patch 8.2.1794: no falsy Coalescing operatorv8.2.1794

Problem:    No falsy Coalescing operator.
Solution:   Add the "??" operator.  Fix mistake with function argument count.

7 files changed, 214 insertions, 94 deletions

diff --git a/src/eval.c b/src/eval.c
index c8c4f6e5f4..911f0abc67 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -2110,6 +2110,7 @@ eval0(
 /*
  * Handle top level expression:
  *	expr2 ? expr1 : expr1
+ *	expr2 ?? expr1
  *
  * "arg" must point to the first non-white of the expression.
  * "arg" is advanced to just after the recognized expression.
@@ -2135,6 +2136,7 @@ eval1(char_u **arg, typval_T *rettv, evalarg_T *evalarg)
     p = eval_next_non_blank(*arg, evalarg, &getnext);
     if (*p == '?')
     {
+	int		op_falsy = p[1] == '?';
 	int		result;
 	typval_T	var2;
 	evalarg_T	*evalarg_used = evalarg;
@@ -2168,11 +2170,12 @@ eval1(char_u **arg, typval_T *rettv, evalarg_T *evalarg)
 	{
 	    int		error = FALSE;
 
-	    if (in_vim9script())
+	    if (in_vim9script() || op_falsy)
 		result = tv2bool(rettv);
 	    else if (tv_get_number_chk(rettv, &error) != 0)
 		result = TRUE;
-	    clear_tv(rettv);
+	    if (error || !op_falsy || !result)
+		clear_tv(rettv);
 	    if (error)
 		return FAIL;
 	}
@@ -2180,6 +2183,8 @@ eval1(char_u **arg, typval_T *rettv, evalarg_T *evalarg)
 	/*
 	 * Get the second variable.  Recursive!
 	 */
+	if (op_falsy)
+	    ++*arg;
 	if (evaluate && in_vim9script() && !IS_WHITE_OR_NUL((*arg)[1]))
 	{
 	    error_white_both(p, 1);
@@ -2187,62 +2192,67 @@ eval1(char_u **arg, typval_T *rettv, evalarg_T *evalarg)
 	    return FAIL;
 	}
 	*arg = skipwhite_and_linebreak(*arg + 1, evalarg_used);
-	evalarg_used->eval_flags = result ? orig_flags
-						 : orig_flags & ~EVAL_EVALUATE;
-	if (eval1(arg, rettv, evalarg_used) == FAIL)
+	evalarg_used->eval_flags = (op_falsy ? !result : result)
+				    ? orig_flags : orig_flags & ~EVAL_EVALUATE;
+	if (eval1(arg, &var2, evalarg_used) == FAIL)
 	{
 	    evalarg_used->eval_flags = orig_flags;
 	    return FAIL;
 	}
+	if (!op_falsy || !result)
+	    *rettv = var2;
 
