@sap/eslint-plugin-cds/lib/rules/sql-null-comparison.js

ESLint plugin including recommended SAP Cloud Application Programming model and environment rules

'use strict'

const { forEachXprInDefinition } = require('../utils/csnTraversal')

const invalidComparisonOperators = [ '=', '<>' ]

module.exports = {
  meta: {
    schema: [{/* to avoid deprecation warning for ESLint 9 */}],
    docs: {
      description: 'Ensure SQL comparisons with \'null\' are valid',
      category: 'Model Validation',
      recommended: false,
      url: 'https://cap.cloud.sap/docs/tools/cds-lint/rules/sql-null-comparison',
    },
    type: 'problem',
    model: 'parsed',
    messages: {
      nullComparison: `Comparisons against 'null' using '=' and '<>' are always null. Did you mean 'is null'/'is not null'?`,
    }
  },
  create(context) {
    const model = context.getModel()
    if (!model?.definitions)
      return

    return function checkSqlNullComparisonsInModel() {
      for (const defName in model.definitions) {
        const def = model.definitions[defName]
        if (def.query || def.projection)
          forEachXprInDefinition(def, checkExpression)
      }
    }

    function checkExpression(xpr, ctx) {
      if (!xpr || !Array.isArray(xpr))
        return

      for (let i = 0; i < xpr.length; i++) {
        if (typeof xpr[i] !== 'object')
          continue // scalar value, etc.

        if (xpr[i]?.val === null) {
          const prev = i > 0 && typeof xpr[i-1] === 'string' ? xpr[i-1] : null
          if (prev && invalidComparisonOperators.includes(prev)) {
            reportComparison(xpr, ctx)
            continue
          }
          const next = i+1 < xpr.length && typeof xpr[i+1] === 'string' ? xpr[i+1] : null
          if (next && invalidComparisonOperators.includes(next))
            reportComparison(xpr, ctx)
        }
      }
    }

    function reportComparison(xpr, ctx) {
      context.report({
        messageId: 'nullComparison',
        loc: context.getLocation('', ctx),
        file: ctx.$location?.file,
      })
    }
  }
}