Add discouraged to schema (and with statement demo feature)

docs/guidelines.md

@@ -309,3 +309,42 @@ For example, don't assign a feature to both `css` and `fonts`, since `css` is th
 
 Do assign features to groups when there's an opportunity for future feature composition (see [#971](https://github.com/web-platform-dx/web-features/issues/971)).
 For example, several features for the JavaScript `Array` interface are members of the `array` group.
+
+## Discouraged
+
+Rarely, the developers should not use a platform feature because it's the consensus of relevant stakeholders (i.e., a standards body and implementers), even if that feature is still implemented in browsers.
+Mark a feature as discouraged when:
+
+- The specification adopts clear language directing developers to stop using that feature or to prefer to an alternative.
+  This is often through terms like "deprecated", "obsolete", "legacy", or "non-standard."
+  They can also be in the form of one-off recommendations to use alternatives (such as "[…ought to be used instead](https://dom.spec.whatwg.org/#ref-for-concept-event%E2%91%A4%E2%91%A3)").
+
+- The specification removes that feature from the specification without a succession plan (such as moving it to another specification).
+
+- The specification editors intend to discourage or remove the feature from the specification.
+  For example, meeting minutes show that a committee achieved consensus to remove a feature from a specification, even if the removal is not complete.
+
+- All of the (present) implementers issue warnings when using that feature or have published something expressing an intention to unship that feature.
+
+
+Do not mark a feature as discouraged when:
+
+- The feature is merely old or unpopular, no matter how many [_considered harmful_](https://en.wikipedia.org/wiki/Considered_harmful) blog posts it may have garnered.
+  For example, despite the existence of `fetch`, `XMLHttpRequest` is not a discouraged feature.
+
+- The feature is controversial.
+  Opposition to a feature (without consensus) is not sufficient to mark a feature as discouraged.
+  For example, do not mark a feature as discouraged because a vendor has given it a negative standards position.
+
+- The feature is buggy or not implemented in one or more browsers.
+  Contribute to accurate support data instead.
+
+When you set a `discouraged` block in a feature file, do:
+
+- Set a (required) `according_to` URL, linking to evidence that the feature is discouraged.
+  If possible, use the single most broadly applicable reference, such as specification text.
+  If a feature is removed from a specification, link to an issue, pull request, or commit showing the removal.
+
+- Set one or more (optional) `alternative` feature IDs that are whole or partial substitutes for the discouraged feature.
+  An alternative doesn't have to be a narrow drop-in replacement for the discouraged feature but it must handle some use case of the discouraged feature.
+  Guide developers to the most relevant features that would help them stop using the discouraged feature.

features/symbol.yml

@@ -23,6 +23,5 @@ compat_features:
   - javascript.builtins.Symbol.toString
   - javascript.builtins.Symbol.toStringTag
   - javascript.builtins.Symbol.toStringTag.dom_objects
-  - javascript.builtins.Symbol.unscopables
   - javascript.builtins.Symbol.valueOf
   - javascript.builtins.Symbol.@@toPrimitive

features/symbol.yml.dist

@@ -45,19 +45,6 @@ compat_features:
   - javascript.builtins.Symbol.for
   - javascript.builtins.Symbol.keyFor
 
-  # baseline: high
-  # baseline_low_date: 2016-08-02
-  # baseline_high_date: 2019-02-02
-  # support:
-  #   chrome: "38"
-  #   chrome_android: "38"
-  #   edge: "12"
-  #   firefox: "48"
-  #   firefox_android: "48"
-  #   safari: "9"
-  #   safari_ios: "9"
-  - javascript.builtins.Symbol.unscopables
-
   # baseline: high
   # baseline_low_date: 2016-09-20
   # baseline_high_date: 2019-03-20

features/with.yml

@@ -0,0 +1,24 @@
+name: with
+description: The `with` JavaScript statement adds a given object to the chain of scopes used to evaluate names.
+spec: https://tc39.es/ecma262/multipage/ecmascript-language-statements-and-declarations.html#sec-with-statement
+group: javascript
+discouraged:
+  # One thing that is potentially missing here is a "reason" like this:
+
+  # reason: browser-warning
+  # reason: spec-caution
+  # reason: pending-removal
+
+  # This would allow us to signal to tools how "fatal" the discouragement is
+  # (e.g., pending-removal should trigger noisy errors for developers but spec
+  # caution would not). I'm not sure the full range of these yet; I think it
+  # might be easier to choose the set of reasons after we've enumerated a bunch
+  # of discouraged features.
+  according_to:
+    - https://tc39.es/ecma262/multipage/ecmascript-language-statements-and-declarations.html#sec-with-statement
+  alternatives:
+    - destructuring
+compat_features:
+  - javascript.statements.with
+  - javascript.builtins.Symbol.unscopables
+  - javascript.builtins.Array.@@unscopables

