Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

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

1 files changed, 803 insertions, 0 deletions

diff --git a/devtools/shared/webconsole/js-property-provider.js b/devtools/shared/webconsole/js-property-provider.js
new file mode 100644
index 0000000000..c261fed40d
--- /dev/null
+++ b/devtools/shared/webconsole/js-property-provider.js
@@ -0,0 +1,803 @@
+/* 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/. */
+
+"use strict";
+
+const DevToolsUtils = require("resource://devtools/shared/DevToolsUtils.js");
+
+const {
+  evalWithDebugger,
+} = require("resource://devtools/server/actors/webconsole/eval-with-debugger.js");
+
+if (!isWorker) {
+  loader.lazyRequireGetter(
+    this,
+    "getSyntaxTrees",
+    "resource://devtools/shared/webconsole/parser-helper.js",
+    true
+  );
+}
+const lazy = {};
+ChromeUtils.defineESModuleGetters(lazy, {
+  Reflect: "resource://gre/modules/reflect.sys.mjs",
+});
+loader.lazyRequireGetter(
+  this,
+  [
+    "analyzeInputString",
+    "shouldInputBeAutocompleted",
+    "shouldInputBeEagerlyEvaluated",
+  ],
+  "resource://devtools/shared/webconsole/analyze-input-string.js",
+  true
+);
+
+// Provide an easy way to bail out of even attempting an autocompletion
+// if an object has way too many properties. Protects against large objects
+// with numeric values that wouldn't be tallied towards MAX_AUTOCOMPLETIONS.
+const MAX_AUTOCOMPLETE_ATTEMPTS = (exports.MAX_AUTOCOMPLETE_ATTEMPTS = 100000);
+// Prevent iterating over too many properties during autocomplete suggestions.
+const MAX_AUTOCOMPLETIONS = (exports.MAX_AUTOCOMPLETIONS = 1500);
+
+/**
+ * Provides a list of properties, that are possible matches based on the passed
+ * Debugger.Environment/Debugger.Object and inputValue.
+ *
+ * @param {Object} An object of the following shape:
+ * - {Object} dbgObject
+ *        When the debugger is not paused this Debugger.Object wraps
+ *        the scope for autocompletion.
+ *        It is null if the debugger is paused.
+ * - {Object} environment
+ *        When the debugger is paused this Debugger.Environment is the
+ *        scope for autocompletion.
+ *        It is null if the debugger is not paused.
+ * - {String} inputValue
+ *        Value that should be completed.
+ * - {Number} cursor (defaults to inputValue.length).
+ *        Optional offset in the input where the cursor is located. If this is
+ *        omitted then the cursor is assumed to be at the end of the input
+ *        value.
+ * - {Array} authorizedEvaluations (defaults to []).
+ *        Optional array containing all the different properties access that the engine
+ *        can execute in order to retrieve its result's properties.
+ *        ⚠️ This should be set to true *ONLY* on user action as it may cause side-effects
+ *        in the content page ⚠️
+ * - {WebconsoleActor} webconsoleActor
+ *        A reference to a webconsole actor which we can use to retrieve the last
+ *        evaluation result or create a debuggee value.
+ * - {String}: selectedNodeActor
+ *        The actor id of the selected node in the inspector.
+ * - {Array<string>}: expressionVars
+ *        Optional array containing variable defined in the expression. Those variables
+ *        are extracted from CodeMirror state.
+ * @returns null or object
+ *          If the inputValue is an unsafe getter and invokeUnsafeGetter is false, the
+ *          following form is returned:
+ *
+ *          {
+ *            isUnsafeGetter: true,
+ *            getterPath: {Array<String>} An array of the property chain leading to the
+ *                        getter. Example: ["x", "myGetter"]
+ *          }
+ *
+ *          If no completion valued could be computed, and the input is not an unsafe
+ *          getter, null is returned.
+ *
+ *          Otherwise an object with the following form is returned:
+ *            {
+ *              matches: Set<string>
+ *              matchProp: Last part of the inputValue that was used to find
+ *                         the matches-strings.
+ *              isElementAccess: Boolean set to true if the evaluation is an element
+ *                               access (e.g. `window["addEvent`).
