Add support for specifying exemptPrefixes/exemptNames for UnusedVariable via flags

core/src/main/java/com/google/errorprone/bugpatterns/UnusedVariable.java

@@ -117,9 +117,9 @@
     severity = WARNING,
     documentSuppression = false)
 public final class UnusedVariable extends BugChecker implements CompilationUnitTreeMatcher {
-  private static final String EXEMPT_PREFIX = "unused";
+  private final ImmutableList<String> exemptPrefixes;
 
-  private static final ImmutableSet<String> EXEMPT_NAMES = ImmutableSet.of("ignored");
+  private final ImmutableSet<String> exemptNames;
 
   /**
    * The set of annotation full names which exempt annotated element from being reported as unused.
@@ -163,6 +163,18 @@ public UnusedVariable(ErrorProneFlags flags) {
         .ifPresent(methodAnnotationsExemptingParameters::addAll);
     this.methodAnnotationsExemptingParameters = methodAnnotationsExemptingParameters.build();
     this.reportInjectedFields = flags.getBoolean("Unused:ReportInjectedFields").orElse(false);
+
+    ImmutableSet.Builder<String> exemptNames = ImmutableSet.<String>builder().add("ignored");
+    flags
+        .getList("Unused:exemptNames")
+        .ifPresent(exemptNames::addAll);
+    this.exemptNames = exemptNames.build();
+
+    ImmutableList.Builder<String> exemptPrefixes = ImmutableList.<String>builder().add("unused");
+    flags
+        .getList("Unused:exemptPrefixes")
+        .ifPresent(exemptPrefixes::addAll);
+    this.exemptPrefixes = exemptPrefixes.build();
   }
 
   @Override
@@ -542,12 +554,6 @@ private static boolean exemptedByAnnotation(
     return false;
   }
 
-  private static boolean exemptedByName(Name name) {
-    String nameString = name.toString();
-    return Ascii.toLowerCase(nameString).startsWith(EXEMPT_PREFIX)
-        || EXEMPT_NAMES.contains(nameString);
-  }
-
   private class VariableFinder extends TreePathScanner<Void, Void> {
     private final Map<Symbol, TreePath> unusedElements = new HashMap<>();
 
@@ -610,6 +616,13 @@ && exemptedFieldBySuperType(getType(variableTree), state)) {
       return null;
     }
 
+    private boolean exemptedByName(Name name) {
+      String nameString = name.toString();
+      String nameStringLower = Ascii.toLowerCase(nameString);
+      return exemptPrefixes.stream().anyMatch(nameStringLower::startsWith)
+          || exemptNames.contains(nameString);
+    }
+
     private boolean exemptedFieldBySuperType(Type type, VisitorState state) {
       return EXEMPTING_FIELD_SUPER_TYPES.stream()
           .anyMatch(t -> isSubtype(type, state.getTypeFromString(t), state));

core/src/test/java/com/google/errorprone/bugpatterns/UnusedMethodTest.java

@@ -14,6 +14,7 @@
 
 package com.google.errorprone.bugpatterns;
 
+import com.google.common.collect.ImmutableList;
 import com.google.errorprone.BugCheckerRefactoringTestHelper;
 import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
 import com.google.errorprone.CompilationTestHelper;
@@ -102,10 +103,18 @@ public void exemptedByName() {
             "Unuseds.java",
             "package unusedvars;",
             "class ExemptedByName {",
-            "  private void unused1(int a, int unusedParam) {",
+            "  private void unused1(" +
+            "     int a, int unusedParam, " +
+            "     int customUnused1, int customUnused2, " +
+            "     int prefixUnused1Param, int prefixUnused2Param" +
+            "  ) {",
             "    int unusedLocal = a;",
             "  }",
             "}")
+        .setArgs(
+            "-XepOpt:Unused:exemptNames=customUnused1,customUnused2",
+            "-XepOpt:Unused:exemptPrefixes=prefixunused1,prefixunused2"
+        )
         .doTest();
   }
 

core/src/test/java/com/google/errorprone/bugpatterns/UnusedVariableTest.java

@@ -436,7 +436,15 @@ public void exemptedByName() {
             "  private int unusedInt;",
             "  private static final int UNUSED_CONSTANT = 5;",
             "  private int ignored;",
+            "  private int customUnused1;",
+            "  private int customUnused2;",
+            "  private int prefixUnused1Field;",
+            "  private int prefixUnused2Field;",
             "}")
+        .setArgs(
+            "-XepOpt:Unused:exemptNames=customUnused1,customUnused2",
+            "-XepOpt:Unused:exemptPrefixes=prefixunused1,prefixunused2"
+        )
         .doTest();
   }