[ci] Preliminary JDK11 Support (#4567)

Context: https://issuetracker.google.com/issues/150189789
Context: https://developer.android.com/preview/features#signature-scheme-v4
Context: https://developer.android.com/preview/features#incremental

Preliminary JDK 11 support.

The Android SDK Build-tools r30.0.0-rc4 package currently requires
JDK 11 in order to use `apksigner.jar`:

	Task "AndroidApkSigner"
	  Task Parameter:ApkSignerJar=C:\Users\dlab14\android-toolchain\sdk\build-tools\30.0.0-rc4\lib\apksigner.jar
	  …
	  Task Parameter:ToolPath=C:\Program Files\Android\jdk\microsoft_dist_openjdk_1.8.0.25\bin
	  Task Parameter:ManifestFile=obj\Release\android\AndroidManifest.xml
	  C:\Program Files\Android\jdk\microsoft_dist_openjdk_1.8.0.25\bin\java.exe -jar C:\Users\dlab14\android-toolchain\sdk\build-tools\30.0.0-rc4\lib\apksigner.jar sign --ks "C:\Users\dlab14\AppData\Local\Xamarin\Mono for Android\debug.keystore" --ks-pass pass:android --ks-key-alias androiddebugkey --key-pass pass:android --min-sdk-version 21 --max-sdk-version 29  "C:\A\vs2019xam00000Y-1\_work\1\s\bin\TestRelease\temp\BuildAotApplication AndÜmläüts_x86_64_True_True\bin\Release\UnnamedProject.UnnamedProject-Signed.apk"
	  java.lang.UnsupportedClassVersionError: com/android/apksigner/ApkSignerTool has been compiled by a more recent version of the Java Runtime (class file version 53.0), this version of the Java Runtime only recognizes class file versions up to 52.0
	  at java.lang.ClassLoader.defineClass1(Native Method)
	  …
	…\Xamarin.Android.Common.targets(2559,2): error MSB6006: "java.exe" exited with code 1.

This could be triggered by using the Android SDK Manager to install
Build-tools r30.0.0-rc4, then overriding the
`$(AndroidSdkBuildToolsVersion)` MSBuild property in `App.csproj`:

	<PropertyGroup>
	  <AndroidSdkBuildToolsVersion>30.0.0-rc4</AndroidSdkBuildToolsVersion>
	</PropertyGroup>

Many previous commits have added support for JDK 11, e.g. d99facb,
dcee2c8, 4742d50, 89f3dc1, and 895b7bc (among many others).

Additionally, c8ab455 updated the build environment so that *both*
JetBrains OpenJDK 1.8 and 11 were installed, though 1.8 was still used.

Now it's time to "flip the build environment," and use JDK 11 to build
the product, installers, and run (most) unit tests:

  * Update `azure-pipelines.yaml` and `azure-pipelines-oss.yaml` so
    that JDK 11 is used to build everything.

  * Update `xaprepare` so that when `$(JavaSdkDirectory)` isn't
    overridden, JDK 11 is used by default.

  * Override the `JI_JAVA_HOME` environment variable when preparing
    `external/Java.Interop` so that it uses the desired JDK.

  * Update the default `$(LatestSupportedJavaVersion)` value to
    11.0.4, the version of the JDK we install.

  * Update the `<ValidateJavaVersions/>` task so that JDK 11 is
    required when `$(AndroidSdkBuildToolsVersion)` is >= r30.
    This will cause an XA0032 error if JDK 1.8 is used to build a
    project when `$(AndroidSdkBuildToolsVersion)` is >= r30.

  * `apksigner` from Build-tools r30 creates a new `.idsig` file
    next to the `.apk`.  This is to enable a new
    `adb install --incremental` feature.  Add the `.idsig` file
    to `@(FileWrites)`.

  * Update various unit test `.csproj` files to consistently
    `<Import/>` the `Configuration.props` file and use properties
    within it for default values.  This in particular allowed building
    e.g. `samples/HelloWorld` to implicitly use JDK 11.

  * Increase "expected" times in
    `tests/msbuild-times-reference/MSBuildDeviceIntegration.csv`
    as JDK 11 appears to be slower than JDK 1.8 (🙁).

