Prevent use of TextInputType.text when also using TextInputAction.newLine via assert (#55636)

packages/flutter/lib/src/cupertino/text_field.dart

@@ -300,6 +300,11 @@ class CupertinoTextField extends StatefulWidget {
        assert(clearButtonMode != null),
        assert(prefixMode != null),
        assert(suffixMode != null),
+       // Assert the following instead of setting it directly to avoid surprising the user by silently changing the value they set.
+       assert(!identical(textInputAction, TextInputAction.newline) ||
+         maxLines == 1 ||
+         !identical(keyboardType, TextInputType.text),
+         'Use keyboardType TextInputType.multiline when using TextInputAction.newline on a multiline TextField.'),
        keyboardType = keyboardType ?? (maxLines == 1 ? TextInputType.text : TextInputType.multiline),
        toolbarOptions = toolbarOptions ?? (obscureText ?
          const ToolbarOptions(

packages/flutter/lib/src/material/text_field.dart

@@ -376,6 +376,11 @@ class TextField extends StatefulWidget {
        ),
        assert(!obscureText || maxLines == 1, 'Obscured fields cannot be multiline.'),
        assert(maxLength == null || maxLength == TextField.noMaxLength || maxLength > 0),
+       // Assert the following instead of setting it directly to avoid surprising the user by silently changing the value they set.
+       assert(!identical(textInputAction, TextInputAction.newline) ||
+         maxLines == 1 ||
+         !identical(keyboardType, TextInputType.text),
+         'Use keyboardType TextInputType.multiline when using TextInputAction.newline on a multiline TextField.'),
        keyboardType = keyboardType ?? (maxLines == 1 ? TextInputType.text : TextInputType.multiline),
        toolbarOptions = toolbarOptions ?? (obscureText ?
          const ToolbarOptions(