kconfig: Show unsatisfied deps. when assignments don't take

Show which dependencies are unsatisfied when symbols don't get their
assigned value.

For example, assume that FOO below is assigned with CONFIG_FOO=y. Note
that BAR, BAZ, and STR = "hmm" are 'n'.

    config FOO
           bool "foo"
           depends on BAR && BAZ && QAZ && STR = "hmm"

    config BAR
           def_bool n

    config BAZ
           def_bool n

    config QAZ
           def_bool y

    config STR
           def_string "zmh"

This now prints this warning:

    warning: FOO (defined at /home/ulf/z/z/Kconfig:10) was assigned the
    value 'y' but got the value 'n'. Check these unsatisfied
    dependencies: BAR (=n), BAZ (=n), STR = "hmm" (=n). See ...

Fixes: #21888

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>

scripts/kconfig/kconfig.py

@@ -5,7 +5,10 @@
 import sys
 import textwrap
 
-from kconfiglib import Kconfig, BOOL, TRISTATE, TRI_TO_STR
+# 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
 
 
 # Warnings that won't be turned into errors (but that will still be printed),
@@ -58,18 +61,11 @@ def main():
         # output and also assigns promptless symbols.
         check_no_promptless_assign(kconf)
 
-    # Print warnings for symbols whose actual value doesn't match the assigned
-    # value
-    for sym in kconf.unique_defined_syms:
-        # Was the symbol assigned to? Choice symbols are checked separately.
-        if sym.user_value is not None and not sym.choice:
-            check_assigned_sym_value(sym)
-
-    # Print warnings for choices whose actual selection doesn't match the user
-    # selection
-    for choice in kconf.unique_choices:
-        if choice.user_selection:
-            check_assigned_choice_value(choice)
+        # Print warnings for symbols that didn't get the assigned value. Only
+        # do this for handwritten input too, to avoid likely unhelpful warnings
+        # when using an old configuration and updating Kconfig files.
+        check_assigned_sym_values(kconf)
+        check_assigned_choice_values(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
@@ -119,27 +115,75 @@ def check_no_promptless_assign(kconf):
 """ + SYM_INFO_HINT).format(sym))
 
 
-def check_assigned_sym_value(sym):
-    # Verifies that the value assigned to 'sym' "took" (matches the value the
-    # symbol actually got), printing a warning otherwise
+def check_assigned_sym_values(kconf):
+    # Verifies that the values assigned to symbols "took" (matches the value
+    # the symbols actually got), printing warnings otherwise. Choice symbols
+    # are checked separately, in check_assigned_choice_values().
+
+    for sym in kconf.unique_defined_syms:
+        if sym.choice:
+            continue
 
-    # Tristate values are represented as 0, 1, 2. Having them as
-    # "n", "m", "y" is more convenient here, so convert.
-    if sym.type in (BOOL, TRISTATE):
-        user_value = TRI_TO_STR[sym.user_value]
-    else:
         user_value = sym.user_value
+        if user_value is None:
+            continue
+
+        # Tristate values are represented as 0, 1, 2. Having them as "n", "m",
+        # "y" is more convenient here, so convert.
+        if sym.type in (BOOL, TRISTATE):
+            user_value = TRI_TO_STR[user_value]
+
+        if user_value != sym.str_value:
+            msg = f"{sym.name_and_loc} was assigned the value '{user_value}' " \
+                  f"but got the value '{sym.str_value}'. "
+
+            # List any unsatisfied 'depends on' dependencies in the warning
+            mdeps = missing_deps(sym)
+            if mdeps:
+                expr_strs = []
+                for expr in mdeps:
+                    estr = expr_str(expr)
+                    if isinstance(expr, tuple):
+                        # Add () around dependencies that aren't plain symbols.
+                        # Gives '(FOO || BAR) (=n)' instead of
+                        # 'FOO || BAR (=n)', which might be clearer.
+                        estr = f"({estr})"
+                    expr_strs.append(f"{estr} (={TRI_TO_STR[expr_value(expr)]})")
+
+                msg += "Check these unsatisfied dependencies: " + \
+                    ", ".join(expr_strs) + ". "
+
+            warn(msg + SYM_INFO_HINT.format(sym))
+
+
+def missing_deps(sym):
+    # check_assigned_sym_values() helper for finding unsatisfied dependencies.
+    #
+    # Given direct dependencies
+    #
+    #     depends on <expr> && <expr> && ... && <expr>
+    #
+    # on 'sym' (which can also come from e.g. a surrounding 'if'), returns a
+    # list of all <expr>s with a value less than the value 'sym' was assigned
+    # ("less" instead of "not equal" just to be general and handle tristates,
+    # even though Zephyr doesn't use them).
+    #
+    # For string/int/hex symbols, just looks for <expr> = n.
+    #
+    # Note that <expr>s can be something more complicated than just a symbol,
+    # like 'FOO || BAR' or 'FOO = "string"'.
 
-    if user_value != sym.str_value:
-        warn(("""\
-{0.name_and_loc} was assigned the value '{1}' but got the value
-'{0.str_value}'. Check its dependencies. \
-""" + SYM_INFO_HINT).format(sym, user_value))
+    deps = split_expr(sym.direct_dep, AND)
 
+    if sym.type in (BOOL, TRISTATE):
+        return [dep for dep in deps if expr_value(dep) < sym.user_value]
+    # string/int/hex
+    return [dep for dep in deps if expr_value(dep) == 0]
 
-def check_assigned_choice_value(choice):
-    # Verifies that the choice symbol that was selected (by setting it to y)
-    # ended up as the selection, printing a warning otherwise.
+
+def check_assigned_choice_values(kconf):
+    # Verifies that any choice symbols that were selected (by setting them to
+    # y) ended up as the selection, printing warnings otherwise.
     #
     # We check choice symbols separately to avoid warnings when two different
     # choice symbols within the same choice are set to y. This might happen if
@@ -150,17 +194,20 @@ def check_assigned_choice_value(choice):
     # Without special-casing choices, we'd detect that the first symbol set to
     # y ended up as n, and print a spurious warning.
 
-    if choice.user_selection is not choice.selection:
-        warn(("""\
+    for choice in kconf.unique_choices:
+        if choice.user_selection and \
+           choice.user_selection is not choice.selection:
+
+            warn(("""\
 the choice symbol {0.name_and_loc} was selected (set =y), but {1} ended up as
 the choice selection. \
 """ + SYM_INFO_HINT).format(
             choice.user_selection,
             choice.selection.name_and_loc if choice.selection else "no symbol"))
 
 
-# Hint on where to find symbol information. Expects the first argument of
-# format() to be the symbol.
+# Hint on where to find symbol information. Used like
+# SYM_INFO_HINT.format(sym).
 SYM_INFO_HINT = """\
 See http://docs.zephyrproject.org/latest/reference/kconfig/CONFIG_{0.name}.html
 and/or look up {0.name} in the menuconfig/guiconfig interface. The Application