Embed default resources in Servo applications using a servo-default-resources crate (#43182)

This PR considers the following constraints:

- Resources must be available when building servo via a published
crates.io package (i.e. no `../../../resources/<file>` file references).
- Minimal setup when writing tests (`nextest` spawns each test in its
own process, so we don't want to explicitly initialize the resource
handler for every `#[test]` fn)
- Use local resources when developing locally
- Support loading the resources from a proper resource directory if the
embedder wishes so, including via a custom mechanism, not necessarily as
files

(File) Resources that are only accessed from servoshell are out of scope
of this PR, since it mainly focusses on unblocking publishing `libservo`
to crates.io.

Baking the resources into the binary by default simplifies the setup a
lot. We already supported that before, but only for testing purposes and
explicitly not for production builds.

Using [`inventory`](https://crates.io/crates/inventory) adds a simple
way for the embedder to replace the default baked in resources, while
also keeping the test usage of baked in resources simple.

rippy.png is also referenced from image_cache - We simply duplicate it,
since the image is small, to avoid adding unnecessarily complex
solutions like adding a dedicated crate.


Testing: Covered by existing tests. [mach try
full](https://github.com/jschwe/servo/actions/runs/23811669469)
Fixes: Part of #43145

---------

Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>

components/default-resources/resources/debugger.js

@@ -0,0 +1,563 @@
+if ("dbg" in this) {
+    throw new Error("Debugger script must not run more than once!");
+}
+
+const dbg = new Debugger;
+const debuggeesToPipelineIds = new Map;
+const debuggeesToWorkerIds = new Map;
+const sourceIdsToScripts = new Map;
+const frameActorsToFrames = new Map;
+const environmentActorsToEnvironments = new Map;
+
+// <https://searchfox.org/firefox-main/source/devtools/server/actors/thread.js#155>
+// Possible values for the `why.type` attribute in "paused" event
+const PAUSE_REASONS = {
+  INTERRUPTED: "interrupted", // Associated with why.onNext attribute
+  RESUME_LIMIT: "resumeLimit",
+};
+
+// Find script by scriptId within a script tree
+function findScriptById(script, scriptId) {
+    if (script.sourceStart === scriptId) {
+        return script;
+    }
+    for (const child of script.getChildScripts()) {
+        const found = findScriptById(child, scriptId);
+        if (found) return found;
+    }
+    return null;
+}
+
+// Walk script tree and call callback for each script
+function walkScriptTree(script, callback) {
+    callback(script);
+    for (const child of script.getChildScripts()) {
+        walkScriptTree(child, callback);
+    }
+}
+
+// Find a key by a value in a map
+function findKeyByValue(map, search) {
+    for (const [key, value] of map) {
+        if (value === search) return key;
+    }
+    return undefined;
+}
+
+dbg.uncaughtExceptionHook = function(error) {
+    console.error(`[debugger] Uncaught exception at ${error.fileName}:${error.lineNumber}:${error.columnNumber}: ${error.name}: ${error.message}`);
+};
+
+dbg.onNewScript = function(script) {
+    // TODO: handle wasm (`script.source.introductionType == wasm`)
+    sourceIdsToScripts.set(script.source.id, script);
+    notifyNewSource({
+        pipelineId: debuggeesToPipelineIds.get(script.global),
+        workerId: debuggeesToWorkerIds.get(script.global),
+        spidermonkeyId: script.source.id,
+        url: script.source.url,
+        urlOverride: script.source.displayURL,
+        text: script.source.text,
+        introductionType: script.source.introductionType ?? null,
+    });
+};
+
+// Track a new debuggee global
+addEventListener("addDebuggee", event => {
+    const {global, pipelineId, workerId} = event;
+    const debuggerObject = dbg.addDebuggee(global);
+    debuggeesToPipelineIds.set(debuggerObject, pipelineId);
+    if (workerId !== undefined) {
+        debuggeesToWorkerIds.set(debuggerObject, workerId);
+    }
+});
+
+// Maximum number of properties to include in preview
+// <https://searchfox.org/firefox-main/source/devtools/server/actors/object/previewers.js#29>
+const OBJECT_PREVIEW_MAX_ITEMS = 10;
+
