feat(api): add filetype option nvim_get_option_value

- Also adjust the expr-mapping behaviour so normal commands and text
  changes are allowed in internal dummy buffers.

runtime/doc/api.txt

@@ -1969,6 +1969,10 @@ nvim_get_option_value({name}, {*opts})               *nvim_get_option_value()*
                 • win: |window-ID|. Used for getting window local options.
                 • buf: Buffer number. Used for getting buffer local options.
                   Implies {scope} is "local".
+                • filetype: |filetype|. Used to get the default option for a
+                  specific filetype. Cannot be used with any other option.
+                  Note: this is expensive, it is recommended to cache this
+                  value.
 
     Return: ~
         Option value

runtime/doc/news.txt

@@ -210,6 +210,9 @@ The following new APIs or features were added.
   https://tree-sitter.github.io/tree-sitter/syntax-highlighting#language-injection .
   Support for the previous format will be removed in a future release.
 
+• |nvim_get_option_value()| now has a `filetype` option so it can return the
+  default option for a specific filetype.
+
 ==============================================================================
 CHANGED FEATURES                                                 *news-changes*
 

src/nvim/api/keysets.lua

@@ -102,6 +102,7 @@ return {
     "scope";
     "win";
     "buf";
+    "filetype";
   }};
   { 'highlight', {
     "bold";

src/nvim/api/options.c

@@ -24,7 +24,7 @@
 #endif
 
 static int validate_option_value_args(Dict(option) *opts, int *scope, int *opt_type, void **from,
-                                      Error *err)
+                                      char **filetype, Error *err)
 {
   if (HAS_KEY(opts->scope)) {
     VALIDATE_T("scope", kObjectTypeString, opts->scope.type, {
@@ -44,6 +44,14 @@ static int validate_option_value_args(Dict(option) *opts, int *scope, int *opt_t
 
   *opt_type = SREQ_GLOBAL;
 
+  if (filetype != NULL && HAS_KEY(opts->filetype)) {
+    VALIDATE_T("scope", kObjectTypeString, opts->filetype.type, {
+      return FAIL;
+    });
+
+    *filetype = opts->filetype.data.string.data;
+  }
+
   if (HAS_KEY(opts->win)) {
     VALIDATE_T("win", kObjectTypeInteger, opts->win.type, {
       return FAIL;
@@ -69,10 +77,17 @@ static int validate_option_value_args(Dict(option) *opts, int *scope, int *opt_t
     }
   }
 
+  VALIDATE((!HAS_KEY(opts->filetype)
+            || !(HAS_KEY(opts->buf) || HAS_KEY(opts->scope) || HAS_KEY(opts->win))),
+           "%s", "cannot use 'filetype' with 'scope', 'buf' or 'win'", {
+    return FAIL;
+  });
+
   VALIDATE((!HAS_KEY(opts->scope) || !HAS_KEY(opts->buf)), "%s",
            "cannot use both 'scope' and 'buf'", {
     return FAIL;
   });
+
   VALIDATE((!HAS_KEY(opts->win) || !HAS_KEY(opts->buf)), "%s", "cannot use both 'buf' and 'win'", {
     return FAIL;
   });
@@ -80,6 +95,30 @@ static int validate_option_value_args(Dict(option) *opts, int *scope, int *opt_t
   return OK;
 }
 
+/// Create a dummy buffer and run the FileType autocmd on it.
+static buf_T *do_ft_buf(char *filetype, aco_save_T *aco, Error *err)
+{
+  if (filetype == NULL) {
+    return NULL;
+  }
+
+  // Allocate a buffer without putting it in the buffer list.
+  buf_T *ftbuf = buflist_new(NULL, NULL, 1, BLN_DUMMY);
+  if (ftbuf == NULL) {
+    api_set_error(err, kErrorTypeException, "Could not create internal buffer");
+    return NULL;
+  }
+
+  // Set curwin/curbuf to buf and save a few things.
+  aucmd_prepbuf(aco, ftbuf);
+
+  ftbuf->b_p_ft = xstrdup(filetype);
+
+  apply_autocmds(EVENT_FILETYPE, ftbuf->b_p_ft, ftbuf->b_fname, true, ftbuf);
+
+  return ftbuf;
+}
+
 /// Gets the value of an option. The behavior of this function matches that of
 /// |:set|: the local value of an option is returned if it exists; otherwise,
 /// the global value is returned. Local values always correspond to the current
@@ -92,6 +131,10 @@ static int validate_option_value_args(Dict(option) *opts, int *scope, int *opt_t
 ///                  - win: |window-ID|. Used for getting window local options.
 ///                  - buf: Buffer number. Used for getting buffer local options.
 ///                         Implies {scope} is "local".
+///                  - filetype: |filetype|. Used to get the default option for a
+///                    specific filetype. Cannot be used with any other option.
+///                    Note: this is expensive, it is recommended to cache this
+///                    value.
 /// @param[out] err  Error details, if any
 /// @return          Option value
 Object nvim_get_option_value(String name, Dict(option) *opts, Error *err)
@@ -102,14 +145,37 @@ Object nvim_get_option_value(String name, Dict(option) *opts, Error *err)
   int scope = 0;
   int opt_type = SREQ_GLOBAL;
   void *from = NULL;
-  if (!validate_option_value_args(opts, &scope, &opt_type, &from, err)) {
+  char *filetype = NULL;
+
+  if (!validate_option_value_args(opts, &scope, &opt_type, &from, &filetype, err)) {
     return rv;
   }
 
