Prevent overwriting existing file in :write <explicit filename>

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

doc/pages/commands.asciidoc

@@ -58,13 +58,17 @@ of the file onto the filesystem
         Otherwise, does nothing.
 
 
-*write[!]* [-sync] [-method <writemethod>] [<filename>]::
+*write[!]* [-force] [-sync] [-method <writemethod>] [<filename>]::
     *alias* w +
     write buffer to <filename> or use its name if filename is not
     given. If the file is write-protected, its permissions are temporarily
     changed to allow saving the buffer and restored afterwards when
     the write! command is used.
 
+    *-force*:::
+        Equivalent to `!`, allow overwiting existing files if `<filename>`
+        is given and set permissions temporarily if necessary.
+
     *-sync*:::
         Synchronise the filesystem after the write
 

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));
 }
 

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();

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);
 

test/run

@@ -16,7 +16,7 @@ main() {
         try %{ source rc }
         hook global RuntimeError .+ %{
             echo -debug -- error: %val{hook_param}
-            eval -buffer *debug* write debug
+            eval -buffer *debug* write -force debug
             quit!
         }
         try %{ exec -with-maps -with-hooks "%sh{cat cmd}" }
@@ -151,14 +151,14 @@ show_diff() {
 
 finished_commands() {
   printf %s 'eval -client client0 %{
-               eval -buffer *debug* write debug
+               eval -buffer *debug* write -force debug
                nop %sh{
             '
   for env_var in $env_vars; do
     printf 'printf %%s\\\\n "$%s" >%s\n' "$env_var" "$env_var"
   done
   printf %s '  }
-               write out
+               write -force out
                quit!
              }
             '