rust: Simple rust hello_world application

Create the Rust equivalent of the hello_world application.  This shows
the use of printk from Rust as well as accessing a string value from
Kconfig.

Signed-off-by: David Brown <[email protected]>

Author: d3zd3z

samples/rust/.gitignore

@@ -0,0 +1,7 @@
+# Cargo drops lock files in projects to capture resolved dependencies.
+# We don't want to record these.
+Cargo.lock
+
+# Cargo encourates a .cargo/config.toml file to symlink to a generated
+# file.  Don't save these.
+.cargo/

samples/rust/hello_rust/CMakeLists.txt

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+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(hello_world)
+
+rust_cargo_application()

samples/rust/hello_rust/Cargo.toml

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+# Copyright (c) 2024 Linaro LTD
+# SPDX-License-Identifier: Apache-2.0
+
+[package]
+# This must be rustapp for now.
+name = "rustapp"
+version = "0.1.0"
+edition = "2021"
+description = "A sample hello world application in Rust"
+license = "Apache-2.0 or MIT"
+
+[lib]
+crate-type = ["staticlib"]
+
+[dependencies]
+zephyr = "0.1.0"

samples/rust/hello_rust/prj.conf

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+# Copyright (c) 2024 Linaro LTD
+# SPDX-License-Identifier: Apache-2.0
+
+CONFIG_RUST=y

samples/rust/hello_rust/sample.yaml

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+sample:
+  description: Hello world, but in Rust
+  name: hello rust
+common:
+  harness: console
+  harness_config:
+    type: one_line
+    regex:
+      - "Hello world from Rust on (.*)"
+  filter: CONFIG_RUST_SUPPORTED
+tests:
+  sample.rust.hellorust:
+    tags: introduction

samples/rust/hello_rust/src/lib.rs

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+// Copyright (c) 2024 Linaro LTD
+// SPDX-License-Identifier: Apache-2.0
+
+#![no_std]
+
+use zephyr::printkln;
+
+// Reference the Zephyr crate so that the panic handler gets used.  This is only needed if no
+// symbols from the crate are directly used.
+extern crate zephyr;
+
+#[no_mangle]
+extern "C" fn rust_main() {
+    printkln!("Hello world from Rust on {}",
+              zephyr::kconfig::CONFIG_BOARD);
+}