[gobject-introspection] Add GI_SCANNER_DISABLE_CACHE environment variable

[Colin Walters <walters src gnome org>]

commit 2330248ea37ad1251da58700ffb1ea0d578523ee
Author: Colin Walters <walters verbum org>
Date:   Mon May 2 12:25:10 2011 -0400

    Add GI_SCANNER_DISABLE_CACHE environment variable
    
    https://bugzilla.gnome.org/show_bug.cgi?id=649054

 docs/g-ir-scanner.1     |    3 +++
 giscanner/cachestore.py |    2 ++
 2 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/docs/g-ir-scanner.1 b/docs/g-ir-scanner.1
index 7108dda..847c78b 100644
--- a/docs/g-ir-scanner.1
+++ b/docs/g-ir-scanner.1
@@ -133,6 +133,9 @@ Be verbose, include some debugging information.
 The g-ir-scanner uses the XDG_DATA_DIRS variable to check for dirs,
 the gir's are located in XDG_DATA_DIRS/share/gir-1.0. It is normally
 set on a distribution so you shouldn't need to set it yourself.
+
+The variable GI_SCANNER_DISABLE_CACHE ensures that the scanner will
+not write cache data to $HOME.
 .SH BUGS
 Report bugs at http://bugzilla.gnome.org/ in the glib product and
 introspection component.
diff --git a/giscanner/cachestore.py b/giscanner/cachestore.py
index 7b72b29..44e3b04 100644
--- a/giscanner/cachestore.py
+++ b/giscanner/cachestore.py
@@ -41,6 +41,8 @@ def _get_versionhash():
     return hashlib.sha1(''.join(mtimes)).hexdigest()
 
 def _get_cachedir():
+    if 'GI_SCANNER_DISABLE_CACHE' in os.environ:
+        return None
     homedir = os.environ.get('HOME')
     if homedir is None:
         return None