+// <https://searchfox.org/mozilla-central/source/devtools/server/actors/object/previewers.js#80>
+const previewers = {
+    Function: [],
+    Array: [],
+    Object: [],
+    // TODO: Add Map, FormData etc
+};
+
+// Convert debuggee value to property descriptor value
+// <https://searchfox.org/firefox-main/source/devtools/server/actors/object/utils.js#116>
+function createValueGrip(value) {
+    switch (typeof value) {
+        case "undefined":
+            return { valueType: "undefined" };
+        case "boolean":
+            return { valueType: "boolean", booleanValue: value };
+        case "number":
+            return { valueType: "number", numberValue: value };
+        case "string":
+            return { valueType: "string", stringValue: value };
+        case "object":
+            if (value === null) {
+                return { valueType: "null" };
+            }
+            // Debugger.Object - get preview using registered previewers
+            // <https://firefox-source-docs.mozilla.org/js/Debugger/Debugger.Object.html>
+            return {
+                valueType: "object",
+                objectClass: value.class,
+                preview: getPreview(value),
+            };
+        default:
+            return { valueType: "string", stringValue: String(value) };
+    }
+}
+
+// Extract own properties from a debuggee object
+// <https://firefox-source-docs.mozilla.org/devtools-user/debugger-api/debugger.object/index.html#function-properties-of-the-debugger-object-prototype>
+function extractOwnProperties(obj, maxItems = OBJECT_PREVIEW_MAX_ITEMS) {
+    const ownProperties = [];
+    let totalLength = 0;
+
+    let names;
+    try {
+        names = obj.getOwnPropertyNames();
+        totalLength = names.length;
+    } catch (e) {
+        return { ownProperties, ownPropertiesLength: 0 };
+    }
+
+    let count = 0;
+    for (const name of names) {
+        if (count >= maxItems) break;
+        try {
+            const desc = obj.getOwnPropertyDescriptor(name);
+            if (desc) {
+                const prop = {
+                    name: name,
+                    configurable: desc.configurable ?? false,
+                    enumerable: desc.enumerable ?? false,
+                    writable: desc.writable ?? false,
+                    isAccessor: desc.get !== undefined || desc.set !== undefined,
+                    value: createValueGrip(undefined),
+                };
+
+                if (desc.value !== undefined) {
+                    prop.value = createValueGrip(desc.value);
+                } else if (desc.get) {
+                    try {
+                        const result = desc.get.call(obj);
+                        if (result && "return" in result) {
+                            prop.value = createValueGrip(result.return);
+                        }
+                    } catch (e) { }
+                }
+
+                ownProperties.push(prop);
+                count++;
+            }
+        } catch (e) {
+            // For now skip properties that throw on access
+        }
+    }
+
+    return { ownProperties, ownPropertiesLength: totalLength };
+}
+
+// <https://searchfox.org/mozilla-central/source/devtools/server/actors/object/previewers.js#125>
+previewers.Function.push(function FunctionPreviewer(obj) {
+    const { ownProperties, ownPropertiesLength } = extractOwnProperties(obj);
+    return {
+        kind: "Object",
+        ownProperties,
+        ownPropertiesLength,
+        function: {
+            name: obj.name,
+            displayName: obj.displayName,
+            parameterNames: obj.parameterNames,
+            isAsync: obj.isAsyncFunction,
+            isGenerator: obj.isGeneratorFunction,
+        }
+    };
+});
+
+// <https://searchfox.org/mozilla-central/source/devtools/server/actors/object/previewers.js#172>
+// TODO: Add implementation for showing Array items
+previewers.Array.push(function ArrayPreviewer(obj) {
+    const lengthDescriptor = obj.getOwnPropertyDescriptor("length");
+    const length = lengthDescriptor ? lengthDescriptor.value : 0;
+
+    return {
+        kind: "ArrayLike",
+        arrayLength: length,
+    };
+});
+
+// Generic fallback for object previewer
+// <https://searchfox.org/mozilla-central/source/devtools/server/actors/object/previewers.js#856>
+previewers.Object.push(function ObjectPreviewer(obj) {