-	/*
-	 * Check for the ":".
-	 */
-	p = eval_next_non_blank(*arg, evalarg_used, &getnext);
-	if (*p != ':')
-	{
-	    emsg(_(e_missing_colon));
-	    if (evaluate && result)
-		clear_tv(rettv);
-	    evalarg_used->eval_flags = orig_flags;
-	    return FAIL;
-	}
-	if (getnext)
-	    *arg = eval_next_line(evalarg_used);
-	else
+	if (!op_falsy)
 	{
-	    if (evaluate && in_vim9script() && !VIM_ISWHITE(p[-1]))
+	    /*
+	     * Check for the ":".
+	     */
+	    p = eval_next_non_blank(*arg, evalarg_used, &getnext);
+	    if (*p != ':')
+	    {
+		emsg(_(e_missing_colon));
+		if (evaluate && result)
+		    clear_tv(rettv);
+		evalarg_used->eval_flags = orig_flags;
+		return FAIL;
+	    }
+	    if (getnext)
+		*arg = eval_next_line(evalarg_used);
+	    else
+	    {
+		if (evaluate && in_vim9script() && !VIM_ISWHITE(p[-1]))
+		{
+		    error_white_both(p, 1);
+		    clear_tv(rettv);
+		    evalarg_used->eval_flags = orig_flags;
+		    return FAIL;
+		}
+		*arg = p;
+	    }
+
+	    /*
+	     * Get the third variable.  Recursive!
+	     */
+	    if (evaluate && in_vim9script() && !IS_WHITE_OR_NUL((*arg)[1]))
 	    {
 		error_white_both(p, 1);
 		clear_tv(rettv);
 		evalarg_used->eval_flags = orig_flags;
 		return FAIL;
 	    }
-	    *arg = p;
-	}
-
-	/*
-	 * Get the third variable.  Recursive!
-	 */
-	if (evaluate && in_vim9script() && !IS_WHITE_OR_NUL((*arg)[1]))
-	{
-	    error_white_both(p, 1);
-	    clear_tv(rettv);
-	    evalarg_used->eval_flags = orig_flags;
-	    return FAIL;
-	}
-	*arg = skipwhite_and_linebreak(*arg + 1, evalarg_used);
-	evalarg_used->eval_flags = !result ? orig_flags
+	    *arg = skipwhite_and_linebreak(*arg + 1, evalarg_used);
+	    evalarg_used->eval_flags = !result ? orig_flags
 						 : orig_flags & ~EVAL_EVALUATE;
-	if (eval1(arg, &var2, evalarg_used) == FAIL)
-	{
-	    if (evaluate && result)
-		clear_tv(rettv);
-	    evalarg_used->eval_flags = orig_flags;
-	    return FAIL;
+	    if (eval1(arg, &var2, evalarg_used) == FAIL)
+	    {
+		if (evaluate && result)
+		    clear_tv(rettv);
+		evalarg_used->eval_flags = orig_flags;
+		return FAIL;
+	    }
+	    if (evaluate && !result)
+		*rettv = var2;
 	}
-	if (evaluate && !result)
-	    *rettv = var2;
 
 	if (evalarg == NULL)
 	    clear_evalarg(&local_evalarg, NULL);
diff --git a/src/testdir/test_expr.vim b/src/testdir/test_expr.vim
index cfae760d49..1086534dca 100644
--- a/src/testdir/test_expr.vim
+++ b/src/testdir/test_expr.vim
@@ -42,6 +42,28 @@ func Test_version()
   call assert_false(has('patch-9.9.1'))
 endfunc
 
+func Test_op_falsy()
+  call assert_equal(v:true, v:true ?? 456)
+  call assert_equal(123, 123 ?? 456)
+  call assert_equal('yes', 'yes' ?? 456)
+  call assert_equal(0z00, 0z00 ?? 456)
+  call assert_equal([1], [1] ?? 456)
+  call assert_equal(#{one: 1}, #{one: 1} ?? 456)
+  if has('float')
+    call assert_equal(0.1, 0.1 ?? 456)
+  endif
+
+  call assert_equal(456, v:false ?? 456)
+  call assert_equal(456, 0 ?? 456)
+  call assert_equal(456, '' ?? 456)
+  call assert_equal(456, 0z ?? 456)
+  call assert_equal(456, [] ?? 456)
+  call assert_equal(456, {} ?? 456)
+  if has('float')
+    call assert_equal(456, 0.0 ?? 456)
+  endif
+endfunc
+
 func Test_dict()
   let d = {'': 'empty', 'a': 'a', 0: 'zero'}
   call assert_equal('empty', d[''])
diff --git a/src/testdir/test_vim9_disassemble.vim b/src/testdir/test_vim9_disassemble.vim
index f1f358af9b..a8dbe1a3cc 100644
--- a/src/testdir/test_vim9_disassemble.vim
+++ b/src/testdir/test_vim9_disassemble.vim
@@ -1326,6 +1326,33 @@ def Test_disassemble_compare()
   delete('Xdisassemble')
 enddef
 
