range-diff: don't segfault with mode-only changes

In ef283b3699 ("apply: make parse_git_diff_header public", 2019-07-11)
the 'parse_git_diff_header' function was made public and useable by
callers outside of apply.c.

However it was missed that its (then) only caller, 'find_header' did
some error handling, and completing 'struct patch' appropriately.

range-diff then started using this function, and tried to handle this
appropriately itself, but fell short in some cases.  This in turn
would lead to range-diff segfaulting when there are mode-only changes
in a range.

Move the error handling and completing of the struct into the
'parse_git_diff_header' function, so other callers can take advantage
of it.  This fixes the segfault in 'git range-diff'.

Reported-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Acked-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

apply.c

@@ -1361,11 +1361,32 @@ int parse_git_diff_header(struct strbuf *root,
 			if (check_header_line(*linenr, patch))
 				return -1;
 			if (res > 0)
-				return offset;
+				goto done;
 			break;
 		}
 	}
 
+done:
+	if (!patch->old_name && !patch->new_name) {
+		if (!patch->def_name) {
+			error(Q_("git diff header lacks filename information when removing "
+				 "%d leading pathname component (line %d)",
+				 "git diff header lacks filename information when removing "
+				 "%d leading pathname components (line %d)",
+				 parse_hdr_state.p_value),
+			      parse_hdr_state.p_value, *linenr);
+			return -128;
+		}
+		patch->old_name = xstrdup(patch->def_name);
+		patch->new_name = xstrdup(patch->def_name);
+	}
+	if ((!patch->new_name && !patch->is_delete) ||
+	    (!patch->old_name && !patch->is_new)) {
+		error(_("git diff header lacks filename information "
+			"(line %d)"), *linenr);
+		return -128;
+	}
+	patch->is_toplevel_relative = 1;
 	return offset;
 }
 
@@ -1546,26 +1567,6 @@ static int find_header(struct apply_state *state,
 				return -128;
 			if (git_hdr_len <= len)
 				continue;
-			if (!patch->old_name && !patch->new_name) {
-				if (!patch->def_name) {
-					error(Q_("git diff header lacks filename information when removing "
-							"%d leading pathname component (line %d)",
-							"git diff header lacks filename information when removing "
-							"%d leading pathname components (line %d)",
-							state->p_value),
-						     state->p_value, state->linenr);
-					return -128;
-				}
-				patch->old_name = xstrdup(patch->def_name);
-				patch->new_name = xstrdup(patch->def_name);
-			}
-			if ((!patch->new_name && !patch->is_delete) ||
-			    (!patch->old_name && !patch->is_new)) {
-				error(_("git diff header lacks filename information "
-					     "(line %d)"), state->linenr);
-				return -128;
-			}
-			patch->is_toplevel_relative = 1;
 			*hdrsize = git_hdr_len;
 			return offset;
 		}

t/t3206-range-diff.sh

@@ -226,6 +226,46 @@ test_expect_success 'renamed file' '
 	test_cmp expected actual
 '
 
+test_expect_success 'file with mode only change' '
+	git range-diff --no-color --submodule=log topic...mode-only-change >actual &&
+	sed s/Z/\ /g >expected <<-EOF &&
+	1:  fccce22 ! 1:  4d39cb3 s/4/A/
+	    @@ Metadata
+	    ZAuthor: Thomas Rast <trast@inf.ethz.ch>
+	    Z
+	    Z ## Commit message ##
+	    -    s/4/A/
+	    +    s/4/A/ + add other-file
+	    Z
+	    Z ## file ##
+	    Z@@
+	    @@ file
+	    Z A
+	    Z 6
+	    Z 7
+	    +
+	    + ## other-file (new) ##
+	2:  147e64e ! 2:  26c107f s/11/B/
+	    @@ Metadata
+	    ZAuthor: Thomas Rast <trast@inf.ethz.ch>
+	    Z
+	    Z ## Commit message ##
+	    -    s/11/B/
+	    +    s/11/B/ + mode change other-file
+	    Z
+	    Z ## file ##
+	    Z@@ file: A
+	    @@ file: A
+	    Z 12
+	    Z 13
+	    Z 14
+	    +
+	    + ## other-file (mode change 100644 => 100755) ##
+	3:  a63e992 = 3:  4c1e0f5 s/12/B/
+	EOF
+	test_cmp expected actual
+'
+
 test_expect_success 'file added and later removed' '
 	git range-diff --no-color --submodule=log topic...added-removed >actual &&
 	sed s/Z/\ /g >expected <<-EOF &&

t/t3206/history.export

@@ -55,7 +55,7 @@ A
 19
 20
 
-commit refs/heads/topic
+commit refs/heads/mode-only-change
 mark :4
 author Thomas Rast <trast@inf.ethz.ch> 1374485014 +0200
 committer Thomas Rast <trast@inf.ethz.ch> 1374485014 +0200
@@ -678,3 +678,32 @@ s/12/B/
 from :55
 M 100644 :9 renamed-file
 
+commit refs/heads/mode-only-change
+mark :57
+author Thomas Rast <trast@inf.ethz.ch> 1374485024 +0200
+committer Thomas Gummerer <t.gummerer@gmail.com> 1570473767 +0100
+data 24
+s/4/A/ + add other-file
+from :4
+M 100644 :5 file
+M 100644 :49 other-file
+
+commit refs/heads/mode-only-change
+mark :58
+author Thomas Rast <trast@inf.ethz.ch> 1374485036 +0200
+committer Thomas Gummerer <t.gummerer@gmail.com> 1570473768 +0100
+data 33
+s/11/B/ + mode change other-file
+from :57
+M 100644 :7 file
+M 100755 :49 other-file
+
+commit refs/heads/mode-only-change
+mark :59
+author Thomas Rast <trast@inf.ethz.ch> 1374485044 +0200
+committer Thomas Gummerer <t.gummerer@gmail.com> 1570473768 +0100
+data 8
+s/12/B/
+from :58
+M 100644 :9 file
+