[PATCH/RFC v1 1/1] bug fix, diff whitespace ignore options

[Keith Cascio <keith@CS.UCLA.EDU>]

  Fixed bug in diff whitespace ignore options.
  It is now OK to specify more than one whitespace ignore option
  on the command line. In unit test 4015, expect success rather
  than failure for 4 cases.
  Note: I do not fully understand why this fix works, but it passes
  all 68 t4???-* diff test scripts.

The semantics of the three whitespace ignore flags
{ -w, -b, --ignore-space-at-eol }
obey a relation of transitive implication, i.e. the stronger
options imply the weaker options:
-w                    implies the other two
-b                    implies --ignore-space-at-eol
--ignore-space-at-eol implies only itself

Therefore it is never necessary to specify more than one of these
on the command line.  Yet we imagine scenarios where software
wrappers (e.g. GUIs, etc) generate command lines that switch on
more than one of these flags simultaneously.  It is unreasonable
to prohibit specifying more than one, since a new user might not
immediately discern the implication relation.  Now we call such
a command line valid and legal.

Signed-off-by: Keith Cascio <keith@cs.ucla.edu>
---
  t/t4015-diff-whitespace.sh |    8 ++++----
  xdiff/xutils.c             |   22 ++++++++++++----------
  2 files changed, 16 insertions(+), 14 deletions(-)

diff --git a/t/t4015-diff-whitespace.sh b/t/t4015-diff-whitespace.sh
index dbb608c..6d13da3 100755
--- a/t/t4015-diff-whitespace.sh
+++ b/t/t4015-diff-whitespace.sh
@@ -99,11 +99,11 @@ EOF
  git diff -w > out
  test_expect_success 'another test, with -w' 'test_cmp expect out'
  git diff -w -b > out
-test_expect_failure 'another test, with -w -b' 'test_cmp expect out'
+test_expect_success 'another test, with -w -b' 'test_cmp expect out'
  git diff -w --ignore-space-at-eol > out
-test_expect_failure 'another test, with -w --ignore-space-at-eol' 'test_cmp expect out'
+test_expect_success 'another test, with -w --ignore-space-at-eol' 'test_cmp expect out'
  git diff -w -b --ignore-space-at-eol > out
-test_expect_failure 'another test, with -w -b --ignore-space-at-eol' 'test_cmp expect out'
+test_expect_success 'another test, with -w -b --ignore-space-at-eol' 'test_cmp expect out'

  tr 'Q' '\015' << EOF > expect
  diff --git a/x b/x
@@ -123,7 +123,7 @@ EOF
  git diff -b > out
  test_expect_success 'another test, with -b' 'test_cmp expect out'
  git diff -b --ignore-space-at-eol > out
-test_expect_failure 'another test, with -b --ignore-space-at-eol' 'test_cmp expect out'
+test_expect_success 'another test, with -b --ignore-space-at-eol' 'test_cmp expect out'

  tr 'Q' '\015' << EOF > expect
  diff --git a/x b/x
diff --git a/xdiff/xutils.c b/xdiff/xutils.c
index d7974d1..b9bda86 100644
--- a/xdiff/xutils.c
+++ b/xdiff/xutils.c
@@ -245,17 +245,19 @@ static unsigned long xdl_hash_record_with_whitespace(char const **data,
  			while (ptr + 1 < top && isspace(ptr[1])
  					&& ptr[1] != '\n')
  				ptr++;
-			if (flags & XDF_IGNORE_WHITESPACE_CHANGE
-					&& ptr[1] != '\n') {
-				ha += (ha << 5);
-				ha ^= (unsigned long) ' ';
-			}
-			if (flags & XDF_IGNORE_WHITESPACE_AT_EOL
-					&& ptr[1] != '\n') {
-				while (ptr2 != ptr + 1) {
+			if( ! (          flags & XDF_IGNORE_WHITESPACE       )){
+				if(      flags & XDF_IGNORE_WHITESPACE_CHANGE
+						&& ptr[1] != '\n') {
  					ha += (ha << 5);
-					ha ^= (unsigned long) *ptr2;
-					ptr2++;
+					ha ^= (unsigned long) ' ';
+				}
+				else if( flags & XDF_IGNORE_WHITESPACE_AT_EOL
+						&& ptr[1] != '\n') {
+					while (ptr2 != ptr + 1) {
+						ha += (ha << 5);
+						ha ^= (unsigned long) *ptr2;
+						ptr2++;
+					}
  				}
  			}
  			continue;
-- 
1.6.1.203.ga83c8.dirty