Don't store an exception thrown in computeIfAbsent etc.

It doesn't appear that the stored exception is ever used. Tests still pass after this deletion.

Fixes #5438, fixes #7625, fixes #7975.

RELNOTES=Handling of exceptions from compute functions in `Cache.asMap().computeIfAbsent` and the like has been improved. (We do still recommend using Caffeine rather than `com.google.common.cache`.)
PiperOrigin-RevId: 805040984

Author: eamonnmcmanus

guava-tests/test/com/google/common/cache/LocalCacheMapComputeTest.java

@@ -125,6 +125,23 @@ public void onRemoval(RemovalNotification<Integer, Integer> notification) {
     CacheTesting.checkEmpty(cache);
   }
 
+  public void testComputeIfPresent_error() {
+    var cache = CacheBuilder.newBuilder().build();
+    cache.put(key, "1");
+    assertThrows(
+        Error.class,
+        () ->
+            cache
+                .asMap()
+                .computeIfPresent(
+                    key,
+                    (k, v) -> {
+                      throw new Error();
+                    }));
+    assertThat(cache.getIfPresent(key)).isEqualTo("1");
+    assertThat(cache.asMap().computeIfPresent(key, (k, v) -> "2")).isEqualTo("2");
+  }
+
   public void testUpdates() {
     cache.put(key, "1");
     // simultaneous update for same key, some null, some non-null

guava/src/com/google/common/cache/LocalCache.java

@@ -2259,6 +2259,9 @@ V waitForLoadingValue(ReferenceEntry<K, V> e, K key, ValueReference<K, V> valueR
         // the value for the key is already being computed.
         computingValueReference = new ComputingValueReference<>(valueReference);
 
+        // Compute the value now, so if it throws an exception we don't change anything.
+        newValue = computingValueReference.compute(key, function);
+
         if (e == null) {
           createNewEntry = true;
           e = newEntry(key, hash, first);
@@ -2268,7 +2271,6 @@ V waitForLoadingValue(ReferenceEntry<K, V> e, K key, ValueReference<K, V> valueR
           e.setValueReference(computingValueReference);
         }
 
-        newValue = computingValueReference.compute(key, function);
         if (newValue != null) {
           if (valueReference != null && newValue == valueReference.get()) {
             computingValueReference.set(newValue);
@@ -3585,13 +3587,7 @@ public ListenableFuture<V> loadFuture(K key, CacheLoader<? super K, V> loader) {
       } catch (ExecutionException e) {
         previousValue = null;
       }
-      V newValue;
-      try {
-        newValue = function.apply(key, previousValue);
-      } catch (Throwable th) {
-        this.setException(th);
-        throw th;
-      }
+      V newValue = function.apply(key, previousValue);
       this.set(newValue);
       return newValue;
     }