Accept tildes in --override_module

This is useful for adding this in your global ~/.bazelrc file for easy
rules debugging.

See also bazelbuild#15417

src/main/java/com/google/devtools/build/lib/bazel/repository/RepositoryOptions.java

@@ -350,12 +350,12 @@ public ModuleOverride convert(String input) throws OptionsParsingException {
       OptionsUtils.AbsolutePathFragmentConverter absolutePathFragmentConverter =
           new OptionsUtils.AbsolutePathFragmentConverter();
       try {
-        var unused = absolutePathFragmentConverter.convert(pieces[1]);
+        var path = absolutePathFragmentConverter.convert(pieces[1]);
+        return ModuleOverride.create(pieces[0], path.toString());
       } catch (OptionsParsingException e) {
         throw new OptionsParsingException(
             "Module override directory must be an absolute path", input, e);
       }
-      return ModuleOverride.create(pieces[0], pieces[1]);
     }
 
     @Override

src/test/java/com/google/devtools/build/lib/bazel/repository/RepositoryOptionsTest.java

@@ -60,6 +60,13 @@ public void testOverridePathWithTilde() throws Exception {
     assertThat(actual.path()).isEqualTo(PathFragment.create(USER_HOME.value() + "/bar"));
   }
 
+  @Test
+  public void testModuleOverridePathWithTilde() throws Exception {
+    RepositoryOverride actual = converter.convert("foo=~/bar");
+    assertThat(actual.repositoryName()).isEqualTo(RepositoryName.createUnvalidated("foo"));
+    assertThat(actual.path()).isEqualTo(PathFragment.create(USER_HOME.value() + "/bar"));
+  }
+
   @Test
   public void testInvalidOverride() throws Exception {
     expectedException.expect(OptionsParsingException.class);