+  aco_save_T aco;
+
+  buf_T *ftbuf = do_ft_buf(filetype, &aco, err);
+  if (ERROR_SET(err)) {
+    return rv;
+  }
+
+  if (ftbuf != NULL) {
+    assert(!from);
+    from = ftbuf;
+  }
+
   long numval = 0;
   char *stringval = NULL;
   getoption_T result = access_option_value_for(name.data, &numval, &stringval, scope, opt_type,
                                                from, true, err);
+
+  if (ftbuf != NULL) {
+    // restore curwin/curbuf and a few other things
+    aucmd_restbuf(&aco);
+
+    assert(curbuf != ftbuf);  // safety check
+    wipe_buffer(ftbuf, false);
+  }
+
   if (ERROR_SET(err)) {
     return rv;
   }
@@ -164,7 +230,7 @@ void nvim_set_option_value(uint64_t channel_id, String name, Object value, Dict(
   int scope = 0;
   int opt_type = SREQ_GLOBAL;
   void *to = NULL;
-  if (!validate_option_value_args(opts, &scope, &opt_type, &to, err)) {
+  if (!validate_option_value_args(opts, &scope, &opt_type, &to, NULL, err)) {
     return;
   }
 

src/nvim/edit.c

@@ -1245,7 +1245,9 @@ bool edit(int cmdchar, bool startln, long count)
   // Don't allow changes in the buffer while editing the cmdline.  The
   // caller of getcmdline() may get confused.
   // Don't allow recursive insert mode when busy with completion.
-  if (textlock != 0 || ins_compl_active() || compl_busy || pum_visible()) {
+  // Allow in dummy buffers since they are only used internally
+  if (textlock != 0 || ins_compl_active() || compl_busy || pum_visible()
+      || expr_map_locked()) {
     emsg(_(e_textlock));
     return false;
   }

src/nvim/ex_docmd.c

@@ -6326,6 +6326,11 @@ void restore_current_state(save_state_T *sst)
   ui_cursor_shape();  // may show different cursor shape
 }
 
+bool expr_map_locked(void)
+{
+  return expr_map_lock > 0 && !(curbuf->b_flags & BF_DUMMY);
+}
+
 /// ":normal[!] {commands}": Execute normal mode commands.
 static void ex_normal(exarg_T *eap)
 {
@@ -6335,10 +6340,11 @@ static void ex_normal(exarg_T *eap)
   }
   char *arg = NULL;
 
-  if (ex_normal_lock > 0) {
+  if (expr_map_locked()) {
     emsg(_(e_secure));
     return;
   }
+
   if (ex_normal_busy >= p_mmd) {
     emsg(_("E192: Recursive use of :normal too deep"));
     return;

src/nvim/ex_getln.c

@@ -2740,6 +2740,9 @@ bool text_locked(void)
   if (cmdwin_type != 0) {
     return true;
   }
+  if (expr_map_locked()) {
+    return true;
+  }
   return textlock != 0;
 }
 

src/nvim/globals.h

@@ -715,7 +715,7 @@ EXTERN typebuf_T typebuf INIT(= { NULL, NULL, 0, 0, 0, 0, 0, 0, 0 });
 EXTERN bool typebuf_was_empty INIT(= false);
 
 EXTERN int ex_normal_busy INIT(= 0);     // recursiveness of ex_normal()
-EXTERN int ex_normal_lock INIT(= 0);     // forbid use of ex_normal()
+EXTERN int expr_map_lock INIT(= 0);      // running expr mapping, prevent use of ex_normal() and text changes
 EXTERN int ignore_script INIT(= false);  // ignore script input
 EXTERN int stop_insert_mode;             // for ":stopinsert"
 EXTERN bool KeyTyped;                    // true if user typed current char

src/nvim/mapping.c

@@ -1615,8 +1615,7 @@ char *eval_map_expr(mapblock_T *mp, int c)
 
   // Forbid changing text or using ":normal" to avoid most of the bad side
   // effects.  Also restore the cursor position.
-  textlock++;
-  ex_normal_lock++;
+  expr_map_lock++;
   set_vim_var_char(c);    // set v:char to the typed character
   const pos_T save_cursor = curwin->w_cursor;
   const int save_msg_col = msg_col;
@@ -1637,8 +1636,7 @@ char *eval_map_expr(mapblock_T *mp, int c)
     p = eval_to_string(expr, NULL, false);
     xfree(expr);
   }
-  textlock--;
-  ex_normal_lock--;
+  expr_map_lock--;
   curwin->w_cursor = save_cursor;
   msg_col = save_msg_col;
   msg_row = save_msg_row;

src/nvim/undo.c

@@ -96,6 +96,7 @@
 #include "nvim/eval/typval.h"
 #include "nvim/eval/typval_defs.h"
 #include "nvim/ex_cmds_defs.h"
+#include "nvim/ex_docmd.h"
 #include "nvim/ex_getln.h"
 #include "nvim/extmark.h"
 #include "nvim/fileio.h"
@@ -300,7 +301,7 @@ bool undo_allowed(buf_T *buf)
 
   // Don't allow changes in the buffer while editing the cmdline.  The
   // caller of getcmdline() may get confused.
-  if (textlock != 0) {
+  if (textlock != 0 || expr_map_locked()) {
     emsg(_(e_textlock));
     return false;
   }