[Statsig] Typecheck gates (#3467)

* Typecheck gates

* Lint against untyped useGate()

* Alphabetic

eslint/use-typed-gates.js

@@ -0,0 +1,31 @@
+'use strict'
+
+exports.create = function create(context) {
+  return {
+    ImportSpecifier(node) {
+      if (
+        !node.local ||
+        node.local.type !== 'Identifier' ||
+        node.local.name !== 'useGate'
+      ) {
+        return
+      }
+      if (
+        node.parent.type !== 'ImportDeclaration' ||
+        !node.parent.source ||
+        node.parent.source.type !== 'Literal'
+      ) {
+        return
+      }
+      const source = node.parent.source.value
+      if (source.startsWith('.') || source.startsWith('#')) {
+        return
+      }
+      context.report({
+        node,
+        message:
+          "Use useGate() from '#/lib/statsig/statsig' instead of the one on npm.",
+      })
+    },
+  }
+}