Add an option to ignore unused variables starting with '_' (PY-27435)

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

@@ -35,22 +35,24 @@ public class PyUnusedLocalInspection extends PyInspection {
   public boolean ignoreTupleUnpacking = true;
   public boolean ignoreLambdaParameters = true;
   public boolean ignoreLoopIterationVariables = true;
+  public boolean ignoreVariablesStartingWithUnderscore = true;
 
+  @Override
   @NotNull
   @Nls
   public String getDisplayName() {
     return PyBundle.message("INSP.NAME.unused");
   }
 
+  @Override
   @NotNull
-  public PsiElementVisitor buildVisitor(@NotNull ProblemsHolder holder,
-                                        final boolean isOnTheFly,
-                                        @NotNull LocalInspectionToolSession session) {
+  public PsiElementVisitor buildVisitor(@NotNull ProblemsHolder holder, boolean isOnTheFly, @NotNull LocalInspectionToolSession session) {
     final PyUnusedLocalInspectionVisitor visitor = new PyUnusedLocalInspectionVisitor(holder,
                                                                                       session,
                                                                                       ignoreTupleUnpacking,
                                                                                       ignoreLambdaParameters,
-                                                                                      ignoreLoopIterationVariables);
+                                                                                      ignoreLoopIterationVariables,
+                                                                                      ignoreVariablesStartingWithUnderscore);
     // buildVisitor() will be called on injected files in the same session - don't overwrite if we already have one
     final PyUnusedLocalInspectionVisitor existingVisitor = session.getUserData(KEY);
     if (existingVisitor == null) {
@@ -70,10 +72,11 @@ public class PyUnusedLocalInspection extends PyInspection {
 
   @Override
   public JComponent createOptionsPanel() {
-    MultipleCheckboxOptionsPanel panel = new MultipleCheckboxOptionsPanel(this);
+    final MultipleCheckboxOptionsPanel panel = new MultipleCheckboxOptionsPanel(this);
     panel.addCheckbox("Ignore variables used in tuple unpacking", "ignoreTupleUnpacking");
     panel.addCheckbox("Ignore lambda parameters", "ignoreLambdaParameters");
     panel.addCheckbox("Ignore range iteration variables", "ignoreLoopIterationVariables");
+    panel.addCheckbox("Ignore variables starting with '_'", "ignoreVariablesStartingWithUnderscore");
     return panel;
   }
 }

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

@@ -62,6 +62,7 @@ public class PyUnusedLocalInspectionVisitor extends PyInspectionVisitor {
   private final boolean myIgnoreTupleUnpacking;
   private final boolean myIgnoreLambdaParameters;
   private final boolean myIgnoreRangeIterationVariables;
+  private final boolean myIgnoreVariablesStartingWithUnderscore;
   private final HashSet<PsiElement> myUnusedElements;
   private final HashSet<PsiElement> myUsedElements;
 
@@ -69,11 +70,13 @@ public class PyUnusedLocalInspectionVisitor extends PyInspectionVisitor {
                                         @NotNull LocalInspectionToolSession session,
                                         boolean ignoreTupleUnpacking,
                                         boolean ignoreLambdaParameters,
-                                        boolean ignoreRangeIterationVariables) {
+                                        boolean ignoreRangeIterationVariables,
+                                        boolean ignoreVariablesStartingWithUnderscore) {
     super(holder, session);
     myIgnoreTupleUnpacking = ignoreTupleUnpacking;
     myIgnoreLambdaParameters = ignoreLambdaParameters;
     myIgnoreRangeIterationVariables = ignoreRangeIterationVariables;
+    myIgnoreVariablesStartingWithUnderscore = ignoreVariablesStartingWithUnderscore;
     myUnusedElements = new HashSet<>();
     myUsedElements = new HashSet<>();
   }
@@ -395,7 +398,7 @@ public class PyUnusedLocalInspectionVisitor extends PyInspectionVisitor {
                               ProblemHighlightType.LIKE_UNUSED_SYMBOL, null, new ReplaceWithWildCard());
             }
           }
-          else {
+          else if (!myIgnoreVariablesStartingWithUnderscore || !name.startsWith(PyNames.UNDERSCORE)) {
             registerWarning(element, PyBundle.message("INSP.unused.locals.local.variable.isnot.used", name), new PyRemoveStatementQuickFix());
           }
         }

python/testData/inspections/PyUnusedLocalInspection/underscorePrefixed.py

@@ -1,5 +1,5 @@
 def foo():
-    l = [42 for <weak_warning descr="Local variable '_a' value is not used">_a</weak_warning> in xrange(100)]
+    l = [42 for _a in xrange(100)]
     print(l)
 
 

python/testData/inspections/PyUnusedLocalInspection/variableStartingWithUnderscore.py

@@ -0,0 +1,2 @@
+def foo():
+    <weak_warning descr="Local variable '_var' value is not used">_var</weak_warning> = 1

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

@@ -87,6 +87,7 @@ public class PyUnusedLocalInspectionTest extends PyInspectionTestCase {
   }
 
   // PY-3996
+  // PY-27435
   public void testUnderscorePrefixed() {
     doTest();
   }
@@ -101,6 +102,13 @@ public class PyUnusedLocalInspectionTest extends PyInspectionTestCase {
     runWithLanguageLevel(LanguageLevel.PYTHON37, this::doTest);
   }
 
+  // PY-27435
+  public void testVariableStartingWithUnderscore() {
+    final PyUnusedLocalInspection inspection = new PyUnusedLocalInspection();
+    inspection.ignoreVariablesStartingWithUnderscore = false;
+    doTest(inspection);
+  }
+
   @NotNull
   @Override
   protected Class<? extends PyInspection> getInspectionClass() {