kconfig: report recursive dependency involving 'imply'

Currently, Kconfig does not complain about the recursive dependency
where 'imply' keywords are involved.

[Test Code]

  config A
          bool "a"

  config B
          bool "b"
          imply A
          depends on A

In the code above, Kconfig cannot calculate the symbol values correctly
due to the circular dependency.  For example, allyesconfig followed by
syncconfig results in an odd behavior because CONFIG_B becomes visible
in syncconfig.

  $ make allyesconfig
  scripts/kconfig/conf  --allyesconfig Kconfig
  #
  # configuration written to .config
  #
  $ cat .config
  #
  # Automatically generated file; DO NOT EDIT.
  # Main menu
  #
  CONFIG_A=y
  $ make syncconfig
  scripts/kconfig/conf  --syncconfig Kconfig
  *
  * Restart config...
  *
  *
  * Main menu
  *
  a (A) [Y/n/?] y
    b (B) [N/y/?] (NEW)

To detect this correctly, sym_check_expr_deps() should recurse to
not only sym->rev_dep.expr but also sym->implied.expr .

At this moment, sym_check_print_recursive() cannot distinguish
'select' and 'imply' since it does not know the precise context
where the recursive dependency has been hit.  This will be solved
by the next commit.

In fact, even the document and the unit-test are confused.  Using
'imply' does not solve recursive dependency since 'imply' addresses
the unmet direct dependency, which 'select' could cause.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Tested-by: Dirk Gouders <dirk@gouders.net>

Documentation/kbuild/kconfig-language.txt

@@ -545,7 +545,7 @@ make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-02 allnoconfig
 Practical solutions to kconfig recursive issue
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-Developers who run into the recursive Kconfig issue have three options
+Developers who run into the recursive Kconfig issue have two options
 at their disposal. We document them below and also provide a list of
 historical issues resolved through these different solutions.
 
@@ -553,7 +553,6 @@ historical issues resolved through these different solutions.
   b) Match dependency semantics:
 	b1) Swap all "select FOO" to "depends on FOO" or,
 	b2) Swap all "depends on FOO" to "select FOO"
-  c) Consider the use of "imply" instead of "select"
 
 The resolution to a) can be tested with the sample Kconfig file
 Documentation/kbuild/Kconfig.recursion-issue-01 through the removal

scripts/kconfig/symbol.c

@@ -1098,7 +1098,7 @@ static void sym_check_print_recursive(struct symbol *last_sym)
 				sym->name ? sym->name : "<choice>",
 				next_sym->name ? next_sym->name : "<choice>");
 		} else {
-			fprintf(stderr, "%s:%d:\tsymbol %s is selected by %s\n",
+			fprintf(stderr, "%s:%d:\tsymbol %s is selected or implied by %s\n",
 				prop->file->name, prop->lineno,
 				sym->name ? sym->name : "<choice>",
 				next_sym->name ? next_sym->name : "<choice>");
@@ -1161,8 +1161,13 @@ static struct symbol *sym_check_sym_deps(struct symbol *sym)
 	if (sym2)
 		goto out;
 
+	sym2 = sym_check_expr_deps(sym->implied.expr);
+	if (sym2)
+		goto out;
+
 	for (prop = sym->prop; prop; prop = prop->next) {
-		if (prop->type == P_CHOICE || prop->type == P_SELECT)
+		if (prop->type == P_CHOICE || prop->type == P_SELECT ||
+		    prop->type == P_IMPLY)
 			continue;
 		stack.prop = prop;
 		sym2 = sym_check_expr_deps(prop->visible.expr);

scripts/kconfig/tests/err_recursive_dep/Kconfig

+# SPDX-License-Identifier: GPL-2.0
+
 # depends on itself
 
 config A
@@ -31,7 +33,6 @@ config D2
 	bool
 
 # depends on and imply
-# This is not recursive dependency
 
 config E1
 	bool "E1"

scripts/kconfig/tests/err_recursive_dep/expected_stderr

-Kconfig:9:error: recursive dependency detected!
-Kconfig:9:	symbol B is selected by B
+Kconfig:11:error: recursive dependency detected!
+Kconfig:11:	symbol B is selected or implied by B
 For a resolution refer to Documentation/kbuild/kconfig-language.txt
 subsection "Kconfig recursive dependency limitations"
 
-Kconfig:3:error: recursive dependency detected!
-Kconfig:3:	symbol A depends on A
+Kconfig:5:error: recursive dependency detected!
+Kconfig:5:	symbol A depends on A
 For a resolution refer to Documentation/kbuild/kconfig-language.txt
 subsection "Kconfig recursive dependency limitations"
 
-Kconfig:15:error: recursive dependency detected!
-Kconfig:15:	symbol C1 depends on C2
-Kconfig:19:	symbol C2 depends on C1
+Kconfig:17:error: recursive dependency detected!
+Kconfig:17:	symbol C1 depends on C2
+Kconfig:21:	symbol C2 depends on C1
 For a resolution refer to Documentation/kbuild/kconfig-language.txt
 subsection "Kconfig recursive dependency limitations"
 
-Kconfig:30:error: recursive dependency detected!
-Kconfig:30:	symbol D2 is selected by D1
-Kconfig:25:	symbol D1 depends on D2
+Kconfig:32:error: recursive dependency detected!
+Kconfig:32:	symbol D2 is selected or implied by D1
+Kconfig:27:	symbol D1 depends on D2
 For a resolution refer to Documentation/kbuild/kconfig-language.txt
 subsection "Kconfig recursive dependency limitations"
 
-Kconfig:59:error: recursive dependency detected!
-Kconfig:59:	symbol G depends on G
+Kconfig:37:error: recursive dependency detected!
+Kconfig:37:	symbol E1 depends on E2
+Kconfig:42:	symbol E2 is selected or implied by E1
 For a resolution refer to Documentation/kbuild/kconfig-language.txt
 subsection "Kconfig recursive dependency limitations"
 
-Kconfig:50:error: recursive dependency detected!
-Kconfig:50:	symbol F2 depends on F1
-Kconfig:48:	symbol F1 default value contains F2
+Kconfig:60:error: recursive dependency detected!
+Kconfig:60:	symbol G depends on G
+For a resolution refer to Documentation/kbuild/kconfig-language.txt
+subsection "Kconfig recursive dependency limitations"
+
+Kconfig:51:error: recursive dependency detected!
+Kconfig:51:	symbol F2 depends on F1
+Kconfig:49:	symbol F1 default value contains F2
+For a resolution refer to Documentation/kbuild/kconfig-language.txt
+subsection "Kconfig recursive dependency limitations"