Auto merge of #22923 - peterjoel:issue_8539_prefs_refactor, r=jdm

#8539 Config preferences backend restructure

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A procedural macro for generating static structures for use as the backend for config preferences, as well a mapping from string names to accessors.

Preferences can be accessed and updated via a map-like interface with `String` keys, and now also via a convenience macro: `get_pref!(path.to.pref)`. Various `serde`-compatible field attributes are also supported, including renaming the string keys. This could be useful when changing the backend structure without breaking existing usages.

I have added the choice to use `i64` as well as `f64` for storing numbers. As it turns out, none of the existing preferences used non-integer values. Setting a floating point value from a command-line argument requires a decimal point in order to parse correctly.

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #8539

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- [X] There are tests for these changes OR
- [ ] These changes do not require tests because ___

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-----

I have a few outstanding problems or questions:

1. I am unable to get rid of this warning:
    ```
    warning: unnecessary path disambiguator
       --> components/config/prefs.rs:130:51
        |
    130 |         accessor_type = crate::pref_util::Accessor::<Prefs, crate::pref_util::PrefValue>,
        |                                                   ^^ try removing `::`
    ```
    See: https://stackoverflow.com/questions/54710797/how-to-disable-unnecessary-path-disambiguator-warning
2. Several of the preferences in use were not represented in `prefs.json`. Some of these may be in error, but it is hard to tell. For example `js.offthread_compilation.enabled` vs `js.ion.offthread_compilation.enabled` could be different preferences or could be intended to have the same value.
3. Previously, several pieces of code provided default values when accessing a preference that may not be present. For example:
    ```Rust
    let DBL_CLICK_TIMEOUT = Duration::from_millis(
        PREFS
            .get("dom.document.dblclick_timeout")
            .as_u64()
            .unwrap_or(300),
    );
    ```
    Fallback values don't really make sense now and I've added these defaults to `prefs.json`. Does this sound right?
4. I have kept `PrefValue::Missing`, though it doesn't seem very useful any more. An error might be more appropriate now for an incorrect preference key. I've kept this partly because [`webdriver_server` uses it](https://github.com/servo/servo/blob/master/components/webdriver_server/lib.rs#L224).

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components/script/dom/bindings/codegen/CodegenRust.py

@@ -2586,7 +2586,7 @@ class CGConstructorEnabled(CGAbstractMethod):
         pref = iface.getExtendedAttribute("Pref")
         if pref:
             assert isinstance(pref, list) and len(pref) == 1
-            conditions.append('PREFS.get("%s").as_boolean().unwrap_or(false)' % pref[0])
+            conditions.append('prefs::pref_map().get("%s").as_bool().unwrap_or(false)' % pref[0])
 
         func = iface.getExtendedAttribute("Func")
         if func:
@@ -5977,7 +5977,8 @@ def generate_imports(config, cgthings, descriptors, callbacks=None, dictionaries
         'crate::dom::globalscope::GlobalScope',
         'crate::mem::malloc_size_of_including_raw_self',
         'libc',
-        'servo_config::prefs::PREFS',
+        'servo_config::pref',
+        'servo_config::prefs',
         'std::borrow::ToOwned',
         'std::cmp',
         'std::mem',

components/script/dom/bindings/guard.rs

@@ -6,7 +6,7 @@
 
 use js::jsapi::JSContext;
 use js::rust::HandleObject;
-use servo_config::prefs::PREFS;
+use servo_config::prefs;
 
 /// A container with a condition.
 pub struct Guard<T: Clone + Copy> {
@@ -48,7 +48,7 @@ pub enum Condition {
 impl Condition {
     unsafe fn is_satisfied(&self, cx: *mut JSContext, obj: HandleObject) -> bool {
         match *self {
-            Condition::Pref(name) => PREFS.get(name).as_boolean().unwrap_or(false),
+            Condition::Pref(name) => prefs::pref_map().get(name).as_bool().unwrap_or(false),
             Condition::Func(f) => f(cx, obj),
             Condition::Satisfied => true,
         }

components/script/dom/create.rs

@@ -81,7 +81,7 @@ use crate::dom::svgsvgelement::SVGSVGElement;
 use crate::script_thread::ScriptThread;
 use html5ever::{LocalName, Prefix, QualName};
 use js::jsapi::JSAutoCompartment;
-use servo_config::prefs::PREFS;
+use servo_config::pref;
 
 fn create_svg_element(
     name: QualName,
@@ -101,7 +101,7 @@ fn create_svg_element(
         })
     );
 
