patch 9.0.0370: cleaning up afterwards can make a function messy

Problem:    Cleaning up afterwards can make a function messy.
Solution:   Add the :defer command.

runtime/doc/eval.txt

@@ -2979,6 +2979,62 @@ is used as a method: >
 	let y = GetList()->Filter()
 
 
+CLEANING UP IN A FUNCTION ~
+							*:defer*
+:defer {func}({args})	Call {func} when the current function is done.
+			{args} are evaluated here.
+
+Quite often a command in a function has a global effect, which must be undone
+when the function finishes.  Handling this in all kinds of situations can be a
+hassle.  Especially when an unexpected error is encountered.  This can be done
+with `try` / `finally` blocks, but this gets complicated when there is more
+than one.
+
+A much simpler solution is using `defer`.  It schedules a function call when
+the function is returning, no matter if there is an error.  Example: >
+	func Filter(text)
+	  call writefile(a:text, 'Tempfile')
+	  call system('filter < Tempfile > Outfile')
+	  call Handle('Outfile')
+	  call delete('Tempfile')
+	  call delete('Outfile')
+	endfunc
+
+Here 'Tempfile' and 'Outfile' will not be deleted if something causes the
+function to abort.  `:defer` can be used to avoid that: >
+	func Filter(text)
+	  call writefile(a:text, 'Tempfile')
+	  defer delete('Tempfile')
+	  defer delete('Outfile')
+	  call system('filter < Tempfile > Outfile')
+	  call Handle('Outfile')
+	endfunc
+
+Note that deleting "Outfile" is scheduled before calling system(), since it
+can be created even when `system()` fails.
+
+The defered functions are called in reverse order, the last one added is
+executed first.  A useless example: >
+	func Useless()
+	  for s in range(3)
+	    defer execute('echomsg "number ' .. s .. '"')
+	  endfor
+	endfunc
+
+Now `:messages` shows:
+	number 2
+	number 1
+	number 0
+
+Any return value of the deferred function is discarded.  The function cannot
+be followed by anything, such as "->func" or ".member".  Currently `:defer
+GetArg()->TheFunc()` does not work, it may work in a later version.
+
+Errors are reported but do not cause aborting execution of deferred functions.
+
+No range is accepted.
+
+
 AUTOMATICALLY LOADING FUNCTIONS ~
 							*autoload-functions*
 When using many or large functions, it's possible to automatically define them

src/ex_cmdidxs.h

@@ -9,28 +9,28 @@ static const unsigned short cmdidxs1[26] =
   /* b */ 21,
   /* c */ 45,
   /* d */ 112,
-  /* e */ 137,
+  /* e */ 138,
-  /* f */ 166,
+  /* f */ 167,
-  /* g */ 183,
+  /* g */ 184,
-  /* h */ 189,
+  /* h */ 190,
-  /* i */ 199,
+  /* i */ 200,
-  /* j */ 219,
+  /* j */ 220,
-  /* k */ 221,
+  /* k */ 222,
-  /* l */ 226,
+  /* l */ 227,
-  /* m */ 289,
+  /* m */ 290,
-  /* n */ 307,
+  /* n */ 308,
-  /* o */ 327,
+  /* o */ 328,
-  /* p */ 339,
+  /* p */ 340,
-  /* q */ 378,
+  /* q */ 379,
-  /* r */ 381,
+  /* r */ 382,
-  /* s */ 401,
+  /* s */ 402,
-  /* t */ 471,
+  /* t */ 472,
-  /* u */ 517,
+  /* u */ 518,
-  /* v */ 528,
+  /* v */ 529,
-  /* w */ 549,
+  /* w */ 550,
-  /* x */ 563,
+  /* x */ 564,
-  /* y */ 573,
+  /* y */ 574,
-  /* z */ 574
+  /* z */ 575
 };
 
 /*
@@ -44,7 +44,7 @@ static const unsigned char cmdidxs2[26][26] =
   /* a */ {  0,  1,  0,  0,  0,  0,  0,  0,  0,  0,  0,  5,  6,  7,  0,  0,  0,  8, 17,  0, 18,  0,  0,  0,  0,  0 },
   /* b */ {  2,  0,  0,  5,  6,  8,  0,  0,  0,  0,  0,  9, 10, 11, 12, 13,  0, 14,  0,  0,  0,  0, 23,  0,  0,  0 },
   /* c */ {  3, 12, 16, 18, 20, 22, 25,  0,  0,  0,  0, 33, 38, 41, 47, 57, 59, 60, 61,  0, 63,  0, 66,  0,  0,  0 },
-  /* d */ {  0,  0,  0,  0,  0,  0,  0,  0,  8, 18,  0, 19,  0,  0, 20,  0,  0, 22, 23,  0,  0,  0,  0,  0,  0,  0 },
+  /* d */ {  0,  0,  0,  0,  0,  0,  0,  0,  9, 19,  0, 20,  0,  0, 21,  0,  0, 23, 24,  0,  0,  0,  0,  0,  0,  0 },
   /* e */ {  1,  0,  2,  0,  0,  0,  0,  0,  0,  0,  0,  9, 11, 12,  0,  0,  0,  0,  0,  0,  0, 23,  0, 24,  0,  0 },
   /* f */ {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 10,  0,  0,  0,  0,  0, 16,  0,  0,  0,  0,  0 },
   /* g */ {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  1,  0,  0,  2,  0,  0,  4,  5,  0,  0,  0,  0 },
@@ -69,4 +69,4 @@ static const unsigned char cmdidxs2[26][26] =
   /* z */ {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0 }
 };
 
