Skylint: don't report unused variables starting with "unused_"

RELNOTES: none
PiperOrigin-RevId: 173140830
diff --git a/src/tools/skylark/java/com/google/devtools/skylark/skylint/UsageChecker.java b/src/tools/skylark/java/com/google/devtools/skylark/skylint/UsageChecker.java
index a1e00ad..0cc86b2 100644
--- a/src/tools/skylark/java/com/google/devtools/skylark/skylint/UsageChecker.java
+++ b/src/tools/skylark/java/com/google/devtools/skylark/skylint/UsageChecker.java
@@ -189,7 +189,8 @@
     if ("_".equals(name) || nameInfo.kind == Kind.BUILTIN) {
       return;
     }
-    if ((nameInfo.kind == Kind.LOCAL || nameInfo.kind == Kind.PARAMETER) && name.startsWith("_")) {
+    if ((nameInfo.kind == Kind.LOCAL || nameInfo.kind == Kind.PARAMETER)
+        && (name.startsWith("_") || name.startsWith("unused_"))) {
       // local variables starting with an underscore need not be used
       return;
     }
diff --git a/src/tools/skylark/javatests/com/google/devtools/skylark/skylint/UsageCheckerTest.java b/src/tools/skylark/javatests/com/google/devtools/skylark/skylint/UsageCheckerTest.java
index 3fd9760..ba7c87b 100644
--- a/src/tools/skylark/javatests/com/google/devtools/skylark/skylint/UsageCheckerTest.java
+++ b/src/tools/skylark/javatests/com/google/devtools/skylark/skylint/UsageCheckerTest.java
@@ -286,6 +286,8 @@
   @Test
   public void dontReportLocalsStartingWithUnderscore() throws Exception {
     Truth.assertThat(findIssues("def f(_param):", "  _local = [[] for _x in []]")).isEmpty();
+    Truth.assertThat(findIssues("def f(unused_param):", "  unused_local = [[] for unused_x in []]"))
+        .isEmpty();
   }
 
   @Test