xdiff: fix merging of hunks with -W context and -u context

If the function context for a hunk (with -W) reaches the beginning of
the next hunk then we need to merge these two -- otherwise we'd show
some lines twice, which looks strange and even confuses git apply.  We
already do this checking and merging in xdl_emit_diff(), but forget to
consider regular context (with -u or -U).

Fix that by merging hunks already if function context of the first one
touches or overlaps regular context of the second one.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4051-diff-function-context.sh

@@ -66,6 +66,15 @@ test_expect_success 'setup' '
 	mv file.c.new file.c &&
 	commit_and_tag long_common_tail file.c &&
 
+	git checkout initial &&
+	cat "$dir/hello.c" "$dir/dummy.c" >file.c &&
+	commit_and_tag hello_dummy file.c &&
+
+	# overlap function context of 1st change and -u context of 2nd change
+	grep -v "delete me from hello" <"$dir/hello.c" >file.c &&
+	sed 2p <"$dir/dummy.c" >>file.c &&
+	commit_and_tag changed_hello_dummy file.c &&
+
 	git checkout initial &&
 	grep -v "delete me from hello" <file.c >file.c.new &&
 	mv file.c.new file.c &&
@@ -179,4 +188,20 @@ test_expect_success ' context does not include other functions' '
 	test $(grep -c "^[ +-].*Begin" changed_hello_appended.diff) -le 2
 '
 
+check_diff changed_hello_dummy 'changed two consecutive functions'
+
+test_expect_success ' context includes begin' '
+	grep "^ .*Begin of hello" changed_hello_dummy.diff &&
+	grep "^ .*Begin of dummy" changed_hello_dummy.diff
+'
+
+test_expect_success ' context includes end' '
+	grep "^ .*End of hello" changed_hello_dummy.diff &&
+	grep "^ .*End of dummy" changed_hello_dummy.diff
+'
+
+test_expect_success ' overlapping hunks are merged' '
+	test $(grep -c "^@@" changed_hello_dummy.diff) -eq 1
+'
+
 test_done

xdiff/xemit.c

@@ -248,7 +248,7 @@ int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
 			if (xche->next) {
 				long l = XDL_MIN(xche->next->i1,
 						 xe->xdf1.nrec - 1);
-				if (l <= e1 ||
+				if (l - xecfg->ctxlen <= e1 ||
 				    get_func_line(xe, xecfg, NULL, l, e1) < 0) {
 					xche = xche->next;
 					goto post_context_calculation;