Don't highlight 'await' expression statements as having no effect (PY-16094)

python/src/com/jetbrains/python/inspections/PyStatementEffectInspection.java

@@ -21,6 +21,7 @@ import com.intellij.psi.PsiElementVisitor;
 import com.intellij.psi.ResolveResult;
 import com.intellij.psi.util.PsiTreeUtil;
 import com.jetbrains.python.PyBundle;
+import com.jetbrains.python.PyTokenTypes;
 import com.jetbrains.python.inspections.quickfix.StatementEffectFunctionCallQuickFix;
 import com.jetbrains.python.inspections.quickfix.StatementEffectIntroduceVariableQuickFix;
 import com.jetbrains.python.psi.*;
@@ -149,6 +150,10 @@ public class PyStatementEffectInspection extends PyInspection {
           }
         }
       }
+      else if (expression instanceof PyPrefixExpression) {
+        final PyPrefixExpression prefixExpr = (PyPrefixExpression)expression;
+        return prefixExpr.getOperator() == PyTokenTypes.AWAIT_KEYWORD;
+      }
       return false;
     }
   }

python/testData/inspections/PyStatementEffectInspection/await.py

@@ -0,0 +1,8 @@
+async def f(x):
+    y = await x
+    await x
+    if await x:
+        pass
+    f(await x)
+    <warning descr="Statement seems to have no effect">x</warning>
+    return await x

python/testSrc/com/jetbrains/python/inspections/PyStatementEffectInspectionTest.java

@@ -16,6 +16,7 @@
 package com.jetbrains.python.inspections;
 
 import com.jetbrains.python.fixtures.PyInspectionTestCase;
+import com.jetbrains.python.psi.LanguageLevel;
 import org.jetbrains.annotations.NotNull;
 
 /**
@@ -26,6 +27,19 @@ public class PyStatementEffectInspectionTest extends PyInspectionTestCase {
     doTest();
   }
 
+  public void testAwait() {
+    doTest(LanguageLevel.PYTHON35);
+  }
+
+  private void doTest(@NotNull LanguageLevel level) {
+    runWithLanguageLevel(level, new Runnable() {
+      @Override
+      public void run() {
+        doTest();
+      }
+    });
+  }
+
   @NotNull
   @Override
   protected Class<? extends PyInspection> getInspectionClass() {