+def s:FalsyOp()
+  echo g:flag ?? "yes"
+  echo [] ?? "empty list"
+  echo "" ?? "empty string"
+enddef
+
+def Test_dsassemble_falsy_op()
+  var res = execute('disass s:FalsyOp')
+  assert_match('\<SNR>\d*_FalsyOp\_s*' ..
+      'echo g:flag ?? "yes"\_s*' ..
+      '0 LOADG g:flag\_s*' ..
+      '1 JUMP_AND_KEEP_IF_TRUE -> 3\_s*' ..
+      '2 PUSHS "yes"\_s*' ..
+      '3 ECHO 1\_s*' ..
+      'echo \[\] ?? "empty list"\_s*' ..
+      '4 NEWLIST size 0\_s*' ..
+      '5 JUMP_AND_KEEP_IF_TRUE -> 7\_s*' ..
+      '6 PUSHS "empty list"\_s*' ..
+      '7 ECHO 1\_s*' ..
+      'echo "" ?? "empty string"\_s*' ..
+      '\d\+ PUSHS "empty string"\_s*' ..
+      '\d\+ ECHO 1\_s*' ..
+      '\d\+ PUSHNR 0\_s*' ..
+      '\d\+ RETURN',
+      res)
+enddef
+
 def Test_disassemble_compare_const()
   var cases = [
         ['"xx" == "yy"', false],
diff --git a/src/testdir/test_vim9_expr.vim b/src/testdir/test_vim9_expr.vim
index fa33089e84..253e469bfa 100644
--- a/src/testdir/test_vim9_expr.vim
+++ b/src/testdir/test_vim9_expr.vim
@@ -12,7 +12,7 @@ def FuncTwo(arg: number): number
 enddef
 
 " test cond ? expr : expr
-def Test_expr1()
+def Test_expr1_trinary()
   assert_equal('one', true ? 'one' : 'two')
   assert_equal('one', 1 ?
 			'one' :
@@ -61,7 +61,7 @@ def Test_expr1()
   assert_equal(123, Z(3))
 enddef
 
-def Test_expr1_vimscript()
+def Test_expr1_trinary_vimscript()
   # check line continuation
   var lines =<< trim END
       vim9script
@@ -139,7 +139,7 @@ def Test_expr1_vimscript()
   CheckScriptSuccess(lines)
 enddef
 
-func Test_expr1_fails()
+func Test_expr1_trinary_fails()
   call CheckDefFailure(["var x = 1 ? 'one'"], "Missing ':' after '?'", 1)
 
   let msg = "White space required before and after '?'"
@@ -160,6 +160,34 @@ func Test_expr1_fails()
 	\ 'Z()'], 'E119:', 4)
 endfunc
 
+def Test_expr1_falsy()
+  var lines =<< trim END
+      assert_equal(v:true, v:true ?? 456)
+      assert_equal(123, 123 ?? 456)
+      assert_equal('yes', 'yes' ?? 456)
+      assert_equal([1], [1] ?? 456)
+      assert_equal(#{one: 1}, #{one: 1} ?? 456)
+      if has('float')
+        assert_equal(0.1, 0.1 ?? 456)
+      endif
+
+      assert_equal(456, v:false ?? 456)
+      assert_equal(456, 0 ?? 456)
+      assert_equal(456, '' ?? 456)
+      assert_equal(456, [] ?? 456)
+      assert_equal(456, {} ?? 456)
+      if has('float')
+        assert_equal(456, 0.0 ?? 456)
+      endif
+  END
+  CheckDefAndScriptSuccess(lines)
+
+  var msg = "White space required before and after '??'"
+  call CheckDefFailure(["var x = 1?? 'one' : 'two'"], msg, 1)
+  call CheckDefFailure(["var x = 1 ??'one' : 'two'"], msg, 1)
+  call CheckDefFailure(["var x = 1??'one' : 'two'"], msg, 1)
+enddef
+
 " TODO: define inside test function
 def Record(val: any): any
   g:vals->add(val)
diff --git a/src/version.c b/src/version.c
index beca185c76..bd57233f03 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@ static char *(features[]) =
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1794,
+/**/
     1793,
 /**/
     1792,
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 32def6c796..88da80044e 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -4132,14 +4132,20 @@ compile_expr2(char_u **arg, cctx_T *cctx, ppconst_T *ppconst)
 
