package/pkg-cargo: configure cargo profiles

pkg-cargo currently sets the --release flag unless BR2_ENABLE_DEBUG is
set. However, this does not accurately reflect the configured build
settings. In addition, it only works for packages that use the cargo
infrastructure directory and not with packages using the cargo
environment indirectly, such as pyo3 based python packages. To support
these, we really want to pass the necessary flags in PKG_CARGO_ENV.

In order to accurately reflect the configured build settings
(optimization and debug levels), we set the appropriate environment
variables according to the global settings.

There is no way to specify the profile to use through an environment
variable, it has to be set through a cargo flag like --release. Since we
can't easily control the profile flags used by non-cargo package
infrastructures, we instead set the env variables for both root profiles
(dev/release). For the aspects that are not affected by the global
settings (incremental, codegen-units, split-debuginfo), we set them
equal to the default for release - which in our context is the
appropriate choice even when BR2_ENABLE_DEBUG is set.

For reference the default cargo root profile settings are:
https://doc.rust-lang.org/cargo/reference/profiles.html#default-profiles

Cc: Moritz Bitsch <moritz@h6t.eu>
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Tested-by: Moritz Bitsch <moritz@h6t.eu>
Tested-by: Adam Duskett <adam.duskett@amarulasolutions.com>
Reviewed-by: Adam Duskett <adam.duskett@amarulasolutions.com>
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>

package/pkg-cargo.mk

@@ -53,6 +53,106 @@ PKG_CARGO_ENV = \
 	CARGO_HOST_RUSTFLAGS="$(addprefix -C link-args=,$(HOST_LDFLAGS))" \
 	CARGO_TARGET_$(call UPPERCASE,$(RUSTC_TARGET_NAME))_LINKER=$(notdir $(TARGET_CROSS))gcc
 
+# We always set both CARGO_PROFILE_DEV and CARGO_PROFILE_RELEASE
+# as we are unable to select a build profile using the environment.
+#
+# Other cargo profiles generally derive from these two profiles.
+
+# Disable incremental compilation to match release default.
+#
+# Set codegen-units to release default.
+#
+# Set split-debuginfo to default off for ELF platforms.
+PKG_CARGO_ENV += \
+	CARGO_PROFILE_DEV_INCREMENTAL="false" \
+	CARGO_PROFILE_RELEASE_INCREMENTAL="false" \
+	CARGO_PROFILE_DEV_CODEGEN_UNITS="16" \
+	CARGO_PROFILE_RELEASE_CODEGEN_UNITS="16" \
+	CARGO_PROFILE_DEV_SPLIT_DEBUGINFO="off" \
+	CARGO_PROFILE_RELEASE_SPLIT_DEBUGINFO="off"
+
+# Set the optimization level with the release default as fallback.
+ifeq ($(BR2_OPTIMIZE_0),y)
+PKG_CARGO_ENV += \
+	CARGO_PROFILE_DEV_OPT_LEVEL="0" \
+	CARGO_PROFILE_RELEASE_OPT_LEVEL="0"
+else ifeq ($(BR2_OPTIMIZE_1),y)
+PKG_CARGO_ENV += \
+	CARGO_PROFILE_DEV_OPT_LEVEL="1" \
+	CARGO_PROFILE_RELEASE_OPT_LEVEL="1"
+else ifeq ($(BR2_OPTIMIZE_2),y)
+PKG_CARGO_ENV += \
+	CARGO_PROFILE_DEV_OPT_LEVEL="2" \
+	CARGO_PROFILE_RELEASE_OPT_LEVEL="2"
+else ifeq ($(BR2_OPTIMIZE_3),y)
+PKG_CARGO_ENV += \
+	CARGO_PROFILE_DEV_OPT_LEVEL="3" \
+	CARGO_PROFILE_RELEASE_OPT_LEVEL="3"
+else ifeq ($(BR2_OPTIMIZE_G),y)
+PKG_CARGO_ENV += \
+	CARGO_PROFILE_DEV_OPT_LEVEL="0" \
+	CARGO_PROFILE_RELEASE_OPT_LEVEL="0"
+else ifeq ($(BR2_OPTIMIZE_S),y)
+PKG_CARGO_ENV += \
+	CARGO_PROFILE_DEV_OPT_LEVEL="s" \
+	CARGO_PROFILE_RELEASE_OPT_LEVEL="s"
+else ifeq ($(BR2_OPTIMIZE_FAST),y)
+PKG_CARGO_ENV += \
+	CARGO_PROFILE_DEV_OPT_LEVEL="3" \
+	CARGO_PROFILE_RELEASE_OPT_LEVEL="3"
+else
+PKG_CARGO_ENV += \
+	CARGO_PROFILE_DEV_OPT_LEVEL="3" \
+	CARGO_PROFILE_RELEASE_OPT_LEVEL="3"
+endif
+
+ifeq ($(BR2_ENABLE_LTO),y)
+PKG_CARGO_ENV += \
+	CARGO_PROFILE_DEV_LTO="true" \
+	CARGO_PROFILE_RELEASE_LTO="true"
+else
+PKG_CARGO_ENV += \
+	CARGO_PROFILE_DEV_LTO="false" \
+	CARGO_PROFILE_RELEASE_LTO="false"
+endif
+
+
+ifeq ($(BR2_ENABLE_DEBUG),y)
+ifeq ($(BR2_DEBUG_3),y)
+# full debug info
+PKG_CARGO_ENV += \
+	CARGO_PROFILE_DEV_DEBUG="2" \
+	CARGO_PROFILE_RELEASE_DEBUG="2"
+else
+# line tables only
+PKG_CARGO_ENV += \
+	CARGO_PROFILE_DEV_DEBUG="1" \
+	CARGO_PROFILE_RELEASE_DEBUG="1"
+endif
+else
+# no debug info
+PKG_CARGO_ENV += \
+	CARGO_PROFILE_DEV_DEBUG="0" \
+	CARGO_PROFILE_RELEASE_DEBUG="0"
+endif
+
+# Enabling debug-assertions enables the runtime debug_assert! macro.
+#
+# Enabling overflow-checks enables runtime panic on integer overflow.
+ifeq ($(BR2_ENABLE_RUNTIME_DEBUG),y)
+PKG_CARGO_ENV += \
+	CARGO_PROFILE_DEV_DEBUG_ASSERTIONS="true" \
+	CARGO_PROFILE_RELEASE_DEBUG_ASSERTIONS="true" \
+	CARGO_PROFILE_DEV_OVERFLOW_CHECKS="true" \
+	CARGO_PROFILE_RELEASE_OVERFLOW_CHECKS="true"
+else
+PKG_CARGO_ENV += \
+	CARGO_PROFILE_DEV_DEBUG_ASSERTIONS="false" \
+	CARGO_PROFILE_RELEASE_DEBUG_ASSERTIONS="false" \
+	CARGO_PROFILE_DEV_OVERFLOW_CHECKS="false" \
+	CARGO_PROFILE_RELEASE_OVERFLOW_CHECKS="false"
+endif
+
 #
 # This is a workaround for https://github.com/rust-lang/compiler-builtins/issues/420
 # and should be removed when fixed upstream