Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 700 insertions, 0 deletions

diff --git a/js/public/CompileOptions.h b/js/public/CompileOptions.h
new file mode 100644
index 0000000000..99fc5235e5
--- /dev/null
+++ b/js/public/CompileOptions.h
@@ -0,0 +1,700 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * Options for JavaScript compilation.
+ *
+ * In the most common use case, a CompileOptions instance is allocated on the
+ * stack, and holds non-owning references to non-POD option values: strings,
+ * principals, objects, and so on.  The code declaring the instance guarantees
+ * that such option values will outlive the CompileOptions itself: objects are
+ * otherwise rooted, principals have had their reference counts bumped, and
+ * strings won't be freed until the CompileOptions goes out of scope.  In this
+ * situation, CompileOptions only refers to things others own, so it can be
+ * lightweight.
+ *
+ * In some cases, however, we need to hold compilation options with a
+ * non-stack-like lifetime.  For example, JS::CompileOffThread needs to save
+ * compilation options where a worker thread can find them, then return
+ * immediately.  The worker thread will come along at some later point, and use
+ * the options.
+ *
+ * The compiler itself just needs to be able to access a collection of options;
+ * it doesn't care who owns them, or what's keeping them alive.  It does its
+ * own addrefs/copies/tracing/etc.
+ *
+ * Furthermore, in some cases compile options are propagated from one entity to
+ * another (e.g. from a script to a function defined in that script).  This
+ * involves copying over some, but not all, of the options.
+ *
+ * So we have a class hierarchy that reflects these four use cases:
+ *
+ * - TransitiveCompileOptions is the common base class, representing options
+ *   that should get propagated from a script to functions defined in that
+ *   script.  This class is abstract and is only ever used as a subclass.
+ *
+ * - ReadOnlyCompileOptions is the only subclass of TransitiveCompileOptions,
+ *   representing a full set of compile options.  It can be used by code that
+ *   simply needs to access options set elsewhere, like the compiler.  This
+ *   class too is abstract and is only ever used as a subclass.
+ *
+ * - The usual CompileOptions class must be stack-allocated, and holds
+ *   non-owning references to the filename, element, and so on. It's derived
+ *   from ReadOnlyCompileOptions, so the compiler can use it.
+ *
+ * - OwningCompileOptions roots / copies / reference counts of all its values,
+ *   and unroots / frees / releases them when it is destructed. It too is
+ *   derived from ReadOnlyCompileOptions, so the compiler accepts it.
+ */
+
+#ifndef js_CompileOptions_h
+#define js_CompileOptions_h
+
+#include "mozilla/Assertions.h"       // MOZ_ASSERT
+#include "mozilla/MemoryReporting.h"  // mozilla::MallocSizeOf
+
+#include <stddef.h>  // size_t
+#include <stdint.h>  // uint8_t, uint32_t
+
+#include "jstypes.h"  // JS_PUBLIC_API
+
+#include "js/TypeDecls.h"  // JS::MutableHandle (fwd)
+
+namespace JS {
+
+enum class AsmJSOption : uint8_t {
+  Enabled,
+  DisabledByAsmJSPref,
+  DisabledByLinker,
+  DisabledByNoWasmCompiler,
+  DisabledByDebugger,
+};
+
+#define FOREACH_DELAZIFICATION_STRATEGY(_)                                     \
+  /* Do not delazify anything eagerly. */                                      \
+  _(OnDemandOnly)                                                              \
+                                                                               \
+  /*                                                                           \
+   * Compare the stencil produced by concurrent depth first delazification and \
+   * on-demand delazification. Any differences would crash SpiderMonkey with   \
+   * an assertion.                                                             \
+   */                                                                          \
+  _(CheckConcurrentWithOnDemand)                                               \
+                                                                               \
+  /*                                                                           \
+   * Delazifiy functions in a depth first traversal of the functions.          \
+   */                                                                          \
+  _(ConcurrentDepthFirst)                                                      \
+                                                                               \
+  /*                                                                           \
+   * Delazifiy functions strating with the largest function first.             \
+   */                                                                          \
+  _(ConcurrentLargeFirst)                                                      \
+                                                                               \
+  /*                                                                           \
+   * Parse everything eagerly, from the first parse.                           \
+   *                                                                           \
+   * NOTE: Either the Realm configuration or specialized VM operating modes    \
+   * may disallow syntax-parse altogether. These conditions are checked in the \
+   * CompileOptions constructor.                                               \
+   */                                                                          \
+  _(ParseEverythingEagerly)
+
+enum class DelazificationOption : uint8_t {
+#define _ENUM_ENTRY(Name) Name,
+  FOREACH_DELAZIFICATION_STRATEGY(_ENUM_ENTRY)
+#undef _ENUM_ENTRY
+};
+
+class JS_PUBLIC_API InstantiateOptions;
+class JS_PUBLIC_API DecodeOptions;
+
+/**
+ * The common base class for the CompileOptions hierarchy.
