Only warn when trying to modify read-only files

Failing when trying to patch read-only files causes various users of patch to
break.  Instead, warn by default and introduce a command line option for
choosing a different behavior.
* patch.man: Describe the new behavior and command-line option.
* src/patch.c (read_only_behavior): New variable.
(main): Implement the new behavior.
(longopts): Add the new --read-only option.
(option_help): Describe the new behavior.
(get_some_switches): Recognize the new --read-only option.

3 files changed, 34 insertions, 6 deletions

diff --git a/patch.man b/patch.man
index 02e6b90..b0ee8c1 100644
--- a/patch.man
+++ b/patch.man
@@ -314,6 +314,10 @@ and patches should be generated by
 .B "diff\ \*=binary"
 when line endings are significant.)
 .TP
+\fB\*=read\-only=\fP\fIbehavior\fP
+Behave as requested when trying to modify a read-only file: \fBignore\fP the
+potential problem, \fBwarn\fP about it (the default), or \fBfail\fP.
+.TP
 \fB\-c\fP  or  \fB\*=context\fP
 Interpret the patch file as a ordinary context diff.
 .TP
@@ -356,8 +360,8 @@ removes a file, it also attempts to remove any empty ancestor directories.
 \fB\-f\fP  or  \fB\*=force\fP
 Assume that the user knows exactly what he or she is doing, and do not
 ask any questions.  Skip patches whose headers
-do not say which file is to be patched; patch files even though they are
-read-only or have the wrong version for the
+do not say which file is to be patched; patch files even though they have the
+wrong version for the
 .B Prereq:\&
 line in the patch; and assume that
 patches are not reversed even if they look like they are.
diff --git a/src/patch.c b/src/patch.c
index cc9b268..40987c1 100644
--- a/src/patch.c
+++ b/src/patch.c
@@ -76,6 +76,7 @@ static char const *version_control;
 static char const *version_control_context;
 static bool remove_empty_files;
 static bool explicit_inname;
+static enum { RO_IGNORE, RO_WARN, RO_FAIL } read_only_behavior = RO_WARN;
 
 /* true if -R was specified on command line.  */
 static bool reverse_flag_specified;
@@ -244,11 +245,12 @@ main (int argc, char **argv)
 	    }
 	}
 
-      if (! inerrno && ! S_ISLNK (instat.st_mode)
+      if (read_only_behavior != RO_IGNORE
+	  && ! inerrno && ! S_ISLNK (instat.st_mode)
 	  && access (inname, W_OK) != 0)
 	{
 	  say ("File %s is read-only; ", quotearg (inname));
-	  if (force || batch)
+	  if (read_only_behavior == RO_WARN)
 	    say ("trying to patch anyway\n");
 	  else
 	    {
@@ -682,6 +684,7 @@ static struct option const longopts[] =
   {"posix", no_argument, NULL, CHAR_MAX + 7},
   {"quoting-style", required_argument, NULL, CHAR_MAX + 8},
   {"reject-format", required_argument, NULL, CHAR_MAX + 9},
+  {"read-only", required_argument, NULL, CHAR_MAX + 10},
   {NULL, no_argument, NULL, 0}
 };
 
@@ -747,6 +750,8 @@ static char const *const option_help[] =
 "  -d DIR  --directory=DIR  Change the working directory to DIR first.",
 "  --reject-format=FORMAT  Create 'context' or 'unified' rejects.",
 "  --binary  Read and write data in binary mode.",
+"  --read-only=BEHAVIOR  How to handle read-only input files: 'ignore' that they",
+"                        are read-only, 'warn' (default), or 'fail'.",
 "",
 "  -v  --version  Output version info.",
 "  --help  Output this help.",
@@ -961,6 +966,16 @@ get_some_switches (void)
 		else
 		  usage (stderr, 2);
 		break;
+	    case CHAR_MAX + 10:
+		if (strcmp (optarg, "ignore") == 0)
+		  read_only_behavior = RO_IGNORE;
+		else if (strcmp (optarg, "warn") == 0)
+		  read_only_behavior = RO_WARN;
+		else if (strcmp (optarg, "fail") == 0)
+		  read_only_behavior = RO_FAIL;
+		else
+		  usage (stderr, 2);
+		break;
 	    default:
 		usage (stderr, 2);
 	}
diff --git a/tests/read-only-files b/tests/read-only-files
index 7db401b..918b97a 100644
--- a/tests/read-only-files
+++ b/tests/read-only-files
@@ -41,7 +41,7 @@ EOF
 echo one > f
 chmod a=r f
 
-check 'patch -p0 < f.diff || echo "Status: $?"' <<EOF
+check 'patch -p0 --read-only=fail < f.diff || echo "Status: $?"' <<EOF
 File f is read-only; refusing to patch
 1 out of 1 hunk ignored -- saving rejects to file f.rej
 File f is read-only; refusing to patch
@@ -51,9 +51,18 @@ EOF
 
 rm -f f.rej
 
-check 'patch -f -p0 < f.diff || echo "Status: $?"' <<EOF
+check 'patch -f -p0 --read-only=warn < f.diff || echo "Status: $?"' <<EOF
 File f is read-only; trying to patch anyway
 patching file f
 File f is read-only; trying to patch anyway
 patching file f
 EOF
+
+rm -f f
+echo one > f
+chmod a=r f
+
+check 'patch -f -p0 --read-only=ignore < f.diff || echo "Status: $?"' <<EOF
+patching file f
+patching file f
+EOF