 /*
  * Toplevel expression: expr2 ? expr1a : expr1b
- *
  * Produces instructions:
- *	EVAL expr2		Push result of "expr"
+ *	EVAL expr2		Push result of "expr2"
  *      JUMP_IF_FALSE alt	jump if false
  *      EVAL expr1a
  *      JUMP_ALWAYS end
  * alt:	EVAL expr1b
  * end:
+ *
+ * Toplevel expression: expr2 ?? expr1
+ * Produces instructions:
+ *	EVAL expr2		    Push result of "expr2"
+ *      JUMP_AND_KEEP_IF_TRUE end   jump if true
+ *      EVAL expr1
+ * end:
  */
     static int
 compile_expr1(char_u **arg,  cctx_T *cctx, ppconst_T *ppconst)
@@ -4162,13 +4168,13 @@ compile_expr1(char_u **arg,  cctx_T *cctx, ppconst_T *ppconst)
     p = may_peek_next_line(cctx, *arg, &next);
     if (*p == '?')
     {
+	int		op_falsy = p[1] == '?';
 	garray_T	*instr = &cctx->ctx_instr;
 	garray_T	*stack = &cctx->ctx_type_stack;
 	int		alt_idx = instr->ga_len;
 	int		end_idx = 0;
 	isn_T		*isn;
 	type_T		*type1 = NULL;
-	type_T		*type2;
 	int		has_const_expr = FALSE;
 	int		const_value = FALSE;
 	int		save_skip = cctx->ctx_skip;
@@ -4179,9 +4185,10 @@ compile_expr1(char_u **arg,  cctx_T *cctx, ppconst_T *ppconst)
 	    p = skipwhite(*arg);
 	}
 
-	if (!IS_WHITE_OR_NUL(**arg) || !IS_WHITE_OR_NUL(p[1]))
+	if (!IS_WHITE_OR_NUL(**arg) || !IS_WHITE_OR_NUL(p[1 + op_falsy]))
 	{
-	    semsg(_(e_white_space_required_before_and_after_str), "?");
+	    semsg(_(e_white_space_required_before_and_after_str),
+							op_falsy ? "??" : "?");
 	    return FAIL;
 	}
 
@@ -4191,20 +4198,32 @@ compile_expr1(char_u **arg,  cctx_T *cctx, ppconst_T *ppconst)
 	    // expression is to be evaluated.
 	    has_const_expr = TRUE;
 	    const_value = tv2bool(&ppconst->pp_tv[ppconst_used]);
-	    clear_tv(&ppconst->pp_tv[ppconst_used]);
-	    --ppconst->pp_used;
-	    cctx->ctx_skip = save_skip == SKIP_YES || !const_value
-							 ? SKIP_YES : SKIP_NOT;
+	    cctx->ctx_skip = save_skip == SKIP_YES ||
+		 (op_falsy ? const_value : !const_value) ? SKIP_YES : SKIP_NOT;
+
+	    if (op_falsy && cctx->ctx_skip == SKIP_YES)
+		// "left ?? right" and "left" is truthy: produce "left"
+		generate_ppconst(cctx, ppconst);
+	    else
+	    {
+		clear_tv(&ppconst->pp_tv[ppconst_used]);
+		--ppconst->pp_used;
+	    }
 	}
 	else
 	{
 	    generate_ppconst(cctx, ppconst);
-	    generate_JUMP(cctx, JUMP_IF_FALSE, 0);
+	    if (op_falsy)
+		end_idx = instr->ga_len;
+	    generate_JUMP(cctx, op_falsy
+				   ? JUMP_AND_KEEP_IF_TRUE : JUMP_IF_FALSE, 0);
+	    if (op_falsy)
+		type1 = ((type_T **)stack->ga_data)[stack->ga_len];
 	}
 
 	// evaluate the second expression; any type is accepted
-	*arg = skipwhite(p + 1);
-	if (may_get_next_line(p + 1, arg, cctx) == FAIL)
+	*arg = skipwhite(p + 1 + op_falsy);
+	if (may_get_next_line(p + 1 + op_falsy, arg, cctx) == FAIL)
 	    return FAIL;
 	if (compile_expr1(arg, cctx, ppconst) == FAIL)
 	    return FAIL;
@@ -4213,56 +4232,64 @@ compile_expr1(char_u **arg,  cctx_T *cctx, ppconst_T *ppconst)
 	{
 	    generate_ppconst(cctx, ppconst);
 
-	    // remember the type and drop it
-	    --stack->ga_len;
-	    type1 = ((type_T **)stack->ga_data)[stack->ga_len];
+	    if (!op_falsy)
+	    {
+		// remember the type and drop it
+		--stack->ga_len;
+		type1 = ((type_T **)stack->ga_data)[stack->ga_len];
 
