Detector to suggest more efficient collections.

Android offers several efficient alternatives to some upstream
Collections containers, such as SparseIntArray instead of
Map<Integer, Integer>.

Bug: 155703208
Test: atest error_prone_android_framework_test
Change-Id: I080fd9489fb037391b717901345a905a9753b370

2 files changed, 194 insertions, 0 deletions

diff --git a/errorprone/java/com/google/errorprone/bugpatterns/android/EfficientCollectionsChecker.java b/errorprone/java/com/google/errorprone/bugpatterns/android/EfficientCollectionsChecker.java
new file mode 100644
index 000000000000..c4c1ab6482ee
--- /dev/null
+++ b/errorprone/java/com/google/errorprone/bugpatterns/android/EfficientCollectionsChecker.java
@@ -0,0 +1,98 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.errorprone.bugpatterns.android;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.matchers.Matchers.isSubtypeOf;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.NewClassTreeMatcher;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.NewClassTree;
+import com.sun.source.tree.Tree;
+import com.sun.tools.javac.code.Type;
+
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * Android offers several efficient alternatives to some upstream
+ * {@link Collections} containers, such as {@code SparseIntArray} instead of
+ * {@code Map<Integer, Integer>}.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    name = "AndroidFrameworkEfficientCollections",
+    summary = "Verifies efficient collections best-practices",
+    severity = WARNING)
+public final class EfficientCollectionsChecker extends BugChecker implements NewClassTreeMatcher {
+    private static final Matcher<Tree> IS_LIST = isSubtypeOf("java.util.List");
+    private static final Matcher<Tree> IS_MAP = isSubtypeOf("java.util.Map");
+
+    private static final String INTEGER = "java.lang.Integer";
+    private static final String LONG = "java.lang.Long";
+    private static final String BOOLEAN = "java.lang.Boolean";
+
+    @Override
+    public Description matchNewClass(NewClassTree tree, VisitorState state) {
+        final List<Type> types = ASTHelpers.getType(tree).getTypeArguments();
+        if (IS_LIST.matches(tree, state) && types != null && types.size() == 1) {
+            final Type first = types.get(0);
+            if (ASTHelpers.isSameType(first, state.getTypeFromString(INTEGER), state)) {
+                return buildDescription(tree)
+                        .setMessage("Consider replacing with IntArray for efficiency")
+                        .build();
+            } else if (ASTHelpers.isSameType(first, state.getTypeFromString(LONG), state))  {
+                return buildDescription(tree)
+                        .setMessage("Consider replacing with LongArray for efficiency")
+                        .build();
+            }
+        } else if (IS_MAP.matches(tree, state) && types != null && types.size() == 2) {
+            final Type first = types.get(0);
+            final Type second = types.get(1);
+            if (ASTHelpers.isSameType(first, state.getTypeFromString(INTEGER), state)) {
+                if (ASTHelpers.isSameType(second, state.getTypeFromString(INTEGER), state)) {
+                    return buildDescription(tree)
+                            .setMessage("Consider replacing with SparseIntArray for efficiency")
+                            .build();
+                } else if (ASTHelpers.isSameType(second, state.getTypeFromString(LONG), state)) {
+                    return buildDescription(tree)
+                            .setMessage("Consider replacing with SparseLongArray for efficiency")
+                            .build();
+                } else if (ASTHelpers.isSameType(second, state.getTypeFromString(BOOLEAN), state)) {
+                    return buildDescription(tree)
+                            .setMessage("Consider replacing with SparseBooleanArray for efficiency")
+                            .build();
+                } else {
+                    return buildDescription(tree)
+                            .setMessage("Consider replacing with SparseArray for efficiency")
+                            .build();
+                }
+            } else if (ASTHelpers.isSameType(first, state.getTypeFromString(LONG), state)) {
+                return buildDescription(tree)
+                        .setMessage("Consider replacing with LongSparseArray for efficiency")
+                        .build();
+            }
+        }
+        return Description.NO_MATCH;
+    }
+}
diff --git a/errorprone/tests/java/com/google/errorprone/bugpatterns/android/EfficientCollectionsCheckerTest.java b/errorprone/tests/java/com/google/errorprone/bugpatterns/android/EfficientCollectionsCheckerTest.java
new file mode 100644
index 000000000000..e128b6ad2cfd
--- /dev/null
+++ b/errorprone/tests/java/com/google/errorprone/bugpatterns/android/EfficientCollectionsCheckerTest.java
@@ -0,0 +1,96 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.errorprone.bugpatterns.android;
+
+import com.google.errorprone.CompilationTestHelper;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public class EfficientCollectionsCheckerTest {
+    private CompilationTestHelper compilationHelper;
+
+    @Before
+    public void setUp() {
+        compilationHelper = CompilationTestHelper.newInstance(
+                EfficientCollectionsChecker.class, getClass());
+    }
+
+    @Test
+    public void testMap() {
+        compilationHelper
+                .addSourceLines("Example.java",
+                        "import java.util.HashMap;",
+                        "public class Example {",
+                        "  public void exampleInteger() {",
+                        "    // BUG: Diagnostic contains:",
+                        "    HashMap<Integer, Integer> a = new HashMap<>();",
+                        "    // BUG: Diagnostic contains:",
+                        "    HashMap<Integer, Long> b = new HashMap<>();",
+                        "    // BUG: Diagnostic contains:",
+                        "    HashMap<Integer, Boolean> c = new HashMap<>();",
+                        "    // BUG: Diagnostic contains:",
+                        "    HashMap<Integer, String> d = new HashMap<>();",
+                        "  }",
+                        "  public void exampleLong() {",
+                        "    // BUG: Diagnostic contains:",
+                        "    HashMap<Long, String> res = new HashMap<>();",
+                        "  }",
+                        "  public void exampleOther() {",
+                        "    HashMap<String, String> res = new HashMap<>();",
+                        "  }",
+                        "}")
+                .doTest();
+    }
+
+    @Test
+    public void testList() {
+        compilationHelper
+                .addSourceLines("Example.java",
+                        "import java.util.ArrayList;",
+                        "public class Example {",
+                        "  public void exampleInteger() {",
+                        "    // BUG: Diagnostic contains:",
+                        "    ArrayList<Integer> res = new ArrayList<>();",
+                        "  }",
+                        "  public void exampleLong() {",
+                        "    // BUG: Diagnostic contains:",
+                        "    ArrayList<Long> res = new ArrayList<>();",
+                        "  }",
+                        "  public void exampleOther() {",
+                        "    ArrayList<String> res = new ArrayList<>();",
+                        "  }",
+                        "}")
+                .doTest();
+    }
+
+    @Test
+    public void testErasure() {
+        compilationHelper
+                .addSourceLines("Example.java",
+                        "import java.util.HashMap;",
+                        "public class Example {",
+                        "  public void example() {",
+                        "    HashMap a = new HashMap();",
+                        "  }",
+                        "}")
+                .doTest();
+    }
+}