+    const { ownProperties, ownPropertiesLength } = extractOwnProperties(obj);
+    return {
+        kind: "Object",
+        ownProperties,
+        ownPropertiesLength,
+    };
+});
+
+function getPreview(obj) {
+    const className = obj.class;
+
+    // <https://searchfox.org/mozilla-central/source/devtools/server/actors/object.js#295>
+    const typePreviewers = previewers[className] || previewers.Object;
+    for (const previewer of typePreviewers) {
+        const result = previewer(obj);
+        if (result) return result;
+    }
+
+    return { ownProperties: [], ownPropertiesLength: 0 };
+}
+
+// Evaluate some javascript code in the global context of the debuggee
+// <https://firefox-source-docs.mozilla.org/js/Debugger/Debugger.Object.html#executeinglobal-code-options>
+addEventListener("eval", event => {
+    const {code, pipelineId, workerId, frameActorId} = event;
+
+    let completionValue;
+    if (frameActorId) {
+        const frame = frameActorsToFrames.get(frameActorId);
+        // <https://searchfox.org/firefox-main/source/js/src/doc/Debugger/Debugger.Frame.md#223>
+        if (frame?.onStack) {
+            completionValue = frame.eval(code);
+        } else {
+            completionValue = { throw: "Frame not available" };
+        }
+    } else {
+        const object = workerId !== undefined ?
+            findKeyByValue(debuggeesToWorkerIds, workerId) :
+            findKeyByValue(debuggeesToPipelineIds, pipelineId);
+        completionValue = object.executeInGlobal(code);
+    }
+
+    // Completion values: <https://firefox-source-docs.mozilla.org/js/Debugger/Conventions.html#completion-values>
+    let resultValue;
+    if (completionValue === null) {
+        resultValue = { completionType: "terminated", value: createValueGrip(undefined), hasException: false };
+    } else if ("throw" in completionValue) {
+        // <https://firefox-source-docs.mozilla.org/js/Debugger/Debugger.html#adoptdebuggeevalue-value>
+        // <https://searchfox.org/firefox-main/source/devtools/server/actors/webconsole/eval-with-debugger.js#312>
+        // we probably don't need adoptDebuggeeValue, as we only have one debugger instance for now
+        // let value = dbg.adoptDebuggeeValue(completionValue.throw);
+        resultValue = { completionType: "throw", value: createValueGrip(completionValue.throw), hasException: true };
+    } else if ("return" in completionValue) {
+        resultValue = { completionType: "return", value: createValueGrip(completionValue.return), hasException: false };
+    }
+
+    // To avoid recursion errors in the WebIDL, preview needs to live outside of the property descriptor
+    if (resultValue.value.preview) {
+        resultValue.preview = resultValue.value.preview;
+        delete resultValue.value.preview;
+    }
+
+    evalResult(event, resultValue);
+});
+
+addEventListener("getPossibleBreakpoints", event => {
+    const {spidermonkeyId} = event;
+    const script = sourceIdsToScripts.get(spidermonkeyId);
+    const result = [];
+    walkScriptTree(script, (currentScript) => {
+        for (const location of currentScript.getPossibleBreakpoints()) {
+            location["scriptId"] = currentScript.sourceStart;
+            result.push(location);
+        }
+    });
+    getPossibleBreakpointsResult(event, result);
+});
+
+function createFrameActor(frame, pipelineId) {
+    let frameActorId = findKeyByValue(frameActorsToFrames, frame);
+    if (!frameActorId) {
+        // TODO: Check if we already have an actor for this frame
+        frameActorId = registerFrameActor(pipelineId, {
+            // TODO: Some properties throw if terminated is true
+            // TODO: arguments: frame.arguments,
+            displayName: frame.script.displayName,
+            onStack: frame.onStack,
+            oldest: frame.older == null,
+            terminated: frame.terminated,
+            type_: frame.type,
+            url: frame.script.url,
+        });
+
+        if (!frameActorId) {
+            console.error("[debugger] Couldn't create frame");
+            return undefined;
+        }
+        frameActorsToFrames.set(frameActorId, frame);
+    }
+
+    return frameActorId;
+}
+
+function handlePauseAndRespond(frame, pauseReason) {
+    dbg.onEnterFrame = undefined;
+    clearSteppingHooks(frame);
+
