Initial commit

Add a minimal no-core Rust executable built by invoking rustc directly from CMake.

The project avoids Cargo and Rust core, alloc, and std, writes to stdout
through platform APIs, and supports optimized Ninja release builds.

Co-Authored-By: luna (openrouter/openai/gpt-5.6-luna): project setup and build

CMakeLists.txt

@@ -0,0 +1,52 @@
+cmake_minimum_required(VERSION 3.20)
+project(no_core_write LANGUAGES NONE)
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+
+find_program(RUSTC rustc REQUIRED)
+
+set(RUST_SOURCE "${CMAKE_CURRENT_SOURCE_DIR}/main.rs")
+set(RUST_BINARY "${CMAKE_CURRENT_BINARY_DIR}/no_core_write${CMAKE_EXECUTABLE_SUFFIX}")
+
+# no_core is an unstable rustc feature. RUSTC_BOOTSTRAP lets this deliberately
+# minimal example be built with the installed compiler without Cargo or core.
+set(RUSTC_ENV "RUSTC_BOOTSTRAP=1")
+set(RUSTC_FLAGS -C panic=abort)
+
+# CMAKE_BUILD_TYPE does not automatically affect a custom rustc command.
+# Pass the corresponding optimization/debug-info settings explicitly.
+if (CMAKE_BUILD_TYPE STREQUAL "Release")
+    list(APPEND RUSTC_FLAGS -C opt-level=3 -C debuginfo=0)
+elseif (CMAKE_BUILD_TYPE STREQUAL "RelWithDebInfo")
+    list(APPEND RUSTC_FLAGS -C opt-level=3 -C debuginfo=2)
+else()
+    list(APPEND RUSTC_FLAGS -C opt-level=0 -C debuginfo=2)
+endif()
+
+# A no_core binary does not get Rust's normal startup/linker setup. Link the
+# small platform system/runtime library needed by the stdout implementation.
+if (WIN32)
+    # Use Win32 directly instead of the C runtime; this keeps the executable
+    # small while still writing to the console's stdout handle.
+    set(RUSTC_LINK_ARGS
+        -l kernel32
+        -C
+        "link-args=/NODEFAULTLIB /ENTRY:mainCRTStartup /SUBSYSTEM:CONSOLE /OPT:REF /OPT:ICF"
+    )
+elseif (UNIX)
+    set(RUSTC_LINK_ARGS -C "link-args=-lc")
+endif()
+
+add_custom_command(
+    OUTPUT "${RUST_BINARY}"
+    COMMAND "${CMAKE_COMMAND}" -E env "${RUSTC_ENV}" "${RUSTC}"
+            "${RUST_SOURCE}"
+            --crate-name no_core_write
+            --crate-type bin
+            -o "${RUST_BINARY}"
+            ${RUSTC_FLAGS}
+            ${RUSTC_LINK_ARGS}
+    DEPENDS "${RUST_SOURCE}"
+    VERBATIM
+)
+
+add_custom_target(no_core_write ALL DEPENDS "${RUST_BINARY}")