+ *            }
+ */
+// eslint-disable-next-line complexity
+function JSPropertyProvider({
+  dbgObject,
+  environment,
+  frameActorId,
+  inputValue,
+  cursor,
+  authorizedEvaluations = [],
+  webconsoleActor,
+  selectedNodeActor,
+  expressionVars = [],
+}) {
+  if (cursor === undefined) {
+    cursor = inputValue.length;
+  }
+
+  inputValue = inputValue.substring(0, cursor);
+
+  // Analyse the inputValue and find the beginning of the last part that
+  // should be completed.
+  const inputAnalysis = analyzeInputString(inputValue);
+
+  if (!shouldInputBeAutocompleted(inputAnalysis)) {
+    return null;
+  }
+
+  let {
+    lastStatement,
+    isElementAccess,
+    mainExpression,
+    matchProp,
+    isPropertyAccess,
+  } = inputAnalysis;
+
+  // Eagerly evaluate the main expression and return the results properties.
+  // e.g. `obj.func().a` will evaluate `obj.func()` and return properties matching `a`.
+  // NOTE: this is only useful when the input has a property access.
+  if (webconsoleActor && shouldInputBeEagerlyEvaluated(inputAnalysis)) {
+    const eagerResponse = evalWithDebugger(
+      mainExpression,
+      { eager: true, selectedNodeActor, frameActor: frameActorId },
+      webconsoleActor
+    );
+
+    const ret = eagerResponse?.result?.return;
+
+    // Only send matches if eager evaluation returned something meaningful
+    if (ret && ret !== undefined) {
+      const matches =
+        typeof ret != "object"
+          ? getMatchedProps(ret, matchProp)
+          : getMatchedPropsInDbgObject(ret, matchProp);
+
+      return prepareReturnedObject({
+        matches,
+        search: matchProp,
+        isElementAccess,
+      });
+    }
+  }
+
+  // AST representation of the expression before the last access char (`.` or `[`).
+  let astExpression;
+  const startQuoteRegex = /^('|"|`)/;
+  const env = environment || dbgObject.asEnvironment();
+
+  // Catch literals like [1,2,3] or "foo" and return the matches from
+  // their prototypes.
+  // Don't run this is a worker, migrating to acorn should allow this
+  // to run in a worker - Bug 1217198.
+  if (!isWorker && isPropertyAccess) {
+    const syntaxTrees = getSyntaxTrees(mainExpression);
+    const lastTree = syntaxTrees[syntaxTrees.length - 1];
+    const lastBody = lastTree?.body[lastTree.body.length - 1];
+
+    // Finding the last expression since we've sliced up until the dot.
+    // If there were parse errors this won't exist.
+    if (lastBody) {
+      if (!lastBody.expression) {
+        return null;
+      }
+
+      astExpression = lastBody.expression;
+      let matchingObject;
+
+      if (astExpression.type === "ArrayExpression") {
+        matchingObject = getContentPrototypeObject(env, "Array");
+      } else if (
+        astExpression.type === "Literal" &&
+        typeof astExpression.value === "string"
+      ) {
+        matchingObject = getContentPrototypeObject(env, "String");
+      } else if (
+        astExpression.type === "Literal" &&
+        Number.isFinite(astExpression.value)
+      ) {
+        // The parser rightfuly indicates that we have a number in some cases (e.g. `1.`),
+        // but we don't want to return Number proto properties in that case since
+        // the result would be invalid (i.e. `1.toFixed()` throws).
+        // So if the expression value is an integer, it should not end with `{Number}.`
+        // (but the following are fine: `1..`, `(1.).`).
+        if (
+          !Number.isInteger(astExpression.value) ||
+          /\d[^\.]{0}\.$/.test(lastStatement) === false
+        ) {
+          matchingObject = getContentPrototypeObject(env, "Number");
+        } else {
+          return null;
+        }
+      }
+
+      if (matchingObject) {
+        let search = matchProp;
+
+        let elementAccessQuote;
+        if (isElementAccess && startQuoteRegex.test(matchProp)) {
+          elementAccessQuote = matchProp[0];
+          search = matchProp.replace(startQuoteRegex, "");
+        }
+
+        let props = getMatchedPropsInDbgObject(matchingObject, search);
+
+        if (isElementAccess) {
+          props = wrapMatchesInQuotes(props, elementAccessQuote);
+        }
+
+        return {
+          isElementAccess,
+          matchProp,
+          matches: props,
+        };
+      }
+    }
+  }
+
+  // We are completing a variable / a property lookup.