-static const int command_count = 591;
+static const int command_count = 592;

src/ex_cmds.h

@@ -467,6 +467,9 @@ EXCMD(CMD_def,		"def",		ex_function,
 EXCMD(CMD_defcompile,	"defcompile",	ex_defcompile,
 	EX_SBOXOK|EX_CMDWIN|EX_LOCK_OK|EX_TRLBAR|EX_EXTRA,
 	ADDR_NONE),
+EXCMD(CMD_defer,	"defer",	ex_call,
+	EX_NEEDARG|EX_EXTRA|EX_NOTRLCOM|EX_EXPR_ARG|EX_SBOXOK|EX_CMDWIN|EX_LOCK_OK,
+	ADDR_NONE),
 EXCMD(CMD_delcommand,	"delcommand",	ex_delcommand,
 	EX_NEEDARG|EX_WORD1|EX_TRLBAR|EX_CMDWIN|EX_LOCK_OK,
 	ADDR_NONE),

src/proto/userfunc.pro

@@ -58,6 +58,7 @@ void func_ptr_unref(ufunc_T *fp);
 void func_ref(char_u *name);
 void func_ptr_ref(ufunc_T *fp);
 void ex_return(exarg_T *eap);
+void handle_defer(void);
 void ex_call(exarg_T *eap);
 int do_return(exarg_T *eap, int reanimate, int is_cmd, void *rettv);
 void discard_pending_return(void *rettv);

src/proto/vim9cmds.pro

@@ -21,6 +21,7 @@ char_u *compile_finally(char_u *arg, cctx_T *cctx);
 char_u *compile_endtry(char_u *arg, cctx_T *cctx);
 char_u *compile_throw(char_u *arg, cctx_T *cctx);
 char_u *compile_eval(char_u *arg, cctx_T *cctx);
+char_u *compile_defer(char_u *arg_start, cctx_T *cctx);
 char_u *compile_mult_expr(char_u *arg, int cmdidx, cctx_T *cctx);
 char_u *compile_put(char_u *arg, exarg_T *eap, cctx_T *cctx);
 char_u *compile_exec(char_u *line_arg, exarg_T *eap, cctx_T *cctx);

src/proto/vim9expr.pro

@@ -4,6 +4,7 @@ void clear_ppconst(ppconst_T *ppconst);
 int compile_member(int is_slice, int *keeping_dict, cctx_T *cctx);
 int compile_load_scriptvar(cctx_T *cctx, char_u *name, char_u *start, char_u **end);
 int compile_load(char_u **arg, char_u *end_arg, cctx_T *cctx, int is_expr, int error);
+int compile_arguments(char_u **arg, cctx_T *cctx, int *argcount, ca_special_T special_fn);
 char_u *to_name_end(char_u *arg, int use_namespace);
 char_u *to_name_const_end(char_u *arg);
 int get_lambda_tv_and_compile(char_u **arg, typval_T *rettv, int types_optional, evalarg_T *evalarg);

src/proto/vim9instr.pro

@@ -23,7 +23,7 @@ int generate_PUSHS(cctx_T *cctx, char_u **str);
 int generate_PUSHCHANNEL(cctx_T *cctx);
 int generate_PUSHJOB(cctx_T *cctx);
 int generate_PUSHBLOB(cctx_T *cctx, blob_T *blob);
-int generate_PUSHFUNC(cctx_T *cctx, char_u *name, type_T *type);
+int generate_PUSHFUNC(cctx_T *cctx, char_u *name, type_T *type, int may_prefix);
 int generate_AUTOLOAD(cctx_T *cctx, char_u *name, type_T *type);
 int generate_GETITEM(cctx_T *cctx, int index, int with_op);
 int generate_SLICE(cctx_T *cctx, int count);
@@ -52,6 +52,7 @@ int generate_BLOBAPPEND(cctx_T *cctx);
 int generate_CALL(cctx_T *cctx, ufunc_T *ufunc, int pushed_argcount);
 int generate_UCALL(cctx_T *cctx, char_u *name, int argcount);
 int generate_PCALL(cctx_T *cctx, int argcount, char_u *name, type_T *type, int at_top);
+int generate_DEFER(cctx_T *cctx, int var_idx, int argcount);
 int generate_STRINGMEMBER(cctx_T *cctx, char_u *name, size_t len);
 int generate_ECHO(cctx_T *cctx, int with_white, int count);
 int generate_MULT_EXPR(cctx_T *cctx, isntype_T isn_type, int count);

src/structs.h

@@ -1753,6 +1753,7 @@ struct funccall_S
     linenr_T	breakpoint;	// next line with breakpoint or zero
     int		dbg_tick;	// debug_tick when breakpoint was set
     int		level;		// top nesting level of executed function
+    garray_T	fc_defer;	// functions to be called on return
 #ifdef FEAT_PROFILE
     proftime_T	prof_child;	// time spent in a child
 #endif
@@ -1767,6 +1768,14 @@ struct funccall_S
 				// "func"
 };
 
+// structure used as item in "fc_defer"
+typedef struct
+{
+    char_u	*dr_name;	// function name, allocated
+    typval_T	dr_argvars[MAX_FUNC_ARGS + 1];
+    int		dr_argcount;
+} defer_T;
+
 /*
  * Struct used by trans_function_name()
  */
@@ -2850,7 +2859,7 @@ struct file_buffer
     int		b_u_synced;	// entry lists are synced
     long	b_u_seq_last;	// last used undo sequence number
     long	b_u_save_nr_last; // counter for last file write
-    long	b_u_seq_cur;	// hu_seq of header below which we are now
+    long	b_u_seq_cur;	// uh_seq of header below which we are now
     time_T	b_u_time_cur;	// uh_time of header below which we are now
     long	b_u_save_nr_cur; // file write nr after which we are now
 

src/testdir/test_user_func.vim

@@ -529,4 +529,36 @@ func Test_funcdef_alloc_failure()
   bw!
 endfunc
 
+func AddDefer(arg)
+  call extend(g:deferred, [a:arg])
+endfunc
+
+func WithDeferTwo()
+  call extend(g:deferred, ['in Two'])
+  for nr in range(3)
+    defer AddDefer('Two' .. nr)
+  endfor
+  call extend(g:deferred, ['end Two'])
+endfunc
+
+func WithDeferOne()
+  call extend(g:deferred, ['in One'])
+  call writefile(['text'], 'Xfuncdefer')
+  defer delete('Xfuncdefer')
+  defer AddDefer('One')
+  call WithDeferTwo()
+  call extend(g:deferred, ['end One'])
+endfunc
+
+func Test_defer()
+  let g:deferred = []
+  call WithDeferOne()
+
+  call assert_equal(['in One', 'in Two', 'end Two', 'Two2', 'Two1', 'Two0', 'end One', 'One'], g:deferred)
+  unlet g:deferred
+
+  call assert_equal('', glob('Xfuncdefer'))
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab

src/testdir/test_vim9_disassemble.vim

@@ -2900,4 +2900,19 @@ def Test_disassemble_bitshift()
                '10 RETURN void', instr)
 enddef
 
