More precise way to determine if expression is True (PY-19856)

python/src/com/jetbrains/python/codeInsight/controlflow/PyControlFlowBuilder.java

@@ -443,7 +443,7 @@ public class PyControlFlowBuilder extends PyRecursiveElementVisitor {
     boolean isStaticallyTrue = false;
     if (condition != null) {
       condition.accept(this);
-      isStaticallyTrue = PyEvaluator.evaluateBoolean(condition, false);
+      isStaticallyTrue = PyEvaluator.evaluateAsBoolean(condition, false);
     }
     final Instruction head = myBuilder.prevInstruction;
     final PyElsePart elsePart = node.getElsePart();
@@ -813,7 +813,7 @@ public class PyControlFlowBuilder extends PyRecursiveElementVisitor {
     super.visitPyAssertStatement(node);
     final PyExpression[] args = node.getArguments();
     // assert False
-    if (args.length >= 1 && !PyEvaluator.evaluateBoolean(args[0], true)) {
+    if (args.length >= 1 && !PyEvaluator.evaluateAsBoolean(args[0], true)) {
       abruptFlow(node);
       return;
     }

python/src/com/jetbrains/python/psi/impl/PyEvaluator.java

@@ -18,6 +18,7 @@ package com.jetbrains.python.psi.impl;
 import com.intellij.psi.PsiElement;
 import com.intellij.psi.ResolveResult;
 import com.intellij.psi.util.PsiTreeUtil;
+import com.intellij.util.ObjectUtils;
 import com.intellij.util.containers.ContainerUtil;
 import com.jetbrains.python.PyNames;
 import com.jetbrains.python.PyTokenTypes;
@@ -341,16 +342,40 @@ public class PyEvaluator {
     return PyUtil.as(new PyEvaluator().evaluate(expression), resultType);
   }
 
-  public static boolean evaluateBoolean(@Nullable PyExpression expr, boolean defaultValue) {
-    final Object result = new PyEvaluator().evaluate(expr);
+  /**
+   * Shortcut that evaluates expression and tries to determine if `bool` will return true for it
+   *
+   * @param expression expression to evaluate
+   * @return true if expression is evaluated to value so `bool` returns true for it
+   */
+  @Nullable
+  public static Boolean evaluateAsBoolean(@Nullable PyExpression expression) {
+    final PyEvaluator evaluator = new PyEvaluator();
+    evaluator.setEvaluateCollectionItems(false);
+    evaluator.setEvaluateKeys(false);
+
+    final Object result = evaluator.evaluate(expression);
+
     if (result instanceof Boolean) {
       return (Boolean)result;
     }
     else if (result instanceof Integer) {
-      return ((Integer)result) != 0;
+      return (Integer)result != 0;
     }
-    else {
-      return defaultValue;
+    else if (result instanceof String) {
+      return !((String)result).isEmpty();
     }
+    else if (result instanceof Collection) {
+      return !((Collection)result).isEmpty();
+    }
+    else if (result instanceof Map) {
+      return !((Map)result).isEmpty();
+    }
+
+    return null;
+  }
+
+  public static boolean evaluateAsBoolean(@Nullable PyExpression expression, boolean defaultValue) {
+    return ObjectUtils.notNull(evaluateAsBoolean(expression), defaultValue);
   }
 }

python/testSrc/com/jetbrains/python/PyEvaluatorTest.java

@@ -264,6 +264,23 @@ public class PyEvaluatorTest extends PyTestCase {
     assertNull(new PyEvaluator().evaluate(expression));
   }
 
+  public void testEvaluateAsBoolean() {
+    assertTrue(PyEvaluator.evaluateAsBoolean(parseExpression("True")));
+    assertFalse(PyEvaluator.evaluateAsBoolean(parseExpression("False")));
+
+    assertTrue(PyEvaluator.evaluateAsBoolean(parseExpression("\'a\'")));
+    assertFalse(PyEvaluator.evaluateAsBoolean(parseExpression("\'\'")));
+
+    assertTrue(PyEvaluator.evaluateAsBoolean(parseExpression("1")));
+    assertFalse(PyEvaluator.evaluateAsBoolean(parseExpression("0")));
+
+    assertTrue(PyEvaluator.evaluateAsBoolean(parseExpression("{1: 0}")));
+    assertFalse(PyEvaluator.evaluateAsBoolean(parseExpression("{}")));
+
+    assertTrue(PyEvaluator.evaluateAsBoolean(parseExpression("[1]")));
+    assertFalse(PyEvaluator.evaluateAsBoolean(parseExpression("[]")));
+  }
+
   @NotNull
   private <T> T byExpression(@NotNull String expression, @NotNull Class<T> cls) {
     final Object value = new PyEvaluator().evaluate(parseExpression(expression));