-    if !PREFS.get("dom.svg.enabled").as_boolean().unwrap_or(false) {
+    if !pref!(dom.svg.enabled) {
         return Element::new(name.local, name.ns, prefix, document);
     }
 

components/script/dom/document.rs

@@ -137,7 +137,7 @@ use script_traits::{AnimationState, DocumentActivity, MouseButton, MouseEventTyp
 use script_traits::{MsDuration, ScriptMsg, TouchEventType, TouchId, UntrustedNodeAddress};
 use servo_arc::Arc;
 use servo_atoms::Atom;
-use servo_config::prefs::PREFS;
+use servo_config::pref;
 use servo_url::{ImmutableOrigin, MutableOrigin, ServoUrl};
 use std::borrow::ToOwned;
 use std::cell::{Cell, Ref, RefMut};
@@ -1090,16 +1090,9 @@ impl Document {
         let opt = self.last_click_info.borrow_mut().take();
 
         if let Some((last_time, last_pos)) = opt {
-            let DBL_CLICK_TIMEOUT = Duration::from_millis(
-                PREFS
-                    .get("dom.document.dblclick_timeout")
-                    .as_u64()
-                    .unwrap_or(300),
-            );
-            let DBL_CLICK_DIST_THRESHOLD = PREFS
-                .get("dom.document.dblclick_dist")
-                .as_u64()
-                .unwrap_or(1);
+            let DBL_CLICK_TIMEOUT =
+                Duration::from_millis(pref!(dom.document.dblclick_timeout) as u64);
+            let DBL_CLICK_DIST_THRESHOLD = pref!(dom.document.dblclick_dist) as u64;
 
             // Calculate distance between this click and the previous click.
             let line = click_pos - last_pos;
@@ -2423,11 +2416,7 @@ impl Document {
         local_name: &LocalName,
         is: Option<&LocalName>,
     ) -> Option<Rc<CustomElementDefinition>> {
-        if !PREFS
-            .get("dom.customelements.enabled")
-            .as_boolean()
-            .unwrap_or(false)
-        {
+        if !pref!(dom.custom_elements.enabled) {
             return None;
         }
 
@@ -3165,11 +3154,7 @@ impl Document {
             error = true;
         }
 
-        if PREFS
-            .get("dom.fullscreen.test")
-            .as_boolean()
-            .unwrap_or(false)
-        {
+        if pref!(dom.fullscreen.test) {
             // For reftests we just take over the current window,
             // and don't try to really enter fullscreen.
             info!("Tests don't really enter fullscreen.");

components/script/dom/htmlcanvaselement.rs

@@ -42,7 +42,7 @@ use js::jsapi::JSContext;
 use js::rust::HandleValue;
 use profile_traits::ipc;
 use script_layout_interface::{HTMLCanvasData, HTMLCanvasDataSource};
-use servo_config::prefs::PREFS;
+use servo_config::pref;
 use std::cell::Ref;
 use style::attr::{AttrValue, LengthOrPercentageOrAuto};
 
@@ -232,7 +232,7 @@ impl HTMLCanvasElement {
         cx: *mut JSContext,
         options: HandleValue,
     ) -> Option<DomRoot<WebGL2RenderingContext>> {
-        if !PREFS.is_webgl2_enabled() {
+        if !pref!(dom.webgl2.enabled) {
             return None;
         }
         if let Some(ctx) = self.context() {

