Prevent overwriting existing file in :write <explicit filename>

Add a -force (equivalent to w!) switch that enables overwriting.

3 files changed, 16 insertions, 2 deletions

diff --git a/src/commands.cc b/src/commands.cc
index 3a805756..99859127 100644
--- a/src/commands.cc
+++ b/src/commands.cc
@@ -460,6 +460,7 @@ const ParameterDesc write_params{
     {
         { "sync", { false, "force the synchronization of the file onto the filesystem" } },
         { "method", { true, "explicit writemethod (replace|overwrite)" } },
+        { "force", { false, "Allow overwriting existing file with explicit filename" } },
     },
     ParameterDesc::Flags::SwitchesOnlyAtStart, 0, 1
 };
@@ -488,7 +489,12 @@ void do_write_buffer(Context& context, Optional<String> filename, WriteFlags fla
         (not filename or real_path(*filename) == buffer.name()))
         throw runtime_error("cannot overwrite the buffer when in readonly mode");
 
-    auto effective_filename = not filename ? buffer.name() : parse_filename(*filename);
+    auto effective_filename = filename ? parse_filename(*filename) : buffer.name();
+    if (filename and not (flags & WriteFlags::Force) and
+        real_path(effective_filename) != buffer.name() and
+        regular_file_exists(effective_filename))
+        throw runtime_error("cannot overwrite existing file without -force");
+
     auto method = write_method.value_or_compute([&] { return context.options()["writemethod"].get<WriteMethod>(); });
 
     context.hooks().run_hook(Hook::BufWritePre, effective_filename, context);
@@ -502,7 +508,7 @@ void write_buffer(const ParametersParser& parser, Context& context, const ShellC
     return do_write_buffer(context,
                            parser.positional_count() > 0 ? parser[0] : Optional<String>{},
                            (parser.get_switch("sync") ? WriteFlags::Sync : WriteFlags::None) |
-                           (force ? WriteFlags::Force : WriteFlags::None),
+                           (parser.get_switch("force") or force ? WriteFlags::Force : WriteFlags::None),
                            parser.get_switch("method").map(parse_write_method));
 }
 
diff --git a/src/file.cc b/src/file.cc
index 89dee9a3..4c7658be 100644
--- a/src/file.cc
+++ b/src/file.cc
@@ -247,6 +247,13 @@ bool file_exists(StringView filename)
     return stat(filename.zstr(), &st) == 0;
 }
 
+bool regular_file_exists(StringView filename)
+{
+    struct stat st;
+    return stat(filename.zstr(), &st) == 0 and
+           (st.st_mode & S_IFMT) == S_IFREG;
+}
+
 void write(int fd, StringView data)
 {
     const char* ptr = data.data();
diff --git a/src/file.hh b/src/file.hh
index aa32b01d..849b14f4 100644
--- a/src/file.hh
+++ b/src/file.hh
@@ -81,6 +81,7 @@ void write_buffer_to_backup_file(Buffer& buffer);
 
 String find_file(StringView filename, StringView buf_dir, ConstArrayView<String> paths);
 bool file_exists(StringView filename);
+bool regular_file_exists(StringView filename);
 
 Vector<String> list_files(StringView directory);