add sapper:prefetch attribute (#581)

Author: arekbartnik

packages/svelte2tsx/src/htmlxtojsx/nodes/attribute.ts

@@ -39,7 +39,7 @@ export function handleAttribute(htmlx: string, str: MagicString, attr: Node, par
 
     //if we are on an "element" we are case insensitive, lowercase to match our JSX
     if (parent.type == 'Element') {
-        const sapperNoScroll = attr.name === 'sapper:noscroll';
+        const sapperLinkActions = ['sapper:prefetch', 'sapper:noscroll'];
         //skip Attribute shorthand, that is handled below
         if (
             (attr.value !== true &&
@@ -48,7 +48,7 @@ export function handleAttribute(htmlx: string, str: MagicString, attr: Node, par
                     attr.value.length == 1 &&
                     attr.value[0].type == 'AttributeShorthand'
                 )) ||
-            sapperNoScroll
+            sapperLinkActions.includes(attr.name)
         ) {
             let name = attr.name;
             if (!svgAttributes.find((x) => x == name)) {

packages/svelte2tsx/svelte-jsx.d.ts

@@ -726,6 +726,7 @@ declare namespace svelte.JSX {
     interface SapperAnchorProps {
         // transformed from sapper:noscroll so it should be camel case
         sapperNoscroll?: true;
+        sapperPrefetch?: true;
     }
 
     interface SvelteMediaTimeRange {

packages/svelte2tsx/test/htmlx2jsx/samples/sapper-prefetch/expected.jsx

@@ -0,0 +1 @@
+<><a sapperPrefetch></a></>

packages/svelte2tsx/test/htmlx2jsx/samples/sapper-prefetch/input.svelte

@@ -0,0 +1 @@
+<a sapper:prefetch></a>