[mono-runtimes] Try to download Mono archive before building mono (#2265)

Context: https://github.com/xamarin/xamarin-android/projects/10

A goal of the [Mono SDKs Integration][0] project is to allow the
xamarin-android build to consume a "mono archive", which is *like*
our mono bundle (fbfd676, 2956811), but different in that it *only*
contains Mono-related "stuff" (there's no `libzip` in it), and
(more importantly) it's maintained and updated by the mono team.

  * **Mono Bundle**: xamarin-android provided file which contains
    Mono Runtimes, BCL assemblies, unit test assemblies, and various
    other files which are "part of" mono, *plus* some things that
    aren't related to mono at all, such as `libzip` native libs.

  * **Mono Archive**: Mono-team provided file which contains
    Mono Runtimes, BCL assemblies, unit test assemblies, and various
    other files which are part of mono.

The Mono Archive only exists for mono:master and
[soon mono:2018-08][1] -- while xamarin-android is currently on
mono:2018-06, so there is no current mono archive that can be
used (!) -- and even if it did exist, *integration* is still
"in-progress."  In particular, xamarin-android currently has no code
to build `libzip.dll` *on Windows*, so without the Mono Bundle,
xamarin-android cannot currently build on Windows (ignoring the fact
that 38100c0 would cause a Windows build to fail if the Mono Bundle
didn't already exist...).

Introduce some "baby steps" in using the Mono Archive as part of the
xamarin-android build:

 1. `build-tools/download-bundle` still exists, and will attempt to
    download and extract the Mono Bundle.

 2. If the bundle from (1) does not exist and we build
    `src/mono-runtimes`, `mono-runtimes` will try to download the
    Mono Archive.

 3. If (2) *fails* -- which *currently* will always be the case --
    then "fallback" to a "from source" mono build, as we've been
    doing since time immemorial.

 4. If (2) *succeeds* -- which hasn't been tested on a PR machine,
    but has been manually tested, so there may be dragons here! -- 
    then the Mono Archive will be extracted and the contents of the
    Mono Archive copied to where the rest of the xamarin-android
    build expects those files to be.

 5. "Later" in the build, the `build-tools/create-bundle` project
    will *still* be executed, and thus the Mono Bundle will *still*
    be created, and the Mono Bundle will *still* be uploaded to
    Jenkins when run as part of the [Jenkins job][2].

At some future point in time, we *may* stop using the Mono Bundle.
That time is not nigh, and may never happen.

[0]: https://github.com/xamarin/xamarin-android/projects/10
[1]: https://xamarinhq.slack.com/archives/C03CEGRUW/p1539362217000100
[2]: https://jenkins.mono-project.com/view/Xamarin.Android/job/xamarin-android/

Author: luhenry

build-tools/xa-prep-tasks/Xamarin.Android.BuildTools.PrepTasks/GitCommitHash.cs

@@ -16,6 +16,9 @@ public sealed class GitCommitHash : Git
 		[Output]
 		public                  string      AbbreviatedCommitHash       { get; set; }
 
+		[Output]
+		public                  string      CommitHash       { get; set; }
+
 		protected   override    bool        LogTaskMessages             {
 			get { return false; }
 		}
@@ -38,17 +41,18 @@ public override bool Execute ()
 
 		protected override string GenerateCommandLineCommands ()
 		{
-			return "log --no-color --first-parent -n1 --pretty=format:%h";
+			return "rev-parse HEAD";
 		}
 
 		protected override void LogEventsFromTextOutput (string singleLine, MessageImportance messageImportance)
 		{
 			if (string.IsNullOrEmpty (singleLine))
 				return;
-			if (singleLine.Length < RequiredHashLength) {
-				Log.LogError ("Abbreviated commit hash `{0}` is shorter than required length of {1} characters", singleLine, RequiredHashLength);
+			if (singleLine.Length < 40) {
+				Log.LogError ("Commit hash `{0}` is shorter than required length of {1} characters", singleLine, 40);
 				return;
 			}
+			CommitHash = singleLine;
 			AbbreviatedCommitHash = singleLine.Substring (0, RequiredHashLength);
 		}
 	}