  * *Disable* support for `@(JavaSourceJar)` when JDK 11 is used.
    JDK 11 changes the HTML generated by the `javadoc` command, and
    we need to update our HTML parser to handle it.  In the interest
    of expediency, disable this for now.

The Android Designer integration tests continue to use JDK 1.8,
as the Designer doesn't currently build under JDK 11.

TODO:

  * Fix `@(JavaSourceJar)` support:
    #4789
  * Allow Android Designer to work with JDK 11, run Designer
    integration tests using JDK 11.
  * Figure out how to not accidentally bitrot JDK 1.8 support.

Co-authored-by: Jonathan Pryor <jonpryor@vt.edu>
Co-authored-by: Jonathan Peppers <jonathan.peppers@microsoft.com>
Co-authored-by: Jonathan Pobst <jonathan.pobst@microsoft.com>
Co-authored-by: Peter Collins <pecolli@microsoft.com>

Documentation/release-notes/4567.md

@@ -0,0 +1,32 @@
+### Preliminary JDK 11 Support
+
+Xamarin.Android can now use JDK 11 to build libraries and applications.
+
+JDK 11 is required in order to use Android SDK Build-tools r30,
+currently a release candidate.  Future versions of the Android SDK
+*may* require JDK 11 for more scenarios.  JDK 11 *is not required*
+at this point in time.
+
+Project authors can try switching to JDK 11 now to prepare
+potential future JDK 11 requirements.
+
+To do so:
+
+ 1. Install JDK 11, for example
+    [JetBrains Runtime](https://confluence.jetbrains.com/display/JBR/JetBrains+Runtime)
+
+ 2. Tell Xamarin.Android to use JDK 11.  This can be done within
+    [Visual Studio](https://docs.microsoft.com/en-us/xamarin/android/troubleshooting/questions/update-jdk?tabs=windows),
+    or can be done by setting the the `$(JavaSdkDirectory)` MSBuild
+    property to refer to the root of the JDK installation from (1).
+
+#### Known Issues
+
+When JDK 11 is used, the `@(JavaSourceJar)` Build action is not supported,
+and binding projects will not parse Javadoc to determine parameter names.
+This may result in different parameter names for existing bindings projects.
+Authors of bindings projects affected by this change are recommended to
+continue to use JDK 8 to build the bindings projects until this issue is
+resolved.
+
+The fix is being tracked as: https://github.com/xamarin/xamarin-android/issues/4789

build-tools/automation/azure-pipelines-oss.yaml

@@ -17,7 +17,8 @@ pr:
 # Predefined variables: https://docs.microsoft.com/en-us/azure/devops/pipelines/build/variables?view=azure-devops&tabs=yaml
 # https://dev.azure.com/xamarin/public/_apps/hub/ms.vss-ciworkflow.build-ci-hub?_a=edit-build-definition&id=48&view=Tab_Variables
 variables:
-  XA.Jdk.Folder: jdk-1.8
+  XA.Jdk8.Folder: jdk-1.8
+  XA.Jdk11.Folder: jdk-11
   XA.Build.MacOSSPool: VSEng-Xamarin-RedmondMacMojaveBuildPool-Android-OSS
   XA.Build.LinuxOSSPool: Xamarin-Android-Ubuntu-Public
 
@@ -158,7 +159,7 @@ stages:
     - script: echo "##vso[task.setvariable variable=HOME]$(Agent.HomeDirectory)"
       displayName: set HOME to agent directory
 
-    - script: echo "##vso[task.setvariable variable=PATH]$PATH:$(Agent.HomeDirectory)/android-toolchain/$(XA.Jdk.Folder)/bin"
+    - script: echo "##vso[task.setvariable variable=PATH]$PATH:$(Agent.HomeDirectory)/android-toolchain/$(XA.Jdk11.Folder)/bin"
       displayName: append jdk tools to PATH
 
     - script: make jenkins V=1 PREPARE_CI_PR=1 PREPARE_AUTOPROVISION=1 CONFIGURATION=$(XA.Build.Configuration)

build-tools/automation/azure-pipelines.yaml

@@ -44,7 +44,8 @@ resources:
 
