Prevent Refaster UMemberSelect from matching method parameters

See google#2456.

core/src/main/java/com/google/errorprone/refaster/UMemberSelect.java

@@ -65,7 +65,7 @@ public Choice<Unifier> visitMemberSelect(MemberSelectTree fieldAccess, Unifier u
   @Override
   public Choice<Unifier> visitIdentifier(IdentifierTree ident, Unifier unifier) {
     Symbol sym = ASTHelpers.getSymbol(ident);
-    if (sym != null && sym.owner.type != null) {
+    if (sym != null && sym.owner.type != null && sym.owner.type.isReference()) {
       JCExpression thisIdent = unifier.thisExpression(sym.owner.type);
       return getIdentifier()
           .unify(ident.getName(), unifier)

core/src/test/java/com/google/errorprone/refaster/TemplateIntegrationTest.java

@@ -374,4 +374,9 @@ public void suppressWarnings() throws IOException {
   public void typeArgumentsMethodInvocation() throws IOException {
     runTest("TypeArgumentsMethodInvocationTemplate");
   }
+
+  @Test
+  public void memberSelectAndMethodParameterDisambiguation() throws IOException {
+    runTest("MemberSelectAndMethodParameterDisambiguationTemplate");
+  }
 }

core/src/test/java/com/google/errorprone/refaster/testdata/input/MemberSelectAndMethodParameterDisambiguationTemplateExample.java

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2021 The Error Prone Authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.errorprone.refaster.testdata;
+
+import java.util.Objects;
+
+/** Test data for {@code MemberSelectAndMethodParameterDisambiguationTemplate}. */
+public class MemberSelectAndMethodParameterDisambiguationTemplateExample {
+  int example(int length) {
+    return Objects.hashCode(length);
+  }
+}

core/src/test/java/com/google/errorprone/refaster/testdata/output/MemberSelectAndMethodParameterDisambiguationTemplateExample.java

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2021 The Error Prone Authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.errorprone.refaster.testdata;
+
+import java.util.Objects;
+
+/** Test data for {@code MemberSelectAndMethodParameterDisambiguationTemplate}. */
+public class MemberSelectAndMethodParameterDisambiguationTemplateExample {
+  int example(int length) {
+    return Objects.hashCode(length);
+  }
+}

core/src/test/java/com/google/errorprone/refaster/testdata/template/MemberSelectAndMethodParameterDisambiguationTemplate.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2021 The Error Prone Authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+package com.google.errorprone.refaster.testdata.template;
+
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import java.util.Objects;
+
+/**
+ * Example template that references a field ("length") with a name which also commonly occurs as a
+ * method parameter name.
+ */
+public class MemberSelectAndMethodParameterDisambiguationTemplate<T> {
+  @BeforeTemplate
+  public int before(T[] array) {
+    return Objects.hashCode(array.length);
+  }
+
+  @AfterTemplate
+  public int after(T[] array) {
+    return Objects.hashCode(array);
+  }
+}