DO NOT SUBMIT - this is just a prototye

java/src/com/google/template/soy/jbcsrc/api/SoySauce.java

@@ -23,6 +23,7 @@
 import com.google.common.collect.ImmutableSet;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.annotations.CheckReturnValue;
+import com.google.template.soy.data.LoggingAdvisingAppendable;
 import com.google.template.soy.data.SanitizedContent;
 import com.google.template.soy.data.SanitizedContent.ContentKind;
 import com.google.template.soy.data.SoyInjector;
@@ -225,6 +226,19 @@ default WriteContinuation renderHtml(Appendable out) throws IOException {
       return renderHtml(asAdvisingAppendable(out));
     }
 
+    /**
+     * Renders the configured html template to the given appendable, returning a continuation. If
+     * captureLogs is true, logs are writtent to the {@link LoggingAdvisingAppendable}.
+     *
+     * <p>Verifies that the content type is {@link ContentKind.HTML} (corresponding to kind="html"
+     * in the template).
+     *
+     * <p>See {@link #renderHtml(AdvisingAppendable out)} for more details).
+     */
+    @CheckReturnValue
+    WriteContinuation renderHtml(LoggingAdvisingAppendable out, boolean captureLogs)
+        throws IOException;
+
     /**
      * Renders the configured html template to a {@link SanitizedContent}. Verifies that the content
      * type is {@link ContentKind.HTML} (corresponding to kind="html" in the template).

java/src/com/google/template/soy/jbcsrc/api/SoySauceImpl.java

@@ -28,6 +28,7 @@
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSortedSet;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
+import com.google.template.soy.data.LoggingAdvisingAppendable;
 import com.google.template.soy.data.RecordProperty;
 import com.google.template.soy.data.SanitizedContent;
 import com.google.template.soy.data.SanitizedContent.ContentKind;
@@ -278,6 +279,12 @@ public WriteContinuation renderHtml(AdvisingAppendable out) throws IOException {
       return startRender(out, ContentKind.HTML);
     }
 
+    @Override
+    public WriteContinuation renderHtml(LoggingAdvisingAppendable out, boolean captureLogs)
+        throws IOException {
+      return startRender(out, ContentKind.HTML, captureLogs);
+    }
+
     @Override
     public Continuation<SanitizedContent> renderHtml() {
       return startRenderToSanitizedContent(ContentKind.HTML);
@@ -359,11 +366,21 @@ Continuation<T> startRenderToValue(ContentKind contentKind) {
 
     private WriteContinuation startRender(AdvisingAppendable out, ContentKind contentKind)
         throws IOException {
+      return startRender(out, contentKind, /* captureLogs= */ false);
+    }
+
+    private WriteContinuation startRender(
+        AdvisingAppendable out, ContentKind contentKind, boolean captureLogs) throws IOException {
       enforceContentKind(contentKind);
 
       ParamStore params = data == null ? ParamStore.EMPTY_INSTANCE : data;
       RenderContext context = makeContext();
-      OutputAppendable output = OutputAppendable.create(out, context.getLogger());
+      LoggingAdvisingAppendable output;
+      if (captureLogs && out instanceof LoggingAdvisingAppendable) {
+        output = (LoggingAdvisingAppendable) out;
+      } else {
+        output = OutputAppendable.create(out, context.getLogger());
+      }
       return doRender(template, params, output, context);
     }
 
@@ -386,7 +403,10 @@ private void enforceContentKind(ContentKind expectedContentKind) {
   }
 
   private static WriteContinuation doRender(
-      CompiledTemplate template, ParamStore params, OutputAppendable output, RenderContext context)
+      CompiledTemplate template,
+      ParamStore params,
+      LoggingAdvisingAppendable output,
+      RenderContext context)
       throws IOException {
     RenderResult result;
     try {
@@ -420,7 +440,7 @@ abstract static class ContinuationImpl {
     // ThreadSafety guaranteed by the guarded write on hasContinueBeenCalled
     final CompiledTemplate template;
     final ParamStore params;
-    final OutputAppendable output;
+    final LoggingAdvisingAppendable output;
     final RenderContext context;
 
     boolean hasContinueBeenCalled;
@@ -433,7 +453,7 @@ public RenderResult result() {
         RenderResult result,
         CompiledTemplate template,
         ParamStore params,
-        OutputAppendable output,
+        LoggingAdvisingAppendable output,
         RenderContext context) {
       checkArgument(!result.isDone());
       this.result = checkNotNull(result);
@@ -457,7 +477,7 @@ private static final class WriteContinuationImpl extends ContinuationImpl
         RenderResult result,
         CompiledTemplate template,
         ParamStore params,
-        OutputAppendable output,
+        LoggingAdvisingAppendable output,
         RenderContext context) {
       super(result, template, params, output, context);
     }
@@ -475,7 +495,7 @@ Continuation<T> doRenderToValue(
           StringBuilder underlying,
           CompiledTemplate template,
           ParamStore params,
-          OutputAppendable output,
+          LoggingAdvisingAppendable output,
           RenderContext context) {
     RenderResult result;
     try {
@@ -519,7 +539,7 @@ private static final class ValueContinuationImpl<
         RenderResult result,
         CompiledTemplate template,
         ParamStore params,
-        OutputAppendable output,
+        LoggingAdvisingAppendable output,
         RenderContext context) {
       super(result, template, params, output, context);
       this.targetKind = checkNotNull(targetKind);