Fix IDEA-173235 Control flow analysis does not know about 'Collections.empty...()' and 'Collections.singleton...()'

java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/ControlFlowAnalyzer.java

@@ -18,6 +18,7 @@ package com.intellij.codeInspection.dataFlow;
 import com.intellij.codeInsight.AnnotationUtil;
 import com.intellij.codeInsight.ExceptionUtil;
 import com.intellij.codeInspection.dataFlow.inliner.CallInliner;
+import com.intellij.codeInspection.dataFlow.inliner.CollectionFactoryInliner;
 import com.intellij.codeInspection.dataFlow.inliner.LambdaInliner;
 import com.intellij.codeInspection.dataFlow.inliner.OptionalChainInliner;
 import com.intellij.codeInspection.dataFlow.instructions.*;
@@ -1683,7 +1684,7 @@ public class ControlFlowAnalyzer extends JavaElementVisitor {
   @Override public void visitClass(PsiClass aClass) {
   }
 
-  static final CallInliner[] INLINERS = {new OptionalChainInliner(), new LambdaInliner()};
+  static final CallInliner[] INLINERS = {new OptionalChainInliner(), new LambdaInliner(), new CollectionFactoryInliner()};
 
   /**
    * A facade for building control flow graph used by {@link CallInliner} implementations

java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/inliner/CollectionFactoryInliner.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2000-2017 JetBrains s.r.o.
+ *
+ * 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.intellij.codeInspection.dataFlow.inliner;
+
+import com.intellij.codeInspection.dataFlow.ControlFlowAnalyzer;
+import com.intellij.codeInspection.dataFlow.Nullness;
+import com.intellij.codeInspection.dataFlow.SpecialField;
+import com.intellij.codeInspection.dataFlow.value.DfaValueFactory;
+import com.intellij.codeInspection.dataFlow.value.DfaVariableValue;
+import com.intellij.psi.PsiExpression;
+import com.intellij.psi.PsiMethodCallExpression;
+import com.intellij.psi.PsiParameter;
+import com.intellij.psi.PsiType;
+import com.siyeh.ig.callMatcher.CallMapper;
+
+import static com.intellij.codeInspection.dataFlow.SpecialField.COLLECTION_SIZE;
+import static com.intellij.codeInspection.dataFlow.SpecialField.MAP_SIZE;
+import static com.intellij.psi.CommonClassNames.JAVA_UTIL_COLLECTIONS;
+import static com.siyeh.ig.callMatcher.CallMatcher.staticCall;
+
+public class CollectionFactoryInliner implements CallInliner {
+  static final class FactoryInfo {
+    int mySize;
+    SpecialField mySizeField;
+
+    public FactoryInfo(int size, SpecialField sizeField) {
+      mySize = size;
+      mySizeField = sizeField;
+    }
+  }
+
+  private static final CallMapper<FactoryInfo> STATIC_FACTORIES = new CallMapper<FactoryInfo>()
+    .register(staticCall(JAVA_UTIL_COLLECTIONS, "emptyList", "emptySet").parameterCount(0), new FactoryInfo(0, COLLECTION_SIZE))
+    .register(staticCall(JAVA_UTIL_COLLECTIONS, "singletonList", "singleton").parameterCount(1), new FactoryInfo(1, COLLECTION_SIZE))
+    .register(staticCall(JAVA_UTIL_COLLECTIONS, "emptyMap").parameterCount(0), new FactoryInfo(0, MAP_SIZE))
+    .register(staticCall(JAVA_UTIL_COLLECTIONS, "singletonMap").parameterCount(2), new FactoryInfo(1, MAP_SIZE));
+
+  @Override
+  public boolean tryInlineCall(ControlFlowAnalyzer.CFGBuilder builder, PsiMethodCallExpression call) {
+    FactoryInfo factoryInfo = STATIC_FACTORIES.mapFirst(call);
+    if (factoryInfo == null) return false;
+    PsiExpression[] args = call.getArgumentList().getExpressions();
+    for (PsiExpression arg : args) {
+      builder.pushExpression(arg).pop();
+    }
+    PsiParameter variable = builder.createTempVariable(call.getType());
+    DfaValueFactory factory = builder.getFactory();
+    DfaVariableValue variableValue = factory.getVarFactory().createVariableValue(variable, false);
+    builder.pushVariable(variable) // tmpVar = <Value of collection type>
+      .push(factory.createTypeValue(call.getType(), Nullness.NOT_NULL))
+      .assign() // leave tmpVar on stack: it's result of method call
+      .push(factoryInfo.mySizeField.createValue(factory, variableValue)) // tmpVar.size = <size>
+      .push(factory.getConstFactory().createFromValue(factoryInfo.mySize, PsiType.INT, null))
+      .assign()
+      .pop();
+    return true;
+  }
+}

java/java-tests/testData/inspection/dataFlow/fixture/EmptySingletonMap.java

@@ -0,0 +1,42 @@
+import java.util.*;
+
+public class EmptySingletonMap {
+  void testEmpty() {
+    List<Object> objects = Collections.emptyList();
+    for (Object o : <warning descr="Collection 'objects' is always empty">objects</warning>) {
+      System.out.println("hello");
+    }
+  }
+
+  void testMixed(int x) {
+    Collection<String> strings;
+    if(x > 10) {
+      strings = Collections.singleton("foo");
+    } else if(x > 6) {
+      strings = Collections.emptyList();
+    } else if(x > 2) {
+      strings = Collections.singletonList("bar");
+    } else {
+      strings = Arrays.asList("a", "b", "c");
+    }
+    if(<warning descr="Condition 'strings.size() >= 2 && x > 3' is always 'false'">strings.size() >= 2 && <warning descr="Condition 'x > 3' is always 'false' when reached">x > 3</warning></warning>) {
+      System.out.println("never");
+    }
+  }
+
+  void testMap(boolean b) {
+    Map<String, String> map;
+    if (b) {
+      map = Collections.emptyMap();
+    }
+    else {
+      map = Collections.singletonMap("a", "b");
+    }
+    if(b && <warning descr="Condition 'map.isEmpty()' is always 'true' when reached">map.isEmpty()</warning>) {
+      System.out.println("true");
+    }
+    if(!b && <warning descr="Condition 'map.size() == 1' is always 'true' when reached">map.size() == 1</warning>) {
+      System.out.println("??");
+    }
+  }
+}

java/java-tests/testSrc/com/intellij/java/codeInspection/DataFlowInspectionTest.java

@@ -532,4 +532,5 @@ public class DataFlowInspectionTest extends DataFlowInspectionTestCase {
     assertEmpty(ContainerUtil.findAll(myFixture.getAvailableIntentions(), i -> i.getText().contains("null")));
   }
 
+  public void testEmptySingletonMap() {doTest();}
 }