Block API: Block Context: Filter content, prepare attributes at render, pass block to render

lib/compat.php

@@ -204,7 +204,16 @@ function gutenberg_render_block_with_assigned_block_context( $pre_render, $parse
 
 	/** This filter is documented in src/wp-includes/blocks.php */
 	$parsed_block = apply_filters( 'render_block_data', $parsed_block, $source_block );
-	$context      = array( 'postId' => $post->ID );
+	$context      = array(
+		'postId'   => $post->ID,
+		/*
+		 * The `postType` context is largely unnecessary server-side, since the
+		 * ID is usually sufficient on its own. That being said, since a block
+		 * manifests is expected to be shared between the server and the client,
+		 * it should be included to consistently fulfill the expectation.
+		 */
+		'postType' => $post->post_type,
+	);
 	$block        = new WP_Block( $parsed_block, $context );
 
 	return $block->render();

phpunit/class-block-context-test.php

@@ -129,4 +129,38 @@ function test_provides_block_context() {
 		);
 	}
 
+	/**
+	 * Tests that a block can receive default-provided context through
+	 * render_block.
+	 */
+	function test_provides_default_context() {
+		global $post;
+
+		$provided_context = array();
+
+		$this->register_block_type(
+			'gutenberg/test-context-consumer',
+			array(
+				'context' => array( 'postId', 'postType' ),
+				'render_callback' => function( $attributes, $content, $block ) use ( &$provided_context ) {
+					$provided_context[] = $block->context;
+
+					return '';
+				},
+			)
+		);
+
+		$parsed_blocks = parse_blocks( '<!-- wp:gutenberg/test-context-consumer /-->' );
+
+		render_block( $parsed_blocks[0] );
+
+		$this->assertEquals(
+			array(
+				'postId'   => $post->ID,
+				'postType' => $post->post_type,
+			),
+			$provided_context[0]
+		);
+	}
+
 }