From 5e54e2cd43c5f3c530706291d860ba1bf817986c Mon Sep 17 00:00:00 2001
From: Ulf Magnusson <ulfalizer@gmail.com>
Date: Sun, 7 Jun 2015 06:07:19 +0200
Subject: Unset user values when loading a zero-byte .config.

Minor bug due to an early return from load_config(). Piggyback a
refactoring of the code. Reading the header is unlikely to be
performance-sensitive.

Add a testcase too.
---
 kconfiglib.py | 35 +++++++++++++----------------------
 testsuite.py  |  4 ++++
 2 files changed, 17 insertions(+), 22 deletions(-)

diff --git a/kconfiglib.py b/kconfiglib.py
index e03935a..dac21f6 100644
--- a/kconfiglib.py
+++ b/kconfiglib.py
@@ -231,37 +231,28 @@ class Config(object):
 
         self.config_filename = filename
 
+        #
         # Read header
-
-        self.config_header = None
+        #
 
         def is_header_line(line):
-            return line.startswith("#") and not unset_re_match(line)
-
-        first_line = line_feeder.get_next()
-        if first_line is None:
-            return
-
-        if not is_header_line(first_line):
-            line_feeder.go_back()
-        else:
-            self.config_header = first_line[1:]
+            return line is not None and line.startswith("#") and \
+                   not unset_re_match(line)
 
-            # Read remaining header lines
-            while 1:
-                line = line_feeder.get_next()
-                if line is None:
-                    break
-                if not is_header_line(line):
-                    line_feeder.go_back()
-                    break
-                self.config_header += line[1:]
+        self.config_header = None
 
+        line = line_feeder.peek_next()
+        if is_header_line(line):
+            self.config_header = ""
+            while is_header_line(line_feeder.peek_next()):
+                self.config_header += line_feeder.get_next()[1:]
             # Remove trailing newline
             if self.config_header.endswith("\n"):
                 self.config_header = self.config_header[:-1]
 
-        # Read assignments
+        #
+        # Read assignments. Hotspot for some workloads.
+        #
 
         def warn_override(filename, linenr, name, old_user_val, new_user_val):
             self._warn('overriding the value of {0}. '
diff --git a/testsuite.py b/testsuite.py
index e225cbb..3407e0a 100644
--- a/testsuite.py
+++ b/testsuite.py
@@ -1333,6 +1333,10 @@ def run_selftests():
     verify_value("BOOL", "n")
     verify_value("STRING", "foo bar")
 
+    # Loading a completely empty .config should also reset values
+    c.load_config("Kconfiglib/tests/empty")
+    verify_value("STRING", "")
+
     #
     # get_config()
     #
-- 
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