[json] Provide a means to delegate writing a value to another API

(Based on D87170 by dsanders)

I recently had need to call out to an external API to emit a JSON object as part
of one an LLVM tool was emitting. However, our JSON support didn't provide a way
to delegate part of the JSON output to that API.

Add rawValueBegin() and rawValueEnd() to maintain and check the internal state
while something else is writing to the stream. It's the users responsibility to
ensure that the resulting JSON output is still valid.

Differential Revision: https://reviews.llvm.org/D88902

1 files changed, 21 insertions, 16 deletions

diff --git a/llvm/lib/Support/JSON.cpp b/llvm/lib/Support/JSON.cpp
index d44961b..8471e58 100644
--- a/llvm/lib/Support/JSON.cpp
+++ b/llvm/lib/Support/JSON.cpp
@@ -251,20 +251,13 @@ std::vector<const Object::value_type *> sortedElements(const Object &O) {
 // Prints a one-line version of a value that isn't our main focus.
 // We interleave writes to OS and JOS, exploiting the lack of extra buffering.
 // This is OK as we own the implementation.
-// FIXME: once we have a "write custom serialized value" API, use it here.
-void abbreviate(const Value &V, OStream &JOS, raw_ostream &OS) {
+void abbreviate(const Value &V, OStream &JOS) {
   switch (V.kind()) {
   case Value::Array:
-    JOS.array([&] {
-      if (!V.getAsArray()->empty())
-        OS << " ... ";
-    });
+    JOS.rawValue(V.getAsArray()->empty() ? "[]" : "[ ... ]");
     break;
   case Value::Object:
-    JOS.object([&] {
-      if (!V.getAsObject()->empty())
-        OS << " ... ";
-    });
+    JOS.rawValue(V.getAsObject()->empty() ? "{}" : "{ ... }");
     break;
   case Value::String: {
     llvm::StringRef S = *V.getAsString();
@@ -284,19 +277,19 @@ void abbreviate(const Value &V, OStream &JOS, raw_ostream &OS) {
 
 // Prints a semi-expanded version of a value that is our main focus.
 // Array/Object entries are printed, but not recursively as they may be huge.
-void abbreviateChildren(const Value &V, OStream &JOS, raw_ostream &OS) {
+void abbreviateChildren(const Value &V, OStream &JOS) {
   switch (V.kind()) {
   case Value::Array:
     JOS.array([&] {
       for (const auto &I : *V.getAsArray())
-        abbreviate(I, JOS, OS);
+        abbreviate(I, JOS);
     });
     break;
   case Value::Object:
     JOS.object([&] {
       for (const auto *KV : sortedElements(*V.getAsObject())) {
         JOS.attributeBegin(KV->first);
-        abbreviate(KV->second, JOS, OS);
+        abbreviate(KV->second, JOS);
         JOS.attributeEnd();
       }
     });
@@ -322,7 +315,7 @@ void Path::Root::printErrorContext(const Value &R, raw_ostream &OS) const {
       std::string Comment = "error: ";
       Comment.append(ErrorMessage.data(), ErrorMessage.size());
       JOS.comment(Comment);
-      abbreviateChildren(V, JOS, OS);
+      abbreviateChildren(V, JOS);
     };
     if (Path.empty()) // We reached our target.
       return HighlightCurrent();
@@ -339,7 +332,7 @@ void Path::Root::printErrorContext(const Value &R, raw_ostream &OS) const {
           if (FieldName.equals(KV->first))
             Recurse(KV->second, Path.drop_back(), Recurse);
           else
-            abbreviate(KV->second, JOS, OS);
+            abbreviate(KV->second, JOS);
           JOS.attributeEnd();
         }
       });
@@ -354,7 +347,7 @@ void Path::Root::printErrorContext(const Value &R, raw_ostream &OS) const {
           if (Current++ == S.index())
             Recurse(V, Path.drop_back(), Recurse);
           else
-            abbreviate(V, JOS, OS);
+            abbreviate(V, JOS);
         }
       });
     }
@@ -893,6 +886,18 @@ void llvm::json::OStream::attributeEnd() {
   assert(Stack.back().Ctx == Object);
 }
 
+raw_ostream &llvm::json::OStream::rawValueBegin() {
+  valueBegin();
+  Stack.emplace_back();
+  Stack.back().Ctx = RawValue;
+  return OS;
+}
+
+void llvm::json::OStream::rawValueEnd() {
+  assert(Stack.back().Ctx == RawValue);
+  Stack.pop_back();
+}
+
 } // namespace json
 } // namespace llvm