Allow use of ranges (≤) before the Baseline low date

The `use_ranges_before_baseline_low_date` field controls when generating
the status, but it could also be done in overrides.

Closes web-platform-dx#1018.

features/search-input-type.yml

@@ -5,3 +5,4 @@ group: forms
 caniuse: input-search
 # TODO: investigate minor differences in the early support of the feature
 # between https://caniuse.com/input-search and our generated status.
+use_ranges_before_baseline_low_date: true

features/search-input-type.yml.dist

@@ -6,12 +6,12 @@ status:
   baseline_low_date: 2015-07-29
   baseline_high_date: 2018-01-29
   support:
-    chrome: "5"
+    chrome: ≤5
     chrome_android: "18"
     edge: "12"
-    firefox: "4"
+    firefox: ≤4
     firefox_android: "4"
-    safari: "5"
-    safari_ios: "4.2"
+    safari: ≤5
+    safari_ios: ≤4.2
 compat_features:
   - html.elements.input.type_search

index.ts

@@ -20,16 +20,20 @@ const nameMaxLength = 80;
 // The longest description allowed, to avoid them growing into documentation.
 const descriptionMaxLength = 300;
 
+// The earliest possible Baseline low date, the release date of Edge 12.
+const earliestBaselineLowDate = '2015-07-29';
+
 // Internal symbol to mark draft entries, so that using the draft field outside
 // of a draft directory doesn't work.
 const draft = Symbol('draft');
 
 // Some FeatureData keys aren't (and may never) be ready for publishing.
 // They're not part of the public schema (yet).
 const omittables = [
+    "group",
     "snapshot",
-    "group"
-]
+    "use_ranges_before_baseline_low_date",
+];
 
 function scrub(data: any) {
     for (const key of omittables) {
@@ -168,6 +172,16 @@ for (const [key, data] of yamlEntries('features')) {
         }
     }
 
+    // Ensure that version ranges are only used for prehistoric features.
+    if (data.status?.support) {
+        const versions: string[] = Object.values(data.status.support);
+        if (versions.some((v) => v.startsWith('≤'))) {
+            if (data.status.baseline_low_date !== earliestBaselineLowDate) {
+                throw new Error(`Ranges (≤) used in ${key}.yml(.dist) but can only be used when the baseline_low_date is ${earliestBaselineLowDate}`);
+            }
+        }
+    }
+
     // Check that no BCD key is used twice until the meaning is made clear in
     // https://github.com/web-platform-dx/web-features/issues/1173.
     if (data.compat_features) {

schemas/defs.schema.json

@@ -101,7 +101,7 @@
             },
             "support": {
               "additionalProperties": false,
-              "description": "Browser versions that most-recently introduced the feature",
+              "description": "Browser versions that most-recently introduced the feature. A \"≤\" prefix indicates that support before this point is uncertain and the feature may have been supported earlier.",
               "properties": {
                 "chrome": {
                   "type": "string"

scripts/dist.ts

@@ -1,5 +1,6 @@
 import { computeBaseline, setLogger } from "compute-baseline";
 import { Compat, Feature } from "compute-baseline/browser-compat-data";
+import { Temporal } from '@js-temporal/polyfill';
 import assert from "node:assert/strict";
 import fs from "node:fs";
 import path from "node:path";
@@ -123,7 +124,26 @@ function toDist(sourcePath: string): YAML.Document {
           `${id}: contains at least one deprecated compat feature and can never be Baseline. Was this intentional?`,
         );
       }
-      insertStatus(dist, JSON.parse(status.toJSON()));
+
+      // Add ranges to releases before the Baseline low date. It's not possible
+      // to use ranges more selectively than this.
+      if (yaml.get("use_ranges_before_baseline_low_date")) {
+        const lowDate = Temporal.PlainDate.from(status.baseline_low_date);
+        const statusWithRanges = JSON.parse(status.toJSON());
+        const support = statusWithRanges.support;
+        for (const [browser, release] of status.support.entries()) {
+          if (release.releaseIndex === 0) {
+            continue;
+          }
+          const date = Temporal.PlainDate.from(release.date);
+          if (Temporal.PlainDate.compare(date, lowDate) === -1) {
+            support[browser.id] = `≤${support[browser.id]}`;
+          }
+        }
+        insertStatus(dist, statusWithRanges);
+      } else {
+        insertStatus(dist, JSON.parse(status.toJSON()));
+      }
     }
   }
 

types.ts

@@ -32,7 +32,7 @@ interface SupportStatus {
     baseline_low_date?: string;
     /** Date the feature achieved Baseline high status */
     baseline_high_date?: string;
-    /** Browser versions that most-recently introduced the feature */
+    /** Browser versions that most-recently introduced the feature. A "≤" prefix indicates that support before this point is uncertain and the feature may have been supported earlier. */
     support: {
         [K in browserIdentifier]?: string;
     };