 # Global variables
 variables:
-  XA.Jdk.Folder: jdk-1.8
+  XA.Jdk8.Folder: jdk-1.8
+  XA.Jdk11.Folder: jdk-11
   NuGetArtifactName: nupkgs
   InstallerArtifactName: installers
   TestAssembliesArtifactName: test-assemblies
@@ -97,8 +98,8 @@ stages:
     - checkout: self
       submodules: recursive
 
-    - script: echo "##vso[task.setvariable variable=JAVA_HOME]$HOME/Library/Android/$(XA.Jdk.Folder)"
-      displayName: set JAVA_HOME
+    - script: echo "##vso[task.setvariable variable=JI_JAVA_HOME]$HOME/Library/Android/$(XA.Jdk11.Folder)"
+      displayName: set JI_JAVA_HOME
 
     - template: yaml-templates/use-dot-net.yaml
       parameters:
@@ -234,6 +235,10 @@ stages:
 
     - template: yaml-templates\clean.yaml
 
+    - script: |
+        echo ##vso[task.setvariable variable=JI_JAVA_HOME]%USERPROFILE%\android-toolchain\$(XA.Jdk11.Folder)
+      displayName: set JI_JAVA_HOME
+
     - template: yaml-templates\use-dot-net.yaml
       parameters:
         version: $(DotNetCorePreviewVersion)
@@ -896,7 +901,7 @@ stages:
         if (("$branchName" -ne "master") -and ("$branchName" -notlike "d16*")) {
             $branchName = "master"
         }
-        Set-Location -Path $(System.DefaultWorkingDirectory)
+        Set-Location -Path $(System.DefaultWorkingDirectory)/designer
         git checkout $branchName
         git submodule update -q --init --recursive
       displayName: Clone and update designer
@@ -905,19 +910,31 @@ stages:
       displayName: provision designer dependencies
       inputs:
         github_token: $(GitHub.Token)
-        provisioning_script: $(System.DefaultWorkingDirectory)/bot-provisioning/dependencies.csx
+        provisioning_script: $(System.DefaultWorkingDirectory)/designer/bot-provisioning/dependencies.csx
         provisioning_extra_args: -remove Xamarin.Android -vv DEVDIV_PKGS_NUGET_TOKEN=$(DevDiv.NuGet.Token) SECTOOLS_PKGS_NUGET_TOKEN=$(SecTools.NuGet.Token)
 
-    - template: yaml-templates/run-installer.yaml
+    - template: yaml-templates/setup-test-environment.yaml
+      parameters:
+        xaSourcePath: $(System.DefaultWorkingDirectory)/xamarin-android
+
+    - script: echo "##vso[task.setvariable variable=JavaSdkDirectory]$HOME/Library/Android/$(XA.Jdk8.Folder)"
+      displayName: set JavaSdkDirectory
+
+    - script: echo "##vso[task.setvariable variable=JI_JAVA_HOME]$HOME/Library/Android/$(XA.Jdk8.Folder)"
+      displayName: reset JI_JAVA_HOME for Designer
 
     - template: designer/android-designer-build-mac.yaml@yaml
+      parameters:
+        designerSourcePath: $(System.DefaultWorkingDirectory)/designer
 
     - template: designer/android-designer-tests.yaml@yaml
+      parameters:
+        designerSourcePath: $(System.DefaultWorkingDirectory)/designer
 
