diff: add --no-dereference flag

When diffing files and directories, don't follow symbolic links, instead
compare where the links point to.

Reviewed by:	bapt
Sponsored by:	Klara Inc.
Differential Revision:	https://reviews.freebsd.org/D34203

usr.bin/diff/diff.c

@@ -39,7 +39,7 @@ __FBSDID("$FreeBSD$");
 #include "xmalloc.h"
 
 bool	 lflag, Nflag, Pflag, rflag, sflag, Tflag, cflag;
-bool	 ignore_file_case, suppress_common, color;
+bool	 ignore_file_case, suppress_common, color, noderef;
 int	 diff_format, diff_context, status;
 int	 tabsize = 8, width = 130;
 static int	colorflag = COLORFLAG_NEVER;
@@ -62,6 +62,7 @@ enum {
 	OPT_CHANGED_GROUP_FORMAT,
 	OPT_SUPPRESS_COMMON,
 	OPT_COLOR,
+	OPT_NO_DEREFERENCE,
 };
 
 static struct option longopts[] = {
@@ -97,6 +98,7 @@ static struct option longopts[] = {
 	{ "side-by-side",		no_argument,		NULL,	'y' },
 	{ "ignore-file-name-case",	no_argument,		NULL,	OPT_IGN_FN_CASE },
 	{ "horizon-lines",		required_argument,	NULL,	OPT_HORIZON_LINES },
+	{ "no-dereference",		no_argument,		NULL,	OPT_NO_DEREFERENCE},
 	{ "no-ignore-file-name-case",	no_argument,		NULL,	OPT_NO_IGN_FN_CASE },
 	{ "normal",			no_argument,		NULL,	OPT_NORMAL },
 	{ "strip-trailing-cr",		no_argument,		NULL,	OPT_STRIPCR },
@@ -328,6 +330,10 @@ main(int argc, char **argv)
 				errx(2, "unsupported --color value '%s' (must be always, auto, or never)",
 					optarg);
 			break;
+		case OPT_NO_DEREFERENCE:
+			rflag = true;
+			noderef = true;
+			break;
 		default:
 			usage();
 			break;

usr.bin/diff/diff.h

@@ -101,7 +101,7 @@ struct excludes {
 };
 
 extern bool	lflag, Nflag, Pflag, rflag, sflag, Tflag, cflag;
-extern bool	ignore_file_case, suppress_common, color;
+extern bool	ignore_file_case, suppress_common, color, noderef;
 extern int	diff_format, diff_context, status;
 extern int	tabsize, width;
 extern char	*start, *ifdefname, *diffargs, *label[2];

usr.bin/diff/diffdir.c

@@ -33,6 +33,7 @@ __FBSDID("$FreeBSD$");
 #include <stdlib.h>
 #include <string.h>
 #include <limits.h>
+#include <unistd.h>
 
 #include "diff.h"
 