+  let properties = [];
+
+  if (astExpression) {
+    if (isPropertyAccess) {
+      properties = getPropertiesFromAstExpression(astExpression);
+
+      if (properties === null) {
+        return null;
+      }
+    }
+  } else {
+    properties = lastStatement.split(".");
+    if (isElementAccess) {
+      const lastPart = properties[properties.length - 1];
+      const openBracketIndex = lastPart.lastIndexOf("[");
+      matchProp = lastPart.substr(openBracketIndex + 1);
+      properties[properties.length - 1] = lastPart.substring(
+        0,
+        openBracketIndex
+      );
+    } else {
+      matchProp = properties.pop().trimLeft();
+    }
+  }
+
+  let search = matchProp;
+  let elementAccessQuote;
+  if (isElementAccess && startQuoteRegex.test(search)) {
+    elementAccessQuote = search[0];
+    search = search.replace(startQuoteRegex, "");
+  }
+
+  let obj = dbgObject;
+  if (properties.length === 0) {
+    const environmentProperties = getMatchedPropsInEnvironment(env, search);
+    const expressionVariables = new Set(
+      expressionVars.filter(variableName => variableName.startsWith(matchProp))
+    );
+
+    for (const prop of environmentProperties) {
+      expressionVariables.add(prop);
+    }
+
+    return {
+      isElementAccess,
+      matchProp,
+      matches: expressionVariables,
+    };
+  }
+
+  let firstProp = properties.shift();
+  if (typeof firstProp == "string") {
+    firstProp = firstProp.trim();
+  }
+
+  if (firstProp === "this") {
+    // Special case for 'this' - try to get the Object from the Environment.
+    // No problem if it throws, we will just not autocomplete.
+    try {
+      obj = env.object;
+    } catch (e) {
+      // Ignore.
+    }
+  } else if (firstProp === "$_" && webconsoleActor) {
+    obj = webconsoleActor.getLastConsoleInputEvaluation();
+  } else if (firstProp === "$0" && selectedNodeActor && webconsoleActor) {
+    const actor = webconsoleActor.conn.getActor(selectedNodeActor);
+    if (actor) {
+      try {
+        obj = webconsoleActor.makeDebuggeeValue(actor.rawNode);
+      } catch (e) {
+        // Ignore.
+      }
+    }
+  } else if (hasArrayIndex(firstProp)) {
+    obj = getArrayMemberProperty(null, env, firstProp);
+  } else {
+    obj = getVariableInEnvironment(env, firstProp);
+  }
+
+  if (!isObjectUsable(obj)) {
+    return null;
+  }
+
+  // We get the rest of the properties recursively starting from the
+  // Debugger.Object that wraps the first property
+  for (let [index, prop] of properties.entries()) {
+    if (typeof prop === "string") {
+      prop = prop.trim();
+    }
+
+    if (prop === undefined || prop === null || prop === "") {
+      return null;
+    }
+
+    const propPath = [firstProp].concat(properties.slice(0, index + 1));
+    const authorized = authorizedEvaluations.some(
+      x => JSON.stringify(x) === JSON.stringify(propPath)
+    );
+
+    if (!authorized && DevToolsUtils.isUnsafeGetter(obj, prop)) {
+      // If we try to access an unsafe getter, return its name so we can consume that
+      // on the frontend.
+      return {
+        isUnsafeGetter: true,
+        getterPath: propPath,
+      };
+    }
+
+    if (hasArrayIndex(prop)) {
+      // The property to autocomplete is a member of array. For example
+      // list[i][j]..[n]. Traverse the array to get the actual element.
+      obj = getArrayMemberProperty(obj, null, prop);
+    } else {
+      obj = DevToolsUtils.getProperty(obj, prop, authorized);
+    }
+
+    if (!isObjectUsable(obj)) {
+      return null;
+    }
+  }
+
+  const matches =
+    typeof obj != "object"
+      ? getMatchedProps(obj, search)
+      : getMatchedPropsInDbgObject(obj, search);
+  return prepareReturnedObject({
+    matches,
+    search,
+    isElementAccess,
+    elementAccessQuote,
+  });
+}
+
+function hasArrayIndex(str) {
+  return /\[\d+\]$/.test(str);
+}
+
+/**
+ * For a given environment and constructor name, returns its Debugger.Object wrapped
+ * prototype.