+ *
+ * Use this in code that needs to propagate compile options from one
+ * compilation unit to another.
+ */
+class JS_PUBLIC_API TransitiveCompileOptions {
+  friend class JS_PUBLIC_API DecodeOptions;
+
+ protected:
+  // non-POD options:
+
+  // UTF-8 encoded file name.
+  const char* filename_ = nullptr;
+
+  // UTF-8 encoded introducer file name.
+  const char* introducerFilename_ = nullptr;
+
+  const char16_t* sourceMapURL_ = nullptr;
+
+  // POD options:
+  // WARNING: When adding new fields, don't forget to add them to
+  //          copyPODTransitiveOptions.
+
+  /**
+   * The Web Platform allows scripts to be loaded from arbitrary cross-origin
+   * sources. This allows an attack by which a malicious website loads a
+   * sensitive file (say, a bank statement) cross-origin (using the user's
+   * cookies), and sniffs the generated syntax errors (via a window.onerror
+   * handler) for juicy morsels of its contents.
+   *
+   * To counter this attack, HTML5 specifies that script errors should be
+   * sanitized ("muted") when the script is not same-origin with the global
+   * for which it is loaded. Callers should set this flag for cross-origin
+   * scripts, and it will be propagated appropriately to child scripts and
+   * passed back in JSErrorReports.
+   */
+  bool mutedErrors_ = false;
+
+  // Either the Realm configuration or the compile request may force
+  // strict-mode.
+  bool forceStrictMode_ = false;
+
+  // The Realm of this script is configured to resist fingerprinting.
+  bool shouldResistFingerprinting_ = false;
+
+  // The context has specified that source pragmas should be parsed.
+  bool sourcePragmas_ = true;
+
+  // Flag used to bypass the filename validation callback.
+  // See also SetFilenameValidationCallback.
+  bool skipFilenameValidation_ = false;
+
+  bool hideScriptFromDebugger_ = false;
+
+  // If set, this script will be hidden from the debugger. The requirement
+  // is that once compilation is finished, a call to UpdateDebugMetadata will
+  // be made, which will update the SSO with the appropiate debug metadata,
+  // and expose the script to the debugger (if hideScriptFromDebugger_ isn't
+  // set)
+  bool deferDebugMetadata_ = false;
+
+  // Off-thread delazification strategy is used to tell off-thread tasks how the
+  // delazification should be performed. Multiple strategies are available in
+  // order to test different approaches to the concurrent delazification.
+  DelazificationOption eagerDelazificationStrategy_ =
+      DelazificationOption::OnDemandOnly;
+
+  friend class JS_PUBLIC_API InstantiateOptions;
+
+ public:
+  bool selfHostingMode = false;
+  AsmJSOption asmJSOption = AsmJSOption::DisabledByAsmJSPref;
+  bool throwOnAsmJSValidationFailureOption = false;
+  bool forceAsync = false;
+  bool discardSource = false;
+  bool sourceIsLazy = false;
+  bool allowHTMLComments = true;
+  bool nonSyntacticScope = false;
+
+  // Top-level await is enabled by default but is not supported for chrome
+  // modules loaded with ChromeUtils.importModule.
