merge(3p/git): Merge git subtree at v2.29.2 r/1890

This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because
there is some breakage in the git build related to the netrc
credentials helper which someone has taken care of in nixpkgs.

The stable channel is not used for anything other than git, so this
should be fine.

Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb

1 files changed, 8 insertions, 4 deletions

diff --git a/third_party/git/xdiff-interface.c b/third_party/git/xdiff-interface.c
index 8509f9ea22..4d20069302 100644
--- a/third_party/git/xdiff-interface.c
+++ b/third_party/git/xdiff-interface.c
@@ -84,8 +84,8 @@ static void trim_common_tail(mmfile_t *a, mmfile_t *b)
 {
 	const int blk = 1024;
 	long trimmed = 0, recovered = 0;
-	char *ap = a->ptr + a->size;
-	char *bp = b->ptr + b->size;
+	char *ap = a->size ? a->ptr + a->size : a->ptr;
+	char *bp = b->size ? b->ptr + b->size : b->ptr;
 	long smaller = (a->size < b->size) ? a->size : b->size;
 
 	while (blk + trimmed <= smaller && !memcmp(ap - blk, bp - blk, blk)) {
@@ -250,9 +250,13 @@ void xdiff_set_find_func(xdemitconf_t *xecfg, const char *value, int cflags)
 	ALLOC_ARRAY(regs->array, regs->nr);
 	for (i = 0; i < regs->nr; i++) {
 		struct ff_reg *reg = regs->array + i;
-		const char *ep = strchr(value, '\n'), *expression;
+		const char *ep, *expression;
 		char *buffer = NULL;
 
+		if (!value)
+			BUG("mismatch between line count and parsing");
+		ep = strchr(value, '\n');
+
 		reg->negate = (*value == '!');
 		if (reg->negate && i == regs->nr - 1)
 			die("Last expression must not be negated: %s", value);
@@ -265,7 +269,7 @@ void xdiff_set_find_func(xdemitconf_t *xecfg, const char *value, int cflags)
 		if (regcomp(&reg->re, expression, cflags))
 			die("Invalid regexp to look for hunk header: %s", expression);
 		free(buffer);
-		value = ep + 1;
+		value = ep ? ep + 1 : NULL;
 	}
 }