[build] Use API-21 for all native builds

Up until this commit, we have been building the 64-bit targets (`x86-64`
and `armv8-a` against NDK API 21 while the 32-bit targets (`x86` and
`armv7-a`) against NDK API 16.  This commit changes it so that all
targets build against API 21.  This gives us the ability to speed up
Debug builds on 32-bit platforms via use of  POSIX APIs for directory
traversal that are available starting from API 21 onwards (`openat` and
`fstatat`).  The switch to API 21 was initially planned for .NET5 but
there's no harm in making the change now.

In addition, this commit updates versions of several components:

  * Bump emulator version to 30.0.5
  * Bump NDK version to 21b (21.1.6352462)
  * Bump x86 system image revision to 7

Also, `XABuildConfig.NDKMinimumApiAvailable` is now set to the minimum
supported NDK API level instead of the minimum API level *installed* by
the NDK.

Author: grendello

Configuration.props

@@ -136,8 +136,8 @@
     <AndroidToolPath Condition=" '$(AndroidToolPath)' == '' ">$(AndroidSdkFullPath)\tools</AndroidToolPath>
     <AndroidToolsBinPath Condition=" '$(AndroidToolsBinPath)' == '' ">$(AndroidToolPath)\bin</AndroidToolsBinPath>
     <AndroidToolExe Condition=" '$(AndroidToolExe)' == '' ">android</AndroidToolExe>
-    <EmulatorVersion Condition=" '$(EmulatorVersion)' == '' ">5598178</EmulatorVersion>
-    <EmulatorPkgRevision Condition=" '$(EmulatorPkgRevision)' == '' ">29.0.11</EmulatorPkgRevision>
+    <EmulatorVersion Condition=" '$(EmulatorVersion)' == '' ">6306047</EmulatorVersion>
+    <EmulatorPkgRevision Condition=" '$(EmulatorPkgRevision)' == '' ">30.0.5</EmulatorPkgRevision>
     <EmulatorToolPath Condition=" '$(EmulatorToolPath)' == '' ">$(AndroidSdkFullPath)\emulator</EmulatorToolPath>
     <EmulatorToolExe Condition=" '$(EmulatorToolExe)' == '' ">emulator</EmulatorToolExe>
     <NdkBuildPath Condition=" '$(NdkBuildPath)' == '' And '$(HostOS)' != 'Windows' ">$(AndroidNdkDirectory)\ndk-build</NdkBuildPath>

Documentation/release-notes/4584.md

@@ -0,0 +1,16 @@
+### Minimum compatible Android version now Android 5.0 Lollipop (API level 21)
+
+The minimum compatible Android version for Xamarin.Android apps is now Android
+5.0 Lollipop (API level 21).  Warning XA4216 has been updated to help highlight
+this change for any projects that might still have an older version set for the
+`minSdkVersion` in the `AndroidManifest.xml` file:
+
+```
+warning XA4216: AndroidManifest.xml //uses-sdk/@android:minSdkVersion '20' is less than API-21, this configuration is not supported.
+```
+
+#### Background information
+
+The unmanaged native libraries that are part of Xamarin.Android are now built to
+target Android 5.0 Lollipop (API level 21), so apps built using this release can
+abort due to incompatible APIs if run on earlier Android versions.

build-tools/api-merge/merge-configuration.xml

@@ -21,8 +21,6 @@
     <File Path="api-R.xml.in" Level="R" />
   </Inputs>
   <Outputs>
-    <File Path="android-19\mcw\api.xml" LastLevel="19" />
-    <File Path="android-20\mcw\api.xml" LastLevel="20" />
     <File Path="android-21\mcw\api.xml" LastLevel="21" />
     <File Path="android-22\mcw\api.xml" LastLevel="22" />
     <File Path="android-23\mcw\api.xml" LastLevel="23" />

