Bug 1839396 part 9 - Add Sprinter::releaseJS. r=mgaudet

Sprinter::releaseJS centralize a mechanism which used in many places across the
JS engine, and replaces it with a single function call as well as democratising
the proper handling of UTF8 which might be added to Sprinter allocated strings.

Differential Revision: https://phabricator.services.mozilla.com/D181494

js/public/Printer.h

@@ -117,6 +117,7 @@ class JS_PUBLIC_API Sprinter final : public GenericPrinter {
     return base;
   }
   JS::UniqueChars release();
+  JSString* releaseJS(JSContext* cx);
 
   // Attempt to reserve len + 1 space (for a trailing nullptr byte). If the
   // attempt succeeds, return a pointer to the start of that space and adjust

js/src/builtin/TestingFunctions.cpp

@@ -1807,7 +1807,7 @@ static bool DisassembleNative(JSContext* cx, unsigned argc, Value* vp) {
     fclose(f);
   }
 
-  JSString* str = JS_NewStringCopyZ(cx, sprinter.string());
+  JSString* str = sprinter.releaseJS(cx);
   if (!str) {
     return false;
   }
@@ -6971,11 +6971,7 @@ static bool GetStringRepresentation(JSContext* cx, unsigned argc, Value* vp) {
   }
   str->dumpRepresentation(out, 0);
 
-  if (out.hadOutOfMemory()) {
-    return false;
-  }
-
-  JSString* rep = JS_NewStringCopyN(cx, out.string(), out.getOffset());
+  JSString* rep = out.releaseJS(cx);
   if (!rep) {
     return false;
   }

js/src/shell/js.cpp

@@ -3407,7 +3407,7 @@ static bool Notes(JSContext* cx, unsigned argc, Value* vp) {
     }
   }
 
-  JSString* str = JS_NewStringCopyZ(cx, sprinter.string());
+  JSString* str = sprinter.releaseJS(cx);
   if (!str) {
     return false;
   }
@@ -3502,16 +3502,7 @@ static bool DisassembleToString(JSContext* cx, unsigned argc, Value* vp) {
     return false;
   }
 
-  const char* chars = sprinter.string();
-  size_t len;
-  JS::UniqueTwoByteChars buf(
-      JS::LossyUTF8CharsToNewTwoByteCharsZ(
-          cx, JS::UTF8Chars(chars, strlen(chars)), &len, js::MallocArena)
-          .get());
-  if (!buf) {
-    return false;
-  }
-  JSString* str = JS_NewUCStringCopyN(cx, buf.get(), len);
+  JSString* str = sprinter.releaseJS(cx);
   if (!str) {
     return false;
   }

js/src/vm/BytecodeUtil.cpp

@@ -2798,11 +2798,7 @@ JSString* JS::GetPCCountScriptSummary(JSContext* cx, size_t index) {
 
   json.endObject();
 
-  if (sp.hadOutOfMemory()) {
-    return nullptr;
-  }
-
-  return NewStringCopyZ<CanGC>(cx, sp.string());
+  return sp.releaseJS(cx);
 }
 
 static bool GetPCCountJSON(JSContext* cx, const ScriptAndCounts& sac,
@@ -2962,11 +2958,7 @@ JSString* JS::GetPCCountScriptContents(JSContext* cx, size_t index) {
     }
   }
 
-  if (sp.hadOutOfMemory()) {
-    return nullptr;
-  }
-
-  return NewStringCopyZ<CanGC>(cx, sp.string());
+  return sp.releaseJS(cx);
 }
 
 struct CollectedScripts {

js/src/vm/Printer.cpp

@@ -141,11 +141,12 @@ void Sprinter::checkInvariants() const {
 }
 
 UniqueChars Sprinter::release() {
-  checkInvariants();
   if (hadOOM_) {
+    forwardOutOfMemory();
     return nullptr;
   }
 
+  checkInvariants();
   char* str = base;
   base = nullptr;
   offset = size = 0;
@@ -155,6 +156,60 @@ UniqueChars Sprinter::release() {
   return UniqueChars(str);
 }
 
+JSString* Sprinter::releaseJS(JSContext* cx) {
+  if (hadOOM_) {
+    MOZ_ASSERT_IF(maybeCx, maybeCx == cx);
+    forwardOutOfMemory();
+    return nullptr;
+  }
+
+  checkInvariants();
+
+  // Extract Sprinter data.
+  size_t len = length();
+  UniqueChars str(base);
+
+  // Reset Sprinter.
+  base = nullptr;
+  offset = 0;
+  size = 0;
+#ifdef DEBUG
+  initialized = false;
+#endif
+
+  // Convert extracted data to a JSString, reusing the current buffer whenever
+  // possible.
+  JS::UTF8Chars utf8(str.get(), len);
+  JS::SmallestEncoding encoding = JS::FindSmallestEncoding(utf8);
+  if (encoding == JS::SmallestEncoding::ASCII) {
+    UniqueLatin1Chars latin1(reinterpret_cast<JS::Latin1Char*>(str.release()));
+    return js::NewString<js::CanGC>(cx, std::move(latin1), len);
+  }
+
+  size_t length;
+  if (encoding == JS::SmallestEncoding::Latin1) {
+    UniqueLatin1Chars latin1(
+        UTF8CharsToNewLatin1CharsZ(cx, utf8, &length, js::StringBufferArena)
+            .get());
+    if (!latin1) {
+      return nullptr;
+    }
+
+    return js::NewString<js::CanGC>(cx, std::move(latin1), length);
+  }
+
+  MOZ_ASSERT(encoding == JS::SmallestEncoding::UTF16);
+
+  UniqueTwoByteChars utf16(
+      UTF8CharsToNewTwoByteCharsZ(cx, utf8, &length, js::StringBufferArena)
+          .get());
+  if (!utf16) {
+    return nullptr;
+  }
+
+  return js::NewString<js::CanGC>(cx, std::move(utf16), length);
+}
+
 char* Sprinter::reserve(size_t len) {
   InvariantChecker ic(this);