     - task: CopyFiles@2
       displayName: 'Copy binlogs'
       inputs:
-        sourceFolder: Xamarin.Designer.Android
+        sourceFolder: $(System.DefaultWorkingDirectory)/designer/Xamarin.Designer.Android
         contents: '**/*.binlog'
         targetFolder: $(Build.ArtifactStagingDirectory)/designer-binlogs
         overWrite: true
@@ -960,7 +977,7 @@ stages:
         if (("$branchName" -ne "master") -and ("$branchName" -notlike "d16*")) {
             $branchName = "master"
         }
-        Set-Location -Path $(System.DefaultWorkingDirectory)
+        Set-Location -Path $(System.DefaultWorkingDirectory)\designer
         git checkout $branchName
         git submodule update -q --init --recursive
       displayName: Clone and update designer
@@ -969,19 +986,34 @@ stages:
       displayName: provision designer dependencies
       inputs:
         github_token: $(GitHub.Token)
-        provisioning_script: $(System.DefaultWorkingDirectory)\bot-provisioning\dependencies.csx
+        provisioning_script: $(System.DefaultWorkingDirectory)\designer\bot-provisioning\dependencies.csx
         provisioning_extra_args: -vv DEVDIV_PKGS_NUGET_TOKEN=$(DevDiv.NuGet.Token) SECTOOLS_PKGS_NUGET_TOKEN=$(SecTools.NuGet.Token)
 
-    - template: yaml-templates\run-installer.yaml
+    - template: yaml-templates\setup-test-environment.yaml
+      parameters:
+        xaSourcePath: $(System.DefaultWorkingDirectory)\xamarin-android
+
+    - script: echo "##vso[task.setvariable variable=JI_JAVA_HOME]$HOME/Library/Android/$(XA.Jdk8.Folder)"
+      displayName: reset JI_JAVA_HOME for Designer
+      condition: and(succeeded(), eq(variables['agent.os'], 'Darwin'))
+
+    - script: |
+        echo ##vso[task.setvariable variable=JI_JAVA_HOME]%USERPROFILE%\android-toolchain\$(XA.Jdk8.Folder)
+      displayName: reset JI_JAVA_HOME for Designer
+      condition: and(succeeded(), eq(variables['agent.os'], 'Windows_NT'))
 
     - template: designer\android-designer-build-win.yaml@yaml
+      parameters:
+        designerSourcePath: $(System.DefaultWorkingDirectory)\designer
 
     - template: designer\android-designer-tests.yaml@yaml
+      parameters:
+        designerSourcePath: $(System.DefaultWorkingDirectory)\designer
 
     - task: CopyFiles@2
       displayName: 'Copy binlogs'
       inputs:
-        sourceFolder: Xamarin.Designer.Android
+        sourceFolder: $(System.DefaultWorkingDirectory)/designer/Xamarin.Designer.Android
         contents: '**/*.binlog'
         targetFolder: $(Build.ArtifactStagingDirectory)/designer-binlogs
         overWrite: true

build-tools/automation/yaml-templates/setup-test-environment.yaml

@@ -1,6 +1,7 @@
 parameters:
   configuration: $(XA.Build.Configuration)
   provisionExtraArgs: -vv -f
+  xaSourcePath: $(System.DefaultWorkingDirectory)
 
 steps:
 - checkout: self
@@ -11,6 +12,15 @@ steps:
   parameters:
     provisionExtraArgs: ${{ parameters.provisionExtraArgs }}
 
+- script: echo "##vso[task.setvariable variable=JI_JAVA_HOME]$HOME/Library/Android/$(XA.Jdk11.Folder)"
+  displayName: set JI_JAVA_HOME
+  condition: and(succeeded(), eq(variables['agent.os'], 'Darwin'))
+
+- script: |
+    echo ##vso[task.setvariable variable=JI_JAVA_HOME]%USERPROFILE%\android-toolchain\$(XA.Jdk11.Folder)
+  displayName: set JI_JAVA_HOME
+  condition: and(succeeded(), eq(variables['agent.os'], 'Windows_NT'))
+
 - template: use-dot-net.yaml
   parameters:
     version: $(DotNetCorePreviewVersion)
@@ -33,20 +43,20 @@ steps:
 - task: MSBuild@1
   displayName: build xaprepare
   inputs:
-    solution: build-tools/xaprepare/xaprepare.sln
+    solution: ${{ parameters.xaSourcePath }}/build-tools/xaprepare/xaprepare.sln
     configuration: ${{ parameters.configuration }}
     msbuildArguments: /restore
 
