Bug 1434965 - Add AutoArraySchemaWriter::FreeFormElement so that FillUpTo can be private. r=njn

This may seem like an unnecessary increase in complexity, and it probably is.
But it makes it easier to reason about lifetimes if your mind is accustomed to
Rust, which would enforce a similar solution.

MozReview-Commit-ID: kJZifbjCSU

--HG--
extra : rebase_source : a2906eb296975ca689c2c3a019c33062ba17b0f2

tools/profiler/core/ProfileBufferEntry.cpp

@@ -160,6 +160,12 @@ public:
 // elements when writing new non-null elements. It also automatically opens and
 // closes an array element on the given JSON writer.
 //
+// You grant the AutoArraySchemaWriter exclusive access to the JSONWriter and
+// the UniqueJSONStrings objects for the lifetime of AutoArraySchemaWriter. Do
+// not access them independently while the AutoArraySchemaWriter is alive.
+// If you need to add complex objects, call FreeFormElement(), which will give
+// you temporary access to the writer.
+//
 // Example usage:
 //
 //     // Define the schema of elements in this type of array: [FOO, BAR, BAZ]
@@ -174,14 +180,10 @@ public:
 //       writer.IntElement(FOO, getFoo());
 //     }
 //     ... etc ...
+//
+//     The elements need to be added in-order.
 class MOZ_RAII AutoArraySchemaWriter
 {
-  friend class AutoObjectWriter;
-
-  SpliceableJSONWriter& mJSONWriter;
-  UniqueJSONStrings&    mStrings;
-  uint32_t              mNextFreeIndex;
-
 public:
   AutoArraySchemaWriter(SpliceableJSONWriter& aWriter, UniqueJSONStrings& aStrings)
     : mJSONWriter(aWriter)
@@ -195,12 +197,6 @@ public:
     mJSONWriter.EndArray();
   }
 
-  void FillUpTo(uint32_t aIndex) {
-    MOZ_ASSERT(aIndex >= mNextFreeIndex);
-    mJSONWriter.NullElements(aIndex - mNextFreeIndex);
-    mNextFreeIndex = aIndex + 1;
-  }
-
   void IntElement(uint32_t aIndex, uint32_t aValue) {
     FillUpTo(aIndex);
     mJSONWriter.IntElement(aValue);
@@ -215,6 +211,25 @@ public:
     FillUpTo(aIndex);
     mStrings.WriteElement(mJSONWriter, aValue);
   }
+
+  // Write an element using a callback that takes a JSONWriter& and a
+  // UniqueJSONStrings&.
+  template<typename LambdaT>
+  void FreeFormElement(uint32_t aIndex, LambdaT aCallback) {
+    FillUpTo(aIndex);
+    aCallback(mJSONWriter, mStrings);
+  }
+
+private:
+  void FillUpTo(uint32_t aIndex) {
+    MOZ_ASSERT(aIndex >= mNextFreeIndex);
+    mJSONWriter.NullElements(aIndex - mNextFreeIndex);
+    mNextFreeIndex = aIndex + 1;
+  }
+
+  SpliceableJSONWriter& mJSONWriter;
+  UniqueJSONStrings& mStrings;
+  uint32_t mNextFreeIndex;
 };
 
 class StreamOptimizationAttemptsOp : public JS::ForEachTrackedOptimizationAttemptOp
@@ -420,6 +435,54 @@ UniqueStacks::StreamNonJITFrame(const FrameKey& aFrame)
   }
 }
 
