package/pkg-cargo: allow building in a sub-directory

Some packages have their rust sources as a sub-directory, rather
than at the root of the source tree.

Do like we do for autotools-package, and use the package's _SRCDIR
rather than the top-level directory $(@D).

Additionally, in such a situation, it is more than probable that
the Cargo.toml is also present in that sub-directory, so use that
when vendoring the package.

Signed-off-by: Yann E. MORIN <yann.morin@orange.com>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

docs/manual/adding-packages-cargo.txt

@@ -73,6 +73,11 @@ A few additional variables, specific to the Cargo infrastructure, can
 also be defined. Many of them are only useful in very specific cases,
 typical packages will therefore only use a few of them.
 
+* +FOO_SUBDIR+ may contain the name of a subdirectory inside the package
+  that contains the Cargo.toml file. This is useful, if for example, it
+  is not at the root of the tree extracted by the tarball. If
+  +HOST_FOO_SUBDIR+ is not specified, it defaults to +FOO_SUBDIR+.
+
 * +FOO_CARGO_ENV+ can be used to pass additional variables in the
   environment of +cargo+ invocations. It used at both build and
   installation time

package/pkg-cargo.mk

@@ -71,6 +71,11 @@ $(2)_DOWNLOAD_DEPENDENCIES += host-rustc
 $(2)_DOWNLOAD_POST_PROCESS = cargo
 $(2)_DL_ENV += CARGO_HOME=$$(HOST_DIR)/share/cargo
 
+# If building in a sub directory, use that to find the Cargo.toml
+ifneq ($$($(2)_SUBDIR),)
+$(2)_DL_ENV += BR_CARGO_MANIFEST_PATH=$$($(2)_SUBDIR)/Cargo.toml
+endif
+
 # Due to vendoring, it is pretty likely that not all licenses are
 # listed in <pkg>_LICENSE.
 $(2)_LICENSE += , vendored dependencies licenses probably not listed
@@ -97,7 +102,7 @@ $(2)_LICENSE += , vendored dependencies licenses probably not listed
 ifndef $(2)_BUILD_CMDS
 ifeq ($(4),target)
 define $(2)_BUILD_CMDS
-	cd $$(@D) && \
+	cd $$($$(PKG)_SRCDIR) && \
 	$$(TARGET_MAKE_ENV) \
 		$$(TARGET_CONFIGURE_OPTS) \
 		$$(PKG_CARGO_ENV) \
@@ -111,7 +116,7 @@ define $(2)_BUILD_CMDS
 endef
 else # ifeq ($(4),target)
 define $(2)_BUILD_CMDS
-	cd $$(@D) && \
+	cd $$($$(PKG)_SRCDIR) && \
 	$$(HOST_MAKE_ENV) \
 		RUSTFLAGS="$$(addprefix -C link-args=,$$(HOST_LDFLAGS))" \
 		$$(HOST_CONFIGURE_OPTS) \
@@ -133,7 +138,7 @@ endif # ifndef $(2)_BUILD_CMDS
 #
 ifndef $(2)_INSTALL_TARGET_CMDS
 define $(2)_INSTALL_TARGET_CMDS
-	cd $$(@D) && \
+	cd $$($$(PKG)_SRCDIR) && \
 	$$(TARGET_MAKE_ENV) \
 		$$(TARGET_CONFIGURE_OPTS) \
 		$$(PKG_CARGO_ENV) \
@@ -152,7 +157,7 @@ endif
 
 ifndef $(2)_INSTALL_CMDS
 define $(2)_INSTALL_CMDS
-	cd $$(@D) && \
+	cd $$($$(PKG)_SRCDIR) && \
 	$$(HOST_MAKE_ENV) \
 		RUSTFLAGS="$$(addprefix -C link-args=,$$(HOST_LDFLAGS))" \
 		$$(HOST_CONFIGURE_OPTS) \