 - script: >
-    mono build-tools/xaprepare/xaprepare/bin/${{ parameters.configuration }}/xaprepare.exe --s=UpdateMono --auto-provision=yes --auto-provision-uses-sudo=yes --no-emoji --run-mode=CI &&
-    mono build-tools/xaprepare/xaprepare/bin/${{ parameters.configuration }}/xaprepare.exe --s=Required --auto-provision=yes --auto-provision-uses-sudo=yes --no-emoji --run-mode=CI &&
-    mono build-tools/xaprepare/xaprepare/bin/${{ parameters.configuration }}/xaprepare.exe --s=AndroidToolchain --no-emoji --run-mode=CI
+    mono ${{ parameters.xaSourcePath }}/build-tools/xaprepare/xaprepare/bin/${{ parameters.configuration }}/xaprepare.exe --s=UpdateMono --auto-provision=yes --auto-provision-uses-sudo=yes --no-emoji --run-mode=CI &&
+    mono ${{ parameters.xaSourcePath }}/build-tools/xaprepare/xaprepare/bin/${{ parameters.configuration }}/xaprepare.exe --s=Required --auto-provision=yes --auto-provision-uses-sudo=yes --no-emoji --run-mode=CI &&
+    mono ${{ parameters.xaSourcePath }}/build-tools/xaprepare/xaprepare/bin/${{ parameters.configuration }}/xaprepare.exe --s=AndroidToolchain --no-emoji --run-mode=CI
   displayName: install test dependencies
   condition: and(succeeded(), eq(variables['agent.os'], 'Darwin'))
 
 - script: >
-    $(System.DefaultWorkingDirectory)\build-tools\xaprepare\xaprepare\bin\${{ parameters.configuration }}\xaprepare.exe --s=Required --auto-provision=yes --no-emoji --run-mode=CI &&
-    $(System.DefaultWorkingDirectory)\build-tools\xaprepare\xaprepare\bin\${{ parameters.configuration }}\xaprepare.exe --s=AndroidToolchain --no-emoji --run-mode=CI
+    ${{ parameters.xaSourcePath }}\build-tools\xaprepare\xaprepare\bin\${{ parameters.configuration }}\xaprepare.exe --s=Required --auto-provision=yes --no-emoji --run-mode=CI &&
+    ${{ parameters.xaSourcePath }}\build-tools\xaprepare\xaprepare\bin\${{ parameters.configuration }}\xaprepare.exe --s=AndroidToolchain --no-emoji --run-mode=CI
   displayName: install test dependencies
   condition: and(succeeded(), eq(variables['agent.os'], 'Windows_NT'))
 
@@ -59,17 +69,17 @@ steps:
   displayName: nuget restore Xamarin.Android.Build.Tasks.sln
   inputs:
     command: custom
-    arguments: restore Xamarin.Android.Build.Tasks.sln -ConfigFile NuGet.config
+    arguments: restore ${{ parameters.xaSourcePath }}/Xamarin.Android.Build.Tasks.sln -ConfigFile ${{ parameters.xaSourcePath }}/NuGet.config -Verbosity detailed
 
 - task: NuGetCommand@2
   displayName: nuget restore Xamarin.Android-Tests.sln
   inputs:
     command: custom
-    arguments: restore Xamarin.Android-Tests.sln -ConfigFile NuGet.config
+    arguments: restore ${{ parameters.xaSourcePath }}/Xamarin.Android-Tests.sln -ConfigFile ${{ parameters.xaSourcePath }}/NuGet.config -Verbosity detailed
 
 - task: MSBuild@1
   displayName: build Xamarin.Android.Tools.BootstrapTasks.csproj
   inputs:
-    solution: build-tools/xamarin.Android.Tools.BootstrapTasks/Xamarin.Android.Tools.BootstrapTasks.csproj
+    solution: ${{ parameters.xaSourcePath }}/build-tools/xamarin.Android.Tools.BootstrapTasks/Xamarin.Android.Tools.BootstrapTasks.csproj
     configuration: ${{ parameters.configuration }}
-    msbuildArguments: /restore /bl:$(System.DefaultWorkingDirectory)/bin/Test${{ parameters.configuration }}/BootstrapTasks.binlog
+    msbuildArguments: /restore /bl:${{ parameters.xaSourcePath }}/bin/Test${{ parameters.configuration }}/BootstrapTasks.binlog

build-tools/xaprepare/xaprepare/ConfigAndData/Configurables.cs

@@ -54,7 +54,7 @@ public static partial class Defaults
 		{
 			public static readonly char[] PropertyListSeparator            = new [] { ':' };
 