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

@@ -5,8 +5,8 @@ namespace Xamarin.Android.Prepare
 {
 	class BuildAndroidPlatforms
 	{
-		public const string AndroidNdkVersion = "21";
-		public const string AndroidNdkPkgRevision = "21.0.6113669";
+		public const string AndroidNdkVersion = "21b";
+		public const string AndroidNdkPkgRevision = "21.1.6352462";
 
 		public static readonly List<AndroidPlatform> AllPlatforms = new List<AndroidPlatform> {
 			new AndroidPlatform (apiName: "",                       apiLevel: 1,  platformID: "1"),
@@ -27,8 +27,8 @@ class BuildAndroidPlatforms
 			new AndroidPlatform (apiName: "Jelly Bean",             apiLevel: 16, platformID: "16",  include: "v4.1"),
 			new AndroidPlatform (apiName: "Jelly Bean",             apiLevel: 17, platformID: "17",  include: "v4.2"),
 			new AndroidPlatform (apiName: "Jelly Bean",             apiLevel: 18, platformID: "18",  include: "v4.3"),
-			new AndroidPlatform (apiName: "Kit Kat",                apiLevel: 19, platformID: "19",  include: "v4.4",    framework: "v4.4"),
-			new AndroidPlatform (apiName: "Kit Kat + Wear support", apiLevel: 20, platformID: "20",  include: "v4.4.87", framework: "v4.4.87"),
+			new AndroidPlatform (apiName: "Kit Kat",                apiLevel: 19, platformID: "19",  include: "v4.4"),
+			new AndroidPlatform (apiName: "Kit Kat + Wear support", apiLevel: 20, platformID: "20",  include: "v4.4.87"),
 			new AndroidPlatform (apiName: "Lollipop",               apiLevel: 21, platformID: "21",  include: "v5.0",    framework: "v5.0"),
 			new AndroidPlatform (apiName: "Lollipop",               apiLevel: 22, platformID: "22",  include: "v5.1",    framework: "v5.1"),
 			new AndroidPlatform (apiName: "Marshmallow",            apiLevel: 23, platformID: "23",  include: "v6.0",    framework: "v6.0"),
@@ -42,9 +42,9 @@ class BuildAndroidPlatforms
 		};
 
 		public static readonly Dictionary<string, uint> NdkMinimumAPI = new Dictionary<string, uint> {
-			{ AbiNames.TargetJit.AndroidArmV7a, 16 },
+			{ AbiNames.TargetJit.AndroidArmV7a, 21 },
 			{ AbiNames.TargetJit.AndroidArmV8a, 21 },
-			{ AbiNames.TargetJit.AndroidX86,    16 },
+			{ AbiNames.TargetJit.AndroidX86,    21 },
 			{ AbiNames.TargetJit.AndroidX86_64, 21 },
 		};
 	}

build-tools/xaprepare/xaprepare/ConfigAndData/Dependencies/AndroidToolchain.cs

@@ -44,7 +44,10 @@ public AndroidToolchain ()
 
 				new AndroidToolchainComponent ("docs-24_r01",                                       destDir: "docs", pkgRevision: "1"),
 				new AndroidToolchainComponent ("android_m2repository_r47",                          destDir: Path.Combine ("extras", "android", "m2repository"), pkgRevision: "47.0.0"),
-				new AndroidToolchainComponent ("x86-29_r06",                                        destDir: Path.Combine ("system-images", "android-29", "default", "x86"), relativeUrl: new Uri ("sys-img/android/", UriKind.Relative), pkgRevision: "6"),
+
+				// NOTE: for some reason x86-29_r07 zips are tagged with the OS name, JUST this system image - when
+				// updating to a latter version check if that's changed or not.
+				new AndroidToolchainComponent ($"x86-29_r07-{osTag}",                               destDir: Path.Combine ("system-images", "android-29", "default", "x86"), relativeUrl: new Uri ("sys-img/android/", UriKind.Relative), pkgRevision: "7"),
 				new AndroidToolchainComponent ($"android-ndk-r{AndroidNdkVersion}-{osTag}-x86_64",  destDir: AndroidNdkDirectory, pkgRevision: AndroidPkgRevision),
 				new AndroidToolchainComponent ($"build-tools_r{XABuildToolsVersion}-{altOsTag}",    destDir: Path.Combine ("build-tools", XABuildToolsFolder), isMultiVersion: true),
 				new AndroidToolchainComponent ($"platform-tools_r{XAPlatformToolsVersion}-{osTag}", destDir: "platform-tools", pkgRevision: XAPlatformToolsVersion),

