Wrap strings in literal if contains $ (#1144)

JAVA-4884

Author: katcharov

driver-core/src/main/com/mongodb/client/model/mql/MqlValues.java

@@ -233,7 +233,7 @@ public static MqlArray<MqlDate> ofDateArray(final Instant... array) {
      */
     public static MqlString of(final String of) {
         Assertions.notNull("String", of);
-        return new MqlExpression<>((codecRegistry) -> new AstPlaceholder(new BsonString(of)));
+        return new MqlExpression<>((codecRegistry) -> new AstPlaceholder(wrapString(of)));
     }
 
     /**
@@ -249,11 +249,20 @@ public static MqlArray<MqlString> ofStringArray(final String... array) {
         List<BsonValue> result = new ArrayList<>();
         for (String e : array) {
             Assertions.notNull("elements of array", e);
-            result.add(new BsonString(e));
+            result.add(wrapString(e));
         }
         return new MqlExpression<>((cr) -> new AstPlaceholder(new BsonArray(result)));
     }
 
+    private static BsonValue wrapString(final String s) {
+        BsonString bson = new BsonString(s);
+        if (s.contains("$")) {
+            return new BsonDocument("$literal", bson);
+        } else {
+            return bson;
+        }
+    }
+
     /**
      * Returns a reference to the "current"
      * {@linkplain MqlDocument document} value.

driver-core/src/test/functional/com/mongodb/client/model/mql/ArrayMqlValuesFunctionalTest.java

@@ -77,6 +77,12 @@ public void literalsTest() {
                 Arrays.asList("a", "b", "c"),
                 ofStringArray("a", "b", "c"),
                 "['a', 'b', 'c']");
+        // must escape:
+        assertExpression(
+                Arrays.asList("$a", "b", "$c.d"),
+                ofStringArray("$a", "b", "$c.d"),
+                "[{'$literal': '$a'}, 'b', {'$literal': '$c.d'}]");
+
         // Date
         assertExpression(
                 Arrays.asList(Instant.parse("2007-12-03T10:15:30.00Z")),

driver-core/src/test/functional/com/mongodb/client/model/mql/StringMqlValuesFunctionalTest.java

@@ -38,6 +38,12 @@ public void literalsTest() {
         assertExpression("abc", of("abc"), "'abc'");
         assertThrows(IllegalArgumentException.class, () -> of((String) null));
         assertExpression(fish, of(fish), "'" + fish + "'");
+
+        // must escape:
+        assertExpression(
+                "$abc",
+                of("$abc"),
+                "{'$literal': '$abc'}");
     }
 
     @Test