-			public static readonly string JdkFolder                        = "jdk-1.8";
+			public static readonly string JdkFolder                        = "jdk-11";
 
 			public static readonly Version JetBrainsOpenJDK11Version = new Version (Configurables.JetBrainsOpenJDK11Version);
 			public static readonly Version JetBrainsOpenJDK11Release = new Version (Configurables.JetBrainsOpenJDK11Release);

build-tools/xaprepare/xaprepare/Steps/Step_PrepareExternalJavaInterop.Unix.cs

@@ -20,6 +20,7 @@ async Task<bool> ExecuteOSSpecific (Context context)
 					"prepare",
 					"V=1",
 					$"CONFIGURATION={context.Configuration}",
+					$"JI_JAVA_HOME={context.OS.JavaHome}",
 					$"JAVA_HOME={context.OS.JavaHome}",
 					$"JI_MAX_JDK={Configurables.Defaults.MaxJDKVersion}",
 				}

samples/HelloWorld/HelloLibrary/HelloLibrary.csproj

@@ -13,9 +13,15 @@
     <AssemblyName>HelloLibrary</AssemblyName>
     <FileAlignment>512</FileAlignment>
     <AndroidApplication>false</AndroidApplication>
-    <AndroidUseLatestPlatformSdk>True</AndroidUseLatestPlatformSdk>
     <DebugType>portable</DebugType>
   </PropertyGroup>
+  <Import
+      Condition="Exists('..\..\..\Configuration.props')"
+      Project="..\..\..\Configuration.props"
+  />
+  <PropertyGroup Condition="Exists('..\..\..\Configuration.props')">
+    <TargetFrameworkVersion>$(AndroidFrameworkVersion)</TargetFrameworkVersion>
+  </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>
     <Optimize>false</Optimize>

samples/HelloWorld/HelloWorld.csproj

@@ -14,8 +14,6 @@
     <AndroidManifest>Properties\AndroidManifest.xml</AndroidManifest>
     <MonoAndroidResourcePrefix>Resources</MonoAndroidResourcePrefix>
     <MonoAndroidAssetsPrefix>Assets</MonoAndroidAssetsPrefix>
-    <AndroidUseLatestPlatformSdk>true</AndroidUseLatestPlatformSdk>
-    <TargetFrameworkVersion>v7.1</TargetFrameworkVersion>
     <AndroidDexTool Condition=" '$(AndroidDexTool)' == '' ">d8</AndroidDexTool>
     <DebugType>portable</DebugType>
   </PropertyGroup>

src/Xamarin.Android.Build.Tasks/MSBuild/Xamarin/Android/Xamarin.Android.Bindings.Documentation.targets

@@ -16,7 +16,12 @@ This file is only used by binding projects. .NET 5 can eventually use it, once `
   <UsingTask TaskName="Xamarin.Android.Tasks.MDoc"          AssemblyFile="Xamarin.Android.Build.Tasks.dll" />
   <UsingTask TaskName="Xamarin.Android.Tasks.Unzip"         AssemblyFile="Xamarin.Android.Build.Tasks.dll" />
 
+  <PropertyGroup>
+    <_JavadocSupported Condition=" $(_JdkVersion.StartsWith ('1.8')) ">True</_JavadocSupported>
+  </PropertyGroup>
+
   <Target Name="_ExtractJavaDocJars"
+      Condition=" '$(_JavadocSupported)' == 'True' "
       Inputs="@(JavaDocJar)"
       Outputs="@(JavaDocJar->'$(IntermediateOutputPath)javadocs\%(FileName).stamp')">
     <Unzip
@@ -30,6 +35,7 @@ This file is only used by binding projects. .NET 5 can eventually use it, once `
   </Target>
 
