Support for skipping type parameter constraints when merging interfaces is order dependent

[mattmccutchen]

TypeScript Version: master (618da24)

Search Terms: type parameter same merging constraint

Code

// Error: "All declarations of 'A' must have identical type parameters."
interface A<T> { }
interface A<T extends string> { }

// No error
interface B<T extends string> { }
interface B<T> { }

Expected behavior: Same for A and B.

Actual behavior: Different behavior for A and B as indicated.

Playground Link: link

Related Issues: #20018

I noticed this while trying to understand the code of areTypeParametersIdentical for another project. The problem is that getConstraintDeclaration always looks at the first declaration.

[mattmccutchen]

Now I read #20883 and it sounds like the order dependence was an intentional decision made late in the process and not documented in the original issue.