performance: don't ask next TemplateContextProvider for references if previous one gave a satisfactory result (PY-7384)

python/openapi/src/com/jetbrains/python/templateLanguages/TemplateContextProvider.java

@@ -18,6 +18,7 @@ package com.jetbrains.python.templateLanguages;
 import com.intellij.codeInsight.lookup.LookupElement;
 import com.intellij.openapi.extensions.ExtensionPointName;
 import com.intellij.psi.PsiFile;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.Collection;
 
@@ -34,7 +35,8 @@ public interface TemplateContextProvider {
    * name of the variable; the object is the PsiElement declaring the variable.
    *
    * @param template the template file
-   * @return the list of variables
+   * @return the list of variables, or null if the template is not used in the context handled by this processor.
    */
+  @Nullable
   Collection<LookupElement> getTemplateContext(PsiFile template);
 }

python/testSrc/com/jetbrains/python/PythonCompletionTest.java

@@ -606,4 +606,10 @@ public class PythonCompletionTest extends PyTestCase {
                             "    pass\n" +
                             "except IOError <caret>").contains("as"));
   }
+
+  public void testElseInFor() {  // PY-6755
+    assertTrue(doTestByText("for item in range(10):\n" +
+                            "    pass\n" +
+                            "el<caret>").contains("else"));
+  }
 }