Disable linker cache when we need to link for HMR

tools/isobuild/compiler-plugin.js

@@ -82,6 +82,13 @@ const LINKER_CACHE = new LRU({
   }
 });
 
+// For HMR to work, we have to do a full link during the initial
+// build and each time the bundle changes. Here we store
+// the previous cache key for the app's web.browser arch
+// to check if it was modified or if we can use the cache
+// TODO: support HMR when using the linker cache
+let previousLinkKey = null;
+
 const serverLibPackages = {
   // Make sure fibers is defined, if nothing else.
   fibers: true
@@ -1688,7 +1695,10 @@ export class PackageSourceBatch {
     }));
     const cacheKey = `${cacheKeyPrefix}_${cacheKeySuffix}`;
 
-    if (LINKER_CACHE.has(cacheKey)) {
+    const canUseHMR = isApp && bundleArch === 'web.browser';
+    const canUseCache = !canUseHMR || previousLinkKey === cacheKey; 
+
+    if (canUseCache && LINKER_CACHE.has(cacheKey)) {
       if (CACHE_DEBUG) {
         console.log('LINKER IN-MEMORY CACHE HIT:',
                     linkerOptions.name, bundleArch);
@@ -1711,7 +1721,7 @@ export class PackageSourceBatch {
       });
     }
 
-    if (cacheFilename) {
+    if (canUseCache && cacheFilename) {
       let diskCached = null;
       try {
         diskCached = optimisticReadJsonOrNull(cacheFilename);
@@ -1786,6 +1796,10 @@ export class PackageSourceBatch {
       }
     }
 
+    if (canUseHMR) {
+      previousLinkKey = cacheKey;
+    }
+
     return ret;
   }
 }