+ *
+ * @param {Environment} env
+ * @param {String} name: Name of the constructor object we want the prototype of.
+ * @returns {Debugger.Object|null} the prototype, or null if it not found.
+ */
+function getContentPrototypeObject(env, name) {
+  // Retrieve the outermost environment to get the global object.
+  let outermostEnv = env;
+  while (outermostEnv?.parent) {
+    outermostEnv = outermostEnv.parent;
+  }
+
+  const constructorObj = DevToolsUtils.getProperty(outermostEnv.object, name);
+  if (!constructorObj) {
+    return null;
+  }
+
+  return DevToolsUtils.getProperty(constructorObj, "prototype");
+}
+
+/**
+ * @param {Object} ast: An AST representing a property access (e.g. `foo.bar["baz"].x`)
+ * @returns {Array|null} An array representing the property access
+ *                       (e.g. ["foo", "bar", "baz", "x"]).
+ */
+function getPropertiesFromAstExpression(ast) {
+  let result = [];
+  if (!ast) {
+    return result;
+  }
+  const { type, property, object, name, expression } = ast;
+  if (type === "ThisExpression") {
+    result.unshift("this");
+  } else if (type === "Identifier" && name) {
+    result.unshift(name);
+  } else if (type === "OptionalExpression" && expression) {
+    result = (getPropertiesFromAstExpression(expression) || []).concat(result);
+  } else if (
+    type === "MemberExpression" ||
+    type === "OptionalMemberExpression"
+  ) {
+    if (property) {
+      if (property.type === "Identifier" && property.name) {
+        result.unshift(property.name);
+      } else if (property.type === "Literal") {
+        result.unshift(property.value);
+      }
+    }
+    if (object) {
+      result = (getPropertiesFromAstExpression(object) || []).concat(result);
+    }
+  } else {
+    return null;
+  }
+  return result;
+}
+
+function wrapMatchesInQuotes(matches, quote = `"`) {
+  return new Set(
+    [...matches].map(p => {
+      // Escape as a double-quoted string literal
+      p = JSON.stringify(p);
+
+      // We don't have to do anything more when using double quotes
+      if (quote == `"`) {
+        return p;
+      }
+
+      // Remove surrounding double quotes
+      p = p.slice(1, -1);
+
+      // Unescape inner double quotes (all must be escaped, so no need to count backslashes)
+      p = p.replace(/\\(?=")/g, "");
+
+      // Escape the specified quote (assuming ' or `, which are treated literally in regex)
+      p = p.replace(new RegExp(quote, "g"), "\\$&");
+
+      // Template literals treat ${ specially, escape it
+      if (quote == "`") {
+        p = p.replace(/\${/g, "\\$&");
+      }
+
+      // Surround the result with quotes
+      return `${quote}${p}${quote}`;
+    })
+  );
+}
+
+/**
+ * Get the array member of obj for the given prop. For example, given
+ * prop='list[0][1]' the element at [0][1] of obj.list is returned.
+ *
+ * @param object obj
+ *        The object to operate on. Should be null if env is passed.
+ * @param object env
+ *        The Environment to operate in. Should be null if obj is passed.
+ * @param string prop
+ *        The property to return.
+ * @return null or Object
+ *         Returns null if the property couldn't be located. Otherwise the array
+ *         member identified by prop.
+ */
+function getArrayMemberProperty(obj, env, prop) {
+  // First get the array.
+  const propWithoutIndices = prop.substr(0, prop.indexOf("["));
+
+  if (env) {
+    obj = getVariableInEnvironment(env, propWithoutIndices);
+  } else {
+    obj = DevToolsUtils.getProperty(obj, propWithoutIndices);
+  }
+
+  if (!isObjectUsable(obj)) {
+    return null;
+  }
+
+  // Then traverse the list of indices to get the actual element.
+  let result;
+  const arrayIndicesRegex = /\[[^\]]*\]/g;
+  while ((result = arrayIndicesRegex.exec(prop)) !== null) {
+    const indexWithBrackets = result[0];
+    const indexAsText = indexWithBrackets.substr(
+      1,
+      indexWithBrackets.length - 2
+    );
+    const index = parseInt(indexAsText, 10);
+
+    if (isNaN(index)) {
+      return null;
+    }
+
+    obj = DevToolsUtils.getProperty(obj, index);
+
+    if (!isObjectUsable(obj)) {
+      return null;
+    }
+  }
+
+  return obj;
+}
+
+/**
+ * Check if the given Debugger.Object can be used for autocomplete.