external/mono

@@ -1,5 +1,9 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <ItemGroup>
+    <_MonoBcl Include="bcl" />
+  </ItemGroup>
+
   <ItemGroup>
     <_MonoRuntime Include="armeabi-v7a" Condition=" $(AndroidSupportedTargetJitAbisForConditionalChecks.Contains (':armeabi-v7a:')) ">
       <Strip>$(AndroidToolchainDirectory)\toolchains\armeabi-v7a-clang\bin\arm-linux-androideabi-strip</Strip>
@@ -60,27 +64,16 @@
       <OutputMonoBtlsFilename></OutputMonoBtlsFilename>
       <OutputMonoPosixHelperFilename>libMonoPosixHelper</OutputMonoPosixHelperFilename>
     </_MonoRuntime>
-    <_MonoRuntime Include="host-Darwin" Condition="$(AndroidSupportedHostJitAbisForConditionalChecks.Contains (':Darwin:'))">
-      <Strip>strip</Strip>
-      <StripFlags>-S</StripFlags>
-      <OutputRuntimeFilename>libmonosgen-2.0</OutputRuntimeFilename>
-      <NativeLibraryExtension>dylib</NativeLibraryExtension>
-      <OutputProfilerFilename>libmono-profiler-log</OutputProfilerFilename>
-      <OutputAotProfilerFilename>libmono-profiler-aot</OutputAotProfilerFilename>
-      <OutputMonoBtlsFilename></OutputMonoBtlsFilename>
-      <OutputMonoPosixHelperFilename>libMonoPosixHelper</OutputMonoPosixHelperFilename>
-      <BuildTests>True</BuildTests>
-    </_MonoRuntime>
-    <_MonoRuntime Include="host-Linux" Condition="$(AndroidSupportedHostJitAbisForConditionalChecks.Contains (':Linux:'))">
+    <_MonoRuntime Include="host-$(HostOS)" Condition="$(AndroidSupportedHostJitAbisForConditionalChecks.Contains (':$(HostOS):')) And ( '$(HostOS)' == 'Darwin' Or '$(HostOS)' == 'Linux' )">
       <Strip>strip</Strip>
       <StripFlags>-S</StripFlags>
       <OutputRuntimeFilename>libmonosgen-2.0</OutputRuntimeFilename>
-      <NativeLibraryExtension>so</NativeLibraryExtension>
+      <NativeLibraryExtension Condition=" '$(HostOS)' == 'Darwin' ">dylib</NativeLibraryExtension>
+      <NativeLibraryExtension Condition=" '$(HostOS)' == 'Linux' ">so</NativeLibraryExtension>
       <OutputProfilerFilename>libmono-profiler-log</OutputProfilerFilename>
       <OutputAotProfilerFilename>libmono-profiler-aot</OutputAotProfilerFilename>
       <OutputMonoBtlsFilename></OutputMonoBtlsFilename>
       <OutputMonoPosixHelperFilename>libMonoPosixHelper</OutputMonoPosixHelperFilename>
-      <BuildTests>True</BuildTests>
     </_MonoRuntime>
   </ItemGroup>
 
@@ -91,15 +84,13 @@
       <InstallBinaries>true</InstallBinaries>
       <InstallPath Condition="$(AndroidSupportedHostJitAbisForConditionalChecks.Contains (':Darwin:'))">Darwin/</InstallPath>
       <InstallPath Condition="$(AndroidSupportedHostJitAbisForConditionalChecks.Contains (':Linux:'))">Linux/</InstallPath>
-      <PackageOptions>llvm-llvm32_CC="$(HostCc32)" llvm-llvm32_CXX="$(HostCxx32)"</PackageOptions>
     </_LlvmRuntime>
 
     <_LlvmRuntime Include="llvm64" Condition=" ($(AndroidSupportedTargetAotAbisForConditionalChecks.Contains (':arm64:')) Or $(AndroidSupportedTargetAotAbisForConditionalChecks.Contains (':x86_64:'))) And '$(HostBits)' == '64' ">
       <ExeSuffix></ExeSuffix>
       <InstallBinaries>true</InstallBinaries>
       <InstallPath Condition="$(AndroidSupportedHostJitAbisForConditionalChecks.Contains (':Darwin:'))">Darwin/</InstallPath>
       <InstallPath Condition="$(AndroidSupportedHostJitAbisForConditionalChecks.Contains (':Linux:'))">Linux/</InstallPath>
-      <PackageOptions>llvm-llvm64_CC="$(HostCc64)" llvm-llvm64_CXX="$(HostCxx64)"</PackageOptions>
     </_LlvmRuntime>
 
     <_LlvmRuntime Include="llvmwin32" Condition=" ($(AndroidSupportedTargetAotAbisForConditionalChecks.Contains (':win-armeabi-v7a:')) Or $(AndroidSupportedTargetAotAbisForConditionalChecks.Contains (':win-x86:'))) ">