+def s:OneDefer()
+  defer delete("file")
+enddef
+
+def Test_disassemble_defer()
+  var instr = execute('disassemble s:OneDefer')
+  assert_match('OneDefer\_s*' ..
+        'defer delete("file")\_s*' ..
+        '\d PUSHFUNC "delete"\_s*' ..
+        '\d PUSHS "file"\_s*' ..
+        '\d DEFER 1 args\_s*' ..
+        '\d RETURN\_s*',
+        instr)
+enddef
+
 " vim: ts=8 sw=2 sts=2 expandtab tw=80 fdm=marker

src/testdir/test_vim9_func.vim

@@ -4272,6 +4272,36 @@ def Test_cexpr_errmsg_line_number()
   v9.CheckScriptFailure(lines, 'E777', 2)
 enddef
 
+def AddDefer(s: string)
+  g:deferred->extend([s])
+enddef
+
+def DeferTwo()
+  g:deferred->extend(['in Two'])
+  for n in range(3)
+    defer g:AddDefer('two' .. n)
+  endfor
+  g:deferred->extend(['end Two'])
+enddef
+
+def DeferOne()
+  g:deferred->extend(['in One'])
+  defer g:AddDefer('one')
+  g:DeferTwo()
+  g:deferred->extend(['end One'])
+
+  writefile(['text'], 'XdeferFile')
+  defer delete('XdeferFile')
+enddef
+
+def Test_defer()
+  g:deferred = []
+  g:DeferOne()
+  assert_equal(['in One', 'in Two', 'end Two', 'two2', 'two1', 'two0', 'end One', 'one'], g:deferred)
+  unlet g:deferred
+  assert_equal('', glob('XdeferFile'))
+enddef
+
 " The following messes up syntax highlight, keep near the end.
 if has('python3')
   def Test_python3_command()

src/userfunc.c

@@ -1728,44 +1728,36 @@ emsg_funcname(char *ermsg, char_u *name)
 }
 
 /*
- * Allocate a variable for the result of a function.
+ * Get function arguments at "*arg" and advance it.
- * Return OK or FAIL.
+ * Return them in "*argvars[MAX_FUNC_ARGS + 1]" and the count in "argcount".
  */
-    int
+    static int
-get_func_tv(
+get_func_arguments(
-    char_u	*name,		// name of the function
+	char_u	    **arg,
-    int		len,		// length of "name" or -1 to use strlen()
+	evalarg_T   *evalarg,
-    typval_T	*rettv,
+	int	    partial_argc,
-    char_u	**arg,		// argument, pointing to the '('
+	typval_T    *argvars,
-    evalarg_T	*evalarg,	// for line continuation
+	int	    *argcount)
-    funcexe_T	*funcexe)	// various values
 {
-    char_u	*argp;
+    char_u	*argp = *arg;
     int		ret = OK;
-    typval_T	argvars[MAX_FUNC_ARGS + 1];	// vars for arguments
-    int		argcount = 0;		// number of arguments found
     int		vim9script = in_vim9script();
     int		evaluate = evalarg == NULL
 			       ? FALSE : (evalarg->eval_flags & EVAL_EVALUATE);
 
-    /*
+    while (*argcount < MAX_FUNC_ARGS - partial_argc)
-     * Get the arguments.
-     */
-    argp = *arg;
-    while (argcount < MAX_FUNC_ARGS - (funcexe->fe_partial == NULL ? 0
-					       : funcexe->fe_partial->pt_argc))
     {
 	// skip the '(' or ',' and possibly line breaks
 	argp = skipwhite_and_linebreak(argp + 1, evalarg);
 
 	if (*argp == ')' || *argp == ',' || *argp == NUL)
 	    break;
-	if (eval1(&argp, &argvars[argcount], evalarg) == FAIL)
+	if (eval1(&argp, &argvars[*argcount], evalarg) == FAIL)
 	{
 	    ret = FAIL;
 	    break;
 	}
-	++argcount;
+	++*argcount;
 	// The comma should come right after the argument, but this wasn't
 	// checked previously, thus only enforce it in Vim9 script.
 	if (vim9script)
@@ -1791,11 +1783,41 @@ get_func_tv(
 	    break;
 	}
     }
+
     argp = skipwhite_and_linebreak(argp, evalarg);
     if (*argp == ')')
 	++argp;
     else
 	ret = FAIL;
+    *arg = argp;
+    return ret;
+}
+
+/*
+ * Call a function and put the result in "rettv".
+ * Return OK or FAIL.
+ */
+    int
+get_func_tv(
+    char_u	*name,		// name of the function
+    int		len,		// length of "name" or -1 to use strlen()
+    typval_T	*rettv,
+    char_u	**arg,		// argument, pointing to the '('
+    evalarg_T	*evalarg,	// for line continuation
+    funcexe_T	*funcexe)	// various values
+{
+    char_u	*argp;
+    int		ret = OK;
+    typval_T	argvars[MAX_FUNC_ARGS + 1];	// vars for arguments
+    int		argcount = 0;			// number of arguments found
+    int		vim9script = in_vim9script();
+    int		evaluate = evalarg == NULL
+			       ? FALSE : (evalarg->eval_flags & EVAL_EVALUATE);
+
+    argp = *arg;
+    ret = get_func_arguments(&argp, evalarg,
+	    (funcexe->fe_partial == NULL ? 0 : funcexe->fe_partial->pt_argc),
+							   argvars, &argcount);
 
     if (ret == OK)
     {
@@ -2884,6 +2906,9 @@ call_user_func(
 	do_cmdline(NULL, get_func_line, (void *)fc,
 				     DOCMD_NOWAIT|DOCMD_VERBOSE|DOCMD_REPEAT);
 
