patch 8.2.4173: cannot use an import in 'foldexpr'

Problem:    Cannot use an import in 'foldexpr'.
Solution:   Set the script context to where 'foldexpr' was set. (closes #9584)
            Fix that the script context was not set for all buffers.

src/eval.c

@@ -772,7 +772,7 @@ call_func_retlist(
     return rettv.vval.v_list;
 }
 
-#ifdef FEAT_FOLDING
+#if defined(FEAT_FOLDING) || defined(PROTO)
 /*
  * Evaluate "arg", which is 'foldexpr'.
  * Note: caller must set "curwin" to match "arg".
@@ -780,14 +780,19 @@ call_func_retlist(
  * give error messages.
  */
     int
-eval_foldexpr(char_u *arg, int *cp)
+eval_foldexpr(win_T *wp, int *cp)
 {
+    char_u	*arg;
     typval_T	tv;
     varnumber_T	retval;
     char_u	*s;
+    sctx_T	saved_sctx = current_sctx;
     int		use_sandbox = was_set_insecurely((char_u *)"foldexpr",
 								   OPT_LOCAL);
 
+    arg = wp->w_p_fde;
+    current_sctx = wp->w_p_script_ctx[WV_FDE];
+
     ++emsg_off;
     if (use_sandbox)
 	++sandbox;
@@ -818,6 +823,7 @@ eval_foldexpr(char_u *arg, int *cp)
 	--sandbox;
     --textwinlock;
     clear_evalarg(&EVALARG_EVALUATE, NULL);
+    current_sctx = saved_sctx;
 
     return (int)retval;
 }

src/fold.c

@@ -3307,7 +3307,7 @@ foldlevelExpr(fline_T *flp)
     // KeyTyped may be reset to 0 when calling a function which invokes
     // do_cmdline().  To make 'foldopen' work correctly restore KeyTyped.
     save_keytyped = KeyTyped;
-    n = eval_foldexpr(flp->wp->w_p_fde, &c);
+    n = eval_foldexpr(flp->wp, &c);
     KeyTyped = save_keytyped;
 
     switch (c)

src/option.c

@@ -2604,7 +2604,13 @@ set_option_sctx_idx(int opt_idx, int opt_flags, sctx_T script_ctx)
 	if (indir & PV_BUF)
 	    curbuf->b_p_script_ctx[indir & PV_MASK] = new_script_ctx;
 	else if (indir & PV_WIN)
+	{
 	    curwin->w_p_script_ctx[indir & PV_MASK] = new_script_ctx;
+	    if (both)
+		// also setting the "all buffers" value
+		curwin->w_allbuf_opt.wo_script_ctx[indir & PV_MASK] =
+								new_script_ctx;
+	}
     }
 }
 

src/proto/eval.pro

@@ -18,11 +18,9 @@ char_u *eval_to_string_safe(char_u *arg, int use_sandbox);
 varnumber_T eval_to_number(char_u *expr);
 typval_T *eval_expr(char_u *arg, exarg_T *eap);
 int call_vim_function(char_u *func, int argc, typval_T *argv, typval_T *rettv);
-varnumber_T call_func_retnr(char_u *func, int argc, typval_T *argv);
-int call_func_noret(char_u *func, int argc, typval_T *argv);
 void *call_func_retstr(char_u *func, int argc, typval_T *argv);
 void *call_func_retlist(char_u *func, int argc, typval_T *argv);
-int eval_foldexpr(char_u *arg, int *cp);
+int eval_foldexpr(win_T *wp, int *cp);
 char_u *get_lval(char_u *name, typval_T *rettv, lval_T *lp, int unlet, int skip, int flags, int fne_flags);
 void clear_lval(lval_T *lp);
 void set_var_lval(lval_T *lp, char_u *endp, typval_T *rettv, int copy, int flags, char_u *op, int var_idx);

src/structs.h

@@ -3695,6 +3695,8 @@ struct window_S
      */
     winopt_T	w_onebuf_opt;
     winopt_T	w_allbuf_opt;
+    // transform a pointer to a "onebuf" option into a "allbuf" option
+#define GLOBAL_WO(p)	((char *)p + sizeof(winopt_T))
 
     // A few options have local flags for P_INSECURE.
 #ifdef FEAT_STL_OPT
@@ -3718,9 +3720,6 @@ struct window_S
     int		w_briopt_list;      // additional indent for lists
 #endif
 
-    // transform a pointer to a "onebuf" option into a "allbuf" option
-#define GLOBAL_WO(p)	((char *)p + sizeof(winopt_T))
-
     long	w_scbind_pos;
 
 #ifdef FEAT_EVAL

src/testdir/test_vim9_import.vim

@@ -673,6 +673,45 @@ def Test_use_autoload_import_in_insert_completion()
   &rtp = save_rtp
 enddef
 
+def Test_use_autoload_import_in_fold_expression()
+  mkdir('Xdir/autoload', 'p')
+  var save_rtp = &rtp
+  exe 'set rtp^=' .. getcwd() .. '/Xdir'
+
+  var lines =<< trim END
+      vim9script
+      export def Expr(): string
+        return getline(v:lnum) =~ '^#' ? '>1' : '1'
+      enddef
+      g:fold_loaded = 'yes'
+  END
+  writefile(lines, 'Xdir/autoload/fold.vim')
+
+  lines =<< trim END
+      vim9script
+      import autoload 'fold.vim'
+      &foldexpr = 'fold.Expr()'
+      &foldmethod = 'expr'
+      &debug = 'throw'
+  END
+  new
+  setline(1, ['# one', 'text', '# two', 'text'])
+  g:fold_loaded = 'no'
+  CheckScriptSuccess(lines)
+  assert_equal('no', g:fold_loaded)
+  redraw
+  assert_equal('yes', g:fold_loaded)
+
+  # Check that script context of 'foldexpr' is copied to another buffer.
+  edit! otherfile
+  redraw
+
+  set foldexpr= foldmethod&
+  bwipe!
+  delete('Xdir', 'rf')
+  &rtp = save_rtp
+enddef
+
 def Test_export_fails()
   CheckScriptFailure(['export var some = 123'], 'E1042:')
   CheckScriptFailure(['vim9script', 'export var g:some'], 'E1022:')

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4173,
 /**/
     4172,
 /**/