Merge #18820: build: Propagate well-known vars into depends

f0d7ed10b4 depends: Propagate only specific CLI variables to sub-makes (Carl Dong)
0a33803f1c depends: boost: Use clang toolset if clang in CXX (Carl Dong)
1ce74bcde3 depends: boost: Split target-os from toolset (Carl Dong)
2d4e480813 depends: boost: Specify toolset to bootstrap.sh (Carl Dong)
3d6603e340 depends: Propagate well-known vars into depends (Carl Dong)

Pull request description:

  From: https://github.com/bitcoin/bitcoin/pull/18308#issuecomment-598301117

  The following monstrosity is quite useful when invoked inside `depends`, and reviewers can use it to compare the behaviour of this change against master.
  ```bash
  make print-{{,{host,{,{i686,x86_64,riscv64}_}linux}_}{CC,CXX},boost_{cc,cxx}}
  ```

  It would also be helpful to make sure that setting `HOST`, `CC`, and `CXX` does the right thing. The 3 hosts I found offered good coverage were: `{x86_64,i686,riscv64}-linux-gnu`. As we special-case the `x86_64` and `i686` hosts in `depends/hosts/linux.mk`, and `riscv64` is a sanity check for a non-special-cased host.

ACKs for top commit:
  hebasto:
    ACK f0d7ed10b4, tested on Linux Mint 19.3 (x86_64):
  practicalswift:
    ACK f0d7ed10b4 -- patch looks correct
  laanwj:
    Code review and concept ACK f0d7ed10b4
  ryanofsky:
    Code review ACK f0d7ed10b4. Changes since last review: adding comment explaining check for predefined make variables, dropping freetype commit, adding commit whitelisting overrides for recursive makes

Tree-SHA512: b6b8e76f713c26a0add6cd685824e2f5639109236ee9f89338f7c79cb1b1f2c3897bfb62b80b023d6d1943b5a6eb282a2f827f1f499c5e556eca015d6635fa65

depends/Makefile

@@ -4,6 +4,30 @@
 print-%:
 	@echo $* = $($*)
 
+# When invoking a sub-make, keep only the command line variable definitions
+# matching the pattern in the filter function.
+#
+# e.g. invoking:
+#   $ make A=1 C=1 print-MAKEOVERRIDES print-MAKEFLAGS
+#
+# with the following in the Makefile:
+#   MAKEOVERRIDES := $(filter A=% B=%,$(MAKEOVERRIDES))
+#
+# will print:
+#   MAKEOVERRIDES = A=1
+#   MAKEFLAGS = -- A=1
+#
+# this is because as the GNU make manual says:
+#   The command line variable definitions really appear in the variable
+#   MAKEOVERRIDES, and MAKEFLAGS contains a reference to this variable.
+#
+# and since the GNU make manual also says:
+#   variables defined on the command line are passed to the sub-make through
+#   MAKEFLAGS
+#
+# this means that sub-makes will be invoked as if:
+#   $(MAKE) A=1 blah blah
+MAKEOVERRIDES := $(filter V=%,$(MAKEOVERRIDES))
 SOURCES_PATH ?= $(BASEDIR)/sources
 WORK_PATH = $(BASEDIR)/work
 BASE_CACHE ?= $(BASEDIR)/built

depends/hosts/default.mk

@@ -13,9 +13,18 @@ default_host_OTOOL = $(host_toolchain)otool
 default_host_NM = $(host_toolchain)nm
 
 define add_host_tool_func
+ifneq ($(filter $(origin $1),undefined default),)
+# Do not consider the well-known var $1 if it is undefined or is taking a value
+# that is predefined by "make" (e.g. the make variable "CC" has a predefined
+# value of "cc")
 $(host_os)_$1?=$$(default_host_$1)
 $(host_arch)_$(host_os)_$1?=$$($(host_os)_$1)
 $(host_arch)_$(host_os)_$(release_type)_$1?=$$($(host_os)_$1)
+else
+$(host_os)_$1=$(or $($1),$($(host_os)_$1),$(default_host_$1))
+$(host_arch)_$(host_os)_$1=$(or $($1),$($(host_arch)_$(host_os)_$1),$$($(host_os)_$1))
+$(host_arch)_$(host_os)_$(release_type)_$1=$(or $($1),$($(host_arch)_$(host_os)_$(release_type)_$1),$$($(host_os)_$1))
+endif
 host_$1=$$($(host_arch)_$(host_os)_$1)
 endef
 

depends/packages/boost.mk

@@ -9,9 +9,9 @@ $(package)_config_opts_release=variant=release
 $(package)_config_opts_debug=variant=debug
 $(package)_config_opts=--layout=tagged --build-type=complete --user-config=user-config.jam
 $(package)_config_opts+=threading=multi link=static -sNO_BZIP2=1 -sNO_ZLIB=1
-$(package)_config_opts_linux=threadapi=pthread runtime-link=shared
-$(package)_config_opts_darwin=--toolset=clang-darwin runtime-link=shared
-$(package)_config_opts_mingw32=binary-format=pe target-os=windows threadapi=win32 runtime-link=static
+$(package)_config_opts_linux=target-os=linux threadapi=pthread runtime-link=shared
+$(package)_config_opts_darwin=target-os=darwin runtime-link=shared
+$(package)_config_opts_mingw32=target-os=windows binary-format=pe threadapi=win32 runtime-link=static
 $(package)_config_opts_x86_64_mingw32=address-model=64
 $(package)_config_opts_i686_mingw32=address-model=32
 $(package)_config_opts_i686_linux=address-model=32 architecture=x86
@@ -20,8 +20,11 @@ $(package)_config_opts_aarch64_android=address-model=64
 $(package)_config_opts_x86_64_android=address-model=64
 $(package)_config_opts_armv7a_android=address-model=32
 $(package)_toolset_$(host_os)=gcc
+$(package)_toolset_darwin=clang
+ifneq (,$(findstring clang,$($(package)_cxx)))
+   $(package)_toolset_$(host_os)=clang
+endif
 $(package)_archiver_$(host_os)=$($(package)_ar)
-$(package)_toolset_darwin=clang-darwin
 $(package)_config_libraries=filesystem,system,thread,test
 $(package)_cxxflags=-std=c++11 -fvisibility=hidden
 $(package)_cxxflags_linux=-fPIC
@@ -33,13 +36,13 @@ define $(package)_preprocess_cmds
 endef
 
 define $(package)_config_cmds
-  ./bootstrap.sh --without-icu --with-libraries=$($(package)_config_libraries)
+  ./bootstrap.sh --without-icu --with-libraries=$($(package)_config_libraries) --with-toolset=$($(package)_toolset_$(host_os))
 endef
 
 define $(package)_build_cmds
-  ./b2 -d2 -j2 -d1 --prefix=$($(package)_staging_prefix_dir) $($(package)_config_opts) stage
+  ./b2 -d2 -j2 -d1 --prefix=$($(package)_staging_prefix_dir) $($(package)_config_opts) toolset=$($(package)_toolset_$(host_os)) stage
 endef
 
 define $(package)_stage_cmds
-  ./b2 -d0 -j4 --prefix=$($(package)_staging_prefix_dir) $($(package)_config_opts) install
+  ./b2 -d0 -j4 --prefix=$($(package)_staging_prefix_dir) $($(package)_config_opts) toolset=$($(package)_toolset_$(host_os)) install
 endef