Allow string enum in element access #18029
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Previously literal union types were disallowed to improve errors by printing `boolean` instead of `true | false`. But string enums are literal union types that should be allowed, so now only booleans are disallowed.
ghost
reviewed
Aug 25, 2017
src/compiler/checker.ts
Outdated
| @@ -7688,7 +7688,7 @@ namespace ts { | |||
| } | |||
| // In the following we resolve T[K] to the type of the property in T selected by K. | |||
| const apparentObjectType = getApparentType(objectType); | |||
| if (indexType.flags & TypeFlags.Union && !(indexType.flags & TypeFlags.Primitive)) { | |||
| if (indexType.flags & TypeFlags.Union && !(indexType.flags & TypeFlags.Boolean)) { | |||
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Could you add a comment explaining that we are avoiding TypeFlags.Boolean here for stylistic reasons to ensure that we show boolean and not true in error messages? Might also want to link to keyofAndIndexedAccessErrors.errors.txt, which is the only test that fails (i.e., has slightly different error messages) if this check isn't here.
Booleans are not treated like other unions in order to skip straight to error reporting so that the error is reported with 'boolean' instead of 'true'.
ghost
approved these changes
Aug 28, 2017
mhegazy
approved these changes
Aug 28, 2017
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Fixes #16760
Previously literal union types were disallowed to improve errors by printing
booleaninstead oftrue | false. But string enums are literal union types that should be allowed, so now only booleans are disallowed.