Allow successful inlining of methods whose body just returns a single input parameter

core/src/main/java/com/google/errorprone/bugpatterns/inlineme/Inliner.java

@@ -234,7 +234,17 @@ && stringContainsComments(state.getSourceForNode(tree), state.context)) {
               "\\b" + Pattern.quote(typeName.getKey()) + "\\b",
               Matcher.quoteReplacement(typeName.getValue()));
     }
+
     for (int i = 0; i < varNames.size(); i++) {
+      // The replacement logic below assumes the existence of another token after the parameter
+      // in the replacement string (ex: a trailing parens, comma, dot, etc.). However, in the case
+      // where the replacement is _just_ one parameter, there isn't a trailing token. We just make
+      // the direct replacement here.
+      if (replacement.equals(varNames.get(i))) {
+        replacement = callingVars.get(i);
+        break;
+      }
+
       // Ex: foo(int a, int... others) -> this.bar(a, others)
       // If caller passes 0 args in the varargs position, we want to remove the preceding comma to
       // make this.bar(a) (as opposed to "this.bar(a, )"

core/src/test/java/com/google/errorprone/bugpatterns/inlineme/InlinerTest.java

@@ -29,9 +29,10 @@
 /** Tests for the {@link Inliner}. */
 @RunWith(JUnit4.class)
 public class InlinerTest {
-  /* We expect that all @InlineMe annotations we try to use as inlineable targets are valid,
-   so we run both checkers here. If the Validator trips on a method, we'll suggest some
-   replacement which should trip up the checker.
+  /*
+    We expect that all @InlineMe annotations we try to use as inlineable targets are valid,
+    so we run both checkers here. If the Validator trips on a method, we'll suggest some
+    replacement which should trip up the checker.
   */
   private final BugCheckerRefactoringTestHelper refactoringTestHelper =
       BugCheckerRefactoringTestHelper.newInstance(
@@ -912,9 +913,7 @@ public void replaceWithJustParameter() {
             "public final class Caller {",
             "  public void doTest() {",
             "    Client client = new Client();",
-            // TODO(b/180976346): replacements of the form that terminate in a parameter by itself
-            //  don't work with the new replacement tool, but this is uncommon enough
-            "    int x = client.identity(42);",
+            "    int x = 42;",
             "  }",
             "}")
         .doTest();