shared/runtime/pyexec: Provide support for compile-only mode.

When `MICROPY_PYEXEC_COMPILE_ONLY` is enabled and the global
`mp_compile_only` is True, code is compiled but not executed.

Also add comprehensive tests for compile-only functionality covering both
successful compilation and syntax error detection.

Signed-off-by: Andrew Leech <andrew.leech@planetinnovation.com.au>

pyproject.toml

@@ -30,6 +30,7 @@ target-version = "py37"
 
 [tool.ruff.lint]
 exclude = [  # Ruff finds Python SyntaxError in these files
+  "tests/cmdline/cmd_compile_only_error.py",
   "tests/cmdline/repl_autocomplete.py",
   "tests/cmdline/repl_autocomplete_underscore.py",
   "tests/cmdline/repl_autoindent.py",
@@ -69,4 +70,9 @@ mccabe.max-complexity = 40
 #   basics: needs careful attention before applying automatic formatting
 #   repl_: not real python files
 #   viper_args: uses f(*)
-exclude = ["tests/basics/*.py", "tests/*/repl_*.py", "tests/micropython/viper_args.py"]
+exclude = [
+  "tests/basics/*.py",
+  "tests/*/repl_*.py",
+  "tests/cmdline/cmd_compile_only_error.py",
+  "tests/micropython/viper_args.py",
+]

shared/runtime/pyexec.c

@@ -130,7 +130,12 @@ static int parse_compile_execute(const void *source, mp_parse_input_kind_t input
         #if MICROPY_REPL_INFO
         start = mp_hal_ticks_ms();
         #endif
-        mp_call_function_0(module_fun);
+        #if MICROPY_PYEXEC_COMPILE_ONLY
+        if (!mp_compile_only)
+        #endif
+        {
+            mp_call_function_0(module_fun);
+        }
         mp_hal_set_interrupt_char(-1); // disable interrupt
         mp_handle_pending(true); // handle any pending exceptions (and any callbacks)
         nlr_pop();
@@ -706,6 +711,7 @@ int pyexec_file(const char *filename) {
     return parse_compile_execute(filename, MP_PARSE_FILE_INPUT, EXEC_FLAG_SOURCE_IS_FILENAME);
 }
 
+
 int pyexec_file_if_exists(const char *filename) {
     #if MICROPY_MODULE_FROZEN
     if (mp_find_frozen_module(filename, NULL, NULL) == MP_IMPORT_STAT_FILE) {

tests/cmdline/cmd_compile_only.py

@@ -0,0 +1,13 @@
+# cmdline: -X compile-only
+# test compile-only functionality
+print("This should not be printed")
+x = 1 + 2
+
+
+def hello():
+    return "world"
+
+
+class TestClass:
+    def __init__(self):
+        self.value = 42

tests/cmdline/cmd_compile_only.py.exp

@@ -0,0 +1 @@
+

tests/cmdline/cmd_compile_only_error.py

@@ -0,0 +1,6 @@
+# cmdline: -X compile-only
+# test compile-only with syntax error
+print("This should not be printed")
+def broken_syntax(
+    # Missing closing parenthesis
+    return "error"

tests/cmdline/cmd_compile_only_error.py.exp

@@ -0,0 +1 @@
+CRASH