Allow -> as placeholder separator

Author: fluentfuture

mug-errorprone/src/main/java/com/google/mu/errorprone/FormatStringUtils.java

@@ -33,15 +33,17 @@
 final class FormatStringUtils {
   static final Substring.Pattern PLACEHOLDER_PATTERN =
       consecutive(CharMatcher.noneOf("{}")::matches).immediatelyBetween("{", INCLUSIVE, "}", INCLUSIVE);
+  static final Substring.Pattern PLACEHOLDER_SEPARATOR =
+      Stream.of("=", "->").map(Substring::first).collect(firstOccurrence());
   static final Substring.RepeatingPattern PLACEHOLDER_NAMES_PATTERN =
       consecutive(CharMatcher.noneOf("{}")::matches).immediatelyBetween("{", "}").repeatedly();
 
   static ImmutableList<String> placeholderVariableNames(String formatString) {
-    Substring.Pattern beforeEqualSign = Substring.before(first('='));
+    Substring.Pattern beforeSeparator = Substring.before(PLACEHOLDER_SEPARATOR);
     return PLACEHOLDER_NAMES_PATTERN
         .from(formatString)
         // for Cloud resource name syntax
-        .map(n -> beforeEqualSign.from(n).map(whitespace()::trimTrailingFrom).orElse(n))
+        .map(n -> beforeSeparator.from(n).map(whitespace()::trimTrailingFrom).orElse(n))
         .collect(toImmutableList());
   }
 

mug-errorprone/src/test/java/com/google/mu/errorprone/StringFormatPlaceholderNamesCheckTest.java

@@ -244,6 +244,19 @@ public void trailingSpacesBeforeEqualSignIgnored() {
         .doTest();
   }
 
+  @Test
+  public void trailingSpacesBeforeArrowIgnored() {
+    helper
+        .addSourceLines(
+            "Test.java",
+            "import com.google.mu.util.StringFormat;",
+            "class Test {",
+            "  private static final StringFormat FORMAT =",
+            "      new StringFormat(\"{shows_id -> id,}\");",
+            "}")
+        .doTest();
+  }
+
   @Ignore
   @Test
   public void squareBracketedPlaceholdersChecked() {