+  bool topLevelAwait = true;
+
+  bool importAssertions = false;
+
+  // When decoding from XDR into a Stencil, directly reference data in the
+  // buffer (where possible) instead of copying it. This is an optional
+  // performance optimization, and may also reduce memory if the buffer is going
+  // remain alive anyways.
+  //
+  // NOTE: The XDR buffer must remain alive as long as the Stencil does. Special
+  //       care must be taken that there are no addition shared references to
+  //       the Stencil.
+  //
+  // NOTE: Instantiated GC things may still outlive the buffer as long as the
+  //       Stencil was cleaned up. This is covers a typical case where a decoded
+  //       Stencil is instantiated once and then thrown away.
+  bool borrowBuffer = false;
+
+  // Similar to `borrowBuffer`, but additionally the JSRuntime may directly
+  // reference data in the buffer for JS bytecode. The `borrowBuffer` flag must
+  // be set if this is set. This can be a memory optimization in multi-process
+  // architectures where a (read-only) XDR buffer is mapped into multiple
+  // processes.
+  //
+  // NOTE: When using this mode, the XDR buffer must live until JS_Shutdown is
+  // called. There is currently no mechanism to release the data sooner.
+  bool usePinnedBytecode = false;
+
+  // When performing off-thread task that generates JS::Stencil as output,
+  // allocate JS::InstantiationStorage off main thread to reduce the
+  // main thread allocation.
+  bool allocateInstantiationStorage = false;
+
+  // De-optimize ES module's top-level `var`s, in order to define all of them
+  // on the ModuleEnvironmentObject, instead of local slot.
+  //
+  // This is used for providing all global variables in Cu.import return value
+  // (see bug 1766761 for more details), and this is temporary solution until
+  // ESM-ification finishes.
+  //
+  // WARNING: This option will eventually be removed.
+  bool deoptimizeModuleGlobalVars = false;
+
+  /**
+   * |introductionType| is a statically allocated C string. See JSScript.h
+   * for more information.
+   */
+  const char* introductionType = nullptr;
+
+  unsigned introductionLineno = 0;
+  uint32_t introductionOffset = 0;
+  bool hasIntroductionInfo = false;
+
+  // WARNING: When adding new fields, don't forget to add them to
+  //          copyPODTransitiveOptions.
+
+ protected:
+  TransitiveCompileOptions() = default;
+
+  // Set all POD options (those not requiring reference counts, copies,
+  // rooting, or other hand-holding) to their values in |rhs|.
+  void copyPODTransitiveOptions(const TransitiveCompileOptions& rhs);
+
+  bool isEagerDelazificationEqualTo(DelazificationOption val) const {
+    return eagerDelazificationStrategy() == val;
+  }
+
+  template <DelazificationOption... Values>
+  bool eagerDelazificationIsOneOf() const {
+    return (isEagerDelazificationEqualTo(Values) || ...);
+  }
+
+ public:
+  // Read-only accessors for non-POD options. The proper way to set these
+  // depends on the derived type.
