[Microsoft.Android.Build.Tasks] Generate typemap ProGuard rules

.github/skills/tests/references/test-catalog.md

@@ -39,6 +39,13 @@ These tests can be run immediately with `dotnet test` on the `.csproj`, even if
 
 ---
 
+The NativeAOT object/MSBuild integration cases in the trimmable type map suite
+also require the NDK `llvm-readobj` and adjacent `llvm-objdump` and `clang` executables. Pass
+`-p:_NativeAotLlvmReadObjPath=/path/to/ndk/toolchains/llvm/prebuilt/<host>/bin/llvm-readobj`
+(with `.exe` on Windows) to execute those cases; without it, those cases are
+reported as skipped. The NativeFormat parser and other typemap unit tests do
+not require native tools.
+
 ## Host-Side MSBuild Tests (full-build — requires local SDK)
 
 Assembly: `bin/TestDebug/${TFM}/Xamarin.Android.Build.Tests.dll`

Documentation/docs-mobile/TOC.yml

@@ -382,6 +382,10 @@
         href: messages/xa4325.md
       - name: XA4326
         href: messages/xa4326.md
+      - name: XA4327
+        href: messages/xa4327.md
+      - name: XA4328
+        href: messages/xa4328.md
     - name: "XA5xxx: GCC and toolchain"
       items:
       - name: "XA5xxx: GCC and toolchain"

Documentation/docs-mobile/building-apps/build-properties.md

@@ -1145,6 +1145,12 @@ An enum-style property that specifies how `r8` obfuscates Java names when
 
 This property does not disable R8 code shrinking.
 
+When managed-trimmed CoreCLR builds use retained typemap rules, all Java
+names are preserved regardless of this setting, but R8 optimization remains
+enabled. This path uses the optimizing Android defaults together with
+`-dontobfuscate` and `--no-minification`; disabling renaming does not disable
+optimization.
+
 This property was introduced in a .NET 10 servicing release. It defaults to
 `disabled` in .NET 10 and to `private-members` in .NET 11 and later.
 

Documentation/docs-mobile/messages/index.md

@@ -255,14 +255,16 @@ Either change the value in the AndroidManifest.xml to match the $(SupportedOSPla
 + [XA4316](xa4316.md): Specified input file '{file}' does not exist. Ignoring.
 + [XA4317](xa4317.md): Input file '{file}' does not start with `<replacements/>`. Skipping.
 + [XA4318](xa4318.md): Input file '{file}' could not be read: {message}. Skipping.
-+ [XA4319](xa4319.md): No NativeAOT DGML files were provided.
-+ [XA4320](xa4320.md): ACW map file '{file}' was not found.
-+ [XA4321](xa4321.md): NativeAOT DGML file '{file}' was not found.
++ [XA4319](xa4319.md): Retired: No NativeAOT DGML files were provided.
++ [XA4320](xa4320.md): Retired: ACW map file '{file}' was not found.
++ [XA4321](xa4321.md): Retired: NativeAOT DGML file '{file}' was not found.
 + [XA4322](xa4322.md): Skipping library ProGuard configuration file '{file}' (from {source}) because it contains the unsupported global option '{option}'. Global ProGuard options are only allowed in application projects.
 + [XA4323](xa4323.md): Ignoring directory '{directory}' as it does not exist.
 + [XA4324](xa4324.md): [{arch}] Unable to delete source file '{file}'.
 + [XA4325](xa4325.md): Failed to rewrite managed JNI names for R8. {message}
 + [XA4326](xa4326.md): Unable to safely rewrite a JNI member lookup because its class handle does not have one structurally unambiguous `JNIEnv.FindClass` source.
++ [XA4327](xa4327.md): Could not extract Java type map keys from '{0}': {1}
++ [XA4328](xa4328.md): Could not generate typemap ProGuard configuration from '{0}': {1}
 