+ *
+ * @param Debugger.Object object
+ *        The Debugger.Object to check.
+ * @return boolean
+ *         True if further inspection into the object is possible, or false
+ *         otherwise.
+ */
+function isObjectUsable(object) {
+  if (object == null) {
+    return false;
+  }
+
+  if (typeof object == "object" && object.class == "DeadObject") {
+    return false;
+  }
+
+  return true;
+}
+
+/**
+ * @see getExactMatchImpl()
+ */
+function getVariableInEnvironment(environment, name) {
+  return getExactMatchImpl(environment, name, DebuggerEnvironmentSupport);
+}
+
+function prepareReturnedObject({
+  matches,
+  search,
+  isElementAccess,
+  elementAccessQuote,
+}) {
+  if (isElementAccess) {
+    // If it's an element access, we need to wrap properties in quotes (either the one
+    // the user already typed, or `"`).
+
+    matches = wrapMatchesInQuotes(matches, elementAccessQuote);
+  } else if (!isWorker) {
+    // If we're not performing an element access, we need to check that the property
+    // are suited for a dot access. (reflect.sys.mjs is not available in worker context yet,
+    // see Bug 1507181).
+    for (const match of matches) {
+      try {
+        // In order to know if the property is suited for dot notation, we use Reflect
+        // to parse an expression where we try to access the property with a dot. If it
+        // throws, this means that we need to do an element access instead.
+        lazy.Reflect.parse(`({${match}: true})`);
+      } catch (e) {
+        matches.delete(match);
+      }
+    }
+  }
+
+  return { isElementAccess, matchProp: search, matches };
+}
+
+/**
+ * @see getMatchedPropsImpl()
+ */
+function getMatchedPropsInEnvironment(environment, match) {
+  return getMatchedPropsImpl(environment, match, DebuggerEnvironmentSupport);
+}
+
+/**
+ * @see getMatchedPropsImpl()
+ */
+function getMatchedPropsInDbgObject(dbgObject, match) {
+  return getMatchedPropsImpl(dbgObject, match, DebuggerObjectSupport);
+}
+
+/**
+ * @see getMatchedPropsImpl()
+ */
+function getMatchedProps(obj, match) {
+  if (typeof obj != "object") {
+    obj = obj.constructor.prototype;
+  }
+  return getMatchedPropsImpl(obj, match, JSObjectSupport);
+}
+
+/**
+ * Get all properties in the given object (and its parent prototype chain) that
+ * match a given prefix.
+ *
+ * @param {Mixed} obj
+ *        Object whose properties we want to filter.
+ * @param {string} match
+ *        Filter for properties that match this string.
+ * @returns {Set} List of matched properties.
+ */
+function getMatchedPropsImpl(obj, match, { chainIterator, getProperties }) {
+  const matches = new Set();
+  let numProps = 0;
+
+  const insensitiveMatching = match && match[0].toUpperCase() !== match[0];
+  const propertyMatches = prop => {
+    return insensitiveMatching
+      ? prop.toLocaleLowerCase().startsWith(match.toLocaleLowerCase())
+      : prop.startsWith(match);
+  };
+
+  // We need to go up the prototype chain.
+  const iter = chainIterator(obj);
+  for (obj of iter) {
+    const props = getProperties(obj);
+    if (!props) {
+      continue;
+    }
+    numProps += props.length;
+
+    // If there are too many properties to event attempt autocompletion,
+    // or if we have already added the max number, then stop looping
+    // and return the partial set that has already been discovered.
+    if (
+      numProps >= MAX_AUTOCOMPLETE_ATTEMPTS ||
+      matches.size >= MAX_AUTOCOMPLETIONS
+    ) {
+      break;
+    }
+
+    for (let i = 0; i < props.length; i++) {
+      const prop = props[i];
+      if (!propertyMatches(prop)) {
+        continue;
+      }
+
+      // If it is an array index, we can't take it.
+      // This uses a trick: converting a string to a number yields NaN if
+      // the operation failed, and NaN is not equal to itself.