+  bool mutedErrors() const { return mutedErrors_; }
+  bool shouldResistFingerprinting() const {
+    return shouldResistFingerprinting_;
+  }
+  bool forceFullParse() const {
+    return eagerDelazificationIsOneOf<
+        DelazificationOption::ParseEverythingEagerly>();
+  }
+  bool forceStrictMode() const { return forceStrictMode_; }
+  bool consumeDelazificationCache() const {
+    return eagerDelazificationIsOneOf<
+        DelazificationOption::ConcurrentDepthFirst,
+        DelazificationOption::ConcurrentLargeFirst>();
+  }
+  bool populateDelazificationCache() const {
+    return eagerDelazificationIsOneOf<
+        DelazificationOption::CheckConcurrentWithOnDemand,
+        DelazificationOption::ConcurrentDepthFirst,
+        DelazificationOption::ConcurrentLargeFirst>();
+  }
+  bool waitForDelazificationCache() const {
+    return eagerDelazificationIsOneOf<
+        DelazificationOption::CheckConcurrentWithOnDemand>();
+  }
+  bool checkDelazificationCache() const {
+    return eagerDelazificationIsOneOf<
+        DelazificationOption::CheckConcurrentWithOnDemand>();
+  }
+  DelazificationOption eagerDelazificationStrategy() const {
+    return eagerDelazificationStrategy_;
+  }
+  bool sourcePragmas() const { return sourcePragmas_; }
+  const char* filename() const { return filename_; }
+  const char* introducerFilename() const { return introducerFilename_; }
+  const char16_t* sourceMapURL() const { return sourceMapURL_; }
+
+  TransitiveCompileOptions(const TransitiveCompileOptions&) = delete;
+  TransitiveCompileOptions& operator=(const TransitiveCompileOptions&) = delete;
+
+#if defined(DEBUG) || defined(JS_JITSPEW)
+  template <typename Printer>
+  void dumpWith(Printer& print) const {
+#  define PrintFields_(Name) print(#Name, Name)
+    PrintFields_(filename_);
+    PrintFields_(introducerFilename_);
+    PrintFields_(sourceMapURL_);
+    PrintFields_(mutedErrors_);
+    PrintFields_(forceStrictMode_);
+    PrintFields_(shouldResistFingerprinting_);
+    PrintFields_(sourcePragmas_);
+    PrintFields_(skipFilenameValidation_);
+    PrintFields_(hideScriptFromDebugger_);
+    PrintFields_(deferDebugMetadata_);
+    PrintFields_(eagerDelazificationStrategy_);
+    PrintFields_(selfHostingMode);
+    PrintFields_(asmJSOption);
+    PrintFields_(throwOnAsmJSValidationFailureOption);
+    PrintFields_(forceAsync);
+    PrintFields_(discardSource);
+    PrintFields_(sourceIsLazy);
+    PrintFields_(allowHTMLComments);
+    PrintFields_(nonSyntacticScope);
+    PrintFields_(topLevelAwait);
+    PrintFields_(importAssertions);
+    PrintFields_(borrowBuffer);
+    PrintFields_(usePinnedBytecode);
+    PrintFields_(allocateInstantiationStorage);
+    PrintFields_(deoptimizeModuleGlobalVars);
+    PrintFields_(introductionType);
+    PrintFields_(introductionLineno);
+    PrintFields_(introductionOffset);
+    PrintFields_(hasIntroductionInfo);
+#  undef PrintFields_
+  }
+#endif  // defined(DEBUG) || defined(JS_JITSPEW)
+};
+
+/**
+ * The class representing a full set of compile options.
+ *
+ * Use this in code that only needs to access compilation options created
+ * elsewhere, like the compiler.  Don't instantiate this class (the constructor
+ * is protected anyway); instead, create instances only of the derived classes:
+ * CompileOptions and OwningCompileOptions.
+ */
+class JS_PUBLIC_API ReadOnlyCompileOptions : public TransitiveCompileOptions {
+ public:
+  // POD options.
+  unsigned lineno = 1;
+  unsigned column = 0;
+
+  // The offset within the ScriptSource's full uncompressed text of the first
+  // character we're presenting for compilation with this CompileOptions.
+  //
+  // When we compile a lazy script, we pass the compiler only the substring of
+  // the source the lazy function occupies. With chunked decompression, we may
+  // not even have the complete uncompressed source present in memory. But parse
+  // node positions are offsets within the ScriptSource's full text, and
+  // BaseScript indicate their substring of the full source by its starting and
+  // ending offsets within the full text. This scriptSourceOffset field lets the
+  // frontend convert between these offsets and offsets within the substring
+  // presented for compilation.