-	    end_idx = instr->ga_len;
-	    generate_JUMP(cctx, JUMP_ALWAYS, 0);
+		end_idx = instr->ga_len;
+		generate_JUMP(cctx, JUMP_ALWAYS, 0);
 
-	    // jump here from JUMP_IF_FALSE
-	    isn = ((isn_T *)instr->ga_data) + alt_idx;
-	    isn->isn_arg.jump.jump_where = instr->ga_len;
+		// jump here from JUMP_IF_FALSE
+		isn = ((isn_T *)instr->ga_data) + alt_idx;
+		isn->isn_arg.jump.jump_where = instr->ga_len;
+	    }
 	}
 
-	// Check for the ":".
-	p = may_peek_next_line(cctx, *arg, &next);
-	if (*p != ':')
+	if (!op_falsy)
 	{
-	    emsg(_(e_missing_colon));
-	    return FAIL;
-	}
-	if (next != NULL)
-	{
-	    *arg = next_line_from_context(cctx, TRUE);
-	    p = skipwhite(*arg);
-	}
+	    // Check for the ":".
+	    p = may_peek_next_line(cctx, *arg, &next);
+	    if (*p != ':')
+	    {
+		emsg(_(e_missing_colon));
+		return FAIL;
+	    }
+	    if (next != NULL)
+	    {
+		*arg = next_line_from_context(cctx, TRUE);
+		p = skipwhite(*arg);
+	    }
 
-	if (!IS_WHITE_OR_NUL(**arg) || !IS_WHITE_OR_NUL(p[1]))
-	{
-	    semsg(_(e_white_space_required_before_and_after_str), ":");
-	    return FAIL;
-	}
+	    if (!IS_WHITE_OR_NUL(**arg) || !IS_WHITE_OR_NUL(p[1]))
+	    {
+		semsg(_(e_white_space_required_before_and_after_str), ":");
+		return FAIL;
+	    }
 
-	// evaluate the third expression
-	if (has_const_expr)
-	    cctx->ctx_skip = save_skip == SKIP_YES || const_value
+	    // evaluate the third expression
+	    if (has_const_expr)
+		cctx->ctx_skip = save_skip == SKIP_YES || const_value
 							 ? SKIP_YES : SKIP_NOT;
-	*arg = skipwhite(p + 1);
-	if (may_get_next_line(p + 1, arg, cctx) == FAIL)
-	    return FAIL;
-	if (compile_expr1(arg, cctx, ppconst) == FAIL)
-	    return FAIL;
+	    *arg = skipwhite(p + 1);
+	    if (may_get_next_line(p + 1, arg, cctx) == FAIL)
+		return FAIL;
+	    if (compile_expr1(arg, cctx, ppconst) == FAIL)
+		return FAIL;
+	}
 
 	if (!has_const_expr)
 	{
+	    type_T	**typep;
+
 	    generate_ppconst(cctx, ppconst);
 
 	    // If the types differ, the result has a more generic type.
-	    type2 = ((type_T **)stack->ga_data)[stack->ga_len - 1];
-	    common_type(type1, type2, &type2, cctx->ctx_type_list);
+	    typep = ((type_T **)stack->ga_data) + stack->ga_len - 1;
+	    common_type(type1, *typep, typep, cctx->ctx_type_list);
 
-	    // jump here from JUMP_ALWAYS
+	    // jump here from JUMP_ALWAYS or JUMP_AND_KEEP_IF_TRUE
 	    isn = ((isn_T *)instr->ga_data) + end_idx;
 	    isn->isn_arg.jump.jump_where = instr->ga_len;
 	}
diff --git a/src/vim9type.c b/src/vim9type.c
index 931b575b66..b5866bc400 100644
--- a/src/vim9type.c
+++ b/src/vim9type.c
@@ -924,6 +924,10 @@ common_type(type_T *type1, type_T *type2, type_T **dest, garray_T *type_gap)
 	    }
 	    else
 		*dest = alloc_func_type(common, -1, type_gap);
+	    // Use the minimum of min_argcount.
+	    (*dest)->tt_min_argcount =
+			type1->tt_min_argcount < type2->tt_min_argcount
+			     ? type1->tt_min_argcount : type2->tt_min_argcount;
 	    return;
 	}
     }