no-dupe-on-directives.ts

import type { AST } from "svelte-eslint-parser"
import type { TSESTree } from "@typescript-eslint/types"
import { createRule } from "../utils"
import { equalTokens } from "../utils/ast-utils"

export default createRule("no-dupe-on-directives", {
  meta: {
    docs: {
      description: "disallow duplicate `on:` directives",
      category: "Possible Errors",
      recommended: false,
    },
    schema: [],
    messages: {
      duplication:
        "This `on:{{type}}` directive is the same and duplicate directives in L{{lineNo}}.",
    },
    type: "problem",
  },
  create(context) {
    const sourceCode = context.getSourceCode()

    const directiveDataMap = new Map<
      string, // event type
      {
        expression: null | TSESTree.Expression
        nodes: AST.SvelteEventHandlerDirective[]
      }[]
    >()
    return {
      SvelteDirective(node) {
        if (node.kind !== "EventHandler") return

        const directiveDataList = directiveDataMap.get(node.key.name.name)
        if (!directiveDataList) {
          directiveDataMap.set(node.key.name.name, [
            {
              expression: node.expression,
              nodes: [node],
            },
          ])
          return
        }
        const directiveData = directiveDataList.find((data) => {
          if (!data.expression || !node.expression) {
            return data.expression === node.expression
          }
          return equalTokens(data.expression, node.expression, sourceCode)
        })
        if (!directiveData) {
          directiveDataList.push({
            expression: node.expression,
            nodes: [node],
          })
          return
        }

        directiveData.nodes.push(node)
      },
      "SvelteStartTag:exit"() {
        for (const [type, directiveDataList] of directiveDataMap) {
          for (const { nodes } of directiveDataList) {
            if (nodes.length < 2) {
              continue
            }
            for (const node of nodes) {
              context.report({
                node,
                messageId: "duplication",
                data: {
                  type,
                  lineNo: String(
                    (nodes[0] !== node ? nodes[0] : nodes[1]).loc.start.line,
                  ),
                },
              })
            }
          }
        }
        directiveDataMap.clear()
      },
    }
  },
})