We now have a real use-case for tracking/bubbling up collations in the query tree. With the new primitive collection support in 8.0, we do much wider type mapping inference as before. For example:

 var query = db.Blogs
    .Where(b => ids.Contains(b.Id))
    .ToList();

... now generates:

SELECT [b].[Id]
FROM [Blogs] AS [b]
WHERE [b].[Id] IN (
    SELECT [i].[value]
    FROM OPENJSON(@__ids_0) WITH ([value] nvarchar(450) '$') AS [i]
)

Note that in this query, the collation of b.Id is inferred and applied to the output column of the OPENJSON function inside the subquery.

The same thing needs to happen with the collation of the b.Id column: OPENJSON outputs columns with the collation of its input expression; since that's a parameter above (@__ids_0), these columns get the default database collation, and if b.Id has a non-default collation, the query fails because of conflicting collations (see #32147).

To properly fix this, we should make the collation part of the type mapping, so that it can bubble up (in case there's a complex expression tree instead of just a single column), and then have it inferred and applied to the OPENJSON parameter.

Make collation part of type mapping #29620

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