+      // eslint-disable-next-line no-self-compare
+      if (+prop != +prop) {
+        matches.add(prop);
+      }
+
+      if (matches.size >= MAX_AUTOCOMPLETIONS) {
+        break;
+      }
+    }
+  }
+
+  return matches;
+}
+
+/**
+ * Returns a property value based on its name from the given object, by
+ * recursively checking the object's prototype.
+ *
+ * @param object obj
+ *        An object to look the property into.
+ * @param string name
+ *        The property that is looked up.
+ * @returns object|undefined
+ *        A Debugger.Object if the property exists in the object's prototype
+ *        chain, undefined otherwise.
+ */
+function getExactMatchImpl(obj, name, { chainIterator, getProperty }) {
+  // We need to go up the prototype chain.
+  const iter = chainIterator(obj);
+  for (obj of iter) {
+    const prop = getProperty(obj, name, obj);
+    if (prop) {
+      return prop.value;
+    }
+  }
+  return undefined;
+}
+
+var JSObjectSupport = {
+  *chainIterator(obj) {
+    while (obj) {
+      yield obj;
+      try {
+        obj = Object.getPrototypeOf(obj);
+      } catch (error) {
+        // The above can throw e.g. for some proxy objects.
+        return;
+      }
+    }
+  },
+
+  getProperties(obj) {
+    try {
+      return Object.getOwnPropertyNames(obj);
+    } catch (error) {
+      // The above can throw e.g. for some proxy objects.
+      return null;
+    }
+  },
+
+  getProperty() {
+    // getProperty is unsafe with raw JS objects.
+    throw new Error("Unimplemented!");
+  },
+};
+
+var DebuggerObjectSupport = {
+  *chainIterator(obj) {
+    while (obj) {
+      yield obj;
+      try {
+        // There could be transparent security wrappers, unwrap to check if it's a proxy.
+        const unwrapped = DevToolsUtils.unwrap(obj);
+        if (unwrapped === undefined) {
+          // Objects belonging to an invisible-to-debugger compartment can't be unwrapped.
+          return;
+        }
+
+        if (unwrapped.isProxy) {
+          // Proxies might have a `getPrototypeOf` method, which is triggered by `obj.proto`,
+          // but this does not impact the actual prototype chain.
+          // In such case, we need to use the proxy target prototype.
+          // We retrieve proxyTarget from `obj` (and not `unwrapped`) to avoid exposing
+          // the unwrapped target.
+          obj = unwrapped.proxyTarget;
+        }
+        obj = obj.proto;
+      } catch (error) {
+        // The above can throw e.g. for some proxy objects.
+        return;
+      }
+    }
+  },
+
+  getProperties(obj) {
+    try {
+      return obj.getOwnPropertyNames();
+    } catch (error) {
+      // The above can throw e.g. for some proxy objects.
+      return null;
+    }
+  },
+
+  getProperty(obj, name, rootObj) {
+    // This is left unimplemented in favor to DevToolsUtils.getProperty().
+    throw new Error("Unimplemented!");
+  },
+};
+
+var DebuggerEnvironmentSupport = {
+  *chainIterator(obj) {
+    while (obj) {
+      yield obj;
+      obj = obj.parent;
+    }
+  },
+
+  getProperties(obj) {
+    const names = obj.names();
+
+    // Include 'this' in results (in sorted order)
+    for (let i = 0; i < names.length; i++) {
+      if (i === names.length - 1 || names[i + 1] > "this") {
+        names.splice(i + 1, 0, "this");
+        break;
+      }
+    }
+
+    return names;
+  },
+
+  getProperty(obj, name) {
+    let result;
+    // Try/catch since name can be anything, and getVariable throws if
+    // it's not a valid ECMAScript identifier name
+    try {
+      // TODO: we should use getVariableDescriptor() here - bug 725815.
+      result = obj.getVariable(name);
+    } catch (e) {
+      // Ignore.
+    }
+
+    // FIXME: Need actual UI, bug 941287.
+    if (
+      result == null ||
+      (typeof result == "object" &&
+        (result.optimizedOut || result.missingArguments))
+    ) {
+      return null;
+    }
+    return { value: result };
+  },
+};
+
+exports.JSPropertyProvider = DevToolsUtils.makeInfallible(JSPropertyProvider);
+
+// Export a version that will throw (for tests)
+exports.FallibleJSPropertyProvider = JSPropertyProvider;