 ## XA5xxx: GCC and toolchain
 

Documentation/docs-mobile/messages/xa4319.md

@@ -1,26 +1,13 @@
 ---
 title: .NET for Android error XA4319
 description: XA4319 error code
-ms.date: 05/27/2026
+ms.date: 09/18/2026
 f1_keywords:
   - "XA4319"
 ---
 
 # .NET for Android error XA4319
 
-## Example messages
-
-```
-error XA4319: No NativeAOT DGML files were provided.
-```
-
-## Issue
-
-The .NET for Android build could not find any NativeAOT DGML files to use when
-generating trimmable type map ProGuard configuration.
-
-## Solution
-
-This error is expected only for internal build state inconsistencies. Ensure the
-project is building with the intended Runtime Identifier settings and that the
-NativeAOT compile produced its DGML scan file.
+This diagnostic has been retired. NativeAOT Java trimming reads ILC object
+files and does not require dependency graphs. See [XA4327](xa4327.md) for
+current typemap extraction failures.

Documentation/docs-mobile/messages/xa4320.md

@@ -1,25 +1,13 @@
 ---
 title: .NET for Android error XA4320
 description: XA4320 error code
-ms.date: 05/27/2026
+ms.date: 09/18/2026
 f1_keywords:
   - "XA4320"
 ---
 
 # .NET for Android error XA4320
 
-## Example messages
-
-```
-error XA4320: ACW map file '{file}' was not found.
-```
-
-## Issue
-
-The .NET for Android build could not find the Android Callable Wrapper (ACW) map
-file needed to generate trimmable type map ProGuard configuration.
-
-## Solution
-
-This error is expected only for internal build state inconsistencies. Rebuild
-the project from a clean state so the ACW map is regenerated.
+This diagnostic has been retired. NativeAOT Java trimming reads ILC object
+files instead of joining dependency graphs with an ACW map. See
+[XA4327](xa4327.md) for current typemap extraction failures.

Documentation/docs-mobile/messages/xa4321.md

@@ -1,26 +1,13 @@
 ---
 title: .NET for Android error XA4321
 description: XA4321 error code
-ms.date: 05/27/2026
+ms.date: 09/18/2026
 f1_keywords:
   - "XA4321"
 ---
 
 # .NET for Android error XA4321
 
-## Example messages
-
-```
-error XA4321: NativeAOT DGML file '{file}' was not found.
-```
-
-## Issue
-
-The .NET for Android build could not find a NativeAOT DGML scan file needed to
-generate trimmable type map ProGuard configuration.
-
-## Solution
-
-This error is expected only for internal build state inconsistencies. Rebuild
-the project from a clean state and verify the NativeAOT compile produced the
-DGML scan file for the selected Runtime Identifier.
+This diagnostic has been retired. NativeAOT Java trimming reads ILC object
+files and does not require dependency graphs. See [XA4327](xa4327.md) for
+current typemap extraction failures.

Documentation/docs-mobile/messages/xa4327.md

@@ -0,0 +1,37 @@
+---
+title: .NET for Android error XA4327
+description: XA4327 error code
+ms.date: 09/18/2026
+f1_keywords:
+  - "XA4327"
+---
+
+# .NET for Android error XA4327
+
+## Example message
+
+```
+error XA4327: Could not extract Java type map keys from 'typemaps.arm64-v8a.ll': ...
+```
+
+## Issue
+
+The build could not read retained Java class names from a NativeAOT object,
+a CoreCLR LLVM typemap, or linked trimmable typemap assemblies.
+The input is missing, unreadable, malformed, or uses an unsupported representation.
+The diagnostic includes the input and the underlying failure.
+
+An empty, valid typemap is supported. A failed extraction is not treated as an
+empty typemap, because doing so could remove Java classes required at runtime.
+
+## Solution
+
+Fix the reported input or the earlier task that produces it. If the input was
+generated by .NET for Android, clean and rebuild the application. If the error
+persists, [report an issue](https://github.com/dotnet/android/issues/new/choose)
+with a binary build log and the affected typemap input.
+
+NativeAOT object extraction also requires the Android NDK's `llvm-readobj`
+and adjacent `llvm-objdump`.
+Install the NDK selected by `GetAndroidDependencies`, or point
+`AndroidNdkDirectory` at a complete installation.

