Allow absolute negative target patterns without a -- separator

This commit makes `bazel build //foo/... -//bar/...` work, which
previously failed with an invalid option error and required using
`--` as a separator.

src/main/java/com/google/devtools/common/options/OptionsParserImpl.java

@@ -476,6 +476,14 @@ private OptionsParserImplResult parse(
         continue; // not an option arg
       }
 
+      if (arg.startsWith("-//") || arg.startsWith("-@")) {
+        // Do not fail on absolute negative target patterns that aren't separated by `--`.
+        // Relative negative target patterns (e.g. "-pkg:...") aren't readily distinguishable from
+        // options, so these still require a `--` separator.
+        unparsedArgs.add(arg);
+        continue;
+      }
+
       arg = swapShorthandAlias(arg);
 
       if (arg.equals("--")) { // "--" means all remaining args aren't options

src/test/java/com/google/devtools/common/options/OptionsParserTest.java

@@ -2369,6 +2369,15 @@ public void setOptionValueAtSpecificPriorityWithoutExpansion_expandedFlag_setsVa
         .containsExactly("--second=hello");
   }
 
+  @Test
+  public void negativeTargetPatternsAddedToPostDoubleDashArgs() throws OptionsParsingException {
+    OptionsParser parser = OptionsParser.builder().optionsClasses(ExampleFoo.class).build();
+    parser.parse("//foo", "-//bar", "-@repo//bar", "-@@repo//bar", "--", "//bar", "-//baz");
+    assertThat(parser.getResidue()).containsExactly("//foo", "-//bar", "-@repo//bar",
+        "-@@repo//bar", "//bar", "-//baz").inOrder();
+    assertThat(parser.getPostDoubleDashResidue()).containsExactly("//bar", "-//baz").inOrder();
+  }
+
   private static OptionInstanceOrigin createInvocationPolicyOrigin() {
     return createInvocationPolicyOrigin(/*implicitDependent=*/ null, /*expandedFrom=*/ null);
   }