Remove explicit capture of fields (#7282)

* Remove explicit capture of fields

Previously we were capturing directly fields of the current class in
a specific way and use them for condition evaluation, while this
was captured as argument. Now we only capture this and all evaluations
are based on implicit this dereferencing when needed.
NB: Serialization of complex classes no longer capture static fields

* Rename error messsage

remote unnecessary comments and dead code

dd-java-agent/agent-debugger/debugger-bootstrap/src/main/java/datadog/trace/bootstrap/debugger/CapturedContext.java

@@ -29,7 +29,6 @@ public class CapturedContext implements ValueReferenceResolver {
   private Map<String, CapturedValue> locals;
   private CapturedThrowable throwable;
   private Map<String, CapturedValue> staticFields;
-  private Map<String, CapturedValue> fields;
   private Limits limits = Limits.DEFAULT;
   private String thisClassName;
   private String traceId;
@@ -43,20 +42,17 @@ public CapturedContext(
       CapturedValue[] arguments,
       CapturedValue[] locals,
       CapturedValue returnValue,
-      CapturedThrowable throwable,
-      CapturedValue[] fields) {
+      CapturedThrowable throwable) {
     addArguments(arguments);
     addLocals(locals);
     addReturn(returnValue);
     this.throwable = throwable;
-    addFields(fields);
   }
 
   private CapturedContext(CapturedContext other, Map<String, Object> extensions) {
     this.arguments = other.arguments;
     this.locals = other.getLocals();
     this.throwable = other.throwable;
-    this.fields = other.fields;
     this.extensions.putAll(other.extensions);
     this.extensions.putAll(extensions);
   }
@@ -143,7 +139,7 @@ public Object getMember(Object target, String memberName) {
       }
       target = ReflectiveFieldValueResolver.resolve(target, target.getClass(), memberName);
     }
-    checkUndefined(target, memberName, "Cannot dereference to field: ");
+    checkUndefined(target, memberName, "Cannot dereference field: ");
     return target;
   }
 
@@ -168,15 +164,16 @@ private Object tryRetrieve(String name) {
     if (result != null) {
       return result;
     }
-    if (fields != null && !fields.isEmpty()) {
-      result = fields.get(name);
-    }
-    if (result != null) {
-      return result;
-    }
     if (staticFields != null && !staticFields.isEmpty()) {
       result = staticFields.get(name);
     }
+    CapturedValue thisValue;
+    if (arguments != null && (thisValue = arguments.get("this")) != null) {
+      result = getMember(thisValue.getValue(), name);
+      if (result != Values.UNDEFINED_OBJECT) {
+        return result;
+      }
+    }
     return result != null ? result : Values.UNDEFINED_OBJECT;
   }
 
@@ -236,25 +233,15 @@ public void addStaticFields(CapturedValue[] values) {
     }
   }
 
-  public void addFields(CapturedValue[] values) {
-    if (values == null) {
-      return;
-    }
-    for (CapturedValue value : values) {
-      putInFields(value.name, value);
-    }
-    traceId = extractSpecialId("dd.trace_id");
-    spanId = extractSpecialId("dd.span_id");
+  public void addTraceId(CapturedValue capturedValue) {
+    traceId = extractStringId(capturedValue);
   }
 
-  private String extractSpecialId(String idName) {
-    if (fields == null) {
-      return null;
-    }
-    CapturedValue capturedValue = fields.get(idName);
-    if (capturedValue == null) {
-      return null;
-    }
+  public void addSpanId(CapturedValue capturedValue) {
+    spanId = extractStringId(capturedValue);
+  }
+
+  private String extractStringId(CapturedValue capturedValue) {
     Object value = capturedValue.getValue();
     return value instanceof String ? (String) value : null;
   }
@@ -280,10 +267,6 @@ public Map<String, CapturedValue> getStaticFields() {
     return staticFields;
   }
 
-  public Map<String, CapturedValue> getFields() {
-    return fields;
-  }
-
   public Limits getLimits() {
     return limits;
   }
@@ -314,9 +297,6 @@ public void freeze(TimeoutChecker timeoutChecker) {
     if (staticFields != null) {
       staticFields.values().forEach(capturedValue -> capturedValue.freeze(timeoutChecker));
     }
-    if (fields != null) {
-      fields.values().forEach(capturedValue -> capturedValue.freeze(timeoutChecker));
-    }
   }
 
   public Status evaluate(
@@ -359,13 +339,13 @@ public boolean equals(Object o) {
     CapturedContext context = (CapturedContext) o;
     return Objects.equals(arguments, context.arguments)
         && Objects.equals(locals, context.locals)
-        && Objects.equals(throwable, context.throwable)
-        && Objects.equals(fields, context.fields);
+        && Objects.equals(staticFields, context.staticFields)
+        && Objects.equals(throwable, context.throwable);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(arguments, locals, throwable, fields);
+    return Objects.hash(arguments, locals, throwable, staticFields);
   }
 
   @Override
@@ -377,8 +357,8 @@ public String toString() {
         + locals
         + ", throwable="
         + throwable
-        + ", fields="
-        + fields
+        + ", staticFields="
+        + staticFields
         + '}';
   }
 
@@ -396,13 +376,6 @@ private void putInArguments(String name, CapturedValue value) {
     arguments.put(name, value);
   }
 
-  private void putInFields(String name, CapturedValue value) {
-    if (fields == null) {
-      fields = new HashMap<>();
-    }
-    fields.put(name, value);
-  }
-
   private void putInStaticFields(String name, CapturedValue value) {
     if (staticFields == null) {
       staticFields = new HashMap<>();