+    // Invoke functions added with ":defer".
+    handle_defer();
+
     --RedrawingDisabled;
 
     // when the function was aborted because of an error, return -1
@@ -5457,8 +5482,164 @@ ex_return(exarg_T *eap)
     clear_evalarg(&evalarg, eap);
 }
 
+    static int
+ex_call_inner(
+	exarg_T	    *eap,
+	char_u	    *name,
+	char_u	    **arg,
+	char_u	    *startarg,
+	funcexe_T  *funcexe_init,
+	evalarg_T   *evalarg)
+{
+    linenr_T	lnum;
+    int		doesrange;
+    typval_T	rettv;
+    int		failed = FALSE;
+
+    /*
+     * When skipping, evaluate the function once, to find the end of the
+     * arguments.
+     * When the function takes a range, this is discovered after the first
+     * call, and the loop is broken.
+     */
+    if (eap->skip)
+    {
+	++emsg_skip;
+	lnum = eap->line2;	// do it once, also with an invalid range
+    }
+    else
+	lnum = eap->line1;
+    for ( ; lnum <= eap->line2; ++lnum)
+    {
+	funcexe_T funcexe;
+
+	if (!eap->skip && eap->addr_count > 0)
+	{
+	    if (lnum > curbuf->b_ml.ml_line_count)
+	    {
+		// If the function deleted lines or switched to another buffer
+		// the line number may become invalid.
+		emsg(_(e_invalid_range));
+		break;
+	    }
+	    curwin->w_cursor.lnum = lnum;
+	    curwin->w_cursor.col = 0;
+	    curwin->w_cursor.coladd = 0;
+	}
+	*arg = startarg;
+
+	funcexe = *funcexe_init;
+	funcexe.fe_doesrange = &doesrange;
+	rettv.v_type = VAR_UNKNOWN;	// clear_tv() uses this
+	if (get_func_tv(name, -1, &rettv, arg, evalarg, &funcexe) == FAIL)
+	{
+	    failed = TRUE;
+	    break;
+	}
+	if (has_watchexpr())
+	    dbg_check_breakpoint(eap);
+
+	// Handle a function returning a Funcref, Dictionary or List.
+	if (handle_subscript(arg, NULL, &rettv,
+			   eap->skip ? NULL : &EVALARG_EVALUATE, TRUE) == FAIL)
+	{
+	    failed = TRUE;
+	    break;
+	}
+
+	clear_tv(&rettv);
+	if (doesrange || eap->skip)
+	    break;
+
+	// Stop when immediately aborting on error, or when an interrupt
+	// occurred or an exception was thrown but not caught.
+	// get_func_tv() returned OK, so that the check for trailing
+	// characters below is executed.
+	if (aborting())
+	    break;
+    }
+    if (eap->skip)
+	--emsg_skip;
+    return failed;
+}
+
+/*
+ * Core part of ":defer func(arg)".  "arg" points to the "(" and is advanced.
+ * Returns FAIL or OK.
+ */
+    static int
+ex_defer_inner(char_u *name, char_u **arg, evalarg_T *evalarg)
+{
+    typval_T	argvars[MAX_FUNC_ARGS + 1];	// vars for arguments
+    int		argcount = 0;			// number of arguments found
+    defer_T	*dr;
+    int		ret = FAIL;
+    char_u	*saved_name;
+
+    if (current_funccal == NULL)
+    {
+	semsg(_(e_str_not_inside_function), "defer");
+	return FAIL;
+    }
+    if (get_func_arguments(arg, evalarg, FALSE, argvars, &argcount) == FAIL)
+	goto theend;
+    saved_name = vim_strsave(name);
+    if (saved_name == NULL)
+	goto theend;
+
+    if (current_funccal->fc_defer.ga_itemsize == 0)
+	ga_init2(&current_funccal->fc_defer, sizeof(defer_T), 10);
+    if (ga_grow(&current_funccal->fc_defer, 1) == FAIL)
+	goto theend;
+    dr = ((defer_T *)current_funccal->fc_defer.ga_data)
+					  + current_funccal->fc_defer.ga_len++;
+    dr->dr_name = saved_name;
+    dr->dr_argcount = argcount;
+    while (argcount > 0)
+    {
+	--argcount;
+	dr->dr_argvars[argcount] = argvars[argcount];
+    }
+    ret = OK;
+
+theend:
+    while (--argcount >= 0)
+	clear_tv(&argvars[argcount]);
+    return ret;
+}
+
+/*
+ * Invoked after a functions has finished: invoke ":defer" functions.
+ */
+    void
+handle_defer(void)
+{
+    int	    idx;
+
+    for (idx = current_funccal->fc_defer.ga_len - 1; idx >= 0; --idx)
+    {
+	funcexe_T   funcexe;
+	typval_T    rettv;
+	defer_T	    *dr = ((defer_T *)current_funccal->fc_defer.ga_data) + idx;
+	int	    i;
+
+	CLEAR_FIELD(funcexe);
+	funcexe.fe_evaluate = TRUE;
+
+	rettv.v_type = VAR_UNKNOWN;	// clear_tv() uses this
+	call_func(dr->dr_name, -1, &rettv,
+				    dr->dr_argcount, dr->dr_argvars, &funcexe);
+	clear_tv(&rettv);
+	vim_free(dr->dr_name);
+	for (i = dr->dr_argcount - 1; i >= 0; --i)
+	    clear_tv(&dr->dr_argvars[i]);
+    }
+    ga_clear(&current_funccal->fc_defer);
+}
+
 /*
  * ":1,25call func(arg1, arg2)"	function call.
+ * ":defer func(arg1, arg2)"    deferred function call.
  */
     void
 ex_call(exarg_T *eap)
@@ -5468,9 +5649,6 @@ ex_call(exarg_T *eap)
     char_u	*name;
     char_u	*tofree;
     int		len;
-    typval_T	rettv;
-    linenr_T	lnum;
-    int		doesrange;
     int		failed = FALSE;
     funcdict_T	fudi;
     partial_T	*partial = NULL;
@@ -5482,6 +5660,8 @@ ex_call(exarg_T *eap)
     fill_evalarg_from_eap(&evalarg, eap, eap->skip);
     if (eap->skip)
     {
+	typval_T	rettv;
+
 	// trans_function_name() doesn't work well when skipping, use eval0()
 	// instead to skip to any following command, e.g. for:
 	//   :if 0 | call dict.foo().bar() | endif
@@ -5531,82 +5711,29 @@ ex_call(exarg_T *eap)
 	goto end;
     }
 
