Fix parse error when collecting SpEL extensions for queries computed entirely via expression.

pom.xml

@@ -5,7 +5,7 @@
 
 	<groupId>org.springframework.data</groupId>
 	<artifactId>spring-data-mongodb-parent</artifactId>
-	<version>3.3.0-SNAPSHOT</version>
+	<version>3.3.0-GH-3871-SNAPSHOT</version>
 	<packaging>pom</packaging>
 
 	<name>Spring Data MongoDB</name>

spring-data-mongodb-benchmarks/pom.xml

@@ -7,7 +7,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>3.3.0-SNAPSHOT</version>
+		<version>3.3.0-GH-3871-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

spring-data-mongodb-distribution/pom.xml

@@ -14,7 +14,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>3.3.0-SNAPSHOT</version>
+		<version>3.3.0-GH-3871-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

spring-data-mongodb/pom.xml

@@ -11,7 +11,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>3.3.0-SNAPSHOT</version>
+		<version>3.3.0-GH-3871-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/util/json/ParameterBindingDocumentCodec.java

@@ -18,6 +18,7 @@
 import static java.util.Arrays.*;
 import static org.bson.assertions.Assertions.*;
 import static org.bson.codecs.configuration.CodecRegistries.*;
+import static org.springframework.data.mongodb.util.json.ParameterBindingJsonReader.*;
 
 import java.util.ArrayList;
 import java.util.Collection;
@@ -217,6 +218,9 @@ public Document decode(final BsonReader reader, final DecoderContext decoderCont
 			if (bindingReader.currentValue instanceof org.bson.Document) {
 				return (Document) bindingReader.currentValue;
 			}
+			if(ObjectUtils.nullSafeEquals(bindingReader.currentValue, PLACEHOLDER)) {
+				return new Document();
+			}
 		}
 
 		Document document = new Document();
@@ -377,8 +381,6 @@ private List<Object> readList(final BsonReader reader, final DecoderContext deco
 	 */
 	static class DependencyCapturingExpressionEvaluator implements SpELExpressionEvaluator {
 
-		private static final Object PLACEHOLDER = new Object();
-
 		private final ExpressionParser expressionParser;
 		private final List<ExpressionDependencies> dependencies = new ArrayList<>();
 

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/util/json/ParameterBindingJsonReader.java

@@ -61,7 +61,10 @@
  */
 public class ParameterBindingJsonReader extends AbstractBsonReader {
 
+	static final Object PLACEHOLDER = new Object();
+
 	private static final Pattern PARAMETER_ONLY_BINDING_PATTERN = Pattern.compile("^\\?(\\d+)$");
+	private static final Pattern EXPRESSION_ONLY_BINDING_PATTERN = Pattern.compile("^\\?#\\{.*\\}$");
 	private static final Pattern PARAMETER_BINDING_PATTERN = Pattern.compile("\\?(\\d+)");
 	private static final Pattern EXPRESSION_BINDING_PATTERN = Pattern.compile("[\\?:]#\\{.*\\}");
 
@@ -110,11 +113,7 @@ public ParameterBindingJsonReader(String json, ValueProvider accessor, SpelExpre
 		setContext(new Context(null, BsonContextType.TOP_LEVEL));
 
 		this.bindingContext = new ParameterBindingContext(accessor, spelExpressionParser, evaluationContext);
-
-		Matcher matcher = PARAMETER_ONLY_BINDING_PATTERN.matcher(json);
-		if (matcher.find()) {
-			currentValue = bindableValueFor(new JsonToken(JsonTokenType.UNQUOTED_STRING, json)).getValue();
-		}
+		setInitialValueIfFullDocumentExpression(json);
 	}
 
 	public ParameterBindingJsonReader(String json, ParameterBindingContext bindingContext) {
@@ -123,9 +122,13 @@ public ParameterBindingJsonReader(String json, ParameterBindingContext bindingCo
 		setContext(new Context(null, BsonContextType.TOP_LEVEL));
 
 		this.bindingContext = bindingContext;
+		setInitialValueIfFullDocumentExpression(json);
+	}
 
-		Matcher matcher = PARAMETER_ONLY_BINDING_PATTERN.matcher(json);
-		if (matcher.find()) {
+	public void setInitialValueIfFullDocumentExpression(String json) {
+		if (PARAMETER_ONLY_BINDING_PATTERN.matcher(json).find()) {
+			currentValue = bindableValueFor(new JsonToken(JsonTokenType.UNQUOTED_STRING, json)).getValue();
+		} else if (EXPRESSION_ONLY_BINDING_PATTERN.matcher(json).find()) {
 			currentValue = bindableValueFor(new JsonToken(JsonTokenType.UNQUOTED_STRING, json)).getValue();
 		}
 	}

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/util/json/ParameterBindingJsonReaderUnitTests.java

@@ -358,6 +358,15 @@ void evaluatesSpelExpressionDefiningEntireQuery() {
 						new Document("user.supervisor", "wonderwoman"))));
 	}
 
+	@Test // GH-3871
+	public void capturingExpressionDependenciesShouldNotThrowParseErrorForSpelOnlyJson() {
+
+		Object[] args = new Object[] { "1", "2" };
+		String json = "?#{ true ? { 'name': #name } : { 'name' : #name + 'trouble' } }";
+
+		new ParameterBindingDocumentCodec().captureExpressionDependencies(json, (index) -> args[index], new SpelExpressionParser());
+	}
+
 	@Test // DATAMONGO-2571
 	void shouldParseRegexCorrectly() {