components/script/dom/htmlmediaelement.rs

@@ -64,7 +64,7 @@ use net_traits::request::{CredentialsMode, Destination, RequestInit};
 use net_traits::{CoreResourceMsg, FetchChannels, FetchMetadata, FetchResponseListener, Metadata};
 use net_traits::{NetworkError, ResourceFetchTiming, ResourceTimingType};
 use script_layout_interface::HTMLMediaData;
-use servo_config::prefs::PREFS;
+use servo_config::pref;
 use servo_media::player::frame::{Frame, FrameRenderer};
 use servo_media::player::{PlaybackState, Player, PlayerError, PlayerEvent, StreamType};
 use servo_media::ServoMedia;
@@ -1121,13 +1121,12 @@ impl HTMLMediaElement {
                 .unwrap()
                 .render_poster_frame(image);
             self.upcast::<Node>().dirty(NodeDamage::OtherNodeDamage);
-            if let Some(testing_on) = PREFS.get("media.testing.enabled").as_boolean() {
-                if !testing_on {
-                    return;
-                }
+            if pref!(media.testing.enabled) {
                 let window = window_from_node(self);
                 let task_source = window.task_manager().media_element_task_source();
                 task_source.queue_simple_event(self.upcast(), atom!("postershown"), &window);
+            } else {
+                return;
             }
         }
     }

components/script/dom/htmlmetaelement.rs

@@ -21,7 +21,7 @@ use dom_struct::dom_struct;
 use html5ever::{LocalName, Prefix};
 use parking_lot::RwLock;
 use servo_arc::Arc;
-use servo_config::prefs::PREFS;
+use servo_config::pref;
 use std::sync::atomic::AtomicBool;
 use style::attr::AttrValue;
 use style::media_queries::MediaList;
@@ -98,11 +98,7 @@ impl HTMLMetaElement {
     }
 
     fn apply_viewport(&self) {
-        if !PREFS
-            .get("layout.viewport.enabled")
-            .as_boolean()
-            .unwrap_or(false)
-        {
+        if !pref!(layout.viewport.enabled) {
             return;
         }
         let element = self.upcast::<Element>();

components/script/dom/mouseevent.rs

@@ -16,7 +16,7 @@ use crate::dom::uievent::UIEvent;
 use crate::dom::window::Window;
 use dom_struct::dom_struct;
 use euclid::Point2D;
-use servo_config::prefs::PREFS;
+use servo_config::pref;
 use std::cell::Cell;
 use std::default::Default;
 
@@ -194,11 +194,7 @@ impl MouseEventMethods for MouseEvent {
     // This returns the same result as current gecko.
     // https://developer.mozilla.org/en-US/docs/Web/API/MouseEvent/which
     fn Which(&self) -> i32 {
-        if PREFS
-            .get("dom.mouseevent.which.enabled")
-            .as_boolean()
-            .unwrap_or(false)
-        {
+        if pref!(dom.mouse_event.which.enabled) {
             (self.button.get() + 1) as i32
         } else {
             0

components/script/dom/paintworkletglobalscope.rs

@@ -50,7 +50,7 @@ use profile_traits::ipc;
 use script_traits::Painter;
 use script_traits::{DrawAPaintImageResult, PaintWorkletError};
 use servo_atoms::Atom;
-use servo_config::prefs::PREFS;
+use servo_config::pref;
 use servo_url::ServoUrl;
 use std::cell::Cell;
 use std::collections::hash_map::Entry;
@@ -439,10 +439,7 @@ impl PaintWorkletGlobalScope {
                     .expect("Locking a painter.")
                     .schedule_a_worklet_task(WorkletTask::Paint(task));
 
-                let timeout = PREFS
-                    .get("dom.worklet.timeout_ms")
-                    .as_u64()
-                    .unwrap_or(10u64);
+                let timeout = pref!(dom.worklet.timeout_ms) as u64;
 
                 receiver
                     .recv_timeout(Duration::from_millis(timeout))

components/script/dom/permissions.rs

@@ -22,7 +22,7 @@ use js::jsapi::{JSContext, JSObject};
 use js::jsval::{ObjectValue, UndefinedValue};
 #[cfg(target_os = "linux")]
 use servo_config::opts;
-use servo_config::prefs::PREFS;
+use servo_config::pref;
 use std::rc::Rc;
 #[cfg(target_os = "linux")]
 use tinyfiledialogs::{self, MessageBoxIcon, YesNo};
@@ -307,11 +307,7 @@ pub fn get_descriptor_permission_state(
     let state = if allowed_in_nonsecure_contexts(&permission_name) {
         PermissionState::Prompt
     } else {
-        if PREFS
-            .get("dom.permissions.testing.allowed_in_nonsecure_contexts")
-            .as_boolean()
-            .unwrap_or(false)
-        {
+        if pref!(dom.permissions.testing.allowed_in_nonsecure_contexts) {
             PermissionState::Granted
         } else {
             settings