@@ -175,28 +176,87 @@ diffit(struct dirent *dp, char *path1, size_t plen1, char *path2, size_t plen2,
 {
 	flags |= D_HEADER;
 	strlcpy(path1 + plen1, dp->d_name, PATH_MAX - plen1);
-	if (stat(path1, &stb1) != 0) {
-		if (!(Nflag || Pflag) || errno != ENOENT) {
-			warn("%s", path1);
-			return;
-		}
-		flags |= D_EMPTY1;
-		memset(&stb1, 0, sizeof(stb1));
-	}
-
 	strlcpy(path2 + plen2, dp->d_name, PATH_MAX - plen2);
-	if (stat(path2, &stb2) != 0) {
-		if (!Nflag || errno != ENOENT) {
-			warn("%s", path2);
+
+	if (noderef) {
+		if (lstat(path1, &stb1) != 0) {
+			if (!(Nflag || Pflag) || errno != ENOENT) {
+				warn("%s", path1);
+				return;
+			}
+			flags |= D_EMPTY1;
+			memset(&stb1, 0, sizeof(stb1));
+		}
+
+		if (lstat(path2, &stb2) != 0) {
+			if (!Nflag || errno != ENOENT) {
+				warn("%s", path2);
+				return;
+			}
+			flags |= D_EMPTY2;
+			memset(&stb2, 0, sizeof(stb2));
+			stb2.st_mode = stb1.st_mode;
+		}
+		if (stb1.st_mode == 0)
+			stb1.st_mode = stb2.st_mode;
+		if (S_ISLNK(stb1.st_mode) || S_ISLNK(stb2.st_mode)) {
+			if  (S_ISLNK(stb1.st_mode) && S_ISLNK(stb2.st_mode)) {
+				char buf1[PATH_MAX];
+				char buf2[PATH_MAX];
+				ssize_t len1 = 0;
+				ssize_t len2 = 0;
+
+				len1 = readlink(path1, buf1, sizeof(buf1));
+				len2 = readlink(path2, buf2, sizeof(buf2));
+
+				if (len1 < 0 || len2 < 0) {
+					perror("reading links");
+					return;
+				}
+				buf1[len1] = '\0';
+				buf2[len2] = '\0';
+
+				if (len1 != len2 || strncmp(buf1, buf2, len1) != 0) {
+					printf("Symbolic links %s and %s differ\n",
+						path1, path2);
+					status |= 1;
+				}
+
+				return;
+			}
+
+			printf("File %s is a %s while file %s is a %s\n",
+				path1, S_ISLNK(stb1.st_mode) ? "symbolic link" :
+					(S_ISDIR(stb1.st_mode) ? "directory" :
+					(S_ISREG(stb1.st_mode) ? "file" : "error")),
+				path2, S_ISLNK(stb2.st_mode) ? "symbolic link" :
+					(S_ISDIR(stb2.st_mode) ? "directory" :
+					(S_ISREG(stb2.st_mode) ? "file" : "error")));
+			status |= 1;
 			return;
 		}
-		flags |= D_EMPTY2;
-		memset(&stb2, 0, sizeof(stb2));
-		stb2.st_mode = stb1.st_mode;
-	}
-	if (stb1.st_mode == 0)
-		stb1.st_mode = stb2.st_mode;
+	} else {
+		if (stat(path1, &stb1) != 0) {
+			if (!(Nflag || Pflag) || errno != ENOENT) {
+				warn("%s", path1);
+				return;
+			}
+			flags |= D_EMPTY1;
+			memset(&stb1, 0, sizeof(stb1));
+		}
 
+		if (stat(path2, &stb2) != 0) {
+			if (!Nflag || errno != ENOENT) {
+				warn("%s", path2);
+				return;
+			}
+			flags |= D_EMPTY2;
+			memset(&stb2, 0, sizeof(stb2));
+			stb2.st_mode = stb1.st_mode;
+		}
+		if (stb1.st_mode == 0)
+			stb1.st_mode = stb2.st_mode;
+	}
 	if (S_ISDIR(stb1.st_mode) && S_ISDIR(stb2.st_mode)) {
 		if (rflag)
 			diffdir(path1, path2, flags);

usr.bin/diff/tests/diff_test.sh

@@ -20,6 +20,7 @@ atf_test_case report_identical
 atf_test_case non_regular_file
 atf_test_case binary
 atf_test_case functionname
+atf_test_case noderef
 
 simple_body()
 {
@@ -296,6 +297,35 @@ functionname_body()
 		"$(atf_get_srcdir)/functionname.in" "$(atf_get_srcdir)/functionname_objcclassm.in"
 }
 
+noderef_body()
+{
+	atf_check mkdir A B
+
+	atf_check -x "echo 1 > A/test-file"
+	atf_check -x "echo 1 > test-file"
+	atf_check -x "echo 1 > test-file2"
+
+	atf_check ln -s $(pwd)/test-file B/test-file
+
+	atf_check -o empty -s exit:0 diff -r A B
+	atf_check -o inline:"File A/test-file is a file while file B/test-file is a symbolic link\n" \
+		-s exit:1 diff -r --no-dereference A B
+
+	# both test files are now the same symbolic link
+	atf_check rm A/test-file
+
+	atf_check ln -s $(pwd)/test-file A/test-file
+	atf_check -o empty -s exit:0 diff -r A B
+	atf_check -o empty -s exit:0 diff -r --no-dereference A B
+
+	# make test files different symbolic links, but same contents
+	atf_check unlink A/test-file
+	atf_check ln -s $(pwd)/test-file2 A/test-file
+
+	atf_check -o empty -s exit:0 diff -r A B
+	atf_check -o inline:"Symbolic links A/test-file and B/test-file differ\n" -s exit:1 diff -r --no-dereference A B
+}
+
 atf_init_test_cases()
 {
 	atf_add_test_case simple
@@ -318,4 +348,5 @@ atf_init_test_cases()
 	atf_add_test_case non_regular_file
 	atf_add_test_case binary
 	atf_add_test_case functionname
+	atf_add_test_case noderef
 }