[Fontconfig] fontconfig: Branch 'master'

[Akira TAGOH]

 src/fclang.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

New commits:
commit 4970c7e810fec29b5ad40a595850288f14f48e37
Author: Florent Rougon <f.rougon at free.fr>
Date:   Tue Jun 6 23:32:28 2017 +0200

    Fix an off-by-one error in FcLangSetIndex()
    
    This commit fixes a bug that can be reproduced like this:
      - remove all languages starting with 'a' in fc-lang/Makefile.am (in
        ORTH's definition);
      - rebuild fontconfig with this change (-> new fc-lang/fclang.h);
      - create an FcLangSet 'ls1' that contains at least the first language
        from fcLangCharSets (i.e., the first *remaining* in lexicographic
        order); let's assume it is "ba" for the sake of this description;
      - create an FcLangSet 'ls2' that only contains the language "aa" (any
        language starting with 'a' should work as well);
      - check the return value of FcLangSetContains(ls1, ls2);
    
    The expected return value is FcFalse, however it is FcTrue if you use
    the code before this commit.
    
    What happens is that FcLangSetIndex() returns 0, because this is the
    index of the first slot after the not-found language "aa" in
    fcLangCharSets (since we removed all languages starting with 'a').
    However, this index happens to be non-negative, therefore
    FcLangSetContainsLang() mistakenly infers that the language "aa" was
    found in fcLangCharSets, and thus calls FcLangSetBitGet(ls1, 0), which
    returns FcTrue since we've put the first remaining language "ba" in the
    'ls1' language set.
    
    The "return -low;" statement previously in FcLangSetIndex() was
    inconsistent with the final return statement. "return -(low+1);" fixes
    this inconsistency as well as the incorrect behavior described above.

diff --git a/src/fclang.c b/src/fclang.c
index b1fd1bc..19f3ddd 100644
--- a/src/fclang.c
+++ b/src/fclang.c
@@ -505,6 +505,15 @@ bail0:
     return 0;
 }
 
+/* When the language isn't found, the return value r is such that:
+ *  1) r < 0
+ *  2) -r -1 is the index of the first language in fcLangCharSets that comes
+ *     after the 'lang' argument in lexicographic order.
+ *
+ *  The -1 is necessary to avoid problems with language id 0 (otherwise, we
+ *  wouldn't be able to distinguish between “language found, id is 0” and
+ *  “language not found, sorts right before the language with id 0”).
+ */
 static int
 FcLangSetIndex (const FcChar8 *lang)
 {
@@ -529,7 +538,7 @@ FcLangSetIndex (const FcChar8 *lang)
 	high = fcLangCharSetRanges[firstChar - 'a'].end;
 	/* no matches */
 	if (low > high)
-	    return -low; /* next entry after where it would be */
+	    return -(low+1); /* one past next entry after where it would be */
     }
 
     while (low <= high)