How to accept svg image files on your wordpress theme.

functions.php

<?php
// SVGファイルに対応する
add_filter( 'upload_mimes', 'my_add_mime_type' );
if( !function_exists('my_add_mime_type') ) {
	function my_add_mime_type($mime_types)
	{
		$mime_types['svg'] = 'image/svg+xml';
		$mime_types['svgz'] = 'image/svg+xml';
		return $mime_types;
	}
}

add_filter('ext2type', 'my_ext2type');
if( !function_exists('my_ext2type') ) {
	function my_ext2type($ext2types)
	{
		array_push($ext2types['image'], 'svg', 'svgz');
		return $ext2types;
	}
}

add_filter('wp_generate_attachment_metadata', 'my_wp_generate_attachment_metadata',1,2);
if( !function_exists('my_wp_generate_attachment_metadata') ) {
	function my_wp_generate_attachment_metadata($metadata, $attachment_id)
	{
		$attachment_post = $post = get_post($attachment_id);
		$type = $attachment_post->post_mime_type;
		if ($type === 'image/svg+xml' && empty($metadata)) {
			$upload_dir = wp_upload_dir();
			$base_name = basename($attachment_post->guid);
			$metadata = array(
				'file' => $upload_dir['subdir'] . '/' . $base_name
			);
		}
		return $metadata;
	}
}