+    // Get the pipeline ID for this debuggee
+    const pipelineId = debuggeesToPipelineIds.get(frame.script.global);
+    if (!pipelineId) {
+        console.error("[debugger] No pipeline ID for frame's global");
+        return undefined;
+    }
+
+    let frameActorId = createFrameActor(frame, pipelineId);
+
+    // <https://firefox-source-docs.mozilla.org/js/Debugger/Debugger.Script.html#getoffsetmetadata-offset>
+    const offset = frame.offset;
+    const offsetMetadata = frame.script.getOffsetMetadata(offset);
+    const frameOffset = {
+        frameActorId,
+        column: offsetMetadata.columnNumber - 1,
+        line: offsetMetadata.lineNumber
+    };
+
+    // Notify devtools and enter pause loop. This blocks until Resume.
+    pauseAndRespond(
+        pipelineId,
+        frameOffset,
+        pauseReason
+    );
+
+    // <https://firefox-source-docs.mozilla.org/js/Debugger/Conventions.html#resumption-values>
+    // Return undefined to continue execution normally after resume.
+    return undefined;
+}
+
+addEventListener("frames", event => {
+    const {pipelineId, start, count} = event;
+    let frameList = handleListFrames(pipelineId, start, count);
+
+    listFramesResult(frameList);
+})
+
+// <https://searchfox.org/firefox-main/source/devtools/server/actors/thread.js#1425>
+function handleListFrames(pipelineId, start, count) {
+    let frame = dbg.getNewestFrame()
+
+    const walkToParentFrame = () => {
+        if (!frame) {
+            return;
+        }
+
+        const currentFrame = frame;
+        frame = null;
+
+        if (currentFrame.older) {
+            frame = currentFrame.older;
+        }
+    }
+
+    let i = 0;
+    while (frame && i < start) {
+      walkToParentFrame();
+      i++;
+    }
+
+    // Return count frames, or all remaining frames if count is not defined.
+    const frames = [];
+    for (; frame && (!count || i < start + count); i++, walkToParentFrame()) {
+      const frameActorId = createFrameActor(frame, pipelineId);
+      frames.push(frameActorId);
+    }
+
+    return frames;
+}
+
+addEventListener("setBreakpoint", event => {
+    const {spidermonkeyId, scriptId, offset} = event;
+    const script = sourceIdsToScripts.get(spidermonkeyId);
+    const target = findScriptById(script, scriptId);
+    if (target) {
+        target.setBreakpoint(offset, {
+            // <https://firefox-source-docs.mozilla.org/js/Debugger/Debugger.Script.html#setbreakpoint-offset-handler>
+            // The hit handler receives a Debugger.Frame instance representing the currently executing stack frame.
+            hit: (frame) => handlePauseAndRespond(frame, {type_: "breakpoint"})
+        });
+    }
+});
+
+// <https://firefox-source-docs.mozilla.org/js/Debugger/Debugger.Frame.html>
+addEventListener("interrupt", event => {
+    dbg.onEnterFrame = (frame) => handlePauseAndRespond(
+        frame,
+        { type_: PAUSE_REASONS.INTERRUPTED, onNext: true }
+    );
+});
+
+function makeSteppingHooks(steppingType, startFrame) {
+    return {
+        onEnterFrame: (frame) => {
+            const { onStep, onPop } = makeSteppingHooks("next", frame);
+            frame.onStep = onStep;
+            frame.onPop = onPop;
+        },
+        onStep: () => {
+            const meta = startFrame.script.getOffsetMetadata(startFrame.offset);
+            if (meta.isBreakpoint && meta.isStepStart) {
+                return handlePauseAndRespond(startFrame, { type_: PAUSE_REASONS.RESUME_LIMIT });
+            }
+        },
+        onPop: (completion) => {
+            this.reportedPop = true;
+            suspendedFrame = startFrame;
+            if (steppingType !== "finish") {
+                return handlePauseAndRespond(startFrame, completion);
+            }
+            attachSteppingHooks("next", startFrame);
+        },
+    }
+}
+
+function getNextStepFrame(frame) {
+    const endOfFrame = frame.reportedPop;
+    const stepFrame = endOfFrame ? frame.older : frame;
+    if (!stepFrame || !stepFrame.script) {
+      return null;
+    }
+    return stepFrame;
+}
+
+// <https://searchfox.org/firefox-main/source/devtools/server/actors/thread.js#1235>
+function attachSteppingHooks(steppingType, frame) {
+    if (steppingType === "finish" && frame.reportedPop) {
+        steppingType = "next";
+    }
+
+    const stepFrame = getNextStepFrame(frame);