-    /*
+    if (eap->cmdidx == CMD_defer)
-     * When skipping, evaluate the function once, to find the end of the
-     * arguments.
-     * When the function takes a range, this is discovered after the first
-     * call, and the loop is broken.
-     */
-    if (eap->skip)
     {
-	++emsg_skip;
+	arg = startarg;
-	lnum = eap->line2;	// do it once, also with an invalid range
+	failed = ex_defer_inner(name, &arg, &evalarg) == FAIL;
     }
     else
-	lnum = eap->line1;
-    for ( ; lnum <= eap->line2; ++lnum)
     {
 	funcexe_T funcexe;
 
-	if (!eap->skip && eap->addr_count > 0)
-	{
-	    if (lnum > curbuf->b_ml.ml_line_count)
-	    {
-		// If the function deleted lines or switched to another buffer
-		// the line number may become invalid.
-		emsg(_(e_invalid_range));
-		break;
-	    }
-	    curwin->w_cursor.lnum = lnum;
-	    curwin->w_cursor.col = 0;
-	    curwin->w_cursor.coladd = 0;
-	}
-	arg = startarg;
-
 	CLEAR_FIELD(funcexe);
-	funcexe.fe_firstline = eap->line1;
+	funcexe.fe_check_type = type;
-	funcexe.fe_lastline = eap->line2;
-	funcexe.fe_doesrange = &doesrange;
-	funcexe.fe_evaluate = !eap->skip;
 	funcexe.fe_partial = partial;
 	funcexe.fe_selfdict = fudi.fd_dict;
-	funcexe.fe_check_type = type;
+	funcexe.fe_firstline = eap->line1;
+	funcexe.fe_lastline = eap->line2;
 	funcexe.fe_found_var = found_var;
-	rettv.v_type = VAR_UNKNOWN;	// clear_tv() uses this
+	funcexe.fe_evaluate = !eap->skip;
-	if (get_func_tv(name, -1, &rettv, &arg, &evalarg, &funcexe) == FAIL)
+	failed = ex_call_inner(eap, name, &arg, startarg, &funcexe, &evalarg);
-	{
-	    failed = TRUE;
-	    break;
     }
-	if (has_watchexpr())
-	    dbg_check_breakpoint(eap);
-
-	// Handle a function returning a Funcref, Dictionary or List.
-	if (handle_subscript(&arg, NULL, &rettv,
-			   eap->skip ? NULL : &EVALARG_EVALUATE, TRUE) == FAIL)
-	{
-	    failed = TRUE;
-	    break;
-	}
-
-	clear_tv(&rettv);
-	if (doesrange || eap->skip)
-	    break;
-
-	// Stop when immediately aborting on error, or when an interrupt
-	// occurred or an exception was thrown but not caught.
-	// get_func_tv() returned OK, so that the check for trailing
-	// characters below is executed.
-	if (aborting())
-	    break;
-    }
-    if (eap->skip)
-	--emsg_skip;
 
     // When inside :try we need to check for following "| catch" or "| endtry".
     // Not when there was an error, but do check if an exception was thrown.
-    if ((!aborting() || did_throw)
+    if ((!aborting() || did_throw) && (!failed || eap->cstack->cs_trylevel > 0))
-				  && (!failed || eap->cstack->cs_trylevel > 0))
     {
 	// Check for trailing illegal characters and a following command.
 	arg = skipwhite(arg);

src/version.c

@@ -707,6 +707,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    370,
 /**/
     369,
 /**/

src/vim9.h

@@ -113,6 +113,7 @@ typedef enum {
     ISN_FUNCREF,    // push a function ref to dfunc isn_arg.funcref
     ISN_NEWFUNC,    // create a global function from a lambda function
     ISN_DEF,	    // list functions
+    ISN_DEFER,	    // :defer  argument count is isn_arg.number
 
     // expression operations
     ISN_JUMP,	    // jump if condition is matched isn_arg.jump
@@ -419,6 +420,12 @@ typedef struct {
     int		dbg_break_lnum;	    // first line to break after
 } debug_T;
 
+// arguments to ISN_DEFER
+typedef struct {
+    int		defer_var_idx;	    // local variable index for defer list
+    int		defer_argcount;	    // number of arguments
+} deferins_T;
+
 /*
  * Instruction
  */
@@ -468,6 +475,7 @@ struct isn_S {
 	tobool_T	    tobool;
 	getitem_T	    getitem;
 	debug_T		    debug;
+	deferins_T	    defer;
     } isn_arg;
 };
 
@@ -498,6 +506,9 @@ struct dfunc_S {
 
     int		df_varcount;	    // number of local variables
     int		df_has_closure;	    // one if a closure was created
+    int		df_defer_var_idx;   // index of local variable that has a list
+				    // of deferred function calls; zero if not
+				    // set
 };
 
