valid-each-key.ts

import type { AST } from "svelte-eslint-parser"
import { createRule } from "../utils"
import { getScope } from "../utils/ast-utils"

export default createRule("valid-each-key", {
  meta: {
    docs: {
      description:
        "enforce keys to use variables defined in the `{#each}` block",
      category: "Best Practices",
      // TODO Switch to recommended in the major version.
      recommended: false,
    },
    schema: [],
    messages: {
      keyUseEachVars:
        "Expected key to use the variables which are defined by the `{#each}` block.",
    },
    type: "suggestion",
  },
  create(context) {
    return {
      SvelteEachBlock(node: AST.SvelteEachBlock) {
        if (node.key == null) {
          return
        }
        const scope = getScope(context, node.key)
        for (const variable of scope.variables) {
          if (
            !variable.defs.some(
              (def) =>
                (node.context.range[0] <= def.name.range[0] &&
                  def.name.range[1] <= node.context.range[1]) ||
                (node.index &&
                  node.index.range[0] <= def.name.range[0] &&
                  def.name.range[1] <= node.index.range[1]),
            )
          ) {
            // It's not an iteration variable.
            continue
          }
          for (const reference of variable.references) {
            if (
              node.key.range[0] <= reference.identifier.range[0] &&
              reference.identifier.range[1] <= node.key.range[1]
            ) {
              // A variable is used in the key.
              return
            }
          }
        }
        context.report({
          node: node.key,
          messageId: "keyUseEachVars",
        })
      },
    }
  },
})