7525f3afc1
For attribute bindings that target a directive's input, the template type checker is able to verify that the type of the input expression is compatible with the directive's declaration for said input. This checking adheres to the `strictNullChecks` flag as configured in the TypeScript compilation, such that errors are reported for expressions that include `undefined` or `null` in their type if the input's declaration does not include those types. There was a bug with this level of type-checking for directives that also declare coercion members, where binding an expression that includes the `undefined` type to a directive's input that does not include the `undefined` type would not be reported as error. This commit fixes the bug by changing the type-constructor in type-check code to use an intersection type of regular inputs and coerced inputs, instead of a union type. The union type would inadvertently allow `undefined` types to be assigned into the regular inputs, as that would still satisfy the characteristics of a union type. As a result of this change, you may start to see build failures if `strictTemplates` is enabled and `strictInputTypes` is not disabled. These errors are legitimate and some action is required to achieve a successful build: 1. Update the templates for which an error is reported and introduce the non-null assertion operator at the end of the expression. This removes the `undefined` type from the expression's type, making it appear as a valid assignment. 2. Disable `strictNullInputTypes` in the compiler options. This will implicitly add the non-null assertion operators similar to option 1, but all templates in the compilation are affected. 3. Update the directive's input declaration to include the `undefined` type, if the directive is not implemented in an external library. PR Close #38273
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