kconfig: add support for warnings when using experimental features

Kconfig.zephyr

@@ -507,6 +507,20 @@ config MAKEFILE_EXPORTS
  third party Makefile-based build systems.
 
 endmenu
+
+config EXPERIMENTAL
+ bool
+ help
+ Symbol that must be selected by a feature if it is considered to be
+ at an experimental implementation stage.
+
+config WARN_EXPERIMENTAL
+ bool
+ prompt "Warn on experimental usage"
+ help
+ Print a warning when the Kconfig tree is parsed if any experimental
+ features are enabled.
+
 endmenu
 
 

scripts/kconfig/kconfig.py

@@ -17,7 +17,7 @@
 # Zephyr doesn't use tristate symbols. They're supported here just to make the
 # script a bit more generic.
 from kconfiglib import Kconfig, split_expr, expr_value, expr_str, BOOL, \
- TRISTATE, TRI_TO_STR, AND
+ TRISTATE, TRI_TO_STR, AND, OR
 
 
 def main():
@@ -62,6 +62,9 @@ def main():
  check_assigned_sym_values(kconf)
  check_assigned_choice_values(kconf)
 
+ if kconf.syms['WARN_EXPERIMENTAL'].tri_value == 2:
+ check_experimental(kconf)
+
  # Hack: Force all symbols to be evaluated, to catch warnings generated
  # during evaluation. Wait till the end to write the actual output files, so
  # that we don't generate any output if there are warnings-turned-errors.
@@ -202,6 +205,17 @@ def check_assigned_choice_values(kconf):
 """
 
 
+def check_experimental(kconf):
+ experimental = kconf.syms['EXPERIMENTAL']
+ dep_expr = experimental.rev_dep
+
+ if dep_expr is not kconf.n:
+ selectors = [s for s in split_expr(dep_expr, OR) if expr_value(s) == 2]
+ for selector in selectors:
+ selector_name = split_expr(selector, AND)[0].name
+ warn(f'Experimental symbol {selector_name} is enabled.')
+
+
 def promptless(sym):
  # Returns True if 'sym' has no prompt. Since the symbol might be defined in
  # multiple locations, we need to check all locations.