ensure matrix blocks added on Matrix->inputHtml() are registered as delta changes

CHANGELOG.md

@@ -10,6 +10,7 @@
 - Fixed a bug where selectize inputs didn’t have a minimum width. ([#12950](https://github.com/craftcms/cms/issues/12950))
 - Fixed a bug where the wrong tab would appear to be initially selected after an autosave, if the selected tab had changed during the autosave. ([#12960](https://github.com/craftcms/cms/issues/12960))
 - Fixed a bug where it wasn’t possible to add a Dropdown field without a blank option to a global set. ([#12965](https://github.com/craftcms/cms/issues/12965))
+- Fixed a bug where automatically-added Matrix blocks (per the field’s Min Blocks setting) were getting discarded if no changes were made to them. ([#12973](https://github.com/craftcms/cms/issues/12973))
 
 ## 4.4.5 - 2023-03-21
 

src/fields/Matrix.php

@@ -727,7 +727,14 @@ protected function inputHtml(mixed $value, ?ElementInterface $element = null): s
             ');';
 
         // Safe to create the default blocks?
-        if ($createDefaultBlocks) {
+        if ($createDefaultBlocks && count($value) < $this->minBlocks) {
+            // @link https://github.com/craftcms/cms/issues/12973
+            // for matrix fields with minBlocks set Craft.MatrixInput.addBlock() is called before new Craft.ElementEditor(),
+            // so when we get our initialSerializedValue() for the ElementEditor,
+            // the matrix block is already there which means the field is reported as not changed since the init
+            // and so not passed to PHP for save
+            $view->setInitialDeltaValue($this->handle, null);
+
             $blockTypeJs = Json::encode($blockTypes[0]->handle);
             for ($i = count($value); $i < $this->minBlocks; $i++) {
                 $js .= "\nmatrixInput.addBlock($blockTypeJs, null, false);";