components/script/dom/serviceworkerglobalscope.rs

@@ -35,7 +35,7 @@ use net_traits::{load_whole_resource, CustomResponseMediator, IpcSend};
 use script_traits::{
     ScopeThings, ServiceWorkerMsg, TimerEvent, WorkerGlobalScopeInit, WorkerScriptLoadOrigin,
 };
-use servo_config::prefs::PREFS;
+use servo_config::pref;
 use servo_rand::random;
 use servo_url::ServoUrl;
 use std::thread;
@@ -336,10 +336,7 @@ impl ServiceWorkerGlobalScope {
                 thread::Builder::new()
                     .name("SWTimeoutThread".to_owned())
                     .spawn(move || {
-                        let sw_lifetime_timeout = PREFS
-                            .get("dom.serviceworker.timeout_seconds")
-                            .as_u64()
-                            .unwrap();
+                        let sw_lifetime_timeout = pref!(dom.serviceworker.timeout_seconds) as u64;
                         thread::sleep(Duration::new(sw_lifetime_timeout, 0));
                         let _ = timer_chan.send(());
                     })

components/script/dom/servoparser/mod.rs

@@ -52,7 +52,7 @@ use profile_traits::time::{
     profile, ProfilerCategory, TimerMetadata, TimerMetadataFrameType, TimerMetadataReflowType,
 };
 use script_traits::DocumentActivity;
-use servo_config::prefs::PREFS;
+use servo_config::pref;
 use servo_url::ServoUrl;
 use std::borrow::Cow;
 use std::cell::Cell;
@@ -135,11 +135,7 @@ impl ServoParser {
     }
 
     pub fn parse_html_document(document: &Document, input: DOMString, url: ServoUrl) {
-        let parser = if PREFS
-            .get("dom.servoparser.async_html_tokenizer.enabled")
-            .as_boolean()
-            .unwrap()
-        {
+        let parser = if pref!(dom.servoparser.async_html_tokenizer.enabled) {
             ServoParser::new(
                 document,
                 Tokenizer::AsyncHtml(self::async_html::Tokenizer::new(document, url, None)),

components/script/dom/testbinding.rs

@@ -57,7 +57,7 @@ use js::rust::CustomAutoRooterGuard;
 use js::rust::{HandleObject, HandleValue};
 use js::typedarray;
 use script_traits::MsDuration;
-use servo_config::prefs::PREFS;
+use servo_config::prefs;
 use std::borrow::ToOwned;
 use std::ptr;
 use std::ptr::NonNull;
@@ -887,12 +887,15 @@ impl TestBindingMethods for TestBinding {
     #[allow(unsafe_code)]
     unsafe fn PassVariadicObject(&self, _: *mut JSContext, _: Vec<*mut JSObject>) {}
     fn BooleanMozPreference(&self, pref_name: DOMString) -> bool {
-        PREFS.get(pref_name.as_ref()).as_boolean().unwrap_or(false)
+        prefs::pref_map()
+            .get(pref_name.as_ref())
+            .as_bool()
+            .unwrap_or(false)
     }
     fn StringMozPreference(&self, pref_name: DOMString) -> DOMString {
-        PREFS
+        prefs::pref_map()
             .get(pref_name.as_ref())
-            .as_string()
+            .as_str()
             .map(|s| DOMString::from(s))
             .unwrap_or_else(|| DOMString::new())
     }

components/script/dom/webglrenderingcontext.rs

@@ -71,7 +71,7 @@ use net_traits::image_cache::ImageResponse;
 use pixels::{self, PixelFormat};
 use script_layout_interface::HTMLCanvasDataSource;
 use serde::{Deserialize, Serialize};
-use servo_config::prefs::PREFS;
+use servo_config::pref;
 use std::cell::Cell;
 use std::cmp;
 use std::ptr::{self, NonNull};
@@ -173,10 +173,7 @@ impl WebGLRenderingContext {
         size: Size2D<u32>,
         attrs: GLContextAttributes,
     ) -> Result<WebGLRenderingContext, String> {
-        if let Some(true) = PREFS
-            .get("webgl.testing.context_creation_error")
-            .as_boolean()
-        {
+        if pref!(webgl.testing.context_creation_error) {
             return Err("WebGL context creation error forced by pref `webgl.testing.context_creation_error`".into());
         }