makefiles/rust: Use --profile as was stabilized already in Rust 1.51

makefiles/cargo-settings.inc.mk

@@ -1,5 +1,7 @@
-# Setting anything other than "debug" or "release" will necessitate additional
-# -Z unstable-options as of 2021-03 nightlies.
+# The profile with which to build Rust usually `release` or `dev`.
+#
+# This needs to be known to the build scripts because the path of the produced
+# binary is derived from this.
 CARGO_PROFILE ?= release
 
 # Value for CARGO_CHANNEL when using nightly
@@ -42,4 +44,10 @@ CARGO_CHANNEL ?=
 CARGO_TARGET_DIR = $(BINDIR)/target
 
 # The single Rust library to be built.
-CARGO_LIB = $(CARGO_TARGET_DIR)/$(RUST_TARGET)/${CARGO_PROFILE}/lib$(APPLICATION_RUST_MODULE).a
+#
+# The dev->debug and bench->release substitutions represent a historical
+# peculiarity in cargo: "For historical reasons, the `dev` and `test` profiles
+# are stored in the `debug` directory, and the `release` and `bench` profiles
+# are stored in the `release` directory. User-defined profiles are stored in a
+# directory with the same name as the profile".
+CARGO_LIB = $(CARGO_TARGET_DIR)/$(RUST_TARGET)/$(patsubst test,debug,$(patsubst dev,debug,$(patsubst bench,release,${CARGO_PROFILE})))/lib$(APPLICATION_RUST_MODULE).a

makefiles/cargo-targets.inc.mk

@@ -66,7 +66,7 @@ $(CARGO_LIB): $(RIOTBUILD_CONFIG_HEADER_C) $(BUILDDEPS) $(CARGO_COMPILE_COMMANDS
 		cargo $(patsubst +,,+${CARGO_CHANNEL}) \
 			build \
 			--target $(RUST_TARGET) \
-			`if [ x$(CARGO_PROFILE) = xrelease ]; then echo --release; else if [ x$(CARGO_PROFILE) '!=' xdebug ]; then echo "--profile $(CARGO_PROFILE)"; fi; fi` \
+			--profile $(CARGO_PROFILE) \
 			$(CARGO_OPTIONS)
 
 $(APPLICATION_RUST_MODULE).module: $(CARGO_LIB) FORCE