Documentation/docs-mobile/messages/xa4328.md

@@ -0,0 +1,33 @@
+---
+title: .NET for Android error XA4328
+description: XA4328 error code
+ms.date: 09/18/2026
+f1_keywords:
+  - "XA4328"
+---
+
+# .NET for Android error XA4328
+
+## Example message
+
+```
+error XA4328: Could not generate typemap ProGuard configuration from 'typemap.keys.txt': Line 1 contains an invalid retained Java class name: 'example/*'.
+```
+
+## Issue
+
+The class-only ProGuard generator could not read a retained-keys file, found
+an invalid class name, received no input files, or could not write its output.
+Keys must be UTF-8 Java class names using `/` as the package separator, such as
+`example/Outer$Inner`. Wildcards, ProGuard directives, dotted names, type
+descriptors, and typemap alias suffixes are not valid records.
+
+A zero-byte input is valid and produces no class keep rules. A missing file is
+an error, not an empty input.
+
+## Solution
+
+Fix the reported input or output path and permissions. For files generated by
+.NET for Android, clean and rebuild. If the error persists,
+[report an issue](https://github.com/dotnet/android/issues/new/choose) with a
+binary build log and the affected keys file.

Documentation/guides/D8andR8.md

@@ -1,5 +1,104 @@
 This is the D8 and R8 integration specification for .NET for Android.
 