+static void
+StreamJITFrameOptimizations(SpliceableJSONWriter& aWriter,
+                            UniqueJSONStrings& aUniqueStrings,
+                            JSContext* aContext,
+                            const JS::ProfiledFrameHandle& aJITFrame)
+{
+  aWriter.StartObjectElement();
+  {
+    aWriter.StartArrayProperty("types");
+    {
+      StreamOptimizationTypeInfoOp typeInfoOp(aWriter, aUniqueStrings);
+      aJITFrame.forEachOptimizationTypeInfo(typeInfoOp);
+    }
+    aWriter.EndArray();
+
+    JS::Rooted<JSScript*> script(aContext);
+    jsbytecode* pc;
+    aWriter.StartObjectProperty("attempts");
+    {
+      {
+        JSONSchemaWriter schema(aWriter);
+        schema.WriteField("strategy");
+        schema.WriteField("outcome");
+      }
+
+      aWriter.StartArrayProperty("data");
+      {
+        StreamOptimizationAttemptsOp attemptOp(aWriter, aUniqueStrings);
+        aJITFrame.forEachOptimizationAttempt(attemptOp, script.address(), &pc);
+      }
+      aWriter.EndArray();
+    }
+    aWriter.EndObject();
+
+    if (JSAtom* name = js::GetPropertyNameFromPC(script, pc)) {
+      char buf[512];
+      JS_PutEscapedFlatString(buf, mozilla::ArrayLength(buf), js::AtomToFlatString(name), 0);
+      aUniqueStrings.WriteProperty(aWriter, "propertyName", buf);
+    }
+
+    unsigned line, column;
+    line = JS_PCToLineNumber(script, pc, &column);
+    aWriter.IntProperty("line", line);
+    aWriter.IntProperty("column", column);
+  }
+  aWriter.EndObject();
+}
+
 void
 UniqueStacks::StreamJITFrame(const JS::ProfiledFrameHandle& aJITFrame)
 {
@@ -444,47 +507,11 @@ UniqueStacks::StreamJITFrame(const JS::ProfiledFrameHandle& aJITFrame)
                         : "baseline");
 
   if (aJITFrame.hasTrackedOptimizations()) {
-    writer.FillUpTo(OPTIMIZATIONS);
-    mFrameTableWriter.StartObjectElement();
-    {
-      mFrameTableWriter.StartArrayProperty("types");
-      {
-        StreamOptimizationTypeInfoOp typeInfoOp(mFrameTableWriter, mUniqueStrings);
-        aJITFrame.forEachOptimizationTypeInfo(typeInfoOp);
-      }
-      mFrameTableWriter.EndArray();
-
-      JS::Rooted<JSScript*> script(mContext);
-      jsbytecode* pc;
-      mFrameTableWriter.StartObjectProperty("attempts");
-      {
-        {
-          JSONSchemaWriter schema(mFrameTableWriter);
-          schema.WriteField("strategy");
-          schema.WriteField("outcome");
-        }
-
-        mFrameTableWriter.StartArrayProperty("data");
-        {
-          StreamOptimizationAttemptsOp attemptOp(mFrameTableWriter, mUniqueStrings);
-          aJITFrame.forEachOptimizationAttempt(attemptOp, script.address(), &pc);
-        }
-        mFrameTableWriter.EndArray();
-      }
-      mFrameTableWriter.EndObject();
-
-      if (JSAtom* name = js::GetPropertyNameFromPC(script, pc)) {
-        char buf[512];
-        JS_PutEscapedFlatString(buf, mozilla::ArrayLength(buf), js::AtomToFlatString(name), 0);
-        mUniqueStrings.WriteProperty(mFrameTableWriter, "propertyName", buf);
-      }
-
-      unsigned line, column;
-      line = JS_PCToLineNumber(script, pc, &column);
-      mFrameTableWriter.IntProperty("line", line);
-      mFrameTableWriter.IntProperty("column", column);
-    }
-    mFrameTableWriter.EndObject();
+    writer.FreeFormElement(OPTIMIZATIONS,
+      [&](SpliceableJSONWriter& aWriter, UniqueJSONStrings& aUniqueStrings) {
+        StreamJITFrameOptimizations(aWriter, aUniqueStrings, mContext,
+                                    aJITFrame);
+      });
   }
 }