internal/tsetse/rules/property_renaming_safe.ts

import * as ts from 'typescript';

import {Checker} from '../checker';
import {ErrorCode} from '../error_code';
import {AbstractRule} from '../rule';

/**
 * A Tsetse rule that checks for some potential unsafe property renaming
 * patterns.
 *
 * Note: This rule can have false positives.
 */
export class Rule extends AbstractRule {
  readonly ruleName = 'property-renaming-safe';
  readonly code = ErrorCode.PROPERTY_RENAMING_SAFE;

  register(checker: Checker) {
    checker.on(
        ts.SyntaxKind.PropertyAccessExpression,
        checkIndexSignAccessedWithPropAccess, this.code);
  }
}

// Copied from tsickle/src/quoting_transformer.ts, with the intention of
// removing it from there and only keeping a tsetse rule about this.
function checkIndexSignAccessedWithPropAccess(
    checker: Checker, pae: ts.PropertyAccessExpression) {
  // Reject dotted accesses to types that have an index type declared to quoted
  // accesses, to avoid Closure renaming one access but not the other. This can
  // happen because TS allows dotted access to string index types.
  const typeChecker = checker.typeChecker;
  const t = typeChecker.getTypeAtLocation(pae.expression);
  if (!t.getStringIndexType()) return;
  // Types can have string index signatures and declared properties (of the
  // matching type). These properties have a symbol, as opposed to pure string
  // index types.
  const propSym = typeChecker.getSymbolAtLocation(pae.name);
  // The decision to return below is a judgement call. Presumably, in most
  // situations, dotted access to a property is correct, and should not be
  // turned into quoted access even if there is a string index on the type.
  // However it is possible to construct programs where this is incorrect, e.g.
  // where user code assigns into a property through the index access in another
  // location.
  if (propSym) return;

  checker.addFailureAtNode(
      pae.name,
      `Property ${pae.name.text} is not declared on Type ` +
          `${typeChecker.typeToString(t)}. The type has a string index ` +
          `signature, but it is being accessed using a dotted property ` +
          `access.
See http://tsetse.info/property-renaming-safe.`);
}