Introduce StreamMapFilter Refaster rule (#1467)

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/StreamRules.java

@@ -297,6 +297,22 @@ boolean after(Stream<T> stream) {
     }
   }
 
+  /**
+   * Prefer an unconditional {@link Map#get(Object)} call followed by a {@code null} check over a
+   * call to {@link Map#containsKey(Object)}, as the former avoids a second lookup operation.
+   */
+  static final class StreamMapFilter<T, K, V> {
+    @BeforeTemplate
+    Stream<V> before(Stream<T> stream, Map<K, V> map) {
+      return stream.filter(map::containsKey).map(map::get);
+    }
+
+    @AfterTemplate
+    Stream<V> after(Stream<T> stream, Map<K, V> map) {
+      return stream.map(map::get).filter(Objects::nonNull);
+    }
+  }
+
   static final class StreamMin<T> {
     @BeforeTemplate
     @SuppressWarnings("java:S4266" /* This violation will be rewritten. */)

error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/StreamRulesTestInput.java

@@ -141,6 +141,12 @@ boolean testStreamFindAnyIsPresent() {
     return Stream.of(1).findFirst().isPresent();
   }
 
+  Stream<Integer> testStreamMapFilter() {
+    return Stream.of("foo")
+        .filter(ImmutableMap.of(1, 2)::containsKey)
+        .map(ImmutableMap.of(1, 2)::get);
+  }
+
   ImmutableSet<Optional<String>> testStreamMin() {
     return ImmutableSet.of(
         Stream.of("foo").max(comparingInt(String::length).reversed()),

error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/StreamRulesTestOutput.java

@@ -141,6 +141,10 @@ boolean testStreamFindAnyIsPresent() {
     return Stream.of(1).findAny().isPresent();
   }
 
+  Stream<Integer> testStreamMapFilter() {
+    return Stream.of("foo").map(ImmutableMap.of(1, 2)::get).filter(Objects::nonNull);
+  }
+
   ImmutableSet<Optional<String>> testStreamMin() {
     return ImmutableSet.of(
         Stream.of("foo").min(comparingInt(String::length)),