7c6b0

snazhmudinov commented May 22, 2026

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snazhmudinov added 2 commits May 22, 2026 13:36

Make bound checking a bit more readable

962b5e9

Fix the stale comment

4c61322

damianw reviewed May 22, 2026

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Extract rules from each jar

a53a9bf

Create R8Version extractor; read the R8 versionf from jar's Version.j…

5e30c57

…ava class

damianw approved these changes May 26, 2026

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nathan3d added 4 commits November 4, 2026 10:52

snazhmudinov added 3 commits November 4, 2026 13:08

Merge pull request #1 from nathan3d/fix511/read-r8-version

9f9ca29

Read the R8 version without the runfiles library

Merge pull request #2 from nathan3d/fix511/param-file

296fa03

Pass embedded proguard extractor inputs in a param file

Merge pull request #3 from nathan3d/fix511/agp-selection

755bc68

Select embedded R8 rules the way AGP does

ted-xie reviewed Nov 4, 2026

View reviewed changes

nathan3d mentioned this pull request Nov 4, 2026

Extract embedded R8 rules from each runtime JAR with ExtractR8Rules #585

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Extract r8 rules based on version - #511

Extract r8 rules based on version#511
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