Support relations and inference between template literal types #43361
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| const matches: Type[] = []; | ||
| let seg = 0; | ||
| let pos = targetStartText.length; | ||
| for (let i = 1; i < lastTargetIndex; i++) { |
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Some sort of comment (an overview of the algorithm / what it's trying to do, or the name of it if this is a well-known one?) seems justified here
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Yes, I think if you could just explain with examples too, that'd be helpful.
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Ok, I'll add some comments.
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| function getStringLikeTypeForType(type: Type) { | ||
| return type.flags & (TypeFlags.Any | TypeFlags.StringLike) ? type : getTemplateLiteralType(["", ""], [type]); |
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Would it be useful to have a singleton emptyTemplateType?
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Well, the single-element types array varies here, so we can't use a singleton. We could possibly have a singleton for the ["", ""] array, but it's hardly worth the effort as this code doesn't run that often.
| return type.flags & (TypeFlags.Any | TypeFlags.StringLike) ? type : getTemplateLiteralType(["", ""], [type]); | ||
| } | ||
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| function inferFromLiteralPartsToTemplateLiteral(sourceTexts: readonly string[], sourceTypes: readonly Type[], target: TemplateLiteralType): Type[] | undefined { |
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I don't like calling these sourceTexts because it immediately signals to me "BUG" even though you're not actually grabbing out the source text. You're grabbing the normalized text content which is the correct thing to do.
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Hmm, I don't think the current names are that bad. After all the properties are called texts and types in template literals and we want the parameters to reflect the relation.
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Right, I think that even texts would be a better name - I may send a follow-up PR but I'm going to merge this for now.
With this PR we support relations and inference between template literal types. Specifically, when the target side in a type relation is a template literal type, the source side is now permitted to be a compatible (i.e. more specific) template literal type. Likewise, when inferring to a template literal target type, we now permit the source type to also be a template literal type.
Some examples of improved assignment relations:
With this PR all of the above assignments are permitted, where previously only the first assignment was permitted.
Some examples of inference between template literal types:
Fixes #43060.
Fixes #43243.