+# Retained typemap class roots
+
+When managed trimming and R8 are enabled, CoreCLR and trimmable NativeAOT
+builds derive Java class roots from the final typemap rather than retaining
+every class in the ACW map:
+
+| Runtime and typemap | Retained-key source |
+| --- | --- |
+| NativeAOT, trimmable | Retained external typemap records in each RID's final ILC object |
+| CoreCLR, LLVM IR | The generated LLVM Java-name blob, after `GenerateTypeMappings` |
+| CoreCLR, trimmable | Surviving `TypeMapAttribute<T>` records in linked typemap assemblies, including empty stubs |
+
+Inner builds return their exact source paths to the outer build. Keys are
+unioned across the requested RIDs/ABIs; stale files from other builds are not
+discovered by globbing. NativeAOT locates external typemap blobs with
+`llvm-readobj`, resolves Java group identities using bounded `llvm-objdump`
+relocations, reads their object-file byte ranges, and decodes the retained
+NativeFormat keys. It does not require an ACW map or generate dependency graphs.
+
+All three adapters and both ProGuard generators are `Microsoft.Android.Tasks`
+tasks in `Microsoft.Android.Build.Tasks.dll`.
+The adapters write `typemap.keys.txt` in the outer intermediate directory.
+The format is UTF-8 without a BOM, one canonical JNI class name per line,
+ordinal-sorted and distinct, with LF endings and a final LF when nonempty.
+For example:
+
+```text
+android/app/Activity
+example/Outer$Inner
+```
+
+The assembly and NativeAOT object adapters collapse implementation-specific
+numeric aliases before writing this format. Valid JNI array entries contribute
+their reference element class; primitive arrays do not contribute a class.
+A valid zero-byte file means no retained classes;
+missing, unreadable, or unsupported inputs fail the build.
+
+`GenerateTypeMapProguardConfiguration` knows only this format. It accepts a
+union of keys files and writes deterministic class-only rules to
+`proguard/proguard_project_references.cfg`:
+
+```text
+-keep class android.app.Activity
+-keep class example.Outer$Inner
+```
+
+The class-root generator never emits member rules or global R8 options.
+CoreCLR uses a separate `GenerateTypeMapMemberProguardConfiguration` task to
+write `proguard/proguard_typemap_members.cfg` from the same retained keys:
+
+```text
+-keepclassmembers class android.app.Activity { *; }
+-keepclassmembers class example.Outer$Inner { *; }
+```
+
+This preserves JNI-facing methods, constructors, and fields without also
+preserving every member of Java-only dependencies. R8's member matching
+includes inherited accessible methods and superclass fields. The separate
+`proguard_typemap_coreclr.cfg` configuration preserves runtime bootstrap
+classes and their members, plus framework-driven view members. Dynamic JNI
+or reflection access to types or members not represented by retained managed
+bindings still needs application/library ProGuard rules.
+
+NativeAOT continues to use `proguard_typemap.cfg`, which retains members of
+all surviving classes, including third-party classes, while allowing unused
+classes to disappear. Both policies keep explicit runtime bootstrap roots
+rather than whole wrapper packages. User Java source retention and
+application/library ProGuard rules remain separate.
+
+The temporary private override `_AndroidEnableTypemapR8Trimming` controls this
+pipeline. It replaces the old NativeAOT-specific trimming and ProGuard switches.
+Leave it unset for automatic CoreCLR behavior, set it to `true` to enable
+the pipeline in eligible managed-trimmed CoreCLR/NativeAOT R8 builds, or set it
+to `false` to use legacy ACW retention without running the new tasks. Disabling
+it avoids NativeAOT object inspection. The switch does not enable R8 or managed
+trimming in otherwise ineligible builds.
+
+NativeAOT object inspection currently requires explicit `true` and the Android
+NDK's `llvm-readobj` and adjacent `llvm-objdump`, even when using the
+workload-provided native linker. The workload's native tools do not yet include them.
+`GetAndroidDependencies` includes the NDK for this opt-in configuration.
+Leaving the override unset or `false` preserves NativeAOT's no-NDK build path
+and keeps all ACW classes.
+
+This pipeline disables all obfuscation, including private-member
+obfuscation, with both `-dontobfuscate` and R8's `--no-minification` option.
+CoreCLR uses `proguard-android-optimize.txt` so optimization remains enabled
+independently of obfuscation. Its JNI class/member keep rules still protect
+the names and signatures required by managed code. NativeAOT retains its
+existing non-optimizing defaults.
+MonoVM, nonshrinking/multidex-only builds, and the existing complete
+`ProguardConfigFiles` override keep their previous behavior.
+
+Both extraction and rule generation use their real files as incremental
+outputs. A content-sensitive input manifest also tracks source-list and
+runtime/trim-policy changes, so removing a RID or switching modes cannot
+reuse stale class roots. The outputs are registered in `FileWrites` and
+regenerated if deleted.
+
 # What is D8? What is R8?
 
 At a high level, here are the steps that occur during an Android

src/Microsoft.Android.Build.Tasks/Microsoft.Android.Build.Tasks.csproj

@@ -12,6 +12,7 @@
     <TargetFramework>$(DotNetTargetFramework)</TargetFramework>
     <RootNamespace>Microsoft.Android.Tasks</RootNamespace>
     <Nullable>enable</Nullable>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <WarningsAsErrors>Nullable</WarningsAsErrors>
     <!--
       Deliberately *not* the shared tools\ directory. MSBuild probes a task assembly's own
@@ -52,6 +53,8 @@
 
   <ItemGroup>
     <Compile Include="..\Xamarin.Android.Build.Tasks\Utilities\NullableExtensions.cs" Link="Utilities\NullableExtensions.cs" />
+    <Compile Include="..\Xamarin.Android.Build.Tasks\Utilities\MetadataExtensions.cs" Link="Utilities\MetadataExtensions.cs" />
+    <Compile Include="..\Xamarin.Android.Build.Tasks\Utilities\DummyCustomAttributeProvider.cs" Link="Utilities\DummyCustomAttributeProvider.cs" />
     <Compile Include="..\Xamarin.Android.Build.Tasks\Utilities\ManifestPlaceholderResolver.cs" Link="Utilities\ManifestPlaceholderResolver.cs" />
   </ItemGroup>