+    if (!stepFrame) {
+        steppingType = "step";
+    }
+
+    const { onEnterFrame, onStep, onPop } = makeSteppingHooks(
+        steppingType,
+        frame,
+    );
+
+    if (steppingType === "step") {
+        dbg.onEnterFrame = onEnterFrame;
+    }
+
+    if (stepFrame) {
+        switch (steppingType) {
+            case "step":
+            case "next":
+                if (stepFrame.script) {
+                    stepFrame.onStep = onStep;
+                }
+            case "finish":
+                stepFrame.onPop = onPop;
+                break;
+        }
+    }
+}
+
+function clearSteppingHooks(suspendedFrame) {
+    if (suspendedFrame) {
+        suspendedFrame.onStep = undefined;
+        suspendedFrame.onPop = undefined;
+    }
+    let frame = this.youngestFrame;
+    if (frame?.onStack) {
+        while (frame) {
+            frame.onStep = undefined;
+            frame.onPop = undefined;
+            frame = frame.older;
+        }
+    }
+}
+
+// <https://firefox-source-docs.mozilla.org/devtools/backend/protocol.html#resuming-a-thread>
+addEventListener("resume", event => {
+    const {resumeLimitType: steppingType, frameActorID} = event;
+    let frame = dbg.getNewestFrame();
+    if (frameActorID) {
+        frame = frameActorsToFrames.get(frameActorID);
+        if (!frame) {
+            console.error("[debugger] Couldn't find frame");
+        }
+    }
+    if (steppingType) {
+        attachSteppingHooks(steppingType, frame);
+    } else {
+        clearSteppingHooks(frame);
+    }
+});
+
+// <https://firefox-source-docs.mozilla.org/js/Debugger/Debugger.Script.html#clearbreakpoint-handler-offset>
+// There may be more than one breakpoint at the same offset with different handlers, but we don’t handle that case for now.
+addEventListener("clearBreakpoint", event => {
+    const {spidermonkeyId, scriptId, offset} = event;
+    const script = sourceIdsToScripts.get(spidermonkeyId);
+    const target = findScriptById(script, scriptId);
+    if (target) {
+        // <https://firefox-source-docs.mozilla.org/js/Debugger/Debugger.Script.html#clearallbreakpoints-offset>
+        // If the instance refers to a JSScript, remove all breakpoints set in this script at that offset.
+        target.clearAllBreakpoints(offset);
+    }
+});
+
+// TODO: Get variables (scopes don't show if they don't have a variable)
+function createEnvironmentActor(environment) {
+    let actor = findKeyByValue(environmentActorsToEnvironments, environment);
+
+    if (!actor) {
+        let info = {};
+        if (environment.type == "declarative") {
+            info.type_ = environment.calleeScript ? "function" : "block";
+        } else {
+            info.type_ = environment.type;
+        }
+
+        info.scopeKind = environment.scopeKind;
+
+        if (environment.calleeScript) {
+            info.functionDisplayName = environment.calleeScript.displayName;
+        }
+
+        let parent = null;
+        if (environment.parent) {
+            parent = createEnvironmentActor(environment.parent);
+        }
+
+        if (environment.type == "declarative") {
+            info.bindingVariables = buildBindings(environment)
+        }
+
+        // TODO: Update this instead of registering
+        actor = registerEnvironmentActor(info, parent);
+        environmentActorsToEnvironments.set(actor, environment);
+    }
+
+    return actor;
+}
+
+function buildBindings(environment) {
+    let bindingVar = new Map();
+    for (const name of environment.names()) {
+        const value = environment.getVariable(name);
+        // <https://searchfox.org/firefox-main/source/devtools/server/actors/environment.js#87>
+        // We should not do this, it is more of a place holder for now.
+        // TODO: build and pass correct structure for this. This structure is very similar to "eval"
+        bindingVar[name] = JSON.stringify(value);
+    }
+    return bindingVar;
+}
+
+// Get a `Debugger.Environment` instance within which evaluation is taking place.
+// <https://searchfox.org/firefox-main/source/devtools/server/actors/frame.js#109>
+addEventListener("getEnvironment", event => {
+    const {frameActorId} = event;
+    frame = frameActorsToFrames.get(frameActorId);
+
+    const actor = createEnvironmentActor(frame.environment);
+    getEnvironmentResult(actor);
+});