build-tools/xaprepare/xaprepare/Steps/Step_GenerateFiles.cs

@@ -114,10 +114,17 @@ GeneratedFile Get_XABuildConfig_cs (Context context)
 		{
 			const string OutputFileName = "XABuildConfig.cs";
 
+			uint minimumApiAvailable = UInt32.MaxValue;
+			foreach (uint api in BuildAndroidPlatforms.NdkMinimumAPI.Values) {
+				if (api > minimumApiAvailable)
+					continue;
+				minimumApiAvailable = api;
+			}
+
 			var replacements = new Dictionary<string, string> (StringComparer.Ordinal) {
 				{ "@NDK_REVISION@",              context.BuildInfo.NDKRevision },
 				{ "@NDK_RELEASE@",               BuildAndroidPlatforms.AndroidNdkVersion },
-				{ "@NDK_MINIMUM_API_AVAILABLE@", context.BuildInfo.NDKMinimumApiAvailable },
+				{ "@NDK_MINIMUM_API_AVAILABLE@", minimumApiAvailable.ToString () },
 				{ "@NDK_VERSION_MAJOR@",         context.BuildInfo.NDKVersionMajor },
 				{ "@NDK_VERSION_MINOR@",         context.BuildInfo.NDKVersionMinor },
 				{ "@NDK_VERSION_MICRO@",         context.BuildInfo.NDKVersionMicro },

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Tasks/NdkUtilTests.cs

@@ -41,7 +41,7 @@ public void TestNdkUtil ()
 				Assert.IsTrue (NdkUtil.ValidateNdkPlatform (log, ndkDir, arch, enableLLVM: false));
 				Assert.AreEqual (0, errors.Count, "NdkUtil.ValidateNdkPlatform should not have returned false.");
 				int level = NdkUtil.GetMinimumApiLevelFor (arch, ndkDir);
-				int expected = 16;
+				int expected = 21;
 				Assert.AreEqual (expected, level, $"Min Api Level for {arch} should be {expected}.");
 				var compilerNoQuotes = NdkUtil.GetNdkTool (ndkDir, arch, "gcc", level);
 				Assert.AreEqual (0, errors.Count, "NdkUtil.GetNdkTool should not have errored.");

src/monodroid/jni/embedded-assemblies.cc

@@ -583,7 +583,7 @@ EmbeddedAssemblies::typemap_read_header ([[maybe_unused]] int dir_fd, const char
 	struct stat sbuf;
 	int res;
 
-#if __ANDROID_API__ < 21
+#if defined (WINDOWS)
 	simple_pointer_guard<char[]> full_file_path = utils.path_combine (dir_path, file_path);
 	res = stat (full_file_path, &sbuf);
 #else
@@ -600,7 +600,7 @@ EmbeddedAssemblies::typemap_read_header ([[maybe_unused]] int dir_fd, const char
 		return false;
 	}
 
-#if __ANDROID_API__ < 21
+#if defined (WINDOWS)
 	fd = open (full_file_path, O_RDONLY);
 #else
 	fd = openat (dir_fd, file_path, O_RDONLY);
@@ -800,7 +800,7 @@ EmbeddedAssemblies::try_load_typemaps_from_directory (const char *path)
 	}
 
 	int dir_fd;
-#if __ANDROID_API__ < 21
+#if WINDOWS
 	dir_fd = -1;
 #else
 	dir_fd = dirfd (dir);