patch 8.2.1647: Vim9: result of expression with && and || is not a bool

Problem:    Vim9: result of expression with && and || cannot be assigned to a
            bool variable.
Solution:   Add the TTFLAG_BOOL_OK flag and convert the value if needed.

src/testdir/test_vim9_disassemble.vim

@@ -1199,6 +1199,29 @@ def Test_disassemble_invert_bool()
   assert_equal(true, InvertBool())
 enddef
 
+def ReturnBool(): bool
+  let var: bool = "no" && [] || 123
+  return var
+enddef
+
+def Test_disassemble_return_bool()
+  let instr = execute('disassemble ReturnBool')
+  assert_match('ReturnBool\_s*' ..
+        'let var: bool = "no" && \[\] || 123\_s*' ..
+        '0 PUSHS "no"\_s*' ..
+        '1 JUMP_AND_KEEP_IF_FALSE -> 3\_s*' ..
+        '2 NEWLIST size 0\_s*' ..
+        '3 JUMP_AND_KEEP_IF_TRUE -> 5\_s*' ..
+        '4 PUSHNR 123\_s*' ..
+        '5 2BOOL (!!val)\_s*' ..
+        '\d STORE $0\_s*' ..
+        'return var\_s*' ..
+        '\d LOAD $0\_s*' ..   
+        '\d RETURN',
+        instr)
+  assert_equal(true, InvertBool())
+enddef
+
 def Test_disassemble_compare()
   let cases = [
         ['true == isFalse', 'COMPAREBOOL =='],

src/testdir/test_vim9_script.vim

@@ -46,9 +46,16 @@ def Test_assignment_bool()
   assert_equal(v:false, bool2)
 
   let bool3: bool = 0
-  assert_equal(0, bool3)
+  assert_equal(false, bool3)
   let bool4: bool = 1
-  assert_equal(1, bool4)
+  assert_equal(true, bool4)
+
+  let bool5: bool = 'yes' && 'no'
+  assert_equal(true, bool5)
+  let bool6: bool = [] && 99
+  assert_equal(false, bool6)
+  let bool7: bool = [] || #{a: 1} && 99
+  assert_equal(true, bool7)
 
   let lines =<< trim END
     vim9script
@@ -57,8 +64,15 @@ def Test_assignment_bool()
       return flag
     enddef
     let flag: bool = GetFlag()
+    assert_equal(true, flag)
     flag = 0
+    # assert_equal(false, flag)
     flag = 1
+    # assert_equal(true, flag)
+    # flag = 99 || 123
+    # assert_equal(true, flag)
+    # flag = 'yes' && []
+    # assert_equal(false, flag)
   END
   CheckScriptSuccess(lines)
   CheckDefAndScriptFailure(['let x: bool = 2'], 'E1012:')

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1647,
 /**/
     1646,
 /**/

src/vim9compile.c

@@ -729,6 +729,15 @@ need_type(
 	cctx_T	*cctx,
 	int	silent)
 {
+    if (expected == &t_bool && actual != &t_bool
+					&& (actual->tt_flags & TTFLAG_BOOL_OK))
+    {
+	// Using "0", "1" or the result of an expression with "&&" or "||" as a
+	// boolean is OK but requires a conversion.
+	generate_2BOOL(cctx, FALSE);
+	return OK;
+    }
+
     if (check_type(expected, actual, FALSE, 0) == OK)
 	return OK;
     if (actual->tt_type != VAR_ANY
@@ -3926,6 +3935,8 @@ compile_and_or(
     {
 	garray_T	*instr = &cctx->ctx_instr;
 	garray_T	end_ga;
+	garray_T	*stack = &cctx->ctx_type_stack;
+	type_T		**typep;
 
 	/*
 	 * Repeat until there is no following "||" or "&&"
@@ -3985,6 +3996,20 @@ compile_and_or(
 	    isn->isn_arg.jump.jump_where = instr->ga_len;
 	}
 	ga_clear(&end_ga);
+
+	// The resulting type can be used as a bool.
+	typep = ((type_T **)stack->ga_data) + stack->ga_len - 1;
+	if (*typep != &t_bool)
+	{
+	    type_T *type = alloc_type(cctx->ctx_type_list);
+
+	    if (type != NULL)
+	    {
+		*type = **typep;
+		type->tt_flags |= TTFLAG_BOOL_OK;
+		*typep = type;
+	    }
+	}
     }
 
     return OK;