py/profile: Remove the requirement to disable MICROPY_COMP_CONST.

The only reason that const had to be disabled was to make the test output
match CPython when const was involved.  Instead, this commit fixes the test
to handle the lines where const is used.

Also:
- remove the special handling for MICROPY_PERSISTENT_CODE_SAVE in
  unix/mpconfigport.h, and make this automatic.
- move the check for MICROPY_PERSISTENT_CODE_SAVE to where it's used (like
  we do for other similar checks) and add a comment explaining it.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

ports/unix/mpconfigport.h

@@ -134,12 +134,6 @@ typedef long mp_off_t;
 #define MICROPY_STACKLESS_STRICT    (0)
 #endif
 
-// If settrace is enabled then we need code saving.
-#if MICROPY_PY_SYS_SETTRACE
-#define MICROPY_PERSISTENT_CODE_SAVE (1)
-#define MICROPY_COMP_CONST (0)
-#endif
-
 // Unix-specific configuration of machine.mem*.
 #define MICROPY_MACHINE_MEM_GET_READ_ADDR   mod_machine_mem_get_addr
 #define MICROPY_MACHINE_MEM_GET_WRITE_ADDR  mod_machine_mem_get_addr

py/mpconfig.h

@@ -312,9 +312,11 @@
 #define MICROPY_PERSISTENT_CODE_LOAD (0)
 #endif
 
-// Whether to support saving of persistent code
+// Whether to support saving of persistent code, i.e. for mpy-cross to
+// generate .mpy files. Enabling this enables additional metadata on raw code
+// objects which is also required for sys.settrace.
 #ifndef MICROPY_PERSISTENT_CODE_SAVE
-#define MICROPY_PERSISTENT_CODE_SAVE (0)
+#define MICROPY_PERSISTENT_CODE_SAVE (MICROPY_PY_SYS_SETTRACE)
 #endif
 
 // Whether to support saving persistent code to a file via mp_raw_code_save_file
@@ -2013,14 +2015,4 @@ typedef double mp_float_t;
 #define MP_WARN_CAT(x) (NULL)
 #endif
 
-// Feature dependency check.
-#if MICROPY_PY_SYS_SETTRACE
-#if !MICROPY_PERSISTENT_CODE_SAVE
-#error "MICROPY_PY_SYS_SETTRACE requires MICROPY_PERSISTENT_CODE_SAVE to be enabled"
-#endif
-#if MICROPY_COMP_CONST
-#error "MICROPY_PY_SYS_SETTRACE requires MICROPY_COMP_CONST to be disabled"
-#endif
-#endif
-
 #endif // MICROPY_INCLUDED_PY_MPCONFIG_H

py/profile.c

@@ -31,6 +31,12 @@
 
 #if MICROPY_PY_SYS_SETTRACE
 
+#if !MICROPY_PERSISTENT_CODE_SAVE
+// The settrace feature requires that we maintain additional metadata on the raw
+// code object which is normally only done when writing .mpy files.
+#error "MICROPY_PY_SYS_SETTRACE requires MICROPY_PERSISTENT_CODE_SAVE to be enabled"
+#endif
+
 #define prof_trace_cb MP_STATE_THREAD(prof_trace_callback)
 #define QSTR_MAP(context, idx) (context->constants.qstr_table[idx])
 

tests/misc/sys_settrace_features.py

@@ -67,6 +67,11 @@ def trace_tick_handler(frame, event, arg):
     if any(name in frame_name for name in to_ignore):
         return
 
+    # Lines 4,5,7 create the `const` lambda, and line `15` is a `_X = const()` which
+    # MicroPython will not see as it's optimised out.
+    if "sys_settrace_importme" in frame.f_code.co_filename and frame.f_lineno in (4, 5, 7, 15):
+        return trace_tick_handler
+
     print("### trace_handler::main event:", event)
     __prof__.trace_tick(frame, event, arg)
 

tests/misc/sys_settrace_subdir/sys_settrace_importme.py

@@ -3,12 +3,18 @@ print("Yep, I got imported.")
 try:
     x = const(1)
 except NameError:
-    print("const not defined")
+    # Either running on CPython or MICROPY_COMP_CONST disabled.
+    const = lambda x: x
 
-const = lambda x: x
 
+# No const optimisation.
 _CNT01 = "CONST01"
+
+# Const assigned to an underscore name. Invisible to MicroPython with
+# MICROPY_COMP_CONST enabled.
 _CNT02 = const(123)
+
+# Consts assigned to regular name, executed normally.
 A123 = const(123)
 a123 = const(123)