+  unsigned scriptSourceOffset = 0;
+
+  // These only apply to non-function scripts.
+  bool isRunOnce = false;
+  bool noScriptRval = false;
+
+ protected:
+  ReadOnlyCompileOptions() = default;
+
+  void copyPODNonTransitiveOptions(const ReadOnlyCompileOptions& rhs);
+
+  ReadOnlyCompileOptions(const ReadOnlyCompileOptions&) = delete;
+  ReadOnlyCompileOptions& operator=(const ReadOnlyCompileOptions&) = delete;
+
+ public:
+#if defined(DEBUG) || defined(JS_JITSPEW)
+  template <typename Printer>
+  void dumpWith(Printer& print) const {
+    this->TransitiveCompileOptions::dumpWith(print);
+#  define PrintFields_(Name) print(#Name, Name)
+    PrintFields_(lineno);
+    PrintFields_(column);
+    PrintFields_(scriptSourceOffset);
+    PrintFields_(isRunOnce);
+    PrintFields_(noScriptRval);
+#  undef PrintFields_
+  }
+#endif  // defined(DEBUG) || defined(JS_JITSPEW)
+};
+
+/**
+ * Compilation options, with dynamic lifetime. An instance of this type
+ * makes a copy of / holds / roots all dynamically allocated resources
+ * (principals; elements; strings) that it refers to. Its destructor frees
+ * / drops / unroots them. This is heavier than CompileOptions, below, but
+ * unlike CompileOptions, it can outlive any given stack frame.
+ *
+ * Note that this *roots* any JS values it refers to - they're live
+ * unconditionally. Thus, instances of this type can't be owned, directly
+ * or indirectly, by a JavaScript object: if any value that this roots ever
+ * comes to refer to the object that owns this, then the whole cycle, and
+ * anything else it entrains, will never be freed.
+ */
+class JS_PUBLIC_API OwningCompileOptions final : public ReadOnlyCompileOptions {
+ public:
+  // A minimal constructor, for use with OwningCompileOptions::copy.
+  explicit OwningCompileOptions(JSContext* cx);
+  ~OwningCompileOptions();
+
+  /** Set this to a copy of |rhs|.  Return false on OOM. */
+  bool copy(JSContext* cx, const ReadOnlyCompileOptions& rhs);
+
+  size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
+
+  OwningCompileOptions& setIsRunOnce(bool once) {
+    isRunOnce = once;
+    return *this;
+  }
+
+  OwningCompileOptions& setForceStrictMode() {
+    forceStrictMode_ = true;
+    return *this;
+  }
+
+  OwningCompileOptions& setModule() {
+    // ES6 10.2.1 Module code is always strict mode code.
+    setForceStrictMode();
+    setIsRunOnce(true);
+    allowHTMLComments = false;
+    return *this;
+  }
+
+ private:
+  void release();
+
+  OwningCompileOptions(const OwningCompileOptions&) = delete;
+  OwningCompileOptions& operator=(const OwningCompileOptions&) = delete;
+};
+
+/**
+ * Compilation options stored on the stack. An instance of this type
+ * simply holds references to dynamically allocated resources (element;
+ * filename; source map URL) that are owned by something else. If you
+ * create an instance of this type, it's up to you to guarantee that
+ * everything you store in it will outlive it.
+ */
+class MOZ_STACK_CLASS JS_PUBLIC_API CompileOptions final
+    : public ReadOnlyCompileOptions {
+ public:
+  // Default options determined using the JSContext.
+  explicit CompileOptions(JSContext* cx);
+
+  // Copy both the transitive and the non-transitive options from another
+  // options object.
