Fix findIdent incompatibility with Java 13

Fixes #1432
Fixes #1439

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=308794942

check_api/src/main/java/com/google/errorprone/util/FindIdentifiers.java

@@ -61,7 +61,9 @@
 import com.sun.tools.javac.comp.Resolve;
 import com.sun.tools.javac.tree.JCTree.JCCompilationUnit;
 import com.sun.tools.javac.tree.JCTree.JCMethodDecl;
+import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;
 import com.sun.tools.javac.util.Name;
+import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.util.Collections;
 import java.util.List;
@@ -98,17 +100,31 @@ public static Symbol findIdent(String name, VisitorState state, KindSelector kin
       }
     }
     try {
-      Method method =
-          Resolve.class.getDeclaredMethod("findIdent", Env.class, Name.class, KindSelector.class);
-      method.setAccessible(true);
-      Symbol result =
-          (Symbol) method.invoke(Resolve.instance(state.context), env, state.getName(name), kind);
+      Symbol result = findIdent(name, state, kind, env);
       return result.exists() ? result : null;
     } catch (ReflectiveOperationException e) {
       throw new LinkageError(e.getMessage(), e);
     }
   }
 
+  // Signature was changed in Java 13: https://bugs.openjdk.java.net/browse/JDK-8223305
+  private static Symbol findIdent(
+      String name, VisitorState state, KindSelector kind, Env<AttrContext> env)
+      throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
+    if (RuntimeVersion.isAtLeast13()) {
+      Method method =
+          Resolve.class.getDeclaredMethod(
+              "findIdent", DiagnosticPosition.class, Env.class, Name.class, KindSelector.class);
+      method.setAccessible(true);
+      return (Symbol)
+          method.invoke(Resolve.instance(state.context), null, env, state.getName(name), kind);
+    }
+    Method method =
+        Resolve.class.getDeclaredMethod("findIdent", Env.class, Name.class, KindSelector.class);
+    method.setAccessible(true);
+    return (Symbol) method.invoke(Resolve.instance(state.context), env, state.getName(name), kind);
+  }
+
   @Nullable
   private static ClassTree getEnclosingClass(TreePath treePath) {
     while (treePath != null) {
@@ -246,7 +262,7 @@ public static ImmutableSet<VarSymbol> findAllIdents(VisitorState state) {
     }
 
     return result.build().stream()
-        .filter(var -> isVisible(var, state.getPath()))
+        .filter(variable -> isVisible(variable, state.getPath()))
         .collect(toImmutableSet());
   }
 

core/src/test/java/com/google/errorprone/util/RuntimeVersion.java → check_api/src/main/java/com/google/errorprone/util/RuntimeVersion.java

@@ -64,4 +64,9 @@ public static boolean isAtLeast11() {
   public static boolean isAtLeast12() {
     return MAJOR >= 12;
   }
+
+  /** Returns true if the current runtime is JDK 13 or newer. */
+  public static boolean isAtLeast13() {
+    return MAJOR >= 13;
+  }
 }