 // Number of entries used by stack frame for a function call.
@@ -735,6 +746,15 @@ struct cctx_S {
 				    // lhs_name is not NULL
 };
 
+/*
+ * List of special functions for "compile_arguments()".
+ */
+typedef enum {
+    CA_NOT_SPECIAL,
+    CA_SEARCHPAIR,	    // {skip} in searchpair() and searchpairpos()
+    CA_SUBSTITUTE,	    // {sub} in substitute(), when prefixed with \=
+} ca_special_T;
+
 // flags for typval2type()
 #define TVTT_DO_MEMBER	    1
 #define TVTT_MORE_SPECIFIC  2	// get most specific type for member

src/vim9cmds.c

@@ -1654,6 +1654,9 @@ compile_throw(char_u *arg, cctx_T *cctx UNUSED)
     return p;
 }
 
+/*
+ * Compile an expression or function call.
+ */
     char_u *
 compile_eval(char_u *arg, cctx_T *cctx)
 {
@@ -1681,6 +1684,67 @@ compile_eval(char_u *arg, cctx_T *cctx)
     return skipwhite(p);
 }
 
+/*
+ * Compile "defer func(arg)".
+ */
+    char_u *
+compile_defer(char_u *arg_start, cctx_T *cctx)
+{
+    char_u	*p;
+    char_u	*arg = arg_start;
+    int		argcount = 0;
+    dfunc_T	*dfunc;
+    type_T	*type;
+    int		func_idx;
+
+    // Get a funcref for the function name.
+    // TODO: better way to find the "(".
+    p = vim_strchr(arg, '(');
+    if (p == NULL)
+    {
+	semsg(_(e_missing_parenthesis_str), arg);
+	return NULL;
+    }
+    *p = NUL;
+    func_idx = find_internal_func(arg);
+    if (func_idx >= 0)
+	// TODO: better type
+	generate_PUSHFUNC(cctx, (char_u *)internal_func_name(func_idx),
+							   &t_func_any, FALSE);
+    else if (compile_expr0(&arg, cctx) == FAIL)
+	return NULL;
+    *p = '(';
+
+    // check for function type
+    type = get_type_on_stack(cctx, 0);
+    if (type->tt_type != VAR_FUNC)
+    {
+	emsg(_(e_function_name_required));
+	return NULL;
+    }
+
+    // compile the arguments
+    arg = skipwhite(p + 1);
+    if (compile_arguments(&arg, cctx, &argcount, CA_NOT_SPECIAL) == FAIL)
+	return NULL;
+
+    // TODO: check argument count with "type"
+
+    dfunc = ((dfunc_T *)def_functions.ga_data) + cctx->ctx_ufunc->uf_dfunc_idx;
+    if (dfunc->df_defer_var_idx == 0)
+    {
+	lvar_T *lvar = reserve_local(cctx, (char_u *)"@defer@", 7,
+							    TRUE, &t_list_any);
+	if (lvar == NULL)
+	    return NULL;
+	dfunc->df_defer_var_idx = lvar->lv_idx + 1;
+    }
+    if (generate_DEFER(cctx, dfunc->df_defer_var_idx - 1, argcount) == FAIL)
+	return NULL;
+
+    return skipwhite(arg);
+}
+
 /*
  * compile "echo expr"
  * compile "echomsg expr"

src/vim9compile.c

@@ -2373,7 +2373,7 @@ compile_assignment(char_u *arg, exarg_T *eap, cmdidx_T cmdidx, cctx_T *cctx)
 			r = generate_PUSHBLOB(cctx, blob_alloc());
 			break;
 		    case VAR_FUNC:
-			r = generate_PUSHFUNC(cctx, NULL, &t_func_void);
+			r = generate_PUSHFUNC(cctx, NULL, &t_func_void, TRUE);
 			break;
 		    case VAR_LIST:
 			r = generate_NEWLIST(cctx, 0, FALSE);
@@ -2748,6 +2748,7 @@ compile_def_function(
 	    // Was compiled in this mode before: Free old instructions.
 	    delete_def_function_contents(dfunc, FALSE);
 	ga_clear_strings(&dfunc->df_var_names);
+	dfunc->df_defer_var_idx = 0;
     }
     else
     {
@@ -3249,6 +3250,10 @@ compile_def_function(
 		    line = compile_eval(p, &cctx);
 		    break;
 
+	    case CMD_defer:
+		    line = compile_defer(p, &cctx);
+		    break;
+
 	    case CMD_echo:
 	    case CMD_echon:
 	    case CMD_echoconsole:

src/vim9execute.c

@@ -101,9 +101,15 @@ struct ectx_S {
 static garray_T profile_info_ga = {0, 0, sizeof(profinfo_T), 20, NULL};
 #endif
 
+// Get pointer to item in the stack.
+#define STACK_TV(idx) (((typval_T *)ectx->ec_stack.ga_data) + idx)
+
 // Get pointer to item relative to the bottom of the stack, -1 is the last one.
 #define STACK_TV_BOT(idx) (((typval_T *)ectx->ec_stack.ga_data) + ectx->ec_stack.ga_len + (idx))
 
+// Get pointer to a local variable on the stack.  Negative for arguments.
+#define STACK_TV_VAR(idx) (((typval_T *)ectx->ec_stack.ga_data) + ectx->ec_frame_idx + STACK_FRAME_SIZE + idx)
+
     void
 to_string_error(vartype_T vartype)
 {
@@ -610,9 +616,6 @@ call_dfunc(
     return OK;
 }
 
-// Get pointer to item in the stack.
-#define STACK_TV(idx) (((typval_T *)ectx->ec_stack.ga_data) + idx)
-
 // Double linked list of funcstack_T in use.
 static funcstack_T *first_funcstack = NULL;
 
