[Buildroot] [RFC 1/1] support/kconfig: Allow to override 'default' config property

[Vadim Kochan <vadim4j@gmail.com>]

Add kconfig patch which allows to apply last visible config's "default" property.

This allows to override default value for the same config symbol from
other Config.in file, e.g.:

	system/Config.in:
		config BR2_TARGET_GENERIC_GETTY_PORT
			string "TTY port"
			default "console"
			help
			  Specify a port to run a getty on.

now the same symbol value might be overriden by Config.in from external's one:

	${external_vendor_tree}/Config.in:
		config BR2_TARGET_GENERIC_GETTY_PORT
			string
			default "tty1"

But why is the purpose of this if the value might be specified by the
user in defconfig ? So, it allows for external projects to be more easy
used w/o looking into their default defconfigs and specifying these
default values in local defconfig, but external tree project might do
this automatically by specifying default values like in the above
example. And because it is the "default" property the user still can
choose the own value.

Signed-off-by: Vadim Kochan <vadim4j@gmail.com>
---
 .../22-apply-last-visible-default-property.patch     | 20 ++++++++++++++++++++
 support/kconfig/patches/series                       |  1 +
 support/kconfig/symbol.c                             |  6 +++---
 3 files changed, 24 insertions(+), 3 deletions(-)
 create mode 100644 support/kconfig/patches/22-apply-last-visible-default-property.patch

diff --git a/support/kconfig/patches/22-apply-last-visible-default-property.patch b/support/kconfig/patches/22-apply-last-visible-default-property.patch
new file mode 100644
index 0000000000..c57490fe6d
--- /dev/null
+++ b/support/kconfig/patches/22-apply-last-visible-default-property.patch
@@ -0,0 +1,20 @@
+--- kconfig.orig/symbol.c	2019-04-07 03:02:49.263944705 +0300
++++ kconfig/symbol.c	2019-04-07 03:03:15.367944606 +0300
+@@ -114,14 +114,14 @@
+ 
+ static struct property *sym_get_default_prop(struct symbol *sym)
+ {
+-	struct property *prop;
++	struct property *prop, *found = NULL;
+ 
+ 	for_all_defaults(sym, prop) {
+ 		prop->visible.tri = expr_calc_value(prop->visible.expr);
+ 		if (prop->visible.tri != no)
+-			return prop;
++			found = prop;
+ 	}
+-	return NULL;
++	return found;
+ }
+ 
+ static struct property *sym_get_range_prop(struct symbol *sym)
diff --git a/support/kconfig/patches/series b/support/kconfig/patches/series
index e5a6f69d8f..9b3a37c4e6 100644
--- a/support/kconfig/patches/series
+++ b/support/kconfig/patches/series
@@ -10,3 +10,4 @@
 19-merge_config.sh-add-br2-external-support.patch
 20-merge_config.sh-Allow-to-define-config-prefix.patch
 21-Avoid-false-positive-matches-from-comment-lines.patch
+22-apply-last-visible-default-property.patch
diff --git a/support/kconfig/symbol.c b/support/kconfig/symbol.c
index f0b2e3b310..337dc55b5a 100644
--- a/support/kconfig/symbol.c
+++ b/support/kconfig/symbol.c
@@ -114,14 +114,14 @@ struct property *sym_get_env_prop(struct symbol *sym)
 
 static struct property *sym_get_default_prop(struct symbol *sym)
 {
-	struct property *prop;
+	struct property *prop, *found = NULL;
 
 	for_all_defaults(sym, prop) {
 		prop->visible.tri = expr_calc_value(prop->visible.expr);
 		if (prop->visible.tri != no)
-			return prop;
+			found = prop;
 	}
-	return NULL;
+	return found;
 }
 
 static struct property *sym_get_range_prop(struct symbol *sym)
-- 
2.14.1