Add a bunch of Make targets to help rebuilding Mono runtime and BCL

This basically implements the steps described in
Documentation/DevelopmentTips.md for the runtime and BCL assembles. Short help
is available by running

   make rebuild-help

Documentation/DevelopmentTips.md

@@ -4,6 +4,50 @@ Tips and tricks while developing Xamarin.Android.
 
 # How do I rebuild the Mono Runtime and Native Binaries?
 
+## The short way
+
+From the top of the Xamarin Android source tree you can run make for the following
+targets, which implement the steps to rebuild the runtime and BCL described further
+down in the document:
+
+    # Show help on all the rebuild targets
+    make rebuild-help
+
+    # Rebuild Mono runtime for all configured architectures regardless
+    # of whether a cached copy was used.
+    rebuild-mono
+
+    # Rebuild and install Mono runtime for the armeabi architecture only regardless
+    # of whether a cached copy was used.
+    rebuild-armeabi-mono
+
+    # Rebuild and install Mono runtime for the armeabi-v7a architecture only regardless
+    # of whether a cached copy was used.
+    rebuild-armeabi-v7a-mono
+
+    # Rebuild and install Mono runtime for the arm64-v8a architecture only regardless
+    # of whether a cached copy was used.
+    rebuild-arm64-v8a-mono
+
+    # Rebuild and install Mono runtime for the x86 architecture only regardless
+    # of whether a cached copy was used.
+    rebuild-x86-mono
+
+    # Rebuild and install Mono runtime for the x86_64 architecture only regardless
+    # of whether a cached copy was used.
+    rebuild-x86_64-mono
+
+    # Rebuild and install a specific BCL assembly. Assembly name must be passed in the ASSEMBLY Make variable
+    rebuild-bcl-assembly ASSEMBLY=bcl_assembly_name
+
+    # Rebuild and install all the BCL assemblies
+    rebuild-all-bcl
+
+Note that rebuilding Mono using the targets above will modify the commit at the git HEAD by resetting
+its date to the current one (see below for more info) - do *NOT* commit the change to Mono as it rewrites
+history.
+
+## The long way
 The various Mono runtimes -- over *20* of them (!) -- all store object code
 within `build-tools/mono-runtimes/obj/$(Configuration)/TARGET`.
 

Makefile

@@ -141,3 +141,5 @@ run-ji-tests:
 
 run-apk-tests:
 	$(MSBUILD) $(MSBUILD_FLAGS) $(TEST_TARGETS) /t:RunApkTests
+
+include build-tools/scripts/runtime-helpers.mk

build-tools/scripts/runtime-helpers.mk

@@ -0,0 +1,95 @@
+#
+# Various helper/shortcut targets
+#
+MONO_RUNTIMES_DIR = build-tools/mono-runtimes
+MONO_RUNTIMES_PROJECT = $(MONO_RUNTIMES_DIR)/mono-runtimes.mdproj
+MONO_RUNTIMES_BUILD_DIR = $(MONO_RUNTIMES_DIR)/obj/$(CONFIGURATION)
+
+# $(1) - architecture name
+define CreateMonoRebuildRuleForArch
+rebuild-$(1)-mono: touch-mono-head
+	@if ! test -d $$(MONO_RUNTIMES_BUILD_DIR)/$(1); then \
+		echo $$(MONO_RUNTIMES_BUILD_DIR)/$(1) ; \
+		echo Runtime for architecture $(1) and configuration $$(CONFIGURATION) was not built yet or is not enabled in configuration or cached Mono runtime was installed ; \
+		echo In order to build Mono for $(1) please enable it in Configuration.Override.props file and ; \
+		echo Run the following command: make rebuild-mono ; \
+		exit 1 ; \
+	fi
+	$$(MAKE) -C $$(MONO_RUNTIMES_BUILD_DIR)/$(1)
+	$$(MSBUILD) /t:_InstallRuntimes $$(MONO_RUNTIMES_PROJECT)
+
+.PHONY: rebuild-$(1)-mono
+endef
+
+#
+# This is less than ideal, but that's how things are right now.
+# Do NOT push the change to Mono!
+#
+touch-mono-head:
+	@(cd external/mono; git commit --amend -C HEAD --date="`date`")
+
+rebuild-mono: rebuild-all-mono
+rebuild-mono-runtime: rebuild-all-mono
+rebuild-all-mono: touch-mono-head
+	$(MSBUILD) /t:ForceBuild $(MONO_RUNTIMES_PROJECT)
+
+$(foreach arch,$(ALL_JIT_ABIS),$(eval $(call CreateMonoRebuildRuleForArch,$(arch))))
+
+.PHONY: rebuild-mono rebuild-all-mono touch-mono-head
+
+rebuild-mono-bcl-assembly: rebuild-bcl-assembly
+rebuild-bcl-assembly:
+	@if [ -z "$(ASSEMBLY)" ]; then \
+		echo Assembly name required. Run make as follows: ; \
+		echo $(MAKE) ASSEMBLY=bcl_assembly_name ; \
+		exit 1 ; \
+	fi
+	$(MAKE) -C external/mono/mcs/class/$(ASSEMBLY)/ PROFILE=monodroid
+	$(MSBUILD) /t:_InstallBcl $(MONO_RUNTIMES_PROJECT)
+
+rebuild-all-bcl:
+	@if [ ! -d $(MONO_RUNTIMES_BUILD_DIR)/host-$(OS) ]; then \
+		echo Host Mono runtime for $(OS) has not been built ; \
+		echo or cached Mono runtime was installed ; \
+		echo In order to build host Mono for $(OS) please enable it in Configuration.Override.props file and ; \
+		echo Run the following command: make rebuild-mono ; \
+		echo Unable to rebuild all BCL assemblies ; \
+		exit 1 ; \
+	fi
+	make -C $(MONO_RUNTIMES_BUILD_DIR)/host-$(OS)
+
+.PHONY: rebuild-bcl-assembly rebuild-all-bcl
+
+#
+# $(1) - arch name
+#
+# NOTE: the first empty line must stay since Make displays it verbatim...
+#
+define MonoArchRebuildHelp
+
+	@echo "  rebuild-$(1)-mono"
+	@echo "     Rebuild and install Mono runtime for the $(1) architecture only regardless"
+	@echo "     of whether a cached copy was used."
+	@echo
+endef
+
+rebuild-help:
+	@echo Helper targets to rebuild and install the Mono runtime and BCL assemblies
+	@echo
+	@echo "  rebuild-mono-runtime"
+	@echo "     Rebuild and install Mono runtime for all configured architectures regardless"
+	@echo "     of whether a cached copy was used."
+	@echo
+	$(foreach arch,$(ALL_JIT_ABIS),$(call MonoArchRebuildHelp,$(arch)))
+	@echo "  rebuild-mono-bcl-assembly ASSEMBLY=bcl_assembly_name"
+	@echo "     Where 'bcl_assembly_name' is base name of the assembly to rebuild, e.g. 'System' or 'System.Data'"
+	@echo "     Rebuild and install a specific BCL assembly. Assembly name must be passed in the ASSEMBLY Make variable"
+	@echo
+	@echo "  rebuild-all-bcl"
+	@echo "     Rebuild and install all the BCL assemblies"
+	@echo
+	@echo "ALL the rebuild-*-mono targets (including rebuild-mono) will modify the HEAD commit of Mono in external/mono"
+	@echo "DO NOT UNDER ANY CIRCUMSTANCES PUSH THAT CHANGE TO MONO UPSTREAM"
+	@echo
+
+.PHONY: rebuild-help