features/with.yml.dist

@@ -0,0 +1,50 @@
+# Generated from: with.yml
+# Do not edit this file by hand. Edit the source file instead!
+
+status:
+  baseline: false
+  support:
+    chrome: "38"
+    chrome_android: "38"
+    edge: "12"
+    firefox: "48"
+    firefox_android: "48"
+    safari: "10"
+    safari_ios: "10"
+compat_features:
+  # baseline: high
+  # baseline_low_date: 2016-08-02
+  # baseline_high_date: 2019-02-02
+  # support:
+  #   chrome: "38"
+  #   chrome_android: "38"
+  #   edge: "12"
+  #   firefox: "48"
+  #   firefox_android: "48"
+  #   safari: "9"
+  #   safari_ios: "9"
+  - javascript.builtins.Symbol.unscopables
+
+  # baseline: high
+  # baseline_low_date: 2016-09-20
+  # baseline_high_date: 2019-03-20
+  # support:
+  #   chrome: "38"
+  #   chrome_android: "38"
+  #   edge: "12"
+  #   firefox: "48"
+  #   firefox_android: "48"
+  #   safari: "10"
+  #   safari_ios: "10"
+  - javascript.builtins.Array.@@unscopables
+
+  # baseline: false
+  # support:
+  #   chrome: "1"
+  #   chrome_android: "18"
+  #   edge: "12"
+  #   firefox: "1"
+  #   firefox_android: "4"
+  #   safari: "1"
+  #   safari_ios: "1"
+  - javascript.statements.with

index.ts

@@ -182,6 +182,16 @@ for (const [key, data] of yamlEntries('features')) {
     features[key] = data;
 }
 
+// Assert that discouraged feature's alternatives are valid
+for (const [id, feature] of Object.entries(features)) {
+    for (const alternative of feature.discouraged?.alternatives ?? []) {
+        console.log(`Confirming ${alternative} in feature set`);
+        if (!(alternative in features)) {
+            throw new Error(`${id}'s alternative "${alternative}" is not a valid feature ID`);
+        }
+    }
+}
+
 const compat = new Compat();
 const browsers: Partial<WebFeaturesData["browsers"]> = {};
 for (const browser of coreBrowserSet.map(identifier => compat.browser(identifier))) {

packages/web-features/README.md

@@ -1,7 +1,5 @@
 # Curated list of Web platform features
 
-This package is experimental, expect frequent breaking changes!
-
 ## Usage
 
 ```sh
@@ -27,13 +25,18 @@ import schema from "web-features/data.schema.json" with { type: "json" };
 
 ## Rendering Baseline statuses with `web-features`
 
-If you're using `web-features` to render Baseline iconography or browser logos with support markers, then you must follow these procedures to ensure consistent usage.
+If you're using `web-features` to render Baseline iconography or browser logos with support markers, then you must follow the [name and logo usage guidelines](https://web-platform-dx.github.io/web-features/name-and-logo-usage-guidelines/).
 
 For Baseline iconography, follow this procedure for each feature:
 
 1. If `status.baseline` is `"high"`, then show an affirmative "widely available" icon.
 1. If `status.baseline` is `"low"`, then show an affirmative "newly available" icon.
 1. If `status.baseline` is `false`, then show a "limited availability" non-Baseline icon.
+
+   **Note**: All features that have the `discouraged` property are, by definition, non-Baseline, and `status.baseline` will be `false`.
+   If a feature has the `discouraged` property, consider showing a message describing the feature's discouraged status instead of Baseline iconography.
+   Showing Baseline iconography for discouraged features may confuse readers.
+
 1. If `status.baseline` is `undefined`, then **do not** show any Baseline or non-Baseline badge.
 
 For browser support iconography (that is, browser logos and checkmarks and Xs), follow this procedure for each browser:

schemas/data.schema.json

@@ -57,6 +57,30 @@
           "description": "Short description of the feature, as an HTML string",
           "type": "string"
         },
+        "discouraged": {
+          "additionalProperties": false,
+          "description": "Whether developers are formally discouraged from using this feature",
+          "properties": {
+            "according_to": {
+              "description": "Links to a formal discouragement notice, such as specification text, intent-to-unship, etc.",
+              "items": {
+                "description": "URI",
+                "format": "uri",
+                "type": "string"
+              },
+              "type": "array"
+            },
+            "alternatives": {
+              "description": "IDs for features that substitute some or all of this feature's utility",
+              "items": {},
+              "type": "array"
+            }
+          },
+          "required": [
+            "according_to"
+          ],
+          "type": "object"
+        },
         "group": {
           "anyOf": [
             {

scripts/dist.ts

@@ -233,9 +233,7 @@ function toDist(sourcePath: string): YAML.Document {
     checkAncestors: true,
   });
 
-  if (computedStatus.discouraged) {
-    const isDraft: boolean = source.draft_date ?? false;
-
+  if (computedStatus.discouraged && !source.discouraged) {
     if (!source.draft_date) {
       logger.error(
         `${id}: contains at least one deprecated compat feature. This is forbidden for published features.`,

types.ts

@@ -45,6 +45,8 @@ export interface FeatureData {
     status: SupportStatus;
     /** Sources of support data for this feature */
     compat_features?: string[];
+    /** Whether developers are formally discouraged from using this feature */
+    discouraged?: Discouraged;
 }
 
 type BrowserIdentifier = "chrome" | "chrome_android" | "edge" | "firefox" | "firefox_android" | "safari" | "safari_ios";
@@ -69,10 +71,20 @@ interface SupportStatus extends Status {
     by_compat_key?: Record<string, Status>
 }
 
-/** Specification URL
+interface Discouraged {
+    /** Links to a formal discouragement notice, such as specification text, intent-to-unship, etc. */
+    according_to: uri[];
+    /** IDs for features that substitute some or all of this feature's utility */
+    alternatives?: (keyof WebFeaturesData["features"])[];
+}
+
+/** URI
  * @format uri
-*/
-type specification_url = string;
+ */
+type uri = string;
+
+/** Specification URL */
+type specification_url = uri;
 
 export interface GroupData {
     /** Short name */