Have load_config() and write_(min_)config() return messages

Hardcoding load_config() and write_(min_)config() to write any message
to stdout is awkward, because it means that the message can't be easily
reused when stdout is the wrong place to write it to (e.g. in
menuconfig/guiconfig). This gets extra bad now that there's also the "No
change to ..." message.

Modify load_config() and write_(min_)config() to return the message as a
string instead, and have them always return a message, instead of just
when 'filename' is None and verbose=True. This makes things flexible and
straightforward.

Use the new behavior in menuconfig.py and guiconfig.py. They now show
"No change to ..." when saving a file doesn't modify it.

Tools that want to write messages to stdout should now do
print(kconf.load_config()) / print(kconf.write_config()).

There's no clean way to preserve perfect backwards compatibility here,
but keep accepting the 'verbose' argument and print a deprecation
warning if a value is ever passed for it. That way, scripts will keep
running, though possibly with less output on stdout.

This changes the meaning of the load_config() return value as well,
though I suspect it was only ever used by the menuconfig/guiconfig
interfaces.

The new behavior applies for kconfiglib.VERSION >= (12, 0, 0).

4 files changed, 32 insertions, 24 deletions

diff --git a/examples/allnoconfig_walk.py b/examples/allnoconfig_walk.py
index 24b2828..5a8cc23 100644
--- a/examples/allnoconfig_walk.py
+++ b/examples/allnoconfig_walk.py
@@ -63,4 +63,4 @@ while True:
     if not changed:
         break
 
-kconf.write_config()
+print(kconf.write_config())
diff --git a/examples/defconfig_oldconfig.py b/examples/defconfig_oldconfig.py
index 98f97a0..68336c6 100644
--- a/examples/defconfig_oldconfig.py
+++ b/examples/defconfig_oldconfig.py
@@ -36,4 +36,4 @@ for s in kconf.unique_defined_syms:
         s.set_value(0)
 
 # Write the final configuration
-kconf.write_config()
+print(kconf.write_config())
diff --git a/examples/menuconfig_example.py b/examples/menuconfig_example.py
index 4e2560d..b265e69 100644..100755
--- a/examples/menuconfig_example.py
+++ b/examples/menuconfig_example.py
@@ -1,3 +1,5 @@
+#!/usr/bin/env python
+
 # Implements a simple configuration interface on top of Kconfiglib to
 # demonstrate concepts for building a menuconfig-like. Emulates how the
 # standard menuconfig prints menu entries.
@@ -117,6 +119,7 @@
 #
 #   Enter a symbol/choice name, "load_config", or "write_config" (or press CTRL+D to exit): ^D
 
+from __future__ import print_function
 import readline
 import sys
 
@@ -300,27 +303,22 @@ if __name__ == "__main__":
 
         if cmd == "load_config":
             config_filename = input(".config file to load: ")
-
             try:
-                kconf.load_config(config_filename)
+                # Returns a message telling which file got loaded
+                print(kconf.load_config(config_filename))
             except IOError as e:
-                # Print the (spammy) error from Kconfiglib itself
-                print(e.message + "\n")
-            else:
-                print("Configuration loaded from " + config_filename)
+                print(e, file=sys.stderr)
 
             print_menuconfig(kconf)
             continue
 
         if cmd == "write_config":
             config_filename = input("To this file: ")
-
             try:
-                kconf.write_config(config_filename)
+                # Returns a message telling which file got saved
+                print(kconf.write_config(config_filename))
             except IOError as e:
-                print(e.message)
-            else:
-                print("Configuration written to " + config_filename)
+                print(e, file=sys.stderr)
 
             continue
 
@@ -340,5 +338,5 @@ if __name__ == "__main__":
 
             continue
 
-        print("No symbol/choice named '{}' in the configuration"
-              .format(cmd))
+        print("No symbol/choice named '{}' in the configuration".format(cmd),
+              file=sys.stderr)
diff --git a/examples/merge_config.py b/examples/merge_config.py
index ec022d5..6f60375 100644..100755
--- a/examples/merge_config.py
+++ b/examples/merge_config.py
@@ -1,3 +1,5 @@
+#!/usr/bin/env python
+
 # This script functions similarly to scripts/kconfig/merge_config.sh from the
 # kernel tree, merging multiple configurations fragments to produce a complete
 # .config, with unspecified values filled in as for alldefconfig.
@@ -37,7 +39,8 @@
 #
 # conf3 contents:
 #
-#     # Ops... assigned twice
+#     # Assigned twice (would generate warning if 'warn_assign_override' was
+#     # True)
 #     # CONFIG_FOO is not set
 #
 #     # Ops... this symbol doesn't exist
@@ -54,15 +57,20 @@
 # Running:
 #
 #     $ python(3) merge_config.py Kconfig merged conf1 conf2 conf3 conf4
-#     conf3:2: warning: FOO (defined at Kconfig:1) set more than once. Old value: "y", new value: "n".
-#     conf3:5: warning: attempt to assign the value "y" to the undefined symbol OPS
-#     warning: QAZ (defined at Kconfig:10) was assigned the value "y" but got the value "n" -- check dependencies
+#     Merged configuration 'conf1'
+#     Merged configuration 'conf2'
+#     conf3:5: warning: attempt to assign the value 'y' to the undefined symbol OPS
+#     Merged configuration 'conf3'
+#     Merged configuration 'conf4'
+#     Configuration saved to 'merged'
+#     warning: QAZ (defined at Kconfig:10) was assigned the value 'y' but got the value 'n' -- check dependencies
 #     $ cat merged
 #     Generated by Kconfiglib (https://github.com/ulfalizer/Kconfiglib)
 #     # CONFIG_FOO is not set
 #     CONFIG_BAR=y
 #     CONFIG_BAZ="baz string"
 
+from __future__ import print_function
 import sys
 
 from kconfiglib import Kconfig, BOOL, TRISTATE, TRI_TO_STR
@@ -86,12 +94,13 @@ kconf.enable_undef_warnings()
 kconf.disable_override_warnings()
 kconf.disable_redun_warnings()
 
-# Create a merged configuration by loading the fragments with replace=False
+# Create a merged configuration by loading the fragments with replace=False.
+# load_config() and write_config() returns a message to print.
 for config in sys.argv[3:]:
-    kconf.load_config(config, replace=False)
+    print(kconf.load_config(config, replace=False))
 
 # Write the merged configuration
-kconf.write_config(sys.argv[2])
+print(kconf.write_config(sys.argv[2]))
 
 # Print warnings for symbols whose actual value doesn't match the assigned
 # value
@@ -119,5 +128,6 @@ for sym in kconf.defined_syms:
 
         if user_value != sym.str_value:
             print("warning: {} was assigned the value '{}' but got the "
-                  "value '{}' -- check dependencies"
-                  .format(name_and_loc(sym), user_value, sym.str_value))
+                  "value '{}' -- check dependencies".format(
+                      name_and_loc(sym), user_value, sym.str_value),
+                  file=sys.stderr)