Bug 1839396 part 7 - Update Sprinter::put to remove stringAt usage. r=mgaudet

Differential Revision: https://phabricator.services.mozilla.com/D181492

js/public/Printer.h

@@ -118,8 +118,6 @@ class JS_PUBLIC_API Sprinter final : public GenericPrinter {
   }
   JS::UniqueChars release();
 
-  // Returns the string at offset |off|.
-  char* stringAt(ptrdiff_t off) const;
   // Returns the char at offset |off|.
   char& operator[](size_t off);
 

js/src/vm/Printer.cpp

@@ -155,12 +155,6 @@ UniqueChars Sprinter::release() {
   return UniqueChars(str);
 }
 
-char* Sprinter::stringAt(ptrdiff_t off) const {
-  MOZ_ASSERT(!hadOutOfMemory());
-  MOZ_ASSERT(off >= 0 && (size_t)off < size);
-  return base + off;
-}
-
 char& Sprinter::operator[](size_t off) {
   MOZ_ASSERT(!hadOutOfMemory());
   MOZ_ASSERT(off < size);
@@ -192,12 +186,11 @@ bool Sprinter::put(const char* s, size_t len) {
     return false;
   }
 
-  /* s is within the buffer already */
+  // s is within the buffer already
   if (s >= oldBase && s < oldEnd) {
-    /* buffer was realloc'ed */
-    if (base != oldBase) {
-      s = stringAt(s - oldBase); /* this is where it lives now */
-    }
+    // Update the source pointer in case of a realloc-ation.
+    size_t index = s - oldBase;
+    s = &base[index];
     memmove(bp, s, len);
   } else {
     js_memcpy(bp, s, len);