   <Target Name="_GenerateJavaDocFromSourceJars"
+      Condition=" '$(_JavadocSupported)' == 'True' "
       Inputs="@(JavaSourceJar)"
       Outputs="@(JavaSourceJar->'$(IntermediateOutputPath)javadocs\%(FileName).stamp')">
     <Unzip
@@ -51,9 +57,9 @@ This file is only used by binding projects. .NET 5 can eventually use it, once `
   </Target>
 
   <Target Name="BuildDocumentation"
+      Condition=" '@(JavaDocIndex)' != '' And '$(_JavadocSupported)' == 'True' "
       Inputs="@(JavaDocIndex);@(IntermediateAssembly->'$(IntermediateOutputPath)%(filename).xml')"
-      Outputs="@(IntermediateAssembly->'$(OutputPath)%(filename).xml')"
-      Condition=" '@(JavaDocIndex)' != '' ">
+      Outputs="@(IntermediateAssembly->'$(OutputPath)%(filename).xml')">
     <MDoc
         References="@(ReferencePath);@(ReferenceDependencyPaths)"
         TargetAssembly="@(IntermediateAssembly)"

src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.props

@@ -5,7 +5,7 @@
   <PropertyGroup>
     <UsingAndroidNETSdk>true</UsingAndroidNETSdk>
     <AndroidCommandLineToolsVersion Condition=" '$(AndroidCommandLineToolsVersion)' == '' ">1.0</AndroidCommandLineToolsVersion>
-    <LatestSupportedJavaVersion  Condition=" '$(LatestSupportedJavaVersion)' == '' ">1.8.0</LatestSupportedJavaVersion>
+    <LatestSupportedJavaVersion  Condition=" '$(LatestSupportedJavaVersion)' == '' ">11.0.4</LatestSupportedJavaVersion>
     <MinimumSupportedJavaVersion Condition=" '$(MinimumSupportedJavaVersion)' == '' ">1.8.0</MinimumSupportedJavaVersion>
     <EnableDefaultOutputPaths Condition=" '$(EnableDefaultOutputPaths)' == '' And '$(OS)' != 'Windows_NT' ">false</EnableDefaultOutputPaths>
     <EnableDefaultOutputPaths Condition=" '$(EnableDefaultOutputPaths)' == '' ">true</EnableDefaultOutputPaths>

src/Xamarin.Android.Build.Tasks/Tasks/Legacy/ValidateJavaVersion.cs

@@ -48,6 +48,13 @@ protected override bool ValidateJava (string javaExe, Regex versionRegex)
 		Version GetJavaVersionForFramework ()
 		{
 			var apiLevel = MonoAndroidHelper.SupportedVersions.GetApiLevelFromFrameworkVersion (TargetFrameworkVersion);
+			if (apiLevel >= 30) {
+				// At present, it *looks like* API-R works with Build-tools r29, but
+				// historically API-X requires Build-tools rX, so if/when API-30
+				// requires Build-tools r30, it will require JDK11.
+				// return new Version (11, 0);
+				return new Version (1, 8);
+			}
 			if (apiLevel >= 24)
 				return new Version (1, 8);
 			else if (apiLevel == 23)
@@ -58,10 +65,18 @@ Version GetJavaVersionForFramework ()
 
 		Version GetJavaVersionForBuildTools ()
 		{
+			string buildToolsVersionString = AndroidSdkBuildToolsVersion;
+			if (buildToolsVersionString != null) {
+				int index = buildToolsVersionString.IndexOf ('-');
+				if (index != -1)
+					buildToolsVersionString = buildToolsVersionString.Substring (0, index);
+			}
 			Version buildTools;
-			if (!Version.TryParse (AndroidSdkBuildToolsVersion, out buildTools)) {
+			if (!Version.TryParse (buildToolsVersionString, out buildTools)) {
 				return Version.Parse (LatestSupportedJavaVersion);
 			}
+			if (buildTools >= new Version (30, 0, 0))
+				return new Version (11, 0);
 			if (buildTools >= new Version (24, 0, 1))
 				return new Version (1, 8);
 			return Version.Parse (MinimumSupportedJavaVersion);