Add $(python,...) built-in

[jserv]

This introduces a portable $(python,...) preprocessor function that evaluates a Python code string in-process via exec(), returning "y" on success and "n" on exception. 'exec' namespace exposes os, sys, shutil, platform, and a shell-free run(*argv) helper for subprocess checks. Each call receives a fresh globals copy for namespace isolation.

Rewrite all six toolchain functions (cc-option, ld-option, as-instr, as-option, cc-option-bit, rustc-option) to use subprocess.Popen with argument lists (shell=False) and os.devnull, eliminating /dev/null, 2>/dev/null, and printf-pipe constructs. This closes the shell injection vector from environment variables and makes the functions work on Windows.

Add _run_argv() helper with timeout support and proper process cleanup. Remove dead _run_cmd_in_tmpdir(); replaced by TemporaryDirectory context managers in individual functions.

Add quote tracking to the macro expander so that commas and parentheses inside single, double, and triple-quoted strings are not treated as argument separators (required for $(python,assert "a,b" == "a,b")).

Close #41

---

Summary by cubic

Adds a portable $(python,...) built-in for in-process boolean checks and makes all Kbuild toolchain functions shell-free and Windows-compatible. Improves macro expansion with robust quote handling and adds subprocess timeouts. Closes #41.

• New Features

  • Added $(python,code): execs in-process, returns y on success and n on exception; exposes os, sys, shutil, platform, and run(*argv) in a fresh namespace per call.
  • SystemExit(0/None/"") → y; non-zero/truthy → n. AssertionError is silent; other exceptions emit a warning with type and message.
  • Macro expander now tracks single/double/triple quotes and escapes; nested macros inside quotes still expand, and commas/parentheses inside quotes are not treated as separators.
  • Updated KBUILD.md with usage examples, portability guidance, and quoting behavior.

• Refactors

  • Rewrote cc-option, ld-option, as-instr, as-option, cc-option-bit, and rustc-option to use subprocess.Popen with argv (shell=False) and os.devnull; removes shell injection risk and works on Windows.
  • Added _run_argv() with a 30s timeout and proper cleanup; _run_cmd now uses DEVNULL and a timeout. Exposed shell-free run() to $(python,...) code.
  • Removed _run_cmd_in_tmpdir(); callers use TemporaryDirectory. Expanded tests to cover $(python,...) and quote tracking.

^{Written for commit 4c399d9. Summary will update on new commits.}

[jserv]

@eastWillow , You can apply changes below against Mado:

-- Kconfig-old	2026-02-21 20:12:01.979993489 +0800
+++ Kconfig	2026-02-22 01:18:58.406339526 +0800
@@ -7,22 +7,26 @@
 menu "Toolchain Configuration"
 
 # Compiler detection using scripts/detect-compiler.py
-config COMPILER_TYPE
-    string
-    default "$(shell,scripts/detect-compiler.py 2>/dev/null || echo Unknown)"
-
 config CC_IS_EMCC
-    def_bool $(shell,scripts/detect-compiler.py --is Emscripten 2>/dev/null && echo y || echo n)
+    def_bool $(python,assert run(sys.executable, 'scripts/detect-compiler.py', '--is', 'Emscripten'))
 
 config CC_IS_CLANG
-    def_bool $(shell,scripts/detect-compiler.py --is Clang 2>/dev/null && echo y || echo n)
+    def_bool $(python,assert run(sys.executable, 'scripts/detect-compiler.py', '--is', 'Clang'))
 
 config CC_IS_GCC
-    def_bool $(shell,scripts/detect-compiler.py --is GCC 2>/dev/null && echo y || echo n)
+    def_bool $(python,assert run(sys.executable, 'scripts/detect-compiler.py', '--is', 'GCC'))
+
+# Derived from the boolean probes above -- no shell needed.
+config COMPILER_TYPE
+    string
+    default "Emscripten" if CC_IS_EMCC
+    default "Clang" if CC_IS_CLANG
+    default "GCC" if CC_IS_GCC
+    default "Unknown"
 
 # Cross-compilation support detection
 config CROSS_COMPILE_ENABLED
-    def_bool $(shell,test -n "$(CROSS_COMPILE)" && echo y || echo n)
+    def_bool $(python,assert os.environ.get('CROSS_COMPILE'))
 
 config CROSS_COMPILE_PREFIX
     string
@@ -41,32 +45,32 @@
 
 endmenu
 
-# Dependency detection using Kconfiglib shell function
+# Dependency detection via pkg-config (shell-free subprocess).
 # For Emscripten builds, libraries are provided via ports system (-sUSE_*)
-# and do not require host pkg-config detection
+# and do not require host pkg-config detection.
 
 config HAVE_SDL2
     bool
     default n if CC_IS_EMCC
-    default $(shell,pkg-config --exists sdl2 && echo y || echo n) if !CC_IS_EMCC
+    default $(python,assert run('pkg-config', '--exists', 'sdl2')) if !CC_IS_EMCC
 
 config HAVE_PIXMAN
     default n if CC_IS_EMCC
-    def_bool $(shell,pkg-config --exists pixman-1 && echo y || echo n) if !CC_IS_EMCC
+    def_bool $(python,assert run('pkg-config', '--exists', 'pixman-1')) if !CC_IS_EMCC
 
 config HAVE_LIBPNG
     bool
     default y if CC_IS_EMCC
-    default $(shell,pkg-config --exists libpng && echo y || echo n) if !CC_IS_EMCC
+    default $(python,assert run('pkg-config', '--exists', 'libpng')) if !CC_IS_EMCC
 
 config HAVE_LIBJPEG
     bool
     default y if CC_IS_EMCC
-    default $(shell,pkg-config --exists libjpeg && echo y || echo n) if !CC_IS_EMCC
+    default $(python,assert run('pkg-config', '--exists', 'libjpeg')) if !CC_IS_EMCC
 
 config HAVE_CAIRO
     default n if CC_IS_EMCC
-    def_bool $(shell,pkg-config --exists cairo && echo y || echo n) if !CC_IS_EMCC
+    def_bool $(python,assert run('pkg-config', '--exists', 'cairo')) if !CC_IS_EMCC
 
 choice
     prompt "Backend Selection"

Determine if the above resolves Windows regressions.