@@ -842,6 +845,89 @@ set_ref_in_funcstacks(int copyID)
     return FALSE;
 }
 
+/*
+ * Handle ISN_DEFER.  Stack has a function reference and "argcount" arguments.
+ * The local variable that lists deferred functions is "var_idx".
+ * Returns OK or FAIL.
+ */
+    static int
+add_defer_func(int var_idx, int argcount, ectx_T *ectx)
+{
+    typval_T	*defer_tv = STACK_TV_VAR(var_idx);
+    list_T	*defer_l;
+    typval_T	*func_tv;
+    list_T	*l;
+    int		i;
+    typval_T	listval;
+
+    if (defer_tv->v_type != VAR_LIST)
+    {
+	// first one, allocate the list
+	if (rettv_list_alloc(defer_tv) == FAIL)
+	    return FAIL;
+    }
+    defer_l = defer_tv->vval.v_list;
+
+    l = list_alloc_with_items(argcount + 1);
+    if (l == NULL)
+	return FAIL;
+    listval.v_type = VAR_LIST;
+    listval.vval.v_list = l;
+    listval.v_lock = 0;
+    if (list_insert_tv(defer_l, &listval,
+			   defer_l == NULL ? NULL : defer_l->lv_first) == FAIL)
+    {
+	vim_free(l);
+	return FAIL;
+    }
+
+    func_tv = STACK_TV_BOT(-argcount - 1);
+    // TODO: check type is a funcref
+    list_set_item(l, 0, func_tv);
+
+    for (i = 1; i <= argcount; ++i)
+	list_set_item(l, i, STACK_TV_BOT(-argcount + i - 1));
+    ectx->ec_stack.ga_len -= argcount + 1;
+    return OK;
+}
+
+/*
+ * Invoked when returning from a function: Invoke any deferred calls.
+ */
+    static void
+invoke_defer_funcs(ectx_T *ectx)
+{
+    dfunc_T	*dfunc = ((dfunc_T *)def_functions.ga_data)
+							  + ectx->ec_dfunc_idx;
+    typval_T	*defer_tv = STACK_TV_VAR(dfunc->df_defer_var_idx - 1);
+    listitem_T	*li;
+
+    if (defer_tv->v_type != VAR_LIST)
+	return;	 // no function added
+    for (li = defer_tv->vval.v_list->lv_first; li != NULL; li = li->li_next)
+    {
+	list_T	    *l = li->li_tv.vval.v_list;
+	typval_T    rettv;
+	typval_T    argvars[MAX_FUNC_ARGS];
+	int	    i;
+	listitem_T  *arg_li = l->lv_first;
+	funcexe_T   funcexe;
+
+	for (i = 0; i < l->lv_len - 1; ++i)
+	{
+	    arg_li = arg_li->li_next;
+	    argvars[i] = arg_li->li_tv;
+	}
+
+	CLEAR_FIELD(funcexe);
+	funcexe.fe_evaluate = TRUE;
+	rettv.v_type = VAR_UNKNOWN;
+	(void)call_func(l->lv_first->li_tv.vval.v_string, -1,
+				     &rettv, l->lv_len - 1, argvars, &funcexe);
+	clear_tv(&rettv);
+    }
+}
+
 /*
  * Return from the current function.
  */
@@ -876,6 +962,9 @@ func_return(ectx_T *ectx)
     }
 #endif
 
+    if (dfunc->df_defer_var_idx > 0)
+	invoke_defer_funcs(ectx);
+
     // No check for uf_refcount being zero, cannot think of a way that would
     // happen.
     --dfunc->df_ufunc->uf_calls;
@@ -949,8 +1038,6 @@ func_return(ectx_T *ectx)
     return OK;
 }
 
-#undef STACK_TV
-
 /*
  * Prepare arguments and rettv for calling a builtin or user function.
  */
@@ -1732,16 +1819,6 @@ typedef struct subs_expr_S {
     int		subs_status;
 } subs_expr_T;
 
-// Get pointer to item in the stack.
-#define STACK_TV(idx) (((typval_T *)ectx->ec_stack.ga_data) + idx)
-
-// Get pointer to item at the bottom of the stack, -1 is the bottom.
-#undef STACK_TV_BOT
-#define STACK_TV_BOT(idx) (((typval_T *)ectx->ec_stack.ga_data) + ectx->ec_stack.ga_len + idx)
-
-// Get pointer to a local variable on the stack.  Negative for arguments.
-#define STACK_TV_VAR(idx) (((typval_T *)ectx->ec_stack.ga_data) + ectx->ec_frame_idx + STACK_FRAME_SIZE + idx)
-
 // Set when calling do_debug().
 static ectx_T	*debug_context = NULL;
 static int	debug_var_count;
@@ -3670,6 +3747,13 @@ exec_instructions(ectx_T *ectx)
 		}
 		break;
 
+	    // :defer func(arg)
+	    case ISN_DEFER:
+		if (add_defer_func(iptr->isn_arg.defer.defer_var_idx,
+			     iptr->isn_arg.defer.defer_argcount, ectx) == FAIL)
+		    goto on_error;
+		break;
+
 	    // return from a :def function call without a value
 	    case ISN_RETURN_VOID:
 		if (GA_GROW_FAILS(&ectx->ec_stack, 1))
@@ -5024,6 +5108,14 @@ on_fatal_error:
 done:
     ret = OK;
 theend:
+    {
+	dfunc_T	*dfunc = ((dfunc_T *)def_functions.ga_data)
+							  + ectx->ec_dfunc_idx;
+
+	if (dfunc->df_defer_var_idx > 0)
+	    invoke_defer_funcs(ectx);
+    }
+
     dict_stack_clear(dict_stack_len_at_start);
     ectx->ec_trylevel_at_start = save_trylevel_at_start;
     return ret;
@@ -5903,6 +5995,10 @@ list_instructions(char *pfx, isn_T *instr, int instr_count, ufunc_T *ufunc)
 	    case ISN_PCALL_END:
 		smsg("%s%4d PCALL end", pfx, current);
 		break;
+	    case ISN_DEFER:
+		smsg("%s%4d DEFER %d args", pfx, current,
+				      (int)iptr->isn_arg.defer.defer_argcount);
+		break;
 	    case ISN_RETURN:
 		smsg("%s%4d RETURN", pfx, current);
 		break;

