examples/rust: Avoid the infinite loop on sim for hello_rust_cargo

On the sim target (Windows/macOS/Linux), hello_rust_cargo_main() ended
with an infinite `loop {}` that never returned control to NSH, so the
example could not exit and the shell prompt hung.

Introduce a Cargo `sim` feature that is enabled only when CONFIG_ARCH_SIM
is set, and use it to compile out the trailing infinite loop and return 0
instead. Other embedded targets keep the original looping behavior.

Signed-off-by: Shoji Tokunaga <toku@mac.com>

cmake/nuttx_add_rust.cmake

@@ -130,6 +130,8 @@ endfunction()
 #    hello
 #    CRATE_PATH
 #    ${CMAKE_CURRENT_SOURCE_DIR}/hello
+#    FEATURES
+#    sim
 #  )
 # ~~~
 
@@ -142,6 +144,8 @@ function(nuttx_add_rust)
     ONE_VALUE
     CRATE_NAME
     CRATE_PATH
+    MULTI_VALUE
+    FEATURES
     REQUIRED
     CRATE_NAME
     CRATE_PATH
@@ -159,6 +163,10 @@ function(nuttx_add_rust)
     set(RUST_PANIC_FLAGS "")
   endif()
 
+  foreach(feature ${FEATURES})
+    list(APPEND RUST_FEATURE_FLAGS --features ${feature})
+  endforeach()
+
   # Get the Rust target triple
   nuttx_rust_target_triple(${LLVM_ARCHTYPE} ${LLVM_ABITYPE} ${LLVM_CPUTYPE}
                            RUST_TARGET)
@@ -198,7 +206,7 @@ function(nuttx_add_rust)
       RUSTFLAGS=${RUST_PANIC_FLAGS} cargo build ${RUST_PROFILE_FLAG}
       -Zbuild-std=std,panic_abort -Zjson-target-spec --manifest-path
       ${CRATE_PATH}/Cargo.toml --target ${RUST_TARGET} --target-dir
-      ${RUST_BUILD_DIR}
+      ${RUST_BUILD_DIR} ${RUST_FEATURE_FLAGS}
     DEPENDS ${RUST_CRATE_SOURCES}
     COMMENT "Building Rust crate ${CRATE_NAME}"
     VERBATIM)

examples/rust/hello/CMakeLists.txt

@@ -21,7 +21,12 @@
 if(CONFIG_EXAMPLES_HELLO_RUST_CARGO)
 
   # Build the Rust crate using nuttx_add_rust
-  nuttx_add_rust(CRATE_NAME hello CRATE_PATH ${CMAKE_CURRENT_SOURCE_DIR})
+  if(CONFIG_ARCH_SIM)
+    nuttx_add_rust(CRATE_NAME hello CRATE_PATH ${CMAKE_CURRENT_SOURCE_DIR}
+                   FEATURES sim)
+  else()
+    nuttx_add_rust(CRATE_NAME hello CRATE_PATH ${CMAKE_CURRENT_SOURCE_DIR})
+  endif()
 
   nuttx_add_application(
     NAME ${CONFIG_EXAMPLES_HELLO_RUST_CARGO_PROGNAME} STACKSIZE

examples/rust/hello/Cargo.toml

@@ -6,6 +6,9 @@ edition = "2021"
 [lib]
 crate-type = ["staticlib"]
 
+[features]
+sim = []
+
 [profile.dev]
 panic = "abort"
 

examples/rust/hello/Makefile

@@ -30,8 +30,12 @@ MODULE    = $(CONFIG_EXAMPLES_HELLO_RUST_CARGO)
 RUST_LIB  := $(call RUST_GET_BINDIR,hello,$(APPDIR)/examples/rust)
 RUST_SRCS := $(call RUST_CARGO_SRCS,hello,$(APPDIR)/examples/rust)
 
+ifeq ($(CONFIG_ARCH_SIM),y)
+HELLO_RUST_FEATURES := sim
+endif
+
 $(RUST_LIB): $(RUST_SRCS)
-	$(call RUST_CARGO_BUILD,hello,$(APPDIR)/examples/rust)
+	$(call RUST_CARGO_BUILD,hello,$(APPDIR)/examples/rust,$(HELLO_RUST_FEATURES))
 
 context:: $(RUST_LIB)
 

examples/rust/hello/src/lib.rs

@@ -1,6 +1,7 @@
 extern crate serde;
 extern crate serde_json;
 
+use core::ffi::{c_char, c_int};
 use serde::{Deserialize, Serialize};
 
 #[derive(Serialize, Deserialize)]
@@ -11,7 +12,7 @@ struct Person {
 
 // Function hello_rust_cargo without manglng
 #[no_mangle]
-pub extern "C" fn hello_rust_cargo_main() {
+pub extern "C" fn hello_rust_cargo_main(_argc: c_int, _argv: *mut *mut c_char) -> c_int {
     // Print hello world to stdout
 
     let john = Person {
@@ -50,7 +51,11 @@ pub extern "C" fn hello_rust_cargo_main() {
             println!("Hello world from tokio!");
         });
 
+    #[cfg(not(feature = "sim"))]
     loop {
         // Do nothing
     }
+
+    #[cfg(feature = "sim")]
+    0
 }

tools/Rust.mk

@@ -90,11 +90,12 @@ endef
 
 # Build Rust project using cargo
 #
-# Usage:   $(call RUST_CARGO_BUILD,cratename,prefix)
+# Usage:   $(call RUST_CARGO_BUILD,cratename,prefix[,features])
 #
 # Inputs:
 #   cratename - Name of the Rust crate (e.g. hello)
 #   prefix    - Path prefix to the crate (e.g. path/to/project)
+#   features  - Optional Cargo features to enable
 #
 # Output:
 #   None, builds the Rust project
@@ -105,7 +106,8 @@ define RUST_CARGO_BUILD
     RUSTFLAGS="-Zunstable-options -Cpanic=immediate-abort" \
     cargo build --release -Zbuild-std=std,panic_abort -Zjson-target-spec \
 		--manifest-path $(2)/$(1)/Cargo.toml \
-		--target $(call RUST_TARGET_TRIPLE)
+		--target $(call RUST_TARGET_TRIPLE) \
+		$(if $(strip $(3)),--features $(3),)
 endef
 else
 define RUST_CARGO_BUILD
@@ -113,7 +115,8 @@ define RUST_CARGO_BUILD
 	NUTTX_INCLUDE_DIR=$(TOPDIR)/include:$(TOPDIR)/include/arch \
     cargo build -Zbuild-std=std,panic_abort -Zjson-target-spec \
 		--manifest-path $(2)/$(1)/Cargo.toml \
-		--target $(call RUST_TARGET_TRIPLE)
+		--target $(call RUST_TARGET_TRIPLE) \
+		$(if $(strip $(3)),--features $(3),)
 endef
 endif