+  CompileOptions(JSContext* cx, const ReadOnlyCompileOptions& rhs)
+      : ReadOnlyCompileOptions() {
+    copyPODNonTransitiveOptions(rhs);
+    copyPODTransitiveOptions(rhs);
+
+    filename_ = rhs.filename();
+    introducerFilename_ = rhs.introducerFilename();
+    sourceMapURL_ = rhs.sourceMapURL();
+  }
+
+  // Construct CompileOptions for FrontendContext-APIs.
+  struct ForFrontendContext {};
+  explicit CompileOptions(const ForFrontendContext&)
+      : ReadOnlyCompileOptions() {}
+
+  CompileOptions& setFile(const char* f) {
+    filename_ = f;
+    return *this;
+  }
+
+  CompileOptions& setLine(unsigned l) {
+    lineno = l;
+    return *this;
+  }
+
+  CompileOptions& setFileAndLine(const char* f, unsigned l) {
+    filename_ = f;
+    lineno = l;
+    return *this;
+  }
+
+  CompileOptions& setSourceMapURL(const char16_t* s) {
+    sourceMapURL_ = s;
+    return *this;
+  }
+
+  CompileOptions& setMutedErrors(bool mute) {
+    mutedErrors_ = mute;
+    return *this;
+  }
+
+  CompileOptions& setColumn(unsigned c) {
+    column = c;
+    return *this;
+  }
+
+  CompileOptions& setScriptSourceOffset(unsigned o) {
+    scriptSourceOffset = o;
+    return *this;
+  }
+
+  CompileOptions& setIsRunOnce(bool once) {
+    isRunOnce = once;
+    return *this;
+  }
+
+  CompileOptions& setNoScriptRval(bool nsr) {
+    noScriptRval = nsr;
+    return *this;
+  }
+
+  CompileOptions& setSkipFilenameValidation(bool b) {
+    skipFilenameValidation_ = b;
+    return *this;
+  }
+
+  CompileOptions& setSelfHostingMode(bool shm) {
+    selfHostingMode = shm;
+    return *this;
+  }
+
+  CompileOptions& setSourceIsLazy(bool l) {
+    sourceIsLazy = l;
+    return *this;
+  }
+
+  CompileOptions& setNonSyntacticScope(bool n) {
+    nonSyntacticScope = n;
+    return *this;
+  }
+
+  CompileOptions& setIntroductionType(const char* t) {
+    introductionType = t;
+    return *this;
+  }
+
+  CompileOptions& setDeferDebugMetadata(bool v = true) {
+    deferDebugMetadata_ = v;
+    return *this;
+  }
+
+  CompileOptions& setHideScriptFromDebugger(bool v = true) {
+    hideScriptFromDebugger_ = v;
+    return *this;
+  }
+
+  CompileOptions& setIntroductionInfo(const char* introducerFn,
+                                      const char* intro, unsigned line,
+                                      uint32_t offset) {
+    introducerFilename_ = introducerFn;
+    introductionType = intro;
+    introductionLineno = line;
+    introductionOffset = offset;
+    hasIntroductionInfo = true;
+    return *this;
+  }
+
+  // Set introduction information according to any currently executing script.
+  CompileOptions& setIntroductionInfoToCaller(
+      JSContext* cx, const char* introductionType,
+      JS::MutableHandle<JSScript*> introductionScript);
+
+  CompileOptions& setDiscardSource() {
+    discardSource = true;
+    return *this;
+  }
+
+  CompileOptions& setForceFullParse() {
+    eagerDelazificationStrategy_ = DelazificationOption::ParseEverythingEagerly;
+    return *this;
+  }
+
+  CompileOptions& setEagerDelazificationStrategy(
+      DelazificationOption strategy) {
+    // forceFullParse is at the moment considered as a non-overridable strategy.