src/vim9expr.c

@@ -313,7 +313,7 @@ compile_load_scriptvar(
 		// name.  If a '(' follows it must be a function.  Otherwise we
 		// don't know, it can be "script.Func".
 		if (cc == '(' || paren_follows_after_expr)
-		    res = generate_PUSHFUNC(cctx, auto_name, &t_func_any);
+		    res = generate_PUSHFUNC(cctx, auto_name, &t_func_any, TRUE);
 		else
 		    res = generate_AUTOLOAD(cctx, auto_name, &t_any);
 		vim_free(auto_name);
@@ -329,7 +329,7 @@ compile_load_scriptvar(
 		    char_u sid_name[MAX_FUNC_NAME_LEN];
 
 		    func_name_with_sid(exp_name, import->imp_sid, sid_name);
-		    res = generate_PUSHFUNC(cctx, sid_name, &t_func_any);
+		    res = generate_PUSHFUNC(cctx, sid_name, &t_func_any, TRUE);
 		}
 		else
 		    res = generate_OLDSCRIPT(cctx, ISN_LOADEXPORT, exp_name,
@@ -353,7 +353,7 @@ compile_load_scriptvar(
 	    if (ufunc != NULL)
 	    {
 		// function call or function reference
-		generate_PUSHFUNC(cctx, ufunc->uf_name, NULL);
+		generate_PUSHFUNC(cctx, ufunc->uf_name, NULL, TRUE);
 		return OK;
 	    }
 	    return FAIL;
@@ -387,7 +387,7 @@ generate_funcref(cctx_T *cctx, char_u *name, int has_g_prefix)
     if (func_needs_compiling(ufunc, compile_type)
 	      && compile_def_function(ufunc, TRUE, compile_type, NULL) == FAIL)
 	return FAIL;
-    return generate_PUSHFUNC(cctx, ufunc->uf_name, ufunc->uf_func_type);
+    return generate_PUSHFUNC(cctx, ufunc->uf_name, ufunc->uf_func_type, TRUE);
 }
 
 /*
@@ -609,20 +609,11 @@ compile_string(isn_T *isn, cctx_T *cctx, int str_offset)
     return OK;
 }
 
-/*
- * List of special functions for "compile_arguments".
- */
-typedef enum {
-    CA_NOT_SPECIAL,
-    CA_SEARCHPAIR,	    // {skip} in searchpair() and searchpairpos()
-    CA_SUBSTITUTE,	    // {sub} in substitute(), when prefixed with \=
-} ca_special_T;
-
 /*
  * Compile the argument expressions.
  * "arg" points to just after the "(" and is advanced to after the ")"
  */
-    static int
+    int
 compile_arguments(
 	char_u	     **arg,
 	cctx_T	     *cctx,

src/vim9instr.c

@@ -616,7 +616,7 @@ generate_tv_PUSH(cctx_T *cctx, typval_T *tv)
 	case VAR_FUNC:
 	    if (tv->vval.v_string != NULL)
 		iemsg("non-null function constant not supported");
-	    generate_PUSHFUNC(cctx, NULL, &t_func_unknown);
+	    generate_PUSHFUNC(cctx, NULL, &t_func_unknown, TRUE);
 	    break;
 	case VAR_PARTIAL:
 	    if (tv->vval.v_partial != NULL)
@@ -796,9 +796,11 @@ generate_PUSHBLOB(cctx_T *cctx, blob_T *blob)
 
 /*
  * Generate an ISN_PUSHFUNC instruction with name "name".
+ * When "may_prefix" is TRUE prefix "g:" unless "name" is script-local or
+ * autoload.
  */
     int
-generate_PUSHFUNC(cctx_T *cctx, char_u *name, type_T *type)
+generate_PUSHFUNC(cctx_T *cctx, char_u *name, type_T *type, int may_prefix)
 {
     isn_T	*isn;
     char_u	*funcname;
@@ -808,7 +810,8 @@ generate_PUSHFUNC(cctx_T *cctx, char_u *name, type_T *type)
 	return FAIL;
     if (name == NULL)
 	funcname = NULL;
-    else if (*name == K_SPECIAL				    // script-local
+    else if (!may_prefix
+	    || *name == K_SPECIAL			    // script-local
 	    || vim_strchr(name, AUTOLOAD_CHAR) != NULL)	    // autoload
 	funcname = vim_strsave(name);
     else
@@ -1678,6 +1681,22 @@ generate_PCALL(
     return OK;
 }
 
+/*
+ * Generate an ISN_DEFER instruction.
+ */
+    int
+generate_DEFER(cctx_T *cctx, int var_idx, int argcount)
+{
+    isn_T *isn;
+
+    RETURN_OK_IF_SKIP(cctx);
+    if ((isn = generate_instr_drop(cctx, ISN_DEFER, argcount + 1)) == NULL)
+	return FAIL;
+    isn->isn_arg.defer.defer_var_idx = var_idx;
+    isn->isn_arg.defer.defer_argcount = argcount;
+    return OK;
+}
+
 /*
  * Generate an ISN_STRINGMEMBER instruction.
  */
@@ -2240,6 +2259,7 @@ delete_instr(isn_T *isn)
 	case ISN_CONCAT:
 	case ISN_COND2BOOL:
 	case ISN_DEBUG:
+	case ISN_DEFER:
 	case ISN_DROP:
 	case ISN_ECHO:
 	case ISN_ECHOCONSOLE:
@@ -2310,7 +2330,7 @@ delete_instr(isn_T *isn)
 	case ISN_USEDICT:
 	// nothing allocated
 	break;
-}
+    }
 }
 
     void