+    MOZ_RELEASE_ASSERT(eagerDelazificationStrategy_ !=
+                           DelazificationOption::ParseEverythingEagerly ||
+                       strategy ==
+                           DelazificationOption::ParseEverythingEagerly);
+    eagerDelazificationStrategy_ = strategy;
+    return *this;
+  }
+
+  CompileOptions& setForceStrictMode() {
+    forceStrictMode_ = true;
+    return *this;
+  }
+
+  CompileOptions& setModule() {
+    // ES6 10.2.1 Module code is always strict mode code.
+    setForceStrictMode();
+    setIsRunOnce(true);
+    allowHTMLComments = false;
+    return *this;
+  }
+
+  CompileOptions(const CompileOptions& rhs) = delete;
+  CompileOptions& operator=(const CompileOptions& rhs) = delete;
+};
+
+/**
+ * Subset of CompileOptions fields used while instantiating Stencils.
+ */
+class JS_PUBLIC_API InstantiateOptions {
+ public:
+  bool skipFilenameValidation = false;
+  bool hideScriptFromDebugger = false;
+  bool deferDebugMetadata = false;
+
+  InstantiateOptions() = default;
+
+  explicit InstantiateOptions(const ReadOnlyCompileOptions& options)
+      : skipFilenameValidation(options.skipFilenameValidation_),
+        hideScriptFromDebugger(options.hideScriptFromDebugger_),
+        deferDebugMetadata(options.deferDebugMetadata_) {}
+
+  void copyTo(CompileOptions& options) const {
+    options.skipFilenameValidation_ = skipFilenameValidation;
+    options.hideScriptFromDebugger_ = hideScriptFromDebugger;
+    options.deferDebugMetadata_ = deferDebugMetadata;
+  }
+
+  bool hideFromNewScriptInitial() const {
+    return deferDebugMetadata || hideScriptFromDebugger;
+  }
+
+#ifdef DEBUG
+  // Assert that all fields have default value.
+  //
+  // This can be used when instantiation is performed as separate step than
+  // compile-to-stencil, and CompileOptions isn't available there.
+  void assertDefault() const {
+    MOZ_ASSERT(skipFilenameValidation == false);
+    MOZ_ASSERT(hideScriptFromDebugger == false);
+    MOZ_ASSERT(deferDebugMetadata == false);
+  }
+#endif
+};
+
+/**
+ * Subset of CompileOptions fields used while decoding Stencils.
+ */
+class JS_PUBLIC_API DecodeOptions {
+ public:
+  bool borrowBuffer = false;
+  bool usePinnedBytecode = false;
+  bool allocateInstantiationStorage = false;
+  bool forceAsync = false;
+
+  const char* introducerFilename = nullptr;
+
+  // See `TransitiveCompileOptions::introductionType` field for details.
+  const char* introductionType = nullptr;
+
+  unsigned introductionLineno = 0;
+  uint32_t introductionOffset = 0;
+
+  DecodeOptions() = default;
+
+  explicit DecodeOptions(const ReadOnlyCompileOptions& options)
+      : borrowBuffer(options.borrowBuffer),
+        usePinnedBytecode(options.usePinnedBytecode),
+        allocateInstantiationStorage(options.allocateInstantiationStorage),
+        forceAsync(options.forceAsync),
+        introducerFilename(options.introducerFilename()),
+        introductionType(options.introductionType),
+        introductionLineno(options.introductionLineno),
+        introductionOffset(options.introductionOffset) {}
+
+  void copyTo(CompileOptions& options) const {
+    options.borrowBuffer = borrowBuffer;
+    options.usePinnedBytecode = usePinnedBytecode;
+    options.allocateInstantiationStorage = allocateInstantiationStorage;
+    options.forceAsync = forceAsync;
+    options.introducerFilename_ = introducerFilename;
+    options.introductionType = introductionType;
+    options.introductionLineno = introductionLineno;
+    options.introductionOffset = introductionOffset;
+  }
+};
